What are the genetic causes of Tourette syndrome (TS) and other tic disorders?

Updated: May 30, 2019
  • Author: William C Robertson, Jr, MD; Chief Editor: Stephen L Nelson, Jr, MD, PhD, FAACPDM, FAAN, FAAP  more...
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Answer

TS is known to be familial; prevalence of TS in first-degree relatives is 5-15%, or at least 10 times the prevalence in the general population. Chronic motor tics (without vocal tics) are also common in relatives. This is not surprising, since vocal tics are essentially motor tics of the muscles used in speech. In the rest of this article, chronic motor or vocal tic disorder is not distinguished from TS.

Genetic factors are implicated in twin studies, which show that the ratio of concordance in monozygotic versus dizygotic twin pairs is approximately 5:1. [104] By the early 1990s, available data supported a single major autosomal dominant gene with pleiotropic expression (ie, chronic motor tics, TS, or OCD) and incomplete penetrance (about 70% in women, 99% in men). [105, 106] Family linkage methods excluded a single dominant gene in most of the genome, however.

More recent results suggest alternative models. These models include the involvement of several genes rather than one, intermediate penetrance in heterozygotes than in homozygotes, or mixed genetic-environmental causes. [107]

A sibling-pair approach, which may be more sensitive under these conditions, is currently being employed to search for TS genes. The TSA and the National Institutes of Health have supported an international collaborative genetic study using linkage and sibling methods to analyze 500 markers in over 2200 individuals from 269 families. [108] For example, this research has identified DLGAP3 as a promising candidate gene for TS. [109]

Other approaches to identifying specific genes related to TS include examination of families with visible chromosomal abnormalities or a high degree of consanguinity. [110] One such association has been reported, but it affects at most a small minority of people with tics. [111]


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