[Histidine tolerance in low skin histidase activity].

An oral histidine loading test (100 mg L-His/kg body weight) was performed in 8 deaf patients with low histidase activity in the str. corneum of the skin. Beside an elevated plasma phenylalanine level resulting in a Phe/Tyr-quotient of 1,09 +/- 0,15 the basal level of histidine was slightly enhanced in patients with deafness, but without statistical significance. After histidine loading no differences of the histidine tolerance curves could be observed suggesting the heterozygosity state for histidinaemia. Thin-layer chromatographic investigation of imidazole compounds revealed some abnormal findings after loading. The results are discussed with regard to the clinical and biochemical heterogeneity of histidinaemia.