Concentrations of monoamine metabolites in the cerebrospinal fluid of twins and unrelated individuals--a genetic study

The concentrations of the major monoamine metabolites, homovanillic acid (HVA), 3-methoxy-4-hydroxyphenylethylene glycol (MOPEG), and 5-hydroxyindoleacetic acid (5-HIAA) in the cerebrospinal fluid (CSF), of platelet monoamine oxidase (MAO) and of dopamine beta-hydroxylase (DBH)-activity in serum and CSF were determined in pairs of healthy mono- and dizygotic twins, brothers and unrelated individuals. Intraclass correlations were calculated for each category of pairs. Of the monoamine metabolites, only MOPEG was found to be under any major genetic influence. Genetic heritability for MOPEG was 0.74 with no evidence of cultural heritability or environment common to twins. For HVA and 5-HIAA, a familial influence was found, where the cultural heritability was higher than the genetic. As in previous studies of MAO in blood platelets and of DBH activity in serum, there was strong evidence for a genetic component. The genetic heritability for MAO was 0.78. For DBH in serum the genetic component was 0.98, and for DBH in CSF, 0.83. The demonstration of a familial influence on 5-HIAA and HVA in CSF requires a more detailed analysis of the character of such environmental and genetic influences, using more direct techniques.