Gene Structure, Regulation and Function

The human OTC gene has been localized to the short arm of the X chromosome at Xp21.1(1), approximately 12 centimorgans (eM) closer to the centromere than the gene for Duchenne muscular dystrophy. The gene was located in normal cell lines by in situ hybridization to mitotic chromosome spreads, employing a nearly full-length eDNA probe. Finer localization was accomplished by using the probe on chromosomes with known deletions in the p21 region(1), Because it is located on the X chromosome, lyonization of the OTC gene in females due to random inactivation of one of the X-chromosomes(2) leads to a mosaic pattern in the liver which was elegantly demonstrated in the liver of a female heterozygous for OTC deficiency(3).