Mid-childhood autism sibling recurrence in infants with a family history of autism

Autism sibling recurrence in prospective infant family history studies is similar to 20% at 3 years but systematic follow-up to mid-childhood is rare. In population and clinical cohorts autism is not recognized in some children until school-age or later. One hundred and fifty-nine infants with an older sibling with autism underwent research diagnostic assessments at 3 years and mid-childhood (6 to 12 years (mean 9)). We report the autism sibling recurrence rate in mid-childhood and compare developmental and behavioral profiles at mid-childhood and 3 years in those with earlier versus later recognized autism, and those who had, or had not, received a community autism diagnosis. The autism recurrence rate in this sample in mid-childhood was 37.1%, 95% CI [29.9%, 44.9%] and higher in boys than girls. Around half of those diagnosed with autism in mid-childhood had not received a diagnosis at 3 years. Later, diagnosis was more common in girls than boys. While some had sub-threshold symptoms at 3, in others late diagnosis followed a largely typical early presentation. Sibling recurrence based on community clinical diagnosis was 24.5%, 95% CI [18.4%, 31.9%]. Those who also had a community diagnosis tended to be older, have lower adaptive function and higher autism and inattention symptoms. Notwithstanding limitations of a single site study, modest sample size and limits to generalisability, autism sibling recurrence in family history infants may be higher in mid-childhood than in studies reporting diagnostic outcome at 3 years. Findings have implications for families and clinical services, and for prospective family history studies. Autism sibling recurrence in prospective infant family history studies is similar to 20% at 3 years but follow-up to mid-childhood is rare although in some children autism is not recognized until school-age or later. We assessed 159 infants with an older sibling with autism at 3 years and in mid-childhood (9 years). The autism sibling recurrence rate in mid-childhood was 37.1%, 95% CI [29.9%, 44.9%] and higher in boys than girls. Only half of those diagnosed with autism in mid-childhood had received a diagnosis at 3 years and later diagnosis was more common in girls than boys. Clinicians need provide ongoing monitoring of younger siblings of autism probands to be able to offer support to families when they express concern and seek services.