Neurodevelopmental Outcomes of a High-Risk Autism Spectrum Disorders Cohort of Full and Half Siblings

Background: The Markers of Autism Risk in Babies – Learning Early Signs (MARBLES) Study is an autism high-risk cohort that started enrolling families in 2006. Eligible families include an older biological sibling with a confirmed Autism Spectrum Disorders (ASD) diagnosis and a new younger sibling followed prenatally until 36 months. The new younger sibling is referred to as the child of interest (COI). The COIs are followed for early signs of ASD and other developmental delays. Research assessing the risk factors of younger siblings for developing ASD or other non-typical development (non-TD) is limited.

Objectives: To assess the risk of developing ASD or non-TD for younger full and half siblings. To compare Autism Diagnostic Observational Schedule (ADOS) comparison (severity) scores among the COIs with a confirmed ASD or non-TD diagnosis and their sibling relationship (full vs half).

Methods: Logistic regression was used to compare the diagnostic outcomes (ASD, non-TD, or TD) and linear regression on ADOS severity scores to sibling relationship (full versus half siblings). All analyses were adjusted for child gender, race, ethnicity, and birth year; and maternal age and education.

Results: We reviewed 275 COIs (116 females and 160 males) who completed a 36 month developmental assessment including Mullen Scales of Early Learning and ADOS with a final diagnosis of ASD (64), non-TD (70), and typically developing (TD, 141) COIs. Of the 275 COIs, 239 had an older full sibling with ASD (97 females 142 males) and 36 had an older half sibling with ASD (18 females and 18 males). When comparing the sibling relationship and its association with an ASD diagnosis, there was no significant risk associated with being diagnosed with ASD versus TD (p=0.49; OR= 0.722; 95% CI: 0.283,1.843). However, a full younger sibling was associated with a borderline significantly higher risk of being diagnosed with non-TD (p=0.08; OR=.414; 95%; CI: 0.151 1.133) . Younger siblings diagnosed with ASD were compared using their autism severity scores obtained from the ADOS. Being a full siblings was associated with higher autism severity scores (p=0.04). Among children with non-TD, no significant difference severity score was found between full and half siblings (p=0.14).

Conclusions: We found no significant difference in estimated risks of developing ASD or non-TD for younger full and half siblings based on the sibling relationship. Full younger siblings diagnosed with ASD have a higher ADOS severity score, when compared to the half siblings with the same diagnosis. Though our study suggests some differences in outcomes between younger full and half siblings, our sample size is small and larger studies are needed to confirm these findings.