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Description: Ornithine transcarbamylase (OTC) deficiency is the most common of the urea cycle disorders. The hepatic urea cycle is the major route for waste nitrogen disposal. The enzyme catalyzes the condensation of carbamyl phosphate and ornithine to form citrulline, an essential step in the urea cycle. Mutations in the OTC gene cause enzyme deficiency, resulting in hyperammonemia. The gene is on the X-chromosome and is normally expressed in the mitochondrial matrix of the liver. Most of the affected are male, although female carriers may be symptomatic due to skewed X-inactivation. Affected children usually present soon after birth with symptoms including lethargy, vomiting, heavy or rapid breathing, poor feeding, seizures, irritability, decreased muscle tone, and disorientation. Mildly affected individuals and manifesting carriers may experience headaches with protein consumption avoid protein. Acute onset of symptoms may occur when metabolically stressed. The late-onset–affected male usually presents with no prior history consistent with hyperammonemia in childhood and suffers a rapid decompensation and demise, similar to the neonatal pattern. The OTC gene is approximately 73 kb in length, containing 10 exons. More than 100 different mutations have been described. Reasons for Referral:
Testing Methodology: Specimen
Requirements: Turnaround Time: CPT
Codes and Prices: Forms: References: Test Codes: Last Modified: 2-27-08 |