A family study of plasma dopamine-beta-hydroxylase in schizophrenia.

The genetic influence on plasma dopamine-beta-hydroxylase and the possible differences in the activities of this enzyme between schizophrenic patients and their healthy first degree relatives were studied in 103 members of 21 families. The activities of the 24 patients did not differ from those of their 37 healthy siblings or their 42 parents. A control group of 52 subjects without family history of the illness had similar enzyme activities. The correlation coefficients between patients and healthy siblings, between patients and parents, and between healthy siblings and parents were all around 0.50, as is expected for subjects who share half of their genes. Thus, although plasma dopamine-beta-hydroxylase activity is genetically determined, it neither differentiates schizophrenic from healthy family members nor differentiates subjects with a family history of the illness from those without such a history.