Psychiatric Disorders

Some psychiatric disorders, like Tourette's syndrome, have significant overlap (co-morbidity) with other psychiatric disorders (OCD and ADHD in the case of Tourette's). This may make the elucidation of genetic causes more difficult.

Tourette's syndrome is characterized by multiple motor tics and one or more vocal tics. It has onset before eighteen years and is one and one-half to three times more common in males. Twin, adoption, and segregation analysis studies support a genetic etiology for Tourette's syndrome. An autosomal dominant inheritance was initially suggested, but other inheritance patterns have been recently reported. There appears to be a relation with ADHD (up to 50 percent of individuals with Tourette's also have ADHD) and OCD (up to 40 percent of individuals with Tourette's have OCD). First-degree relatives are at high risk for developing tics and obsessive compulsive disorders.

Studying psychiatric disorders for genetic factors in their etiology is difficult because of the phenotype definition, co-morbidity, and multiple causal factors. The summary finding from the genetic studies to date suggest that there are multiple genes of small to moderate effect underlying the predisposition to these complex psychiatric disorders.