Mosaicism for an Intragenic Deletion in a Boy with Mild Ornithine Transcarbamylase Deficiency

ORNITHINE TRANSCARBAMYLASE (OTC) is the X-linked enzyme that catalyzes the condensation of carbamyl phosphate and ornithine, forming citrulline in the urea cycle. Its activity in the mitochondria of liver cells is essential for the detoxification of ammonia, and its complete absence is usually lethal in the neonatal period. 1 The majority of cases of nontransient neonatal hyperammonemia are due to inborn deficiencies of this enzyme. A milder form of OTC deficiency has a later onset and is characterized by episodes of hyperammonemia caused by infection or excessive protein intake. Even when protein intake is limited, male patients with partial OTC deficiency . . .