UCD.- Ornithine transcarbamylase (OTC) deficiency Late onset
Incidence
X-linked recessive. Relatively common. Only males affected.
Clinical Characteristics
Ornithine transcarbamylase deficiency of late onset is a mild form with first recognized episode in late childhood or even in adulthood. 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. Familal 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. 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.
Precipitants
Protein intake.
Provocation Tests
Protein tolerance test. Allopurinol test: following its administration, there is orotidine excreted in the urine.
Diagnostic Procedures
EB-L. 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. Familal 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.