BROADER AUTISM PHENOTYPE - EVIDENCE FROM A FAMILY HISTORY STUDY OF MULTIPLE-INCIDENCE AUTISM FAMILIES

Objective: Studies of families ascertained through a single autistic p roband suggest that the genetic liability for autism may be expressed in nonautistic relatives in a phenotype that is milder but qualitative ly similar to the defining features of autism. The objective of this s tudy was to examine behaviors that may define this broader phenotype i n relatives ascertained through two autistic siblings. Method: The aut hors used a semistructured family history interview to compare the rat es of social and communication deficits and stereotyped behaviors in r elatives ascertained through two autistic siblings (families with mult iple-incidence autism; 25 families) with the rates in relatives of Dow n syndrome probands (30 families). Results: Higher rates of social and communication deficits and stereotyped behaviors were found in the re latives in the families with multiple-incidence autism. Conclusions: T hese data suggest that further studies should be undertaken to delinea te the boundaries of the broader autism phenotype and that this broade r phenotype should be included in some future genetic analyses of this disorder.