Introduction

The Bioecological Systems Theory (Bronfenbrenner, 1977;1979; Tudge et al., 2009) holds that the child’s development results from a complex system of relationships that are influenced by the environment. According to Minuchin’s Family System Theory, family members affect each other, thus when a child is diagnosed with a disability and/or a chronic illness, they are significantly touched (Barnett et al., 2003). Because mothers often are the primary caregivers of children, most of the research carried out on the reaction to the diagnosis of disability in the family (Marvin & Pianta, 1992; Sher-Censor et al., 2022) devoted attention to them. Results highlighted high levels of distress (Al-Kandari & Al-Qashan, 2010; Lecciso et al., 2013a, 2013b; Lecciso et al., 2013a, 2013b; Sato et al., 2015) and depressive symptoms (Dillon-Wallace et al., 2014; Ingersoll & Hambrick, 2011; Rashedi et al., 2013). On fathers, studies reported that they devote more time and energy to work (Keller & Honig, 2004; Zanobini et al., 2002) and show lower depressive symptoms than mothers (McStay et al., 2014; Vasilopoulou & Nisbet, 2016). Over the last few years, a substantial number of studies have been carried out on typically developing siblings (henceforth siblings), whose functioning may be significantly altered by growing up with a brother or sister with a disability. Nevertheless, findings on this topic are mixed. Most studies (Giallo & Gavidia-Payne, 2006; Hastings, 2003; O’Neill & Murray, 2016; Petalas et al., 2009; Ross & Cuskelly, 2009; Rossetti & Hall, 2015; Sharpe & Rossiter, 2002; Stoneman, 2005; Williams et al., 2010) revealed that the brother’s or sister’s disability negatively affected the functioning of the sibling, causing high levels of anxiety and depression, social withdrawal, conduct disorders, and other behavioral problems. Other studies (Kaminsky & Dewey, 2001; Moyson & Roeyers, 2012; Opperman & Alant, 2003; Rossetti & Hall, 2015) showed that having a brother’ or sister’s disability increases empathy and psychosocial development, self-perceived competence, high-quality of life, and improved family cohesion in siblings of persons with disabilities. Finally, albeit they are few (Cuskelly & Gunn, 2003; Hallion et al., 2018), studies have found no difference between siblings of persons with disabilities and siblings of typically developing individuals.

Considering siblings the family members might become the main caregivers for their brother or sister with a disability, we conceived this systematic integrative review to provide an overview of empirical existing studies investigating the psychological impact of disability on this vulnerable population. Previous systematic reviews have been conceived to address this purpose; nevertheless, they examined the impact of disability related to a specific psychological construct, that is well-being (Schamong et al., 2021), parentification (Eun Lee & Burke, 2018), psychological adjustment (Rochefort et al., 2023), empathy and prosocial behaviors (Long et al., 2018; Orm et al., 2021), and general psychopathology (Ma et al., 2015). Overall, albeit high levels of empathy and prosocial behaviors have been developed by growing with a brother or sister with disability (Orm, 2021), the results of these reviews outline a detrimental psychological effect of the disability on the sibling’s experience. Findings highlight that caregiver is the main role served by the siblings of persons with disabilities (Eun Lee & Burke, 2018) and that low well-being and quality of life is experienced (Schamong et al., 2021). In addition, externalizing (e.g., self-aggression) and internalizing (e.g., anxiety) symptoms have been retrieved (Long, 2018; Ma, 2015). Similarly, dysfunctional family relationships consisting of poor parental support (Rochefort et al., 2023) have been reported by siblings.

Additionally, these reviews considered studies on siblings of persons with a specific disability. For instance, neurodevelopmental disorders (Rochefort et al., 2023; Leedham et al., 2020; Orm et al., 2021; Thomas et al., 2015; Watson et al., 2021; Eun Lee & Burke, 2018) or mental health problems (Ma et al., 2015), chronic illnesses (e.g., asthma, and brain injury; Incledon et al., 2015; Knecht et al., 2015), cancer (Long et al., 2018; Yang et al., 2016), congenital heart disease (Parker et al., 2020; Schamong et al., 2021).

Based on the purposes of previous reviews and the target population whom they devoted attention as well, the current systematic review aims at synthesizing the existing literature on what psychological constructs have been explored on siblings of persons with disability. In addition, the current systematic review aimed at covering the last 10-year period to help scholars and health professionals in designing studies and intervention programs as well.

Based on this rationale, following the Population Exposure Outcome (PEO) format, two research questions (RQs) were formulated:

RQ1: What are the main psychological constructs investigated in siblings of persons with disability?

RQ2: What is the main role of each psychological construct in siblings of persons with disabilities experience?

Because the reviewed studies showed great heterogeneity in the way they measured the psychological constructs and reported results, an integrative narrative approach (Whittemore & Knafl, 2005) was adequate to synthetize the findings.

Review Method

Search Strategy

The current systematic review is based on the structure proposed by a published protocol (Levante et al., 2019). In extracting studies, the updated Preferred Reporting Items for Systematic Review and Meta-Analysis (PRISMA) diagram was applied (Page et al., 2021). The electronic search was carried out in 7 databases (i.e., Scopus, MEDLINE, PsychInfo, Cumulative Index to Nursing and Allied Health Literature, ERIC, PubMed, and Web of Sciences) covering the decade 2014–2024.

Table 1 shows the keywords and their MeSH terms selected by the PEO protocol. In each database, all keywords were combined using the Boolean operators “AND” & “OR.”

A set of pre-defined inclusion and exclusion criteria were tabulated (Table 2).

Selection of the Studies

As for the content of the studies, the Population Intervention Comparison Outcome Study (PICOS) protocol (Bowling & Ebrahim, 2005) was used: Participants: siblings of any age with a brother or sister with disabilities; Intervention: empirical studies assessing psychological constructs impacting the disabilities and/or chronic illness of the brother or sister; Comparison: differences according to the siblings’ gender evaluated in the reviewed studies; Outcomes: any psychological constructs; Study: quantitative; qualitative; mixed. Figure 1 shows the PRISMA (Page et al., 2021) diagram.

According to the first step of the PRISMA diagram (i.e., Identification), in each database, we searched papers in which our keywords appeared in either the paper’ title, abstract, subject heading, or keywords list. For each keyword combination, all records were tabulated in a.csv spreadsheet and a total of 1,002 records were alphabetically ordered. A second-hand search was performed to incorporate 49 records according to the reference lists of reviewed studies.

Through an automatic tool included in the.csv spreadsheet, duplicates (n = 620) were removed. A total of 431 papers were screened by two authors (AL & CM) for inclusion. Before the Screening step, the inter-rater agreement was calculated on a set of 50 papers, randomly chosen. They were independently screened by the two authors (AL & CM), and any disagreements were arbitrated by a third author (FL). The inter-rater agreement was good (Cohen’s K = 0.93).

A total of 371 papers were excluded according to the pre-defined criteria and the final number of included papers was 60 (marked with * in the references list) (Avieli et al., 2019; Beffel & Nuttall, 2020; Bhattashali et al., 2018; Braconnier et al., 2018; Brady et al., 2019; Brolin et al., 2024; Cebula et al., 2019; Chiu, 2022; Correia & Seabra-Santos, 2022; Corsano et al., 2017; Cuskelly, 2016; Dorsman et al., 2023; Floyd et al., 2016; Guidotti et al., 2021; Hallion et al., 2018; Hanvey et al., 2022; Hayden et al., 2023; Hemati Alamdarloo et al., 2021; Jones et al., 2019; Kale & Siğirtmaç, 2021; Kulisch et al., 2024; Koukouriki & Soulis, 2020; Lahaije et al., 2023; Lashewicz, 2018; Le Boudec et al., 2021; Eun Lee et al., 2018, 2023; Eun Lee et al., 2019a, 2019b; Eun Lee et al., 2019a, 2019b; Eun Lee et al., 2020; Levante et al., 2023a, 2023b, 2023c; Milevsky & Singer, 2022; Niedbalski, 2023; Noonan et al., 2018; Nuttall et al., 2018; O’Neill & Murray, 2016; Orm et al., 2022; Paul et al., 2022; Perenc & Pęczkowski, 2018; Redquest et al., 2020, 2021; Rossetti et al., 2018, 2020; Shivers, 2019a, 2019b; Shivers et al., 2019; Shivers & Kozimor, 2017; Shojaee et al., 2020; Siman-Tov & Adi Sharabi, 2023; Stock et al., 2016; Tomeny et al., 2016a, 2016b; Tomeny et al., 2016a, 2016b, 2017a, 2017b; Tomeny et al., 2017a, 2017b; Travers et al., 2020; Tsai et al., 2016; Tyerman et al., 2019; Yacoub et al., 2018; Yaldız et al., 2021; Zaidman-Zait et al., 2020).

