Symptoms and the genetics of schizophrenia: implications for diagnosis.

To determine whether genetic influences in schizophrenia are related to the symptoms specified by diagnostic criteria, the case histories of 151 pairs of monozygotic twins from five twin studies of schizophrenia were rated for positive and negative symptoms. Concordance rates in monozygotic twins were significantly higher when probands had a greater number of negative symptoms; no evidence of a similar relationship was found for positive symptoms. The data indicate that negative symptoms may be characteristic of schizophrenia in which there is a greater genetic component. The results have important implications for determining diagnostic criteria and understanding the pathogenesis of schizophrenia.