Two Siblings with Complete Carbamyl Phosphate Synthetase I Deficiency

A female infant, who showed hyperammonemia in the neonatal period, died on 43rd postnatal day. Her female sibling also died on 42nd day after birth with an identical clinical picture and hyperammonemia. Urinary organic acids were negative in both cases. Their blood amino acids showed no specific pattern, and urinary orotic acid excretion was normal. The first two urea cycle enzymes and N-acetyl L-glutamate synthetase of the liver tissues of these two infants obtained at autopsy were assayed. They revealed a selective deficiency of carbamyl phosphate synthetase I.