Methodological Quality Appraisal of Included Studies

The methodological quality appraisal of the included papers has been evaluated using the updated standardized protocol Mixed Method Appraisal Tool (MMAT; Hong et al., 2018). The protocol appraises the studies across five main categories: qualitative research, randomized controlled trials, non-randomized studies, quantitative descriptive studies, and mixed methods research. A set of five questions has been designed for each study category and response options for each question ranged on a 3-point Likert scale (1 = “yes,” 0 = “no,” and 0 = “can’t tell”). The MMAT authors provide a spreadsheet in which the reviewers report the main study information (i.e., reference ID, first author, year of publication, and full citation). Afterward, the reviewers fill out two screening questions (i.e., “Are the research questions clearly stated?” and “Do the data collected address the research questions?”). Whether the answer to these screening questions is “no” or “can’t tell,” the study is excluded. In contrast, if “yes” answers are provided, the reviewers complete the five relevant questions to appraise the methodological quality of the study. The inter-rater agreement is calculated on 20% of the included papers. For the current systematic review, the inter-rater agreement is excellent (Cohen’s κ = 0.95). The MMAT developers do not provide a cut-off to categorize the scores; nevertheless, they suggest using a conservative approach. Similar to another review (Levante et al., 2023a, 2023b, 2023c), the quality appraisal is low if the study reaches 1 or 2 “yes” answers, medium if it scores 3 “yes,” and high if the study reaches 4 or 5 “yes” answers.

Results

Table 3 summarizes the main information provided in the reviewed studies which are clustered according to the psychological constructs examined and the methodological quality appraisal of each study.

Firstly, the global geographic area (Global North vs. Global South) and the Country where each study was conducted were reported. Further methodological details on the study design were extrapolated, in terms of cross-sectional vs. longitudinal design, quantitative, qualitative, or mixed data. Additionally, the characteristics of the participants involved in each reviewed study were tabulated: i.e., the total sample size, gender distribution, the type of disability and/or chronic illness of the sibling’s brother or sister, mean age, standard deviation, and age range of the siblings. The types of disabilities and/or chronic illnesses analyzed in the reviewed studies and the measures administered were reported. Finally, the main findings of each reviewed study were resumed and the methodological quality appraisal was reported.

Methodological Characteristics of the Reviewed Studies

Sixty studies were included in this systematic review. Most of them (n = 54) were carried out in Global North countries, five studies involved participants in Global South countries, while only one collected data both in Global North and South countries. Except one (Floyd et al., 2016), all studies (n = 59) collected data cross-sectionally. Thirty-seven of them were quantitative, 18 were qualitative, and 4 were mixed studies.

As for the recruited sample, a total of 10,146 participants were involved. The sample size ranged from 9 to 1,567 individuals in quantitative studies, from 5 to 30 participants in qualitative ones, and from 44 to 332 individuals in mixed studies. Eleven studies (Hallion et al., 2018; Hemati Alamdarloo et al., 2021; Koukouriki & Soulis, 2020; Le Boudec et al., 2021; O’Neill & Murray, 2016; Orm et al., 2021; Perenc & Pęczkowski, 2018; Shivers, 2019a; Shojaee et al., 2020; Yaldız et al., 2021; Zaidman-Zait et al., 2020) compared the experimental group including siblings of persons with disabilities to a control group made up of siblings of typically developing individuals (henceforth TD individuals). Forty-nine studies involved experimental group only. As for the gender of the recruited siblings of persons with disabilities, in most of the reviewed studies (n = 40), female siblings are more than male counterparts. In eight studies, the sample was gender-balanced, whereas four studies did not provide any detail on the participants’ gender.

The ages of the siblings involved in the reviewed studies ranged from 3 to 78 years of age. Unfortunately, this wide age range does not allow to conduct a sub-analysis (e.g., under and above 18 years) of each psychological construct. Nevertheless, this issue has been discussed in each psychological construct-related section. Except for the studies (n = 30) recruiting adult siblings (i.e., ≥ 18 years old) and for four studies that did not provide any information about the participants’ age, it was not possible to cluster participants by developmental stage.

For the specific purposes of the current systematic review, the types of disabilities mentioned in the reviewed studies were grouped in high-order clusters (labels of the cluster were assigned according to Peterson & Keeley, 2015). More specifically, 5 types of clusters were identified: (1) mental disorders (e.g., autism spectrum disorder, intellectual disabilities), (2) motor disabilities (e.g., mobility disabilities), (3) sensory disabilities (e.g., visual impairment, deafness), (4) genetic diseases (e.g., Down syndrome, CHARGE syndrome, 22q11.2 deletion syndrome, Williams-Beuren syndrome), and (5) neurological diseases (e.g., brain injury, epilepsy). As can see in Table 3, the specific type of disability investigated in each empirical study was mentioned in brackets. Resuming, mental disorders were the most investigated condition in the empirical literature (n = 39).

Standardized questionnaires were the most used data collection strategy in quantitative studies, while semi-structured interviews were mainly used in qualitative studies, together with open-ended question(s) designed to achieve specific objectives. The main strategies used to identify each psychological construct will be detailed in the following subsections.

Methodological Quality Appraisal of Included Studies

Results revealed that most of the papers reached a high (n = 45) appraisal of their methodological quality, whereas fifteen out of 60 studies reported a medium appraisal quality. Considering the 3-category of studies (i.e., qualitative, quantitative, and mixed) that have been reviewed, the following paragraphs resumed the main results.

Quantitative studies. Item 1 of the MMAT assesses whether the sampling strategy is appropriate for addressing the research question(s): All quantitative reviewed studies (n = 37) met this criterion. Item 2 evaluates whether the study sample is representative of the target population: 9 out of 37 studies met the criterion. Item 3 examines the appropriateness of the measurement(s) administered to address the research question(s): 33 out of 37 studies used validated and suitable measures. Item 4 assesses the risk of non-response bias: 23 out of 37 studies met this criterion by either maintaining a low non-response rate or using statistical adjustments like the imputation method. Lastly, Item 5 evaluates the appropriateness of the statistical analysis plan: All studies describe in detail statistical analyses computed according to the study design and research question(s). Overall, the quality appraisal of the quantitative studies is medium for 12 studies and high for 25.

Qualitative studies. Item 1 evaluates the appropriateness of a qualitative approach in addressing the research question(s): All studies (n = 18) met this criterion. Item 2 assesses the adequacy of the data collection method: 14 out of 18 studies met the criterion. Item 3 evaluates whether the data collection methods are aligned with the theoretical framework: All reviewed studies employed methods consistent with their theoretical rationale. Item 4 examines whether the findings’ interpretation is adequately supported by the data: Most of the papers (n = 16) met the criteria. Lastly, Item 5 evaluates the coherence between data collection, analysis, and interpretation: All studies met the criterion. In sum, the overall quality appraisal of the qualitative studies was medium for two studies and high for 16.

Mixed-methods studies. Items 1 and 2 probe whether the mixed-methods studies provided a solid rationale for employing this category integrating quantitative and qualitative design appropriately. Item 3 assesses if the overall interpretation based on the integration of both data types was made: all mixed studies (n = 4) met this criterion. Item 4 appraises whether the quantitative and qualitative components diverge or not: All mixed studies met this criterion. Lastly, Item 5 evaluates the individual quality of the quantitative and qualitative elements: 3 out of four studies met this criterion. In brief, 3 papers out of 4 reached a high methodological quality appraisal.

Psychological Constructs of a Sibling’S Experience

The purpose of this section is to summarize the findings for RQ1, i.e.: What are the main psychological constructs investigated in siblings of persons with disability?

