The occurrence of Tourette's syndrome in two generations of this family and the absence of this and related disorders in the maternal lineage support the conclusion that the syndrome is an autosomal dominant trait in this family. Genomewide analysis, which specified a rate of phenocopy of 1% (i.e., 1% of affected persons may not carry the genetic risk factor), identified complete linkage of a 3.4-centimorgan (cM) segment of chromosome 15 with Tourette's syndrome, with a lod score of 2.05, which approximated the maximum theoretical lod score (2.1) that could be achieved under the model of dominant transmission. No other region had a lod score above 1, and varying the predicted rates of penetrance (i.e., manifestation of the disease in carriers of the genetic risk factor) and phenocopy had no effect on the result (Fig. 2A and 2B). Genotyping of short-tandem-repeat markers defined a lod – 2 interval of 8.13 Mb flanked by the markers D15S126 and GATA153F11 (Fig. 1, and the Supplementary Appendix).
