A new sensitive method for assay of histidase in human skin and detection of heterozygotes for histidinemia.

A new sensitive method was developed for assay of histidase in the stratum corneum of human skin with [14C] histidine as substrate. With this method histidase could be detected using less than 1 mg of stratum corneum. Skin histidase was markedly reduced in seven infants with histidinemia. The enzyme activities in thirteen parents of the patients were about 50% of the normal values, and even the highest values in the parents did not overlap the lowest normal values. Thus heterozygotes in the autosomal recessive form of histidinemia can be distinguished from normal persons by their skin histidase activity measured by this sensitive assay method.