Findings revealed three main psychological constructs: The sibling relationship (n = 17), sibling-focused parentification (i.e., the caring role that the sibling assumes toward the brother/sister; n = 17), and emotional and behavioral adjustment (i.e., individual’s emotional and behavioral adaptive responses to a stressful situation; n = 14). In a few studies on the population of siblings of persons with disabilities (n = 4), well-being was analyzed. Several studies (n = 6) examined more than one of the mentioned psychological constructs and were hence included in a hybrid group. Two papers that were conducted during the COVID-19 pandemic were also part of the studies reviewed. Because the stressful environmental conditions related to the pandemic could have affected the way each psychological construct has been experienced by siblings, these papers were reviewed and tabulated separately.

Impact of Each Investigated Psychological Constructs

This section aims to summarize the findings for RQ2, i.e.: What is the main role of each psychological construct in siblings of persons with disability experience?

The impact of each of the psychological constructs identified by answering RQ1 will be summarized by using a four-step strategy. Firstly, a brief description of the psychological construct will be provided, together with the research design (quantitative vs. qualitative vs. mixed) applied to analyze the construct in each study. Secondly, the high-order clusters of disabilities identified in the reviewed studies will be examined. In addition, the main findings for each psychological construct have been summerized. Finally, the relevant findings according to the socio-demographic features mainly examined in the reviewed studies have been reported. To be accurate, we summed up findings on (a) gender comparisons; (b) the relationship between psychological construct and siblings’ age; and (c) the relationship between psychological construct and severity of the brother’s or sister’s disability and/or chronic illness. Figure 2 shows the strategy.

Sibling Relationship

Sibling relationships may be the most obvious (Noller, 2005) and enduring kinds of relationships (Milevsky, 2011). They are usually characterized by contradictory feelings, such as love and conflict, affection and rivalry (Buist & Vermande, 2014). The quality of sibling relationships may be affected by the behavior and/or functioning of other family members (Cox & Paley, 1997), such as a child’s brother or sister with a disability and/or a chronic illness.

The electronic search identified 17 studies investigating the quality of sibling relationships between persons with disabilities and their siblings (Avieli et al., 2019; Bhattashali et al., 2018; Braconnier et al., 2018; Corsano et al., 2017; Cuskelly, 2016; Floyd et al., 2016; Guidotti et al., 2021; Hemati Alamdarloo et al., 2021; Noonan et al., 2018; Paul et al., 2022; Rossetti et al., 2020; Shivers, 2019a; Stock et al., 2016; Tomeny et al., 2017a, 2017b; Travers et al., 2020; Tyerman et al., 2019; Yacoub et al., 2018).

Data were collected cross-sectionally in all the studies except one (Floyd et al., 2016), for which they were gathered both cross-sectionally and longitudinally. Seven of the 17 reviewed studies were quantitative (Braconnier et al., 2018; Cuskelly, 2016; Floyd et al., 2016; Hemati Alamdarloo et al., 2021; Shivers, 2019a; Tomeny et al., 2017a, 2017b; Travers et al., 2020), 9 qualitative (Avieli et al., 2019; Bhattashali et al., 2018; Corsano et al., 2017; Noonan et al., 2018; Paul et al., 2022; Rossetti et al., 2020; Stock et al., 2016; Tyerman et al., 2019; Yacoub et al., 2018), and one mixed (Guidotti et al., 2021).

Most of the reviewed studies (n = 11) dealt with siblings of persons with mental disorders (Bhattashali et al., 2018; Braconnier et al., 2018; Corsano et al., 2017; Floyd et al., 2016; Guidotti et al., 2021; Noonan et al., 2018; Paul et al., 2022; Shivers, 2019a; Tomeny et al., 2017a, 2017b; Travers et al., 2020; Yacoub et al., 2018). Two studies recruited siblings of people with neurological diseases (Avieli et al., 2019; Tyerman et al., 2019). The other two studies involved siblings of persons with genetic diseases (Cuskelly, 2016; Stock et al., 2016). A study investigated two clusters of disabilities—mental disorders and genetic diseases (Rossetti et al., 2020). The remaining study explored the sibling relationship between TD individuals and their brothers or sisters with sensory diseases (Hemati Alamdarloo et al., 2021).

The reviewed quantitative studies reported mixed findings (Braconnier et al., 2018; Cuskelly, 2016; Floyd et al., 2016; Hemati Alamdarloo et al., 2021; Shivers, 2019a; Tomeny et al., 2017a, 2017b; Travers et al., 2020). On the one hand, several of them showed evidence of good sibling relationships (Braconnier et al., 2018; Cuskelly, 2016; Floyd et al., 2016; Tomeny et al., 2017a, 2017b; Travers et al., 2020). In particular, Travers and colleagues (2020) found that siblings spent more time with their brothers or sisters with disabilities and joined them in recreational activities. A study by Braconnier et al. (2018) revealed that siblings perceived the relationship with their brother or sister with a disability as being more satisfying than the one they had with their parents. Tomeny and colleagues (2017) highlighted that the supportive role played by parents positively affected sibling relationships. Cuskelly’s research (2016) showed that a sibling’s warmth benefited sibling relationships. On the other hand, findings by Hemati Alamdarloo and colleagues (2021) revealed conflictual and poor sibling relationships. Finally, it was shown that both the relationships between persons with disabilities and their siblings and those between TD individuals and their siblings were characterized by the same positive and negative aspects (Shivers, 2019a). The reviewed quantitative studies did not examine gender differences nor the association between the severity of a brother’s or sister’s disability and sibling relationship as a psychological construct. As for the association between the age of the siblings of persons with disabilities and sibling relationship, findings (Floyd et al., 2016) showed that the older the sibling, the better the sibling relationship was.

Findings of qualitative studies (Avieli et al., 2019; Bhattashali et al., 2018; Corsano et al., 2017; Noonan et al., 2018; Paul et al., 2022; Rossetti et al., 2020; Stock et al., 2016; Tyerman et al., 2019; Yacoub et al., 2018) revealed some crucial aspects of sibling relationships. A study by Rossetti and colleagues (2020) showed that the quality of sibling relationships was influenced by the type of a brother’s or sister’s disability. Specific results demonstrated that sibling relationships with brothers or sisters with Down syndrome were characterized by higher levels of reciprocity and involvement in activities compared to sibling relationships with brothers or sisters with autism. Research by Avieli et al. (2019) revealed five sibling relationship patterns: (a) sibling relationships where the sibling was a surrogate parent; (b) sibling relationships characterized by negative feelings, conflict, and rivalry; (c) sibling relationships shaped by ambivalent non-epistemic mental states (i.e., emotions) toward the brother or sister with a disability; (d) sibling relationships where the sibling acted as a mediator in the family; and (e) sibling relationships characterized by closeness and sharing. Several negative factors that may affect the quality of sibling relationships were also identified (Noonan et al., 2018; Paul et al., 2022; Tyerman et al., 2019; Yacoub et al., 2018). These included concern and uncertainty for the future (Corsano et al., 2017; Noonan et al., 2018; Paul et al., 2022), feelings of isolation in the parent-sibling relationship (Stock et al., 2016; Tyerman et al., 2019), difficulty in making friends and sharing one’s situation with others (Corsano et al., 2017), and experience of the social stigma associated with disability (Paul et al., 2022). Furthermore, siblings reported that the pervasive nature of their brother’s or sister’s disability (e.g., autism) negatively affected the quality of the sibling relationship, which was associated with feelings of anxiety, worry, and guilt (Stock et al., 2016; Yacoub et al., 2018).

However, besides an increased sense of responsibility, siblings also reported feelings of love, support, and respect (Bhattashali et al., 2018; Noonan et al., 2018; Paul et al., 2022; Stock et al., 2016; Tyerman et al., 2019; Yacoub et al., 2018), together with a strong sense of personal growth due to their dealing with their brother’s or sister’s disability (Paul et al., 2022). As for gender comparison, a study by Tyerman and colleagues (2019) revealed no significant gender differences in sibling relationships. Findings by Stock et al. (2016) showed that stronger relationships were established between siblings of the same gender. In the other qualitative studies reviewed (Avieli et al., 2019; Bhattashali et al., 2018; Corsano et al., 2017; Noonan et al., 2018; Paul et al., 2022; Rossetti et al., 2020; Yacoub et al., 2018), gender differences were not analyzed. In terms of the association between the age of siblings of persons with disabilities and sibling relationship, Stock et al. (2016) found that the age gap between a sibling and their brother or sister with a disability was directly proportional to their rivalry. To be accurate, considering the developmental stage of the participants' childhood and adolescence (n = 6) and youth and adulthood (n = 6) have been enrolled. The other studies took into account a wide age range (n = 4) and one study does not report this demographic feature. On children and adolescents, studies showed warm and close relationships (Bhattashali et al., 2018; Guidotti et al., 2021) as well as empathy and positive feelings toward their siblings with disabilities (Shivers, 2019a). Nevertheless, these studies reported sporadic family conflicts. On adults, attitudes may depend on the disability. For instance, adult siblings of persons with autism reported fewer positive attitudes compared to those with intellectual disabilities (Rossetti et al., 2020; Tomeny, Ellis et al., 2019), whereas warm and harmonious relationships have been reported by those of persons with Down syndrome (Cuskelly, 2016).

