Five genome wide linkage analyses have been performed to date [55–59]. The Tourette Syndrome Association International Consortium for Genetics (TSAICG) has conducted the largest of these genetic linkage studies. Their sample represents a joint analysis of most of the individuals contained in the four previous studies and consists of 238 nuclear families and 18 large multigenerational families totaling 2,040 individuals [59]. Both parametric and non-parametric analyses were performed using two diagnostic classifications: 1) GTS alone; 2) combination of either GTS or CT. Strong evidence for linkage was observed in the multigenerational families for markers on chromosome 2p23.2 using the combined phenotype of GTS or CT, with suggestive evidence for linkage on chromosomes 5p, and 6p. A combined analysis including both affected sib pair and multigenerational families showed a slightly increased linkage signal on 2p, and the fine mapping of the 15 centiMorgan (cM) critical region yielded a signal with an empirical p=3.8 × 10−5.
