The coding, promoter, and untranslated regions of the HDC gene, encoding l-histidine decarboxylase, were sequenced in DNA samples from 720 persons with Tourette's syndrome as well as 360 controls not screened for psychiatric disorders. The HDC nonsense mutation, W317X, was genotyped with the use of a custom TaqMan assay in 1500 controls. To ensure an appropriate comparison group, an assessment of the ancestral profile of the pedigree was performed with the use of genotyping data and a multidimensional scaling analysis7 comparing samples from the index family and 188 HapMap samples (Fig. S1 in the Supplementary Appendix).