Only one study (Rossetti et al., 2020) investigated the association between sibling relationship and the severity of a brother’s or sister’s disability, with findings revealing that the more pervasive the disorder (e.g., mental disorders), the poorer the sibling relationship was.

Finally, a mixed study by Guidotti and colleagues (2021) found evidence of good sibling relationships. As for gender differences, findings showed that male siblings of persons with disabilities tended to perceive the sibling relationship as being conflictual, while their female counterparts were less inclined to think so. In terms of the association between the age of siblings of persons with disabilities and sibling relationship, findings showed that siblings of adolescents with disabilities were more ashamed, annoyed, and embarrassed than siblings of children with disabilities. The association between sibling relationship and the severity of a brother’s or sister’s disability was not computed in mixed studies.

Sibling-Focused Parentification

Following Hooper and colleagues (2012), parentification is “a type of role reversal, boundary distortion, and inverted hierarchy between parents and other family members in which adolescents assume developmentally inappropriate levels of responsibility in the family of origin” (Hooper et al., 2012; p. 165). The authors argued that this caring role served by the individual can be referred toward the parents (called parent-focused parentification) and/or toward a sibling (called sibling-focused parentification). When a disability occurs, this caring role may be experienced differently by the siblings. For this reason, the review focused on the sibling-focused parentification construct solely.

The electronic search identified 17 studies on the topic (Beffel & Nuttall, 2020; Brady et al., 2019; Brolin et al., 2024; Chiu, 2022; Kale & Siğirtmaç, 2021; Lashewicz, 2018; Eun Lee et al., 2018, 2023; Eun Lee et al., 2019a, 2019b; Eun Lee et al., 2019a, 2019b; Eun Lee et al., 2020; Niedbalski, 2023; Nuttall et al., 2018; Redquest et al., 2020; Rossetti et al., 2018; Tomeny et al., 2016a, 2016b, 2017a, 2017b). Data were collected cross-sectionally in all the studies. In 9 studies (Beffel & Nuttall, 2020; Brolin et al., 2024; Eun Lee et al., 2023; Eun Lee et al., 2019a, 2019b; Eun Lee et al., 2019a, 2019b; Nuttall et al., 2018; Redquest et al., 2020; Tomeny et al., 2016a, 2016b, 2017a, 2017b), quantitative data were gathered, while 6 studies (Brady et al., 2019; Chiu, 2022; Kale & Siğirtmaç, 2021; Lashewicz, 2018; Eun Lee et al., 2018; Niedbalski, 2023), analyzed qualitative data. In 2 studies (Eun Lee et al., 2020; Rossetti et al., 2018), both quantitative and qualitative data were collected.

Most of the reviewed studies examined the experience of siblings of persons with mental disorders. A study by Eun Lee et al., (2019a, 2019b) involved siblings of people with different disabilities: i.e., mental disorders, motor disabilities, and genetic diseases. Research by Kale and Siğirtmaç (2021) focused on siblings of people with genetic diseases and motor disabilities. Finally, the study by Brolin et al. (2024) recruited siblings of people with unspecified disabilities.

The reviewed quantitative studies helped to identify the different roles played by siblings of persons with disabilities. They acted as (a) current and future financial managers (Eun Lee et al., 2019a, 2019b; Redquest et al., 2020), (b) anchors (Eun Lee et al., 2019a, 2019b) or companions (Eun Lee et al., 2019a, 2019b), (c) caregivers (Eun Lee et al., 2019a, 2019b; Tomeny et al., 2016a, 2016b), and (d) facilitators of access to health care services (Eun Lee et al., 2019a, 2019b).

Three studies (Eun Lee et al., 2019a, 2019b; Tomeny et al., 2016a, 2016b, 2017a, 2017b) explored the association between sibling-focused parentification and sibling relationship, revealing conflicting results. More specifically, two studies (Eun Lee et al., 2019a, 2019b; Tomeny et al., 2016a, 2016b) found evidence of good sibling relationships despite the high level of responsibility experienced by the sibling because of parentification. Conversely, a study by Tomeny and colleagues (Tomeny et al., 2017a, 2017b) showed that a high level of responsibility and low perceived social support were associated with poor sibling relationships. Cross-cultural research conducted by Eun Lee et al. (2023) explored sibling-focused parentification in South Korea, Japan, and Taiwan, revealing the siblings’ low engagement in advocacy activities and caregiving. Findings by Beffel et al. (2020) and Nuttall et al. (2018) highlighted the protective role played by the perceived benefits of having a brother or sister with a disability. The authors stated that the siblings’ prosocial behavior (Beffel & Nuttall, 2020) and their future caregiving intentions (Nuttall et al., 2018) were predicted when they perceived their brothers’ or sisters’ disabilities as positively contributing to their own life. Finally, the study by Brolin et al. (2024) found that the caring role was associated with both negative (e.g., mental ill-health, impact on schooling in terms of negative school performance because the caring or being bullied because of the disability of their brother or sister, and a lack of support) and positive outcomes (e.g., increased maturity).

Except for a study by Eun Lee (2023), in which no gender differences were found when exploring sibling-focused parentification as a psychological construct, the other quantitative studies did not examine gender differences.

The age of siblings of persons with disabilities was positively related to parentification (Redquest et al., 2020). In other words, siblings older than 50 years of age showed an increased intensity in caregiving compared to middle-aged (30–49 years) and younger (20–29 years) siblings. One out of 17 reviewed studies recruited children to adolescents, 11 studies considered youth and adulthood, and four studies considered a wide age range. One study did not report the age range of the participants. Together, these studies reported mixed results on children, adolescents, and adults. On the one hand, maturity and personal growth result from the parentification. On the other hand, a low level of general well-being, a negative impact on school performance, and a feeling of lack of support are experiences because related the caring.

Finally, low functioning (Eun Lee et al., 2019a, 2019b), maladaptive behaviors (Eun Lee et al., 2019a, 2019b; Eun Lee et al., 2019a, 2019b), and low level of independence (Eun Lee et al., 2019a, 2019b) shown by brothers/sisters with disabilities were strongly and positively correlated to caregiving demands. The more severe the disability, the higher the level of responsibility perceived by the sibling was.

The reviewed qualitative studies showed that siblings of persons with disabilities mainly played three roles. Firstly, siblings acted as caregivers (Chiu, 2022; Eun Lee et al., 2018; Niedbalski, 2023) on three different levels, being (1) no/minimal caregivers, when they were not or little engaged in intensive caregiving duties; (2) anticipating caregivers, when they stressed the importance of discussing the future of their brother or sister with a disability with their parents; and (3) joint/primary caregivers, when they replaced their parents in caregiving duties. Secondly, findings revealed that siblings also played the role of friend and anchor (Eun Lee et al., 2018), follower (Lashewicz, 2018), and guardian (Brady et al., 2019; Eun Lee et al., 2018) for their brothers or sisters with disabilities. Finally, siblings acted as their brothers’ or sisters’ protectors and advocates within the family (Lashewicz, 2018).

Gender comparisons and the association between sibling-focused parentification and the severity of a brother’s or sister’s disability were not computed in qualitative studies. Only one study (Kale & Siğirtmaç, 2021) argued that parentification occurred regardless of the sibling’s gender. The same study also revealed that older siblings reported having more responsibilities than younger ones. Finally, a study by Chiu (2022) found that siblings—regardless of their age—were willing to help and take care of their brother or sister with a disability.

