Background: Ornithine transcarbamylase is an X-linked mitochondrial enzyme that catalyzes the synthesis of citrulline from carbamoyl phosphate and ornithine. A deficiency of this enzyme leads to hyperammonemia and hyperglutaminemia. In boys the disease is often fatal when its onset occurs during the neonatal period, but it is milder when onset occurs later in childhood. Heterozygous girls may be normal or may have episodes of hyperammonemic encephalopathy and decline in cognitive function. We report here on the long-term outcome in girls with ornithine transcarbamylase deficiency enrolled in studies of treatments designed to activate new pathways of waste-nitrogen excretion.

Methods: We studied 32 girls (age, 1 to 17 years) with ornithine transcarbamylase deficiency who had had at least one episode of encephalopathy. The patients were assigned to treatment that consisted of sodium benzoate, alone or in combination with sodium phenylacetate or sodium phenylbutyrate, or sodium phenylbutyrate alone. Collaborating physicians provided clinical, metabolic, and developmental data at specified intervals.

Results: Patients treated according to these protocols had greater than 90 percent survival at five years and maintained appropriate weight for height. The frequency of hyperammonemic episodes decreased with increasing age and with sodium phenylacetate or sodium phenylbutyrate treatment. Although the mean IQ before treatment was in the low average range, 19 of the 23 girls in whom intelligence was tested longitudinally had stable test scores.

Conclusions: Girls with symptomatic ornithine transcarbamylase deficiency who are treated with drugs that activate new pathways of waste-nitrogen excretion have fewer hyperammonemic episodes and a reduced risk of further cognitive decline.