Genetic analysis in nine unrelated Italian patients affected by OTC deficiency: detection of novel mutations in the OTC gene

Abstract

Ornithine transcarbamylase deficiency (OTCD) is an X-linked urea cycle disorder due to a defect of the mithocondrial enzyme ornithine transcarbamylase (OTC). Genetic analysis in nine unrelated Italian patients affected by OTCD (one male patient and eight female manifesting carriers) led to the detection of three novel mutations and six previously reported mutations in the OTC gene. The analysis was performed by direct sequencing of OTC cDNA, OTC exons, and intron-exon boundaries and enzymatic restriction analysis on the patients' genomic DNA and total RNA isolated from peripheral blood lymphocytes. In the male patient the new mutation S132P due to the nucleotide change c.394T>C was identified. In a manifesting carrier the nucleotide change c.292G>A that leads to the novel amino acid substitution E98K was identified; this mutation is close to the OTC protein's carbamyl phospate binding site. In another manifesting carrier the OTC cDNA analysis revealed the normally spliced transcript and an aberrant transcript with an insertion of two nucleotides (c.77-78insAG). In the patient's genomic DNA we identified a new transvertion IVS1-3C>G at the heterozygous state; this nucleotide change generates a new splice acceptor site in intron 1 that induces an RNA splicing defect. This insertion causes a frame shift in OTC cDNA ORF and leads to a premature stop codon. The previously described mutations N161S, R141Q, T178M, R92X, A208T, M268T were identified in the other six manifesting carriers.