Later Sibling Recurrence of Autism Spectrum Disorder and Attention-Deficit/Hyperactivity Disorder: Clinical and Mechanistic Insights

In this issue of JAMA Pediatrics, Miller and colleagues¹ report on the within- and cross-condition recurrence of attention-deficit/hyperactivity disorder (ADHD) or autism spectrum disorder (ASD) in later-born siblings of children (probands) with those conditions. The relatively high heritability of both conditions is well established from twin studies assessing both trait variance² and diagnostic recurrence.³ Two recent large-scale Scandinavian studies extended this work to show that the 2 conditions also occur together in families.^4,5 One population-based study of children with ASD (N = 3578) estimated the combined (older and younger) sibling recurrence of ASD in siblings to be 10.5%, but also reported that 5.3% had siblings with a diagnosis of ADHD, giving relative risks of 11.8 and 3.7 compared with matched controls without ASD.⁴