Post-meal loss of consciousness in an adult patient with carbamoyl phosphate synthetase 1 deficiency and two newly identified heterozygous variants: a case report

Carbamoyl phosphate synthetase 1 deficiency (CPS1D) is a rare autosomal recessive disorder characterized by urea cycle dysfunction and secondary hyperammonemia. Although primarily observed in neonates, adult cases are exceedingly rare and warrant reporting due to their novelty and potential for misdiagnosis. We present a case of a 34-year-old male who presented with post-meal loss of consciousness, a symptom atypical of the disease’s usual manifestation. A 34-year-old man was admitted with a 2-day history of general fatigue that escalated to unconsciousness over half a day. He also experienced vomiting, bilateral limb convulsions, and a history of epilepsy. Upon admission, he exhibited coma with a Glasgow Coma Scale score of 5/15. Biochemical investigations revealed normal liver and kidney function but a significantly elevated blood ammonia concentration of 597.6 µmol/L. Cranial imaging showed diffuse swelling of the brain parenchyma indicative of encephalopathy. Gene sequencing identified three heterozygous variants in the CPS1 gene, including two novel variants sites. Despite ammonia-lowering treatments, his condition rapidly deteriorated, and he succumbed to hyperammonemia-induced encephalopathy on day 9 of admission. This case highlights the importance of recognizing CPS1D as a potential diagnosis in adults presenting with neurological symptoms, particularly those involving consciousness changes. The rarity and atypical presentation of adult CPS1D underscore the need for early diagnosis through comprehensive evaluation, including blood ammonia measurement and genetic analysis. This case expands the spectrum of clinical manifestations and genetic variants associated with CPS1D and emphasizes the urgency of ammonia-lowering therapy and consideration for liver transplantation in eligible patients.