Skin histidase activity and urine formiminoglutamic acid (FIGLU) in patients with histidinemia found by screening newborn infants

Histidinemia: a biochemical variant or a disease?

Histidemia, first described by Ghadimi in 1961, is caused by a defect in histidase. The defect results in elevated urinary excretion of histidine and its transamination products, and in high blood histidine. Blood histidine levels in histidinemic patients range from 290 to 1420 microM (normal 70-120 microM). The clinical picture of histidinemia varies from complete normality to severe retardation, with many patients being asymptomatic. No correlation has been found between clinical and biochemical data. Most reported cases have been identified in newborn screening programs. Frequency of histidinemia ranges from 1 in 8000 (Japan) to 1 in 37,000 (Sweden). Histidinemia is inherited as an autosomal recessive trait. Maternal histidinemia is believed to be benign. Studies in animal models have shown similar metabolic changes in animals and humans, but clinical changes differ. Histidinemia may be treated with a low-histidine diet, which reduces elevated histidine levels, although in most cases no improvement of clinical symptoms has been observed.

Simultaneous determination of stable isotopically labelled L-histidine and urocanic acid in human plasma by stable isotope dilution mass spectrometry

A capillary gas chromatographic-mass spectrometric method for the simultaneous determination of stable isotopically labelled L-histidine (L-[3,3-2H2,1',3'-15N2]histidine, L-His-[M + 4]) and urocanic acid ([3-2H,1',3'-15N2]urocanic acid, UA-[M + 3]) in human plasma was developed using DL-[2,3,3,5'-2H4,2'-13C,1',3'-15N2]histidine (DL-His-[M + 7]) and [2,3,5'-2H3,2'-13C,1',3'-15N2]urocanic acid (UA-[M + 6]) as internal standards. L-Histidine and urocanic acid were derivatized to alpha N-(trifluoroacetyl)-imN-(ethoxycarbonyl)-L-histidine n-butyl ester and imN-(ethoxycarbonyl)urocanic acid n-butyl ester. Quantification was carried out by selected ion monitoring of the molecular ions of the respective derivatives of L-His-[M + 4], DL-His-[M + 7], UA-[M + 3] and UA-[M + 6]. The sensitivity, specificity, precision and accuracy of the method were demonstrated to be satisfactory for measuring plasma concentrations of L-His-[M + 4] and UA-[M + 3] following administration of trace amounts of L-His-[M + 4] to humans.