A BROADER PHENOTYPE OF AUTISM - THE CLINICAL SPECTRUM IN TWINS

The diagnostic boundaries of the behavioural phenotype for autism were examined in 28 MZ pairs and 20 DZ same-sex twin pairs, where one or b oth twins had autism. In the non-autistic cotwin (i.e. in twin pairs d iscordant for autism) it was common to find language impairments in ch ildhood and social deficits persisting into adulthood. Concordance for this broader phenotype was much greater in MZ pairs than DZ pairs, in dicating a strong genetic component. Behavioural and cognitive manifes tations of autism were compared both within and between MZ twin pairs. The variation was as great within MZ twin pairs as between pairs, sug gesting that it does not index genetic heterogeneity (although aetiolo gical heterogeneity probably exists). Current diagnostic practices nee d reevaluation. Copyright (C) 1996 Association for Child Psychology an d Psychiatry.