The genetics of neurotic-reactive depression: a reanalysis of Shapiro's (1970) twin study using diagnostic criteria

The present study explored the role of genetic factors in the development of neurotic depression. Case studies of 16 monozygotic (MZ) and 14 same-sex dizygotic (DZ) twins from Robert Shapiro's 1970 study of non-endogenous depression were rediagnosed by two raters blind to the zygosity and identity of each twin. Diagnoses were made using Research Diagnostic Criteria (RDC) and George Winokur's 1985 criteria for neurotic-reactive depression. When neurotic depression was operationally defined using Winokur's criteria plus RDC major or definite minor depression, the concordance rate for MZ twins was significantly greater than that for DZ twins. Our results contrast with Shapiro's negative findings, probably due to our use of formal diagnostic criteria and Shapiro's requirement that cotwins be hospitalized to be considered concordant. The present results suggest that genetic factors play a role in the etiology of at least some forms of neurotic depression.