Genetic analysis of carbamoylphosphate synthetase I and ornithine transcarbamylase deficiency using fibroblasts

Deficiencies of carbamoylphosphate synthetase or of ornithine transcarbamylase, two urea cycle enzymes located within mitochondria, often present as severe neonatal hyperammonaemic crises and have a poor prognosis. While genetic analysis of the X-chromosomal transmitted ornithine transcarbamylase deficiency (OTC) is performed by exon-wise mutation screening of genomic DNA in most cases, identification of mutations in the autosomal inherited carbamoylphosphate synthetase (CPS 1) deficiency requires analysis of transcripts due to the unknown genomic structure. We tested the hypothesis that CPS 1 and OTC are expressed at low levels in fibroblasts and indeed were able to amplify full-length cDNA from that source. Using a reverse transcriptase polymerase chain reaction based procedure we completely characterised the genetic background in five patients and identified three novel mutations and a novel polymorphism of the CPS 1 gene (deletion/insertion 2170delGCTCinsCCA, nonsense mutation 2359C > T, missense mutation 3161T > G and Thr1406Asn, respectively), as well as the missense mutations 482A > G and 994T > A of the OTC gene. Conclusion Cultured fibroblasts are an easily accessible source for genetic analysis of inborn errors of urea cycle enzymes which are functionally expressed only in liver and gut.