Two mixed studies were yielded. Both used high-order clustering to investigate the sibling’s role. Research by Eun Lee and colleagues (2020) identified three roles played by siblings of persons with disabilities. These included (1) the non-caregiver, (2) the single caregiver, that is a sibling who takes care of their brother/sister with a disability, and (3) the compound caregiver, a sibling who takes care of both their brother/sister with a disability and another person (e.g., the sibling’s child). A study by Rossetti and colleagues (2018) showed a 5-cluster solution, with the sibling being: (1) a companion, that is, an individual who is a close friend with their brother/sister with a disability; (2) little involved, thus showing low engagement in caregiving; (3) highly involved, when frequently playing the different roles of caregiver, sibling, and advocate; (4) needs-focused, and hence becoming their brother’s or sister’s advocate and informal service coordinator; and (5) professional, that is, their brother’s or sister’s legal representative and advocate. Among the different roles played by siblings of persons with disabilities, those of compound caregivers (Eun Lee et al., 2020) and companions (Rossetti et al., 2018) were the ones associated with a stronger emotional closeness in the sibling relationship.

Gender comparisons, the connection between sibling-focused parentification and the age of siblings of persons with disabilities., and the association between sibling-focused parentification and the severity of a brother’s or sister’s disability were not computed.

Emotional and Behavioral Adjustment

Adjustment is the individual’s emotional and behavioral adaptive response to a stressful environment or situation and its associated challenges (Harrison & Murray, 2015). Due to the considerable effort required when dealing with disabilities, growing up with a brother or sister with a disability and/or a chronic illness may be compared to living in a stressful environment. Thus, the individual emotional and behavioral adjustment may be impaired.

The electronic search identified 14 cross-sectional studies on the topic (Hanvey et al., 2022; Hayden et al., 2023; Le Boudec et al., 2021; Milevsky & Singer, 2022; O’Neill & Murray, 2016; Orm et al., 2022; Perenc & Pęczkowski, 2018; Shivers, 2019b; Shivers & Kozimor, 2017; Shojaee et al., 2020; Siman-Tov & Adi Sharabi, 2023; Tomeny et al., 2016a, 2016b; Tsai et al., 2016; Yaldız et al., 2021), with no longitudinal research being conducted. Eleven of the 13 cross-sectional reviewed studies were quantitative while the remaining two were qualitative (Hanvey et al., 2022; Milevsky & Singer, 2022). No mixed studies investigating the topic were yielded.

Nine of the eleven quantitative studies included data on siblings of persons with mental disorders (Hayden et al., 2023; O’Neill & Murray, 2016; Shivers, 2019b; Shivers & Kozimor, 2017; Shojaee et al., 2020; Siman-Tov & Adi Sharabi, 2023; Tomeny et al., 2016a, 2016b; Tsai et al., 2016; Yaldız et al., 2021). Two quantitative studies (Orm et al., 2022; Perenc & Pęczkowski, 2018) analyzed more than one high-order cluster of disability (e.g., mental disorders and motor disabilities). One study (Le Boudec et al., 2021) involved siblings of persons with disabilities and/or chronic illnesses whose details were not specified.

The two qualitative studies presented data on siblings of persons with more than one disability, that is, mental disorder and genetic disease (Milevsky & Singer, 2022), and mental disorder and neurological disease (Hanvey et al., 2022).

When analyzing emotional/behavioral adjustment as a psychological construct, the main findings of papers exclusively focusing on emotional adjustment (n = 8; Hanvey et al., 2022; Hayden et al., 2023; Milevsky & Singer, 2022; O’Neill & Murray, 2016; Perenc & Pęczkowski, 2018; Shivers, 2019b; Siman-Tov & Adi Sharabi, 2023; Yaldız et al., 2021) and those of studies centered on both emotional and behavioral adjustment (n = 6; Boudec et al., 2021; Orm et al., 2022; Shivers & Kozimor, 2017; Shojaee et al., 2020; Tomeny et al., 2016a, 2016b; Tsai et al., 2016) were examined separately. No studies solely investigating behavioral adjustment were identified.

Emotional Adjustment

Studies exclusively focused on emotional adjustment revealed that the siblings’ main responses to a stressful situation caused by their brothers’ or sisters’ disabilities were guilt, depressive symptoms, anxiety, stress, and empathy (Hanvey et al., 2022; Hayden et al., 2023; Milevsky & Singer, 2022; O’Neill & Murray, 2016; Perenc & Pęczkowski, 2018; Shivers, 2019b). More than 50% of the siblings of persons with disabilities involved in a study (Shivers, 2019b) reported having experienced feelings of guilt, described their sibling relationships as being poor, showed a high level of depressive symptoms and a low level of well-being. However, siblings of people with disabilities who had developed some independent living abilities experienced lower levels of mental distress showed a higher level of well-being and had a better quality of life (Hayden et al., 2023). Depressive symptoms and anxiety were assessed by comparing the experience of siblings of persons with different types of disabilities (O’Neill & Murray, 2016; Siman-Tov & Adi Sharabi, 2023). To be accurate, in the study by O’Neill and Murray (2016) siblings of persons with autism and Prader-Willi syndrome reported higher levels of anxiety than siblings of TD individuals. Siblings of individuals with autism and developmental disorders of unknown etiology showed higher levels of depression than the siblings of TD people. No significant differences in depressive symptoms and anxiety were found between siblings of persons with Down syndrome and siblings of TD individuals. The study by Siman-Tov & Adi Sharabi (2023) compared siblings of brother or sister with autism and intellectual disabilities revealing that the first showed less distress than the latter.

Although the negative impact of disability was reported in most of the reviewed studies, high levels of empathy were also identified in several of them (Milevsky & Singer, 2022; Perenc & Pęczkowski, 2018). Higher levels of cognitive and emotional empathy were reported by siblings of persons with motor disabilities than by siblings of TD individuals (Perenc & Pęczkowski, 2018). Kindness, patience, acceptance of others (Milevsky & Singer, 2022), and more attention to the other’s wants and needs (Yaldız et al., 2021) were also part of the positive aspects reported in the reviewed studies.

In terms of gender differences, most of the reviewed studies exclusively focused on emotional adjustment revealed that female siblings of persons with disabilities showed higher levels of positive and negative emotional symptoms compared to their male counterparts. Both females with a brother/sister with a disability and those of a TD individual reported higher levels of anxiety than male siblings (O’Neill & Murray, 2016; Yaldız et al., 2021). Furthermore, females experienced stronger feelings of guilt than their male counterparts (Shivers, 2019b). Conversely, two studies found that female siblings of persons with disabilities showed a higher level of cognitive and emotional empathy (Perenc & Pęczkowski, 2018), involvement, self-efficacy, and well-being (Siman-Tov & Adi Sharabi, 2023) than males. Only one study (Siman-Tov & Adi Sharabi, 2023) reported that male siblings of persons with disabilities experienced more loneliness than female counterparts.

As for the association between the age of the siblings of persons with disabilities and emotional adjustment as a psychological construct, the findings showed mixed results. On the one hand, the siblings’ age was positively correlated to cognitive empathy (Perenc & Pęczkowski, 2018): the older the sibling, the higher the level of cognitive empathy was. On the other hand, the study by O’Neill and Murray (2016) outlined that younger sibling of persons with genetic diseases (i.e., Down syndrome or Prader-Willi syndrome) showed high levels of anxiety (in the case of Down syndrome) and depressive symptoms (in the case of Prader-Willi syndrome). Furthermore, the authors found that the elder siblings of persons with developmental disorders of unknown etiology showed increased levels of anxiety. Considering children and adolescents of person with disability, they reported high levels of prosocial behaviors suggesting earlier and greater resilience and social engagement. On adults, results showed that less distress and high well-being depending on the level of the independence of their brother or sister with disability.

Finally, the association between the psychological construct and the severity of the brother’s or sister’s disability showed some interesting results. The low level of independence and functioning of the brother/sister with a disability was inversely proportional to the TD sibling’s feelings of guilt (Shivers, 2019b) and levels of emotional symptoms and distress (Hayden et al., 2023), while being directly proportional to the level of the sibling’s well-being (Hayden et al., 2023).

