The frequency and pattern of bilineal transmission in families of 153 consecutive patients with Tourette syndrome (TS) (TS in both parents in 51 family sets), compared with 60 normal control subjects selected from public schools (20 family sets), were evaluated by interview and questionnaire for evidence of TS and associated OCD and ADD at Baylor College of Medicine, Houston, TX.
Evidence for bilineal transmission (both parents of patients with TS with tics, OCD, ADD, or a combination of these features) was found in 25% of patients with TS and 0% of controls. Unilineal transmission (one parent with tics, OCD, ADD) occurred in 57% of patients with TS and 5% of normal controls. More than 80% of patients with TS had at least one parent with tics, OCD, or ADD; and 38% of TS parents had two or more of the TS spectrum traits of tics, OCD, or ADD. In normal control subjects, the prevalence rate of observed tics was 0.4% and TS by history was 0.7% of the school population. Bilineal transmission of TS suggests a polygenic or recessive inheritance. 
COMMENT. Both parents of patients with TS are at increased risk of tics, OCD, and ADD. In the general school population, the prevalence of tics by history is about double that observed at individual interview, and less than 1%.