Results from family studies have suggested that obsessive-compulsive disorder (OCD) is a genetically heterogeneous disorder and have emphasized the importance of identifying valid subgroups of patients. The current study focused on early-onset OCD probands and examined the recurrence risks of OCD and tics among first-degree family members. One hundred six children and adolescents with OCD were recruited from a specialty clinic for OCD and 44 control individuals without OCD were identified by random-digit dialing. These 150 probands and their 465 first-degree relatives were assessed by trained interviewers, using standardized semi-structured interviews. Diagnoses were assigned according to DSM-IV criteria by two experts blind to the proband's diagnosis, through the best-estimate process. These data were analyzed using chi(2) tests, t-tests, logistic regression, and generalized estimating equations (GEE). Case probands had a mean age of onset of OC symptoms of 6.7 years (SD = 2.8), and high comorbid rates with Tourette syndrome (33%) and chronic tics (13.2%). Compared to control relatives, case relatives had higher age-corrected recurrence risks of OCD (22.7% vs. 0.9%, odds ratio (OR) = 32.5, 95% confidence interval (CI) = 4.5-230.8, P = 0.0005), and chronic tics (11.6% vs. 1.7%, OR = 7.9, 95% CI = 1.9-33.1, P = 0.005). A comorbid diagnosis of tics in the relatives was the best predictor of their diagnosis of OCD (OR = 7.35, 95% CI = 3.79-14.25, P < 0.0001). There was a significant correlation between the ages of onset of OCD in probands and their affected relatives. Childhood onset OCD is a highly familial disorder. Some early-onset cases may represent a valid subgroup, with higher genetic loading and shared vulnerability with chronic tic disorders.

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