Ornithine transcarbamylase deficiency unmasked because of gastrointestinalbleeding

Ornithine transcarbamylase (OTC) is a mitochondrial-matrix enzyme that cata lyzes conversion of ornithine and carbamyl phosphate to citrulline, the sec ond step in the urea cycle. The urea cycle is the most important pathway to detoxification of ammonia in human beings. Ornithine transcarbamylase defi ciency (OTCD) is the most common urea cycle disorder, inherited as an X-lin ked disorder that can cause fatal hyperammonemia in male newborns. Women wi th OTCD have a variable expression of their disease, the variability being determined by lyonization (random inactivation) of the X chromosome. We rep ort a case of a 28-year-old woman who presented with hyperammonemic encepha lopathy that was precipitated by a gastrointestinal bleed unmasking OTCD.