Ornithine transcarbamylase deficiency in a male: strict correlation between metabolic control and plasma arginine concentration.

In a male with a partial defect of ornithine transcarbamylase (OTC) we observed that maintenance of arginine supply was crucial for adequate metabolic control in conjunction with a low protein diet. The arginine supplement had to be given such that the concentrations of arginine and ornithine in plasma were above 50 mumol/l. It appears that arginine is needed not only as an essential amino acid for protein synthesis but also as a precursor of ornithine. In this patient the substitution thus aimed at increasing the intramitochondrial ornithine in order to reach a critical substrate concentration for the kinetically abnormal OTC.