Partly because of the lack of success in current efforts to identify TS susceptibility genes, and partly in order to further define and understand this heterogeneous disorder, investigators have begun to re-examine the assumptions underlying the standard study designs, including phenotype definition, mode of transmission, and degree of bilineality. There is renewed interest in examining the heritability of potential alternate phenotypes for TS, including chronic motor or vocal tics (CMVT), OCD or OCB, and ADHD36, 39–41. Additionally, studies have suggested that for TS and related disorders, the mode of transmission is not straightforward, and bilineality may be more common than previously thought8, 22, 42.
