Shared familial transmission of autism spectrum and attention‐deficit/hyperactivity disorders

Background To determine whether familial transmission is shared between autism spectrum disorders and attention‐deficit/hyperactivity disorder, we assessed the prevalence, rates of comorbidity, and familial transmission of both disorders in a large population‐based sample of children during a recent 7 year period. Methods Study participants included all children born to parents with the Kaiser Permanente Northwest ( KPNW ) Health Plan between 1 January 1998 and 31 December 2004 ( n  = 35,073). Children and mothers with physician‐identified autism spectrum disorders ( ASD ) and/or attention‐deficit/hyperactivity disorder ( ADHD ) were identified via electronic medical records maintained for all KPNW members. Results Among children aged 6–12 years, prevalence was 2.0% for ADHD and 0.8% for ASD ; within those groups, 0.2% of the full sample (19% of the ASD sample and 9.6% of the ADHD sample) had co‐occurring ASD and ADHD , when all children were included. When mothers had a diagnosis of ADHD , first born offspring were at 6‐fold risk of ADHD alone ( OR  = 5.02, p  < .0001) and at 2.5‐fold risk of ASD alone ( OR  = 2.52, p  < .01). Results were not accounted for by maternal age, child gestational age, child gender, and child race. Conclusions Autism spectrum disorders shares familial transmission with ADHD . ADHD and ASD have a partially overlapping diathesis.