August 1985

A Twin Study of Tourette Syndrome

Author Affiliations

From the Department of Human Genetics (Drs Price, Kidd, and Pauls), and the Child Study Center (Drs Cohen, Pauls, and Leckman), Yale University School of Medicine, New Haven, Conn. Dr Price is now with the Department of Psychiatry, Hospital of the University of Pennsylvania, Philadelphia.

Arch Gen Psychiatry. 1985;42(8):815-820. doi:10.1001/archpsyc.1985.01790310077011

• In 43 pairs of same-sex twins, in which at least one co-twin had Tourette syndrome (TS), 30 pairs were probably monozygotic (MZ) and 13 were probably dizygotic (DZ). Concordances for TS were 53% and 8% for MZ and DZ pairs, respectively. When diagnostic criteria were broadened to include any tics in co-twins, concordance rates were 77% and 23% for MZ and DZ pairs, respectively. These concordances are consistent with genetic etiology. However, the fact that only 53% of MZ twins were fully concordant indicates nongenetic factors affect expression of TS. Presence of tics in discordant co-twins and timing of onset in partially concordant co-twins support an association between TS and tics in families with TS present. The data are inconclusive on whether some MZ twins with discordant co-twins are etiologically different from those who are concordant.