Identification of new mutations in the ornithine transcarbamylase (OTC) gene in Korean families.

Ornithine transcarbamylase (OTC) deficiency, an X-linked inborn error of the urea cycle, is known to be heterogeneous genetically as well as phenotypically. Molecular defects of Korean patients with OTC deficiency have not been reported. To investigate molecular lesions resulting in OTC deficiency, the OTC genes of unrelated symptomatic or asymptomatic female heterozygotes were amplified exon by exon and analysed by direct sequencing of double-stranded DNA. Three new mutations, two missense and one nonsense, were detected: (1) a C-to-T transition in codon 44 in exon 2 replacing a threonine by an isoleucine (T44I) was found in a late-onset symptomatic female patient but not in her asymptomatic mother; (2) a C-to-T transition in codon 214 creating a new RsaI recognition site in exon 6 and substituting tyrosine for histidine (H214Y) was identified in an asymptomatic female carrier whose son developed acute neonatal onset of OTC deficiency; (3) a C-to-T transition in codon 320 (arginine) abolishing a TaqI recognition site and creating a new BclI site in exon 9 with generation of a stop codon (R320X) leading to premature termination in the enzyme. This nonsense mutation was found in a symptomatic female patient and her asymptomatic mother whose son died of OTC deficiency during the neonatal period. In addition, we found a G-to-A transition in codon 141 in exon 5 causing substitution of glutamine for arginine (R141Q) in a female obligate heterozygote whose previous three sons succumbed to acute neonatal-onset OTC deficiency. This missense mutation has been described previously and is known to eliminate a TaqI recognition site in exon 5.