Hydantoin-5-propionic aciduria in folic acid nondependent formiminoglutamic aciduria observed in two siblings

Characteristics and outcomes of patients with formiminoglutamic aciduria detected through newborn screening

BACKGROUND

Glutamate formiminotransferase deficiency (FTCD deficiency) or formiminoglutamic aciduria is the second most common of the known inherited disorders of folate metabolism. Initial case reports suggested that patients may have severe intellectual disability and megaloblastic anemia. However, these cases were obtained from screening cohorts of patients with developmental delay. Subsequently, patients with milder clinical phenotypes have been reported. The full phenotypic spectrum of this disorder remains unknown.

METHODS

In many states, FTCD deficiency can be incidentally detected on tandem mass spectrometry-based newborn screening of dried blood spots. In this work, we report the outcomes of infants identified to have FTCD deficiency through newborn screening.

RESULTS

During the study period, 18 patients were identified to have FTCD deficiency and were referred and evaluated at one of the two participating metabolic centers. The overall rate of FTCD deficiency detected through the New Jersey screening program over the study time period was 1:58,982. At a mean age of 56 months at last follow-up: 3/18 (16%) had developmental delays requiring individualized education plans, no patients had profound intellectual disability; 4/16 (25%) had mild self-limited anemia, no patients had profound anemia.

CONCLUSIONS

These data suggest that the majority of individuals with FTCD deficiency detected by newborn screening are asymptomatic.

Allelic spectrum of formiminotransferase-cyclodeaminase gene variants in individuals with formiminoglutamic aciduria

Background

Elevated plasma and urine formiminoglutamic acid (FIGLU) levels are commonly indicative of formiminoglutamic aciduria (OMIM #229100), a poorly understood autosomal recessive disorder of histidine and folate metabolism, resulting from formiminotransferase‐cyclodeaminase (FTCD) deficiency, a bifunctional enzyme encoded by FTCD.

Methods

In order to further understanding about the molecular alterations that contribute to FIGLU‐uria, we sequenced FTCD in 20 individuals with putative FTCD deficiency and varying laboratory findings, including increased FIGLU excretion.

Results

Individuals tested had biallelic loss‐of‐function variants in protein‐coding regions of FTCD. The FTCD allelic spectrum comprised of 12 distinct variants including 5 missense alterations that replace conserved amino acid residues (c.223A>C, c.266A>G, c.319T>C, c.430G>A, c.514G>T), an in‐frame deletion (c.1373_1375delTGG), with the remaining alterations predicted to affect mRNA processing/stability. These included two frameshift variants (c.990dup, c.1366dup) and four nonsense variants (c.337C>T, c.451A>T, c.763C>T, c.1607T>A).

Conclusion

We observed additional FTCD alleles leading to urinary FIGLU elevations, and thus, providing molecular evidence of FTCD deficiency in cases identified by newborn screening or clinical biochemical genetic laboratory testing.

The molecular basis of glutamate formiminotransferase deficiency

Glutamate formiminotransferase deficiency, an autosomal recessive disorder and the second most common inborn error of folate metabolism, is presumed to be due to defects in the bifunctional enzyme glutamate formiminotransferase-cyclodeaminase (FTCD). Features of a severe phenotype, first identified in patients of Japanese descent, include elevated levels of formiminoglutamate (FIGLU) in the urine in response to histidine administration, megaloblastic anemia, and mental retardation. Features of a mild phenotype include high urinary excretion of FIGLU in the absence of histidine administration, mild developmental delay, and no hematological abnormalities. We found mutations in the human FTCD gene in three patients with putative glutamate formiminotransferase deficiency. Two siblings were heterozygous for missense mutations, c.457C>T (R135C) and c.940G>C (R299P). Mutagenesis of porcine FTCD and expression in E. coli showed that the R135C mutation reduced formiminotransferase activity to 61% of wild-type, whereas the R299P mutation reduced this activity to 57% of wild-type. The third patient was hemizygous for c.1033insG, with quantitative PCR indicating that the other allele contained a deletion. These mutations are the first identified in glutamate formiminotransferase deficiency and demonstrate that mutations in FTCD represent the molecular basis for the mild phenotype of this disease.

A case of formiminoglutamic aciduria. Clinical and biochemical studies

We describe a boy who excreted massive amounts of formiminoglutamic acid and hydantoin-5-propionic acid in his urine. He was mildly mentally retarded and epileptic, whereas his twin-brother was completely normal. Loading with L-histidine enhanced the excretion of both metabolites. Treatment was attempted with high doses of folic acid and methionine, but both were without effect on the excretion levels.

Inborn errors of molybdenum metabolism: combined deficiencies of sulfite oxidase and xanthine dehydrogenase in a patient lacking the molybdenum cofactor

A patient suffering from a combined deficiency of sulfite oxidase (sulfite dehydrogenase; sulfite:ferricytochrome c oxidoreductase, EC 1.8.2.1) and xanthine dehydrogenase (xanthine:NAD+ oxidoreductase, EC 1.2.1.37) is described. The patient displays severe neurological abnormalities, dislocated ocular lenses, and mental retardation. Urinary excretion of sulfite, thiosulfate, S-sulfocysteine, taurine, hypoxanthine, and xanthine is increased in this individual, while sulfate and urate levels are drastically reduced. The metabolic defect responsible for loss of both enzyme activities appears to be at the level of the molybdenum cofactor common to the two enzymes. Immunological examination of a biopsy sample of liver tissue revealed the presence of the xanthine dehydrogenase protein in near normal amounts. Sulfite oxidase apoprotein was not detected by a variety of immunological techniques. The plasma molybdenum concentration was normal; however, hepatic content of molybdenum and the storage pool of active molybdenum cofactor present in normal livers were below the limits of detection. Fibroblasts cultured from this patient failed to express sulfite oxidase protein or activity, whereas those from the parents and healthy brother of the patient expressed normal levels of this enzyme.

Profiling of human body fluids in healthy and diseased states using gas chromatography and mass spectrometry, with special reference to organic acids

This review summarizes recent advances in the application of gas chromatography and mass spectrometry to the study of human diseases. Emphasis is placed upon the organic acid profiles of the various body fluids. Methods for sample work-up prior to separation and mass spectrometric analysis are reviewed, and artifacts and pitfalls are discussed. Organic acid profiles, obtained with packed or capillary columns attached to mass spectrometers with or without computer systems, have led to the discovery of new normal metabolites, new metabolic disorders, and to new knowledge about a number of other diseases. Stable isotopes and gas chromatography--mass spectrometry are suitable for quantitative analysis of many compounds in the body fluids, and well suited for investigation of metabolic pathways.