Ornithine carbamyl transferase deficiency is a frequent enzymatic disorder transmitted either as a recessive or dominant X-linked trait. Mutations with no residual enzyme activity are always expressed in hemizygote males by a very severe neonatal hyperammonemic coma that generally proves to be fatal. Heterozygous females are either asymptomatic or express orotic aciduria spontaneously or after protein intake. This identifies carriers. Females may also be affected by symptoms with various degrees of intensity, ranging from dislike for proteins to chronic vomiting, growth retardation, hypotonia, psychomotor retardation, hyperammonemic coma, or psychiatric disorders. In females, outcome is extremely variable, depending on the degree of inactivation of the muted X chromosome. Mutations leading to residual enzyme activity result in juvenile or even adult hyperammonemic coma in males, simulating Reye's syndrome or encephalitis. Females remain always asymptomatic. Diagnosis is based on the presence of hyperammonemia and chromatography of aminoacids evidencing major hypocitrullinemia and increased levels of glutamine, alanine, and lysine. High levels of urinary orotic acid are also a common finding during acute phases. Familial history with evidence of an X-linked disease is also strongly suggestive of the disorder. The diagnosis is confirmed by measuring enzymatic activity in liver or intestinal biopsies. Familial investigation is based on molecular analysis, which must be carried out in both affected and healthy relatives. Molecular gene analysis is also used for antenatal diagnosis. Patients are treated with a diet of limited protein intake adapted to their level of tolerance, arginine and citrulline supplementation, and both sodium benzoate and sodium phenylbutyrate. Some severe forms have been successfully treated by liver transplant.
Last update: March 2004