Hyperammonemia in a girl who inherited a likely pathogenic variant of the ornithine transcarbamylase gene from her asymptomatic father-A peculiar pattern of X-linked recessive inheritance.

A three-year-old Chinese girl presented with hyperammonemia was diagnosed biochemically and genetically (heterozygous for a novel likely pathogenic missense variant c.476T>A) as having ornithine transcarbamylase (OTC) deficiency, a rare X-linked recessive urea cycle disorders. Extensive family genetic screening eventually revealed paternal gonadosomatic mosaicism.