Obsessive-compulsive disorder and schizophrenia in three identical twin pairs.

Three monozygotic twin pairs are described who are concordant for DSM-III-R obsessive-compulsive disorder while being discordant for schizophrenia or schizoaffective disorder. Follow-up interview showed the non-psychotic co-twins to have schizotypal personality disorder. It is concluded that obsessive-compulsive and schizophrenia-spectrum disorders can truly co-exist, thus supporting diagnostic changes introduced into DSM-III-R, and may in some cases be inherited together.