Symptom domains in autism and related conditions: Evidence for familiality

Heterogeneity in autism impairs efforts to localize genes underlying this disorder. As autism comprises severe but variable deficits and traits in 3 symptom domains - social, communication, and repetitive behaviors - and shows variability in useful phrase speech, different genetic factors may be associated with each. Sibling-pairs (n = 212), including a autistic proband and 1 + siblings with autism or marked deficits in autism symptom domains, were assessed using the ADI-R. Symptom domain scores were examined to determine within sibling pair similarity. Results showed reduced variance within sibling pairs for repetitive behavior and for delays in and the presence of useful phrase speech. These features and nonverbal communication provided evidence of familiality when only autism was used to define sibling pairs (pairs =136). These same features appeared familial for those with autism-related conditions and their severity varied within sibling pairs independently. The features identified as familial replicate the combined set suggested in earlier, smaller studies. Furthermore, the familiality of these features extend to related but milder conditions and appear indepen-dent. Making symptom severity classification distinctions may be useful for molecular genetic studies of autism.