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Preferential aggregation of OCD spectrum disorders in the schizo-obsessive group supports this unique clinical association. Whether a schizo-obsessive interface represents comorbidity or a specific subtype of schizophrenia warrants further investigation.

A substantial proportion of schizophrenia patients also has obsessive-compulsive disorder (OCD). To further validate the clinical validity of a schizo-obsessive diagnostic entity, we assessed morbid risks for schizophrenia-spectrum disorders and OC-associated disorders in first-degree relatives of schizophrenia probands with and without OCD. Two groups of schizophrenia probands [with OCD (n = 57) and without OCD (n = 60)] and community-based controls (n = 50) were recruited. One hundred eighty two first-degree relatives of probands with OCD-schizophrenia, 210 relatives of non-OCD schizophrenia probands, and 165 relatives of community subjects were interviewed directly [59.3% (108/182), 51.9% (109/210), and 54.5% (90/165), respectively], using the Structured Clinical Interview for Axis-I DSM-IV Disorders and Axis II DSM-III-R Personality Disorders and the remaining relatives were interviewed indirectly, using the Family History Research Diagnostic Criteria. Relatives of OCD-schizophrenia probands had significantly higher morbid risks for OCD-schizophrenia (2.2% vs. 0%; P = 0.033) and OCPD (7.14% vs. 1.90%; P = 0.014), and a trend towards higher morbid risk for OCD (4.41% vs. 1.43%; P = 0.08) compared to relatives of non-OCD schizophrenia probands. When morbid risks for OCD, OCPD, and OCD-schizophrenia were pooled together, the significant between-group difference became robust (13.74% vs. 3.33%; P = 0.0002). In contrast, relatives of the two schizophrenia groups did not differ significantly in morbid risks for schizophrenia-spectrum disorders, mood disorders, or substance abuse disorders. A differential aggregation of OC-associated disorders in relatives of OCD-schizophrenia versus non-OCD schizophrenia probands, provides further support for the validity of a putative OCD-schizophrenia ("schizo-obsessive") diagnostic entity.

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