Biallelic mutations in CAD, impair de novo pyrimidine biosynthesis and decrease glycosylation precursors

Hum Mol Genet. 2015 Jun 1;24(11):3050-7. doi: 10.1093/hmg/ddv057. Epub 2015 Feb 12.

Abstract

In mitochondria, carbamoyl-phosphate synthetase 1 activity produces carbamoyl phosphate for urea synthesis, and deficiency results in hyperammonemia. Cytoplasmic carbamoyl-phosphate synthetase 2, however, is part of a tri-functional enzyme encoded by CAD; no human disease has been attributed to this gene. The tri-functional enzyme contains carbamoyl-phosphate synthetase 2 (CPS2), aspartate transcarbamylase (ATCase) and dihydroorotase (DHOase) activities, which comprise the first three of six reactions required for de novo pyrimidine biosynthesis. Here we characterize an individual who is compound heterozygous for mutations in different domains of CAD. One mutation, c.1843-1G>A, results in an in-frame deletion of exon 13. The other, c.6071G>A, causes a missense mutation (p.Arg2024Gln) in a highly conserved residue that is essential for carbamoyl-phosphate binding. Metabolic flux studies showed impaired aspartate incorporation into RNA and DNA through the de novo synthesis pathway. In addition, CTP, UTP and nearly all UDP-activated sugars that serve as donors for glycosylation were decreased. Uridine supplementation rescued these abnormalities, suggesting a potential therapy for this new glycosylation disorder.

Publication types

  • Case Reports
  • Research Support, N.I.H., Extramural
  • Research Support, N.I.H., Intramural

MeSH terms

  • Animals
  • Aspartate Carbamoyltransferase / genetics*
  • Base Sequence
  • CHO Cells
  • Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing) / genetics*
  • Child, Preschool
  • Cricetinae
  • Cricetulus
  • DNA Mutational Analysis
  • Dihydroorotase / genetics*
  • Genetic Association Studies
  • Glycosylation
  • Heterozygote
  • Humans
  • Male
  • Metabolic Diseases / diagnosis*
  • Metabolic Diseases / genetics
  • Mutation, Missense
  • Protein Processing, Post-Translational*
  • Pyrimidines / biosynthesis*
  • Sequence Deletion

Substances

  • CAD trifunctional enzyme
  • Pyrimidines
  • Aspartate Carbamoyltransferase
  • Dihydroorotase
  • Carbamoyl-Phosphate Synthase (Glutamine-Hydrolyzing)
  • pyrimidine