Metabolic studies of a family with massive formiminoglutamic aciduria

We have described two siblings who excrete massive amounts (up to 3.89 mmol/24 hr) of N-formiminoglutamic acid (FIGLU) in their urine. This unusual compound was isolated from urine, purified, and firmly identified as FIGLU by combined gas chromatography-mass spectrometry. The patients presumably have a deficiency in activity of the hepatic enzyme, glutamate formiminotransferase, which carries out the fourth sequential step in the main pathway of histidine degradation. Unlike children reported previously with this disorder, our patients had normal serum folate levels, had no hematologic abnormalities, and were not mentally retarded. Very small amounts of FIGLU were present in the plasma of one of the patients, but FIGLU was not detectable in the cerebrospinal fluid of either patient. Administration of pharmacologic doses of folic or folinic acid produced a decrease in excretion of FIGLU in urine. Histidine loading caused a small and comparable urinary excretion of FIGLU in the children's parents and in control adult subjects.