Family data support a dominant major gene for Tourette syndrome.

A dominant major gene was supported by analyses of 50 large extended Tourette syndrome (TS) pedigrees and by a subset of families defined by proband's clinical response to the neuroleptic drug haloperidol. Relatives were defined as affected if they ever had tics or TS. Assuming a nearly even sex ratio for TS and related symptoms resulted in the best fit of the genetic model to observed rates in families.