Adjustment in Typically Developing Siblings of Children with ASD: The Impact of Sex, Age, and Birth Order

Background: The current literature investigating adjustment and behavior challenges in typically developing siblings of children with ASD (TD-Sibs) reports inconsistent findings. Some studies report TD-Sibs demonstrate adjustment problems compared to normative samples, while others report no significant differences. However, the inconsistent literature may reflect the influence of modulating factors that impact sibling adjustment. While some modulating factors, such as maternal stress and affected sibling’s ASD severity, have been investigated with mixed results, other potential modulators (e.g. birth order) have yet to be fully explored. Recent literature suggests TD-Sibs younger than their affected sibling may exhibit problem behaviors because of increased stress from birth due to the presence of a sibling with ASD or modeling sibling behavior.

Objectives: To investigate the impact of modulating factors such as sex, age, and birth order on TD-Sib adjustment. We hypothesized that TD-Sibs younger than their sibling with ASD will exhibit more adjustment challenges compared to older TD-Sibs and age-based norms.

Methods: Thirty-four families with at least one TD-Sib (N=34, 6-12 years, mean age=8.9 years) and one child with ASD were recruited through a larger study investigating the effectiveness of a sibling support group. Prior to support group participation, one parent completed the Child Symptom Inventory-4 (CSI-4) and Behavior Assessment System for Children, Second Edition (BASC-2) to measure the TD-Sib’s emotional and behavioral adjustment. To investigate the difference in clinical/subclinical occurrences in adjustment difficulties between TD-Sibs and normative samples, binomial t-tests were conducted for each CSI-4 and BASC-2 subscale. Within the TD-Sib sample, independent sample t-tests were used to compare subscale scores between males and females, TD-Sibs younger or older than the affected sibling, and TD-Sibs younger than eight (<8) or eight and older (8+; cutoff selected to correspond to BASC-2 normative age groupings).

Results: On the CSI-4, male and female TD-Sibs showed no significant differences in adjustment and scored in the normative range on all subscales. However, the proportion of female TD-Sibs with subclinical Depression subscale scores was lower than population norms (p<0.05). TD-Sibs younger than their affected sibling had greater challenges than older TD-Sibs on BASC-2 Daily Living Skills subscale (t(29)=-2.06, p<0.05). Compared to TD-Sibs 8+, TD-Sibs <8 exhibited worse adjustment on BASC-2 Functional Communication (t(32)=2.55, p<0.05) and marginally more impairment on BASC-2 Attention (t(32)=2.01, p=0.053) and Conduct (t(32)=1.10, p=0.054) subscales. Likewise, the proportions of TD-Sibs <8 with subclinical adjustment difficulties on the BASC-2 Depression subscale was higher than population norms (p<0.05). The proportions of TD-Sibs 8+ with adjustment challenges on all CSI-4 and BASC-2 subscales were comparable to or less than population norms (BASC-2 Somatization, Withdrawal, Leadership, Functional Communication, p-values<0.05).

Conclusions: TD-Sibs did not exhibit difficulties in their parent-reported adjustment and scored in the normative range on both adjustment measures. However, our findings suggest an effect of birth order and developmental age, such that TD-Sibs younger than their affected sibling or younger than eight showed more adjustment challenges. Understanding the psychological well-being of TD-Sibs may help inform family and sibling support groups as well as sibling-mediated interventions for children with ASD.