Emotional and Behavioral Adjustment

In the studies focused on both emotional and behavioral adjustment (Le Boudec et al., 2021; Orm et al., 2022; Shivers & Kozimor, 2017; Shojaee et al., 2020; Tomeny et al., 2016a, 2016b; Tsai et al., 2016), the main internalizing/externalizing symptoms detected were hyperactivity, hostility, anxiety, somatic and emotional problems. The levels of hyperactivity of siblings of persons with mental disorders (i.e., autism, intellectual and developmental disorders) were higher than those shown by siblings of TD individuals. Furthermore, the siblings of persons with autism showed more emotional/internalizing symptoms than the siblings of TD individuals (Shojaee et al., 2020). Additionally, siblings without disabilities reported more difficulties in behavioral adjustment in terms of the prosocial domain (Tsai et al., 2016). Siblings of persons with single disabilities reported less hostility and anxiety than siblings of persons with co-occurring disabilities (e.g., intellectual disability and depression or anxiety) (Shivers & Kozimor, 2017). Finally, a study by Orm (2022) found that the siblings of persons with mental disorders or physical disabilities showed higher levels of prosocial behavior than the siblings of TD individuals.

As for gender comparison, findings revealed that female siblings of persons with disabilities reported more somatic problems than their male counterparts, while male siblings of persons with disabilities showed more aggressive behaviors than siblings of TD individuals (Le Boudec et al., 2021). The analysis of the association between the psychological construct and the siblings’ age showed no significant results.

Finally, the severity of the brother’s or sister’s disability was negatively associated with their sibling’s emotional and behavioral adjustment (Tomeny et al., 2016a, 2016b): the more severe the disability was, the higher the levels of maladjustment reported by siblings were.

Well-being

Well-being is a multidimensional psychological construct covering a broad spectrum of domains, including physical, emotional, mental, social, and behavioral components (WHOQoL Group, 1993). When disability occurs in the family, it may not be surprising that this construct may be affected.

The electronic search conducted identified four papers on the topic (Correia & Seabra-Santos, 2022; Hallion et al., 2018; Koukouriki & Soulis, 2020; Lahaije et al., 2023). Three of them analyzed quantitative data (Hallion et al., 2018; Koukouriki & Soulis, 2020; Lahaije et al., 2023), while the remaining one was a qualitative study (Correia & Seabra-Santos, 2022).

In terms of high-order clustering inventoried for the present review purposes (see Methodological Characteristics of the Reviewed Studies section), a study by Hallion and colleagues (2018) involved siblings of persons with chronic illnesses and disabilities whose details were not specified. The other three studies (Correia & Seabra-Santos, 2022; Koukouriki & Soulis, 2020; Lahaije et al., 2023) analyzed the experience of siblings of persons with mental disorders.

Hallion and colleagues (2018) found no differences in the psychological well-being of siblings of persons with disabilities and siblings of TD individuals. A study by Koukouriki et & Soulis (2020) showed that siblings of persons with autism reported lower levels of well-being compared to siblings of TD individuals. Finally, the study by Lahaije and colleagues (2023) revealed that siblings of persons with disabilities perceived higher levels of emotional and material well-being than their parents. A qualitative study by Correia & Seabra-Santos (2022) revealed that the well-being of siblings of persons with disabilities was both positively and negatively impacted by their brother’s or sister’s disability. On the one hand, siblings stated that having a brother/sister with a disability influenced their personal growth, in terms of maturity, tolerance, understanding, patience, and strength. On the other hand, siblings acknowledged the difficulties and limitations imposed by disability.

No gender comparisons were analyzed when investigating well-being. The association between their age and well-being was computed only by Lahaije and colleagues (2023). Nevertheless, the authors included both parents and siblings of persons with disabilities in the analysis. Consequently, a more in-depth sub-analysis according to age range of participants is not possible. The impact of the severity of the disability on siblings’ well-being has not been examined.

Hybrid Studies

Studies that analyzed more than one of the specific psychological constructs identified in RQ1 were clustered as hybrid studies. Six papers met this criterion (Cebula et al., 2019; Jones et al., 2019; Kulisch et al., 2024; Levante et al., 2023a, 2023b, 2023c; Shivers et al., 2019; Zaidman-Zait et al., 2020). Four of them investigated both sibling relationship and emotional/behavioral adjustment, and one of them (Levante et al., 2023a, 2023b, 2023c) focused on sibling-focused parentification, social support, and parent-sibling relationships. The remaining one (Kulisch et al., 2024) investigated both behavioral adjustment and well-being.

In all the hybrid studies reviewed, quantitative data were collected cross-sectionally. Two studies (Jones et al., 2019; Zaidman-Zait et al., 2020) exclusively involved siblings of individuals with mental disorders. Other two studies analyzed more than one disability, with one investigating mental disorders and genetic diseases (Shivers et al., 2019), and the other dealing with genetic diseases, motor disabilities, sensory diseases, and mental disorders (both as a single and co-occurring disability) (Levante et al., 2023a, 2023b, 2023c). One study focused on siblings of persons with genetic diseases (Cebula et al., 2019). Finally, the remaining study (Kulisch et al., 2024) involved siblings of persons with unspecified disabilities.

A study by Shivers and colleagues (2019) found that siblings of persons with autism reported higher levels of emotional and behavioral maladjustment and less warmth in the sibling relationship compared to siblings of individuals with Down syndrome. Furthermore, the levels of emotional and behavioral adjustment reported by siblings of persons with disabilities were similar to those shown by the general population (Cebula et al., 2019). A study by Jones et al. (2019) revealed that siblings showed low levels of emotional and behavioral adjustment when their brother/sister with a disability reported high levels of such problems. Findings by Zaidman-Zait et al. (2020) showed higher levels of closeness and lower levels of conflict in relationships between persons with disabilities and their siblings compared to relationships between TD siblings. Furthermore, Zaidman-Zait et al. (2020) also found that good sibling relationships were associated with the highest levels of emotional and behavioral adjustment. A study by Levante and colleagues (Levante et al., 2023a, 2023b, 2023c) showed that the sibling’s high levels of distress and a negative parent-sibling relationship detrimentally affected the interplay between sibling-focused parentification and sibling relationship. The same study revealed that the benefits of parentification and the social support perceived by the siblings of persons with disabilities contributed to reducing their levels of distress. Finally, the study by Kulisch et al. (2024) revealed that coping strategies (in terms of minimization, situation control, positive self-instructions, and the need for social support) were positively associated with quality of life.

None of the reviewed studies analyzed gender differences nor the association between psychological constructs and the severity of the disability. Only one study (Levante et al., 2023a, 2023b, 2023c) included gender as a covariate in the mediation model, with no differences in terms of gender being found. As for the association between the age of siblings of persons with disabilities and the psychological constructs investigated, on children and adolescents Cebula et al. (2019) found that the older the sibling, the less warm the relationship was.

In terms of hybrid studies, three of them explore the experiences of children and adolescents. The study by Zaidman-Zait et al. (2020) found that siblings of children with disabilities show higher levels of empathy, less conflict and rivalry, and greater support and investment in the sibling relationship than siblings of typically developing (TD) individuals.

The Experience of Siblings of Persons with Disabilities during COVID-19

Although the COVID-19 pandemic heavily affected the functioning of individuals and several studies investigated the impact of restrictive measures on vulnerable populations (Asquini et al., 2021; Corbett et al., 2021; Levante et al., 2019, 2022; Rosencrans et al., 2021), the electronic search conducted identified only two studies (Dorsman et al., 2023; Redquest et al., 2021) focused on the sibling population. These were cross-sectional and mixed studies that aimed to explore the experience of siblings of persons with mental disorders during the pandemic lockdowns. In particular, the study by Redquest et al. (2021) investigated the support given to brothers/sisters with disabilities, the emotional adjustment, and the quality of family relationships. Data were collected from two groups: siblings of individuals with mental disorders who lived in the same house as their brothers or sisters, and siblings of individuals with mental disorders who did not live together with their brothers or sisters. In sum, results showed that all the siblings involved in the study constantly supported their brothers or sisters with disabilities, regardless of where they lived. Similarly, all of the siblings recruited reported being concerned for the health and well-being of their brothers or sisters with disabilities. The siblings who lived with their brothers or sisters with disabilities stated that the increased amount of time spent with them positively affected their sibling relationship.

