The purpose of this study is to identify genes that affect susceptibility to obsessive-compulsive disorder (OCD). By identifying genes that increase or decrease the risk of OCD, researchers can better understand how the condition develops and ultimately improve treatment for people with OCD.

OCD is a severe, familial condition that affects approximately 2% of the population. The way OCD is inherited is not clearly understood, but researchers believe it is complex and involves multiple genes. This study will detect and localize genes that increase or decrease susceptibility to OCD. The data collected from this study will be combined with data from other research studies to determine gene linkage and association.

Obsessive-compulsive disorder (OCD) is a severe, heritable condition with a lifetime prevalence of about two percent of the population. The mode of inheritance is poorly understood but is likely complex, involving multiple loci of small to major effect. Since 1995, the NIMH-IRP has been active in a multi-center family study of OCD, led by Dr. Gerald Nestadt of Johns Hopkins University, which was approved via a competitive NIMH extramural application (MH 502140). An expanded consortium of sites (including new sites at Brown and Harvard Universities) anticipates adding 300 new affected sib-pair families over the next three years. This sample will be used for linkage and association analyses. Data will be shared within this consortium of investigators studying OCD, and will eventually be combined with data obtained from a second consortium.

• INCLUSION CRITERIA:

Must have a diagnosis of obsessive-compulsive disorder, or be a family member (usually a parent or sibling) of someone with obsessive-compulsive disorder.

Certain disorders are considered part of OCD "spectrum" disorders and often include family members with OCD. These include Tourette's Syndrome, other individuals with tics, and Trichotillomania (severe hair pulling), and other forms of repetitive behaviors.

Persons with primary behavioral difficulties who do not fit with the current definitions of "OCD and OCD spectrum disorders" may not be eligible. These include compulsive shopping, gambling, or compulsive sexual behaviors.