Mental Health Disorders in High-Risk Younger Siblings of Children with Autism Spectrum Disorder

Background:  Mental health disorders are common in children with ASD, particularly anxiety and ADHD, but the prevalence and nature of mental health disorders among high-risk younger siblings of children with ASD is not yet known.

Objectives:  The purpose of the current study was to describe mental health disorders in a sample of high-risk younger siblings of children with ASD.

Methods:  Participants were 31 younger siblings of children with ASD from our Canadian multi-site prospective study who were followed from age 6 or 12 months to 8 years. Mental health diagnoses (other than ASD) were determined using the K-SADS-PL (2009 version), a semi-structured interview designed to assess current and past psychopathology in children age 6–18 years according to DSM-IV-TR criteria, administered to participants' parents. Chi-square tests were used to explore diagnostic rates between groups, and file review provided additional details about the cases with mental health diagnoses.

Results:  Based on independent, best-estimate clinical diagnoses at age 8 made with the Autism Diagnostic Interview–Revised, Autism Diagnostic Observational Schedule, and expert clinical judgement using DSM-IV-TR, participants were classified as “non-ASD sibs” (n=17; 47% male) or “ASD sibs” (n=14; 79% male). The groups did not differ in language ability, as measured by the CELF-4 Core Language score (t₍₂₆₎=-1.36, p=.19). Overall, 29% (n=5) of non-ASD sibs and 64% (n=9) of ASD sibs met criteria for one or more lifetime diagnoses other than ASD, Chi²=3.77, p=.05. Psychopathology primarily involved internalizing (mood and anxiety disorders), externalizing (attention-deficit and disruptive behavior disorders), and elimination disorders; no participant met criteria for schizophrenia/psychotic, eating, or tic disorders. The most common diagnosis among non-ASD sibs was Specific Phobia (n=3), whereas the most common among ASD sibs was ADHD (n=6). Anxiety disorders were evident in equivalent proportions in both groups (60% non-ASD sibs; 56% ASD sibs), Chi²=1.31, p=.25.

Conclusions:  This is the first known study of mental health disorders (other than ASD) in younger siblings of children with ASD. Consistent with previous studies of comorbidity in ASD, we found high rates of both internalizing and externalizing disorders among ASD sibs. Correspondingly, almost one-third of non-ASD sibs also had mental health disorders, and in both groups multiple disorders were common. These findings highlight the importance of monitoring mental health status in younger siblings of children with ASD throughout childhood, whether or not they have ASD themselves.