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. OTC deficiency can affect both male and female in X‐linked recessive manner. Cascade screening is important to detect asymptomatic carrier, who could be at risk of decompensation. Parental gonadosomatic mosaicism increases recurrence risk.