UCD.- Ornithine transcarbamylase (OTC) deficiency Neonatal onset.
Incidence
X-linked recessive. It is a common UCD. Only males affected.
Clinical Characteristics
Ornithine carbamyl transferase deficiency is a frequent enzymatic disorder transmitted either as a recessive or dominant X-linked trait. In females, outcome is extremely variable, depending on the degree of inactivation of the muted X chromosome. 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. Campbell et al. (1971, 1973) reported lethal neonatal hyperammonemia due to complete ornithine transcarbamylase deficiency. They suggested that mutation in the gene encoding the enzyme may lead to partial deficiency in heterozygous females and to complete deficiency in hemizygous males. Symptoms include severe vomiting, lethargy, irritability, respiratory alkalosis, seizures, hypotonia and severe hyperammonemia. It is almost always fatal. Neonates are normal the first 24 hours. Rarely develop coma before age 3 days.
Precipitants
Protein intake.
Provocation Tests
Protein ingestion (milk) triggers the acute symptoms and signs.
Diagnostic Procedures
EB-L. The diagnosis is confirmed by measuring enzymatic activity in liver or intestinal biopsies. 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.