Abstract
BACKGROUND: Recent research has demonstrated that subclinical autistic traits of parents amplify the effects of deleterious mutations in the causation of autism spectrum disorder (ASD) in their offspring. Here, we examined the extent to which two neurodevelopmental traits that are non-specific to ASD-inattention/hyperactivity and motor coordination-might contribute to ASD recurrence in siblings of ASD probands. METHODS: Data from a quantitative trait study of 114 ASD probands and their brothers, 26% of whom also had ASD, were analyzed. Autistic trait severity was ascertained using the Social Responsiveness Scale-2, attention/hyperactivity problems using the Achenbach System of Empirically Based Assessment, and motor coordination (in a subset of participants) using the Developmental Coordination Disorder Questionnaire. RESULTS: Among siblings (affected and unaffected), both categorical recurrence of ASD (Nagelkerke R (2) = 0.53) and quantitative ASD trait burden (R (2) = 0.55) were predicted by sibling ADHD and motor coordination impairment scores, even though these traits, on average, were not elevated among the unaffected siblings. CONCLUSIONS: These findings in a clinical family cohort confirm observations from general population studies that inattention/hyperactivity and motor impairment-axes of behavioral development that are non-specific to ASD, and often appreciable before ASD is typically diagnosed-jointly account for over 50% of the variation in autistic impairment of siblings, whether ascertained quantitatively or categorically. This finding within a sibling design suggests that background ASD susceptibilities that are inherited but non-specific ("BASINS") may contribute to additive genetic liability in the same manner that ASD-specific susceptibilities (such as parental subclinical ASD traits and deleterious mutations) engender ASD risk.