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.
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