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Transcript
CLASS OF 2016 SGD - UREA CYCLE Wednesday, 18-7-2012, 10:30 am A male child was born into a family with no history of neonatal deaths. He weighed 2.9 kg at birth and appeared to be healthy until 3 days of age when he developed seizures. The mother had a history of aversion to meat, the eating of which was accompanied by episodes of vomiting and lethargy. The patient had mild alkalosis with blood pH of 7.5 (normal: 7.35 – 7.45). His plasma ammonium ion (NH4+) level was 240 m (normal: 25 – 40 m). Plasma amino acid levels included: glutamine, 2.4 mM (normal: 350 – 650 M); alanine, 750 M (normal: 8 – 25 M); arginine, 5 M (normal: 30 – 125 M); and undetectable citrulline. Urinary orotic acid excretion was 285 g/mg creatinine (normal: 0.3 – 10 g/mg creatinine). Oral therapy was started by administering a combination of essential amino acids (including arginine) at a dose of 1.1g/kg/d. By the seventh day, his plasma NH4+ level was 40 uM, and he appeared clinically well. Learning objectives: Explain mechanisms (transamination and oxidative deamination) for removal of nitrogen from amino acids during amino acid catabolism transport of ammonia in the blood the urea cycle (including enzymes and intermediates, intracellular locations, energy requirements and regulation) the basis of elevated orotic acid in the urine in this patient (pyrimidine synthesis) List why hyperammonemia primarily affects the central nervous system the possible causes of hyperammonemia, especially in relation to deficiencies in urea cycle enzymes