Download CLINICAL CASE (UREA CYCLE)

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