Hyperhistaminemia in patients with histidinemia due to increased decarboxylation of histidine.

Histidinemia results from a defect in the major catabolic pathway of histidine. Among the various alternative metabolic pathways, transamination, methylation and acetylation of histidine have been found to be increased, but increased decarboxylation to histamine has not been reported in histidinemia. In an attempt to confirm the possibility of increased decarboxylation of histidine, plasma histamine levels were determined by reversed-phase high speed liquid chromatography in histidinemic, atopic, and control groups. In the histidinemic group, plasma histamine levels were higher than those in the other two groups, and correlated positively with plasma histidine level. Serum IgE levels, the numbers of eosinophils and basophils, and the histaminopexic power in the histidinemic group were within the normal range. These results suggest that hyperhistaminemia is not due to allergic reactions but results from increased decarboxylation of histidine.