title: Decomposing the autism phenotype into familial dimensions.
abstract: The objective of this article is to decompose the level of functioning phenotype in autism to see if it can be conceptualized as two simpler, but still familial, dimensional phenotypes of language and non-verbal IQ. We assembled 80 sibpairs with either autism, Asperger syndrome or atypical autism. To see whether the familial correlation on language scores was accounted for by the familial correlation on non-verbal IQ, residual language scores were calculated for each member of the sibpair based on a multiple regression equation using their IQ score as an explanatory or independent variable and controlling for the age and gender of the affected individual. These residual scores were then used to calculate intraclass correlations between affected sibs. This process was repeated using IQ as the dependent variable and language as a covariate. Within affected individuals there was a strong relation between non-verbal IQ (as measured by the Leiter performance scale) and language (as measured by the Vineland Communication Scale). In addition, there was familial correlation between sibs on both measures. Evidence of familial aggregation on both non-verbal IQ and language remained even after partialling out the effect of the covariates by regression analysis and by generalized estimating equation. These findings suggest that non-verbal IQ and language in PDD may arise from independent genetic mechanisms. The implications of this finding for linkage analysis and for identifying genetically informative phenotypes are discussed.
authors.affiliation: Department of Psychiatry and Behavioural Neurosciences, McMaster University, Hamilton, Ontario, Canada. szatmar@mcmaster.ca
authors.forename: Peter
authors.initials: P
authors.lastname: Szatmari
authors.forename: Chantal
authors.initials: C
authors.lastname: Mérette
authors.forename: Claudia
authors.initials: C
authors.lastname: Emond
authors.forename: Lonnie
authors.initials: L
authors.lastname: Zwaigenbaum
authors.forename: Marshall B
authors.initials: MB
authors.lastname: Jones
authors.forename: Michel
authors.initials: M
authors.lastname: Maziade
authors.forename: Marc-Andre
authors.initials: MA
authors.lastname: Roy
authors.forename: Roberta
authors.initials: R
authors.lastname: Palmour
mesh_terms: D020817:Asperger Syndrome / Q000235:genetics; D001321:Autistic Disorder / Q000175:diagnosis / Q000235:genetics*; D002648:Child; D002659:Child Development Disorders, Pervasive / Q000235:genetics; D005190:Family; D005260:Female; D008040:Genetic Linkage; D006801:Humans; D007360:Intelligence / Q000235:genetics; D008297:Male; D010641:Phenotype; D035781:Siblings; D014705:Verbal Behavior