Aims 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. We set out 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; (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 tics, tic-related symptoms and associated behavioural problems. Our results, coupled with previous findings, identified a clinical continuum of complex involuntary movements, hyperactivity/impulsivity symptoms, and semantically relevant utterances and gestures. A better characterisation of the GTS phenotypes will help to identify susceptibility genes.