A novel missense mutation in exon 8 of the ornithine transcarbamylase gene in two unrelated male patients with mild ornithine transcarbamylase deficiency.

We studied two unrelated male probands with mild ornithine transcarbamylase (OTC) (E.C.2.1.3.3) deficiency presenting a similar clinical course. Previous analyses of their liver OTCs also revealed similar properties. To identify the underlying molecular defects, we first cloned the entire coding region of the OTC gene from one proband and found a single base-substitution (C to T) leading to the substitution of tryptophan for arginine at amino acid position 277. Using a genomic amplification technique followed by allele specific oligonucleotide hybridization, we identified the same point mutation in the OTC gene of the other proband. We observed the presence of the mutation among family members in at least three generations, and in one asymptomatic hemizygous sibling in each family.