A Novel Two–Nucleotide Deletion in the Ornithine Transcarbamylase Gene Causing Fatal Hyperammonia in Early Pregnancy

Abstract

Ornithine transcarbamylase (OTC) deficiency shows X–linked inheritance. Typically, symptomatic females (who constitute 15%–20% of all carriers) have markedly reduced enzyme activity and show first symptoms in late infancy or early childhood. Here we present the case of a previously asymptomatic 24–year–old woman who died of severe hyperammonemia associated with orotic aciduria but normal OTC activity in the fourth month of pregnancy. DNA analysis revealed a novel mutation in form of the deletion of two nucleotides (T892, G893) in exon 9 of the OTC gene, leading to a frame shift and an aberrant gene product. We suggest that OTC deficiency should be suspected in any patient who presents with hyperammonia in the presence of otherwise normal liver function.