X-chromosome inactivation in human liver: confirmation of X-linkage of ornithine transcarbamylase.

Histochemical assay for ornithine transcarbamylase (OTC) activity in fixed frozen hepatic sections from a woman heterozygous for OTC deficiency revealed two populations of hepatocytes: those with normal activity and those with no activity. This observation, in conjunction with data from previous family studies, confirms the hypothesis that the gene for OTC is X-linked. It also provides the first cytologic demonstration of cellular mosaicism for a liver-specific cell product.