Carbamoyl Phosphate Synthetase I Deficiency (CPSID) is a rare autosomal recessive disorder that is strictly limited to the liver and intestine, and results in congenital hyperammonemia and defective citrulline synthesis. Within their first few days of life, affected infants exhibit the effects of the hyperammonemia in the form of unusual sleepiness, poorly regulated breathing rate or body temperature, unwillingness to feed, vomiting after feeding, unusual body movements, seizures, or coma. In some individuals the signs and symptoms may be less severe and appear later in life.
Diagnosis of the condition is based on hyperammonemia, high plasmatic glutamine, and low citrulline levels. Confirmation can be done by measuring the enzyme activity in the liver or intestine and by detecting mutations in the CPS1 gene. The management of CPSID may include a strict lifelong diet of very limited protein intake, citrulline and arginine supplementation, and administration of both sodium benzoate and sodium phenylbutyrate.
Mutations in the CPS1 gene are the cause of Carbamoyl Phosphate Synthetase I Deficiency. Carbamoyl Phosphate Synthetase I enzyme is one of five enzymes that play a role in the breakdown and removal of nitrogen from the body, a process known as the urea cycle. The lack of CPSI enzyme results in excessive accumulation of nitrogen in the form of ammonia. Ammonia is especially damaging to the brain, and excess ammonia causes neurological problems and other signs and symptoms of CPSID.
Granot et al. (1986) reported an Arab child in whom the diagnosis of partial CPS deficiency was first made when she presented at nine years of age with hyperammonemic coma simulating Reye syndrome. Despite intensive therapy directed toward lowering of ammonia levels, she sustained irreversible brain damage. History showed that on the seventh day of life, the child developed seizures for which phenobarbitone was administered. Her psychomotor development was slow. She attended a regular school, but was a below-average student. She was on a regular diet with no apparent aversion to protein. At the age of six years she began to experience episodes of vomiting, mild abdominal pain, and muscle weakness. These episodes were not associated with any intercurrent infection or dietary change; they lasted for two or three days and occurred up to three times a year. During these attacks she remained mentally alert.
Al-Shamsi et al. (2014) undertook a study to calculate the birth prevalence of IEMs among Emiratis in the UAE by taking into consideration all neonates born with an inherited metabolic condition at Tawam Hospital between 1995 and 2012. A total of 37 distinct IEMs were found in Emirati neonates in this study, providing an estimated IEM birth prevalence of 75.24 per 100,000 live births. The birth prevalence of CPSID was calculated at less than 0.98 per 100,000 live births. A single mutation was identified in the CPS1 gene.
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