The second study (Dorsman et al., 2023) carried out during the pandemic explored the roles served by siblings of persons with disabilities and the impact of pandemic-related restrictive measures on sibling relationship. Results outlined that the most assumed roles by siblings were brother/sister and legal representative/administrator/mentor. In addition, siblings of persons with disabilities reported that the social distancing imposed by the pandemic negatively affected the sibling relationship.

For both studies, gender comparisons were not computed, and the association between psychological constructs and the severity of the brother’s or sister’s disability was not analyzed. Finally, on youths and adults no association between psychological constructs and the age of the siblings of persons with disabilities was found.

Discussion

This systematic integrative review aimed to contribute to summarizing the empirical literature on the developing field of research on the psychological impact of a brother’s or sister’s disability on the functioning of their TD sibling. Therefore, following a PEO format, two research questions were formulated: “What are the main psychological constructs investigated in siblings of persons with disability?” (RQ1), and “What is the main role of each psychological construct in siblings of persons with disability experience” (RQ2). Sixty studies met the inclusion criteria based on the PICOS protocol and were included in the systematic review. Their methodological quality was appraised and showed that most of the reviewed studies reported a high (n = 45) quality; 15 reached a medium quality. The main characteristics and findings were tabulated and summarized narratively.

To identify the strengths and limitations of the reviewed studies, an overview of their methodological characteristics was provided. The findings prompted further considerations.

As most of the reviewed studies were conducted in Global North countries, future studies should involve the sibling population in Global South countries: cross-cultural studies may help to understand how having a brother or sister with a disability may impact the sibling’s experience. In addition, exploring the WEIRD and non-WEIRD populations could be an interesting and novel field of research. Not only would this lead to better identifying the psychological constructs that play a pivotal role in each specific culture, but it may also provide information to design culture-specific intervention programs.

A further issue to consider is related to the design of the reviewed studies, as data were collected cross-sectionally in most of them. Despite being challenging, gathering data longitudinally might help to understand how psychological constructs change over time. Similarly, conducting a meta-analysis combining relevant data might provide evidence of the impact of disability on each psychological construct.

Moreover, just under a fifth of the reviewed studies (n = 11) compared siblings of people with disabilities to siblings of TD individuals. A more comprehensive analysis might lead to identifying the psychological constructs that are most heavily affected by disability.

As for the sample recruited in the reviewed studies, two main issues should be highlighted. The first issue concerns gender distribution, as a descriptive analysis revealed that most of the studies recruited an unbalanced sample in terms of the gender of the siblings of persons with disabilities. This methodological flaw prevented an appropriate interpretation and generalization of the data. The second issue to consider is the wide age range of the siblings of persons with disabilities involved in the studies, a flaw that may be caused by difficulty in recruiting siblings at a specific developmental stage. Again, findings should be interpreted cautiously. Indeed, each developmental stage involves age-specific tasks (Erikson, 1994), based on which psychological constructs should be investigated. Consequently, future studies should solve such issues to provide clinical guidance in designing gender- and developmental stage-specific intervention programs.

Finally, the review of the selected studies showed that the most investigated cluster of disability was that of mental disorders. Although the pervasive nature of mental disorders (Hastings & Petalas, 2014; Mayes et al., 2012) might significantly impact the psychological constructs of a sibling’s well-being (Shojaee et al., 2020; Tomeny et al., 2016a, 2016b), it would also be useful to investigate other clusters of disabilities, considering their different levels of severity.

The first research question addressed by this systematic review aimed to identify the main psychological constructs of a sibling’s experience investigated in the selected studies. Findings revealed that the main psychological constructs analyzed were sibling relationship (n = 17), sibling-focused parentification (n = 17), and emotional/behavioral adjustment (n = 14). Only four of the reviewed studies focused on the well-being of siblings of persons with disabilities. The studies investigating more than one psychological construct were included in a hybrid group (n = 6). Finally, two studies were identified that explored the role of siblings of persons with disabilities, their emotional adjustment, and the quality of family relationships during the COVID-19 lockdowns. Findings suggest that future studies should extend knowledge of the most investigated psychological constructs and inform intervention programs. Additional research should aim at exploring topics that are often overlooked and their potential impact on the functioning of siblings of persons with disabilities.

An analysis of the findings for the second research question, which aimed at summarizing the main role of each identified psychological constructs, has led to making several suggestions.

The main psychological construct investigated among the sibling population was sibling relationship. In the reviewed studies, quantitative, qualitative, and mixed data were collected cross-sectionally. However, longitudinal studies would allow one to examine the magnitude of the change occurring in sibling relationships over time. As the main cluster of disability investigated was that of mental disorders, other clusters should be considered to extend knowledge of the topic. The reviewed studies yielded inconsistent results. On one side, they provided evidence of good, warm, and satisfying sibling relationships characterized by siblings spending time with their brothers or sisters with disability and participating in various activities. On the other side, findings showed conflictual and negative sibling relationships characterized by ambivalent feelings and rivalry.

The second most examined psychological construct was sibling-focused parentification, which was investigated by collecting quantitative, qualitative, and mixed data on siblings of persons with mental disorders. Therefore, longitudinal studies should also be designed, and other clusters of disabilities should be considered. The reviewed studies showed that siblings of persons with disabilities mainly acted as caregivers, with feelings of warmth and closeness being reported, together with a sense of duty toward other family members such as parents. The association between sibling relationship and sibling-focused parentification turned out to be the most examined in the literature. Nevertheless, findings were inconsistent, which suggests that such an interplay should be better analyzed in future longitudinal investigations.

The emotional and behavioral adjustment of siblings of persons with disabilities was the third most investigated psychological construct. As the reviewed studies analyzed quantitative and qualitative data on siblings of persons with mental disorders, it would be advisable to conduct some longitudinal and mixed studies in the future. Findings revealed that anxiety/depression, guilt, empathy, aggressive behaviors, and conduct problems were the most emotional/internalizing and behavioral/externalizing symptoms reported by siblings of persons with disabilities.

As for the studies investigating the well-being of siblings of persons with disabilities, the review findings highlighted that quantitative and qualitative data were collected cross-sectionally. Therefore, mixed and longitudinal studies should also be conducted in the future. The need for more in-depth investigations on the well-being of the siblings of persons with disabilities has been confirmed by both the inconsistent findings of the reviewed research and the low number of studies carried out on the topic. This psychological construct may play a crucial role in the development of intervention programs. Indeed, following the Complete Mental Health model proposed by Keyes (2002), the enhancement of individual well-being is essential to promote human flourishing, in terms of high levels of well-being and the absence of mental illness. Consequently, such a construct should be investigated in more detail.

Finally, all of the studies included in the hybrid cluster were cross-sectional and quantitative. For this reason, qualitative and/or mixed longitudinal studies should also be designed in the future. As for the psychological constructs analyzed, the reviewed studies focused on sibling relationship and the emotional and behavioral adjustment of siblings of persons with mental disorders.

Although this systematic review included papers published during the COVID-19 pandemic, only two of the studies selected focused on the issues faced by the sibling population in that period. Due to the short- and long-term effects that a pandemic may have on vulnerable populations and any individuals’ mental health (Alonso-Esteban et al., 2021; Bianco et al., 2021; Colizzi et al., 2020; Levante et al., 2019, 2022, 2024, 2023a, 2023b, 2023c; Panchal et al., 2021; Petrocchi et al., 2020; Quarta et al., 2022, 2023), further research should be conducted on the matter. The issues to explore should include the changes in the relationship between siblings of persons with disabilities owing to pandemic lockdowns and people being forced to live together, the potential change in the siblings’ role and/or in the perception of their responsibilities, the development and use of strategies to cope with problems arising when dealing with brothers or sisters with disabilities, and caregiving in a period in which it was not possible to access health care services.

The analysis of each psychological construct has led to the identification of three cross-cutting issues that are relevant to each of the constructs. In terms of the gender of the siblings of persons with disabilities, findings showed that females reported stronger feelings of guilt and higher levels of both anxiety and depression compared to their male counterparts. Furthermore, female siblings felt a stronger sense of responsibility than male siblings. Female siblings showed higher levels of empathy and better sibling relationships than male siblings. As for the siblings’ well-being, no gender comparisons were computed. It is important to point out that such results should be interpreted cautiously. When considering the association between the age of the siblings and the investigated psychological constructs, it should be mentioned that the age range of the siblings of persons with disabilities involved in the studies was often wide, which prevented an accurate interpretation of findings. Such an issue will be better discussed in the Future Recommendations section. Finally, the review showed that the severity of a brother’s or sister’s disability significantly impacted the psychological functioning of their sibling. In other words, the higher level of severity of a brother’s or sister’s disability resulted in a poor sibling relationship, more responsibilities in caregiving, and high levels of emotional and behavioral maladjustment. However, these results should be interpreted cautiously, since the main cluster of disability considered was that of mental disorders.

Implications for Practitioners

The findings of this systematic integrative review may play a role in clinical settings, as health professionals could take them into account when designing intervention programs aimed at siblings of persons with disabilities. These interventions may become instrumental in improving the psychological functioning of siblings in several ways. Specifically, our results may put the foundation for suggesting a model nesting the main psychological constructs extracted by the current systematic integrative review. Among them (i.e., sibling relationship, sibling-focused parentification, emotional/behavioral adjustment, and well-being), sibling-focused parentification may be the key psychological construct of target intervention. It may serve as a direct predictive factor of the quality of sibling relationships which, in turn, may have a cascade effect on the sibling’s psychological well-being and emotional/behavioral adjustment. In this vein, sibling relationships may be a simultaneous outcome and mediator. In other words, intervention programs may support the siblings in their caregiver role by mitigating the emotional burden related to the responsibilities and duties because of caregiving for their brother or sister with disabilities. Consequently, low levels of sibling-focused parentification may promote a positive attitude toward their brother/sister with a disability, an optimistic perspective toward the future, and the overall siblings’ well-being and emotional/behavioral adjustment. Therefore, the sibling relationship may directly benefit from low levels of sibling-focused parentification. Also, the sibling relationship may mediate the path between sibling-focused parentification, well-being, and emotional/behavioral adjustment: The lower responsibilities and duties because of the disability of their brother/sister (sibling-focused parentification), the high well-being and emotional/behavioral adjustment via the mediation of a high-quality sibling relationship.

Albeit the suggested model pieces together the main psychological constructs investigated in the sibling population, an additional innovative construct could moderate the suggested relationship between sibling-focused parentification and sibling relationships. Considering the scarce literature on the acceptance of disability as a resource in sibling populations than other ones (i.e., parents; Lecciso et al., 2013a, 2013b), the suggested model may pave the way for adding this construct in further investigations. For instance, the acceptance of disability may be conceived as a personal resource that arranges the sibling to face caregiving demands positively affecting the sibling relationship. Last, but not least exploring the role of sociodemographic features—i.e., siblings’ gender and age—and of the type of disability in the suggested model. Additionally, may be key to test the model considering the cultural background of the target sibling population. It is worth highlighting that although each relationship suggested in the model is supported by a sound theoretical framework, it has to be tested cross-culturally and in a gender-balanced sample.

Future Research and Intervention Recommendations

The systematic integrative review carried out has led to providing a series of recommendations for future research and intervention on the vulnerable population analyzed in the selected studies.

On the research field, it would be interesting to understand whether a sibling’s culture may influence how they are psychologically affected by having a brother or sister with a disability. As the systematic review showed, most of the studies were carried out in Global North countries, while only a few investigated the sibling population in Global South countries. In particular, one of the psychological constructs identified in this systematic review was the role played by siblings of persons with disabilities, which may also be analyzed in terms of cultural aspects (Rossetti & Hall, 2015). More in-depth investigations may help to address different research questions, such as “Are there any differences in the caregiving roles played by siblings of persons with disabilities in different cultures?”, and/or “How does parental education impact the siblings’ perception of their caregiving responsibilities toward their brothers or sisters with disabilities?”.

A second issue concerns the characteristics of the sample recruited in the studies, in terms of (1) the groups of participants, (2) the gender of the siblings of persons with disabilities, and (3) the age of the siblings of persons with disabilities. As for the groups of participants involved in the studies, descriptive results showed that most of the analyses explored psychological constructs only in the experimental group including siblings of persons with disabilities. This did not help to understand what psychological construct(s) was(were) the most affected by the brother’s or sister’s disability. Therefore, future investigations could compare the functioning of the siblings of persons with disabilities to that of siblings of TD individuals. Furthermore, as our review showed that studies have mostly focused on siblings of people with mental disorders, further research is needed on other clusters of disabilities (e.g., motor disability, sensory disability). This will allow a more comprehensive understanding of siblings' experiences in different disability contexts.

As for the gender of the siblings of persons with disabilities, the systematic review showed that about 82% of the studies involved more female than male participants. The Social Role Theory (Eagly, 2009; Pinho & Gaunt, 2024) helps to read this result. According to authors, societal expectations and norms shape female behaviors: women learn that they are the main family care providers, who manage home duties, and take care to each family member, especially when disability occurs earliest. Albeit vicious, this trend is supported by the high prevalence of females in participating in studies. More studies on male siblings are required to deepen their perspective and experiences regarding the disability of their brother and sister.

Furthermore, it would be interesting to investigate gender differences regarding the siblings’ culture. Investigating gender differences in sibling roles across cultures would provide deeper insights into how these roles are culturally constructed and the impact they have on family dynamics and individual well-being.

Finally, when considering the characteristics of the sample recruited in the selected studies, the age range of the siblings of persons with disabilities was wide, which led to interpreting findings cautiously. According to Erikson’s theory of psychosocial development (1994), each age range is characterized by specific tasks and goals, which should be considered when exploring psychological dimensions. For instance, the types of roles served by siblings of persons with disabilities could change if they are children (whom developmental tasks are to play and discover the social world), adolescents (who work for a sense of belonging to a group of peers and for the development of one’s identity), or adults (who engage in decision-making processes about their future, as moving out, pursuing a career, and that of their brothers or sisters with disabilities). The way to experience the impact of disability has a cascade effect on the quality of sibling relationship, emotional/behavioral adjustment, and well-being as well. Therefore, future studies should focus on specific age ranges, and/or samples should be clustered according to life-cycle tasks (Arnett, 2000).

Another aspect that should be considered in future investigations is related to the study design (longitudinal vs. cross-sectional) and the types of data collected (quantitative vs. qualitative vs. mixed). As the review showed, no longitudinal studies were carried out, which meant that causality relationships between constructs could not be identified. Although cross-sectional results provided general information about the psychological impact of disabilities on the functioning of siblings, the direction of the relationship between variables could not be determined.

A final issue concerns the strategies to be used in future studies. In several of the reviewed studies, strategies were specifically developed for each study, and/or no standardized qualitative strategies were applied. Therefore, results had to be interpreted cautiously. Future studies should aim at extending the range of tools used in this field of research to interpret the findings more accurately.

Findings summarize the psychological constructs mainly investigated by scholars, and which can be considered in individual and systemic as well intervention programs. For instance, they could be focused on the care burden experienced by siblings to develop and/or promote adaptive coping strategies. In turn, sibling could be trained to use these strategies to match their caring responsibilities without carelessness of their personal and professional needs and interests. Individual well-being could benefit from this. Additionally, family dynamics could be gained from sibling-focused interventions. For instance, the pivotal role served by the trust in promoting interpersonal relationships (Petrocchi et al., 2021) and theory of mind ability (Rotenberg et al., 2015) has been demonstrated. The essential role of these competencies is undoubted. Thus, intervention promoting this trait (i.e., interpersonal trust) could improve not only the quality of the parent-sibling relationship but also the sibling relationship. Additionally, the quality of sibling relationship and the individual well-being may benefit from interventions promoting the siblings’ acceptance of their brother or sister diagnosis. To our knowledge, trust in sibling relationship has been poorly investigated (Persram et al., 2022) and no studies on siblings’ reaction to diagnosis of disability has been carried out; thus, much more investigations are needed.

Strengths and Limitations

The main strength of this systematic review lies in its focus on how siblings are psychologically affected by their brothers’ or sisters’ disability, regardless of the clusters of disabilities identified in the selected studies. Such an approach has helped to explore all the psychological constructs investigated in the empirical literature.

The limitations of this systematic review are connected with the studies selected. Several studies involved more female than male participants. In several studies, the participants’ age range was too wide. In other cases, the sample size was not adequate. All these limitations restrict the transferability and generalization of the findings of this review.