Mehrdad Talebi - M.Sc., Department of Medical Genetics, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
Mohammad Yahya Vahidi Mehrjardi - Ph.D., Medical Genetics Research Center, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
Kambiz Kalhor - M.Sc., Department of Biological Science, Faculty of Science, University of Kordestan, Sanandaj, Iran
Mohammadreza Dehghani - M.D., Ph.D, Medical Genetics Research Center, Shahid Sadoughi University of Medical Sciences, Yazd, Iran- Reproductive and Genetic Unit, Yazd Research and Clinical Center for Infertility, ShahidSadoughi University of Medical Sciences, Yazd, Iran

Background: Carbamoyl phosphate synthetase 1 (CPS1) is a liver-specific enzyme withthe lowest enzymatic rate, which determines the overall rate of the other reactions inthe pathway that converts ammonia to carbamoyl phosphate in the first step of the ureacycle. Carbamoyl phosphate synthetase 1 deficiency (CPS1D), which usