Consanguineous Iranian kindreds with severe Tourette syndrome.

The search for vulnerability genes for Tourette syndrome has been ongoing for nearly three decades. The contribution of recessive loci with reduced penetrance is one possibility that has been difficult to explore. Homozygosity mapping has been successfully used to detect recessive loci within populations with high rates of consanguinity. Using this technique, even quite small inbred families can be informative due to autozygosity in which the two alleles at an autosomal locus are identical by descent (i.e., copies of a single ancestral gene). To explore the utility of this approach, we identified 12 consanguineous Iranian families. Remarkably, these families were seen with an unusual natural history characterized by the early onset of vocal tics and coprolalia and frequent comorbidity with obsessive-compulsive disorder. Genotyping the affected and unaffected members of these pedigrees has the potential to identify rare recessive contributions to this disorder.