Carbamyl phosphate synthetase (CPS) is an enzyme that converts ammonia to carbamyl phosphate in the urea cycle. CPS deficiency is a genetic disorder that causes hyperammonemia because of enzyme activity deficiency. It is primarily diagnosed in neonates and infants and has a poor prognosis. We report an adult woman with CPS deficiency who developed hyperammonemia postpartum.
Carbamyl phosphate synthetase (CPS) is an enzyme that converts carbamyl phosphate into ammonia in the urea cycle ( Figure ). CPS deficiency is a genetic disorder of this active enzyme, and deficient enzyme activity causes hyperammonemia.
CPS deficiency occurs with a frequency of 1 per 1 million. CPS deficiency is inherited as an autosomal recessive trait with its locus at 2q35; it almost always presents in newborns and infants, and the prognosis is poor, although the late onset occurs in some cases.
Herein we report a very rare case in which a parturient developed hyperammonemia on 2 separate occasions following delivery of 2 children and was diagnosed with CPS deficiency.
Case Report
The patient is a 27 year old gravid 2, para 2. The histories of the present disease, family, drugs, and mental disorders were noncontributory. On becoming pregnant at 23 years of age, she visited a local doctor for prenatal care. The pregnancy culminated with a vaginal delivery at 38 weeks 6 days.
On postpartum day 4, the patient’s level of awareness declined and she was brought to our hospital for emergency evaluation. She had a 5 on the Glasgow Coma Scale (motor response, 3; verbal response, 1; eye opening, 1) and showed neurologic impairments including the Babinski’s sign.
A head computed tomography, magnetic resonance imaging, and electroencephalogram showed no abnormalities. Blood tests, including electrolyte levels, were performed to identify the cause of the decreased awareness. The blood ammonia was elevated at 262 μg/dL.
Intravenous fluids, lactulose, and kanamycin were administered for hepatic encephalopathy, but there was no improvement. On postpartum day 7, hemodialysis was started; the patient’s blood ammonia was 284 μg/dL. The ammonia level declined thereafter to 22 μg/dL, and on postpartum day 11, hemodialysis was stopped.
The clinical symptoms, including the decreased level of awareness, improved as the blood ammonia level was lowered. Analysis results of blood amino acid levels were as follows: citrinin, 5.2 nmol/mL (29.8-49.0 nmol/mL), and glutamine, 821.1 nmol/mL (478.3-658.5 nmol/mL).
These results suggested an abnormal enzyme deficiency in the urea cycle, and a liver biopsy was performed. The histologic findings revealed normal ornithine transcarbamylase activity but no carbamyl phosphate synthetase activity, Thus, CPS deficiency was diagnosed. Protein restriction and arginine supplementation were implemented and the patient was followed up on an outpatient basis with no change.
At 26 years of age, the patient became pregnant again and visited a local doctor for prenatal care. A cesarean section was performed at 38 weeks 5 days because of a breech presentation.
On postpartum day 8, the patient experienced lethargy leading to restlessness, and she was brought to our hospital for emergency evaluation. She had an elevated blood ammonia of 233 μg/dL. Hemodialysis was performed for 6 days and the blood ammonia level improved to 33 μg/dL. Protein restriction and arginine supplementation were implemented and the patient has been followed up on an outpatient basis. In the ensuing year, there have been no elevated ammonia levels.
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