Table 2

Studies on symptom factors/clusters in GTS

Study	Country	Subjects	Variables	Methods	Factors/clusters
Alsobrook and Pauls 20029	USA	85	26 (clusters of tic symptoms)	HCA+PCFA	Aggression Tics Compulsions Tapping+absence of grunting
Eapen et al 200410	UK	91	11 (behavioural symptoms only)	PCFA	Obsessionality Anxiety/depression
Storch et al 200411	USA	76	15 (tic symptoms+ behavioural symptoms)	PCFA	Aggression ADHD OCD Tics
Mathews et al 200712	USA	254	38 (tic symptoms+ specific complex tics)	HCA	Simple tics Complex tics+OCS
Robertson and Cavanna 20078	UK	69 from 1 large pedigree	18 (clusters of tic symptoms+ behavioural symptoms)	HCA+PCFA	Tics ADHD+aggression Anxiety/depression/obsessionality+SIB
Grados et al 200813	International	952 subjects from 222 families	3 (diagnosis of GTS+OCD+ ADHD)	LCA	GTS+OCS/OCB GTS+OCD GTS+OCD+ADHD Minimally affected class CMT+ CD
Robertson et al 200814 ^*	UK	410	20 (clusters of tic symptoms+ specific complex tics)	HCA+PCFA	NOSIB+CVT CMT Simple tics Compulsions Self touching

↵* Study based on a subset of the present data.
ADHD, attention deficit hyperactivity disorder; CMT, complex motor tics; CVT, complex vocal tics; GTS, Gilles de la Tourette syndrome; HCA, hierarchical cluster analysis; LCA, latent class analysis; NOSIB, non-obscene socially inappropriate behaviours; OCB, obsessive compulsive behaviours; OCD, obsessive compulsive disorder; OCS, obsessive compulsive symptoms; PCFA, principal component factor analysis; SIB, self-injurious behaviours.