Dissecting the Gilles de la Tourette spectrum: A factor analytic study on 639 patients

Background: Recent studies using quantitative methods, such as principal component factor analysis, hierarchical cluster analysis and latent class analysis have suggested that Gilles de la Tourette syndrome (GTS) should no longer be considered a unitary condition as in current classification systems. Objective: To identify quantitative components of GTS symptomatology using a large, well characterised cohort of singleton individuals with GTS in order to inform future genetic studies with more homogeneous phenotypes. Methods: Principal component factor analysis with oblique rotation was used to analyse symptom data from a sample of 639 patients recruited at two tertiary referral centres using identical schedules during the period 1980-2008. Results: Three Factors were identified: (1) complex motor tics and echo-paliphenomena; (2) attention deficit and hyperactivity symptoms plus aggressive behaviours; and (3) complex vocal tics and coprophenomena. Obsessive compulsive behaviours loaded significantly on the first two factors. The three factors accounted for 48.5% of the total symptomatic variance. Conclusions: GTS is a phenotypically heterogeneous condition encompassing simple tics, specific complex tics and associated behavioural problems. The results, coupled with previous findings, identified a clinical continuum of complex tics, hyperactivity/impulsivity symptoms and semantically relevant utterances and gestures. A better characterisation of the GTS phenotypes will help to identify susceptibility genes.