The Gilles de la Tourette Syndrome: A principal component factor analytic study of a large pedigree

BACKGROUND: The genetics and phenotypes of Gilles de la Tourette syndrome are complicated. Once indicated to be inherited as a single major autosomal dominant condition, several areas of interest on many chromosomes and one gene have been identified for Gilles de la Tourette syndrome, but no results have been replicated. Factor analytic studies suggest that there are more than one Gilles de la Tourette syndrome phenotype and it is not a unitary condition. OBJECTIVE: To characterize Gilles de la Tourette syndrome phenotypes in a group of individuals who underwent a complete genome scan. METHODS: We studied 85 members of a multiply affected multigenerational kindred, of whom 69 displayed Gilles de la Tourette syndrome-related symptoms (tics, obsessive-compulsive behaviours, obsessive-compulsive symptoms, attention deficit hyperactivity symptoms), using first a hierarchical cluster analysis followed by a principal component factor analysis. RESULTS: Three significant factors resulted from our analysis, accounting for approximately 42% of the symptomatic variance: Factor 1 (predominantly 'pure tics'), Factor 2 (predominantly 'attention deficit hyperactivity disorder and aggressive behaviours') and Factor 3 (predominantly 'depression-anxiety-obsessional symptoms and self-injurious behaviours'). Different kinds of tics occurred in all three factors. Only frowning/raising eyebrows and sniffing/smelling loaded significantly on both Factors 1 and 3. CONCLUSION: Our results give further evidence that the genetics of Gilles de la Tourette syndrome is complex and suggest that Gilles de la Tourette syndrome is not a unitary condition, thus confirming the results of earlier studies which have described several Gilles de la Tourette syndrome phenotypes. Although a genome scan on the pedigree reported three areas of interest and the present study found three factors, further studies would have to be undertaken to elucidate whether the three factors 'mapped' with the genetic data. Possible reasons for our findings and suggestions for future research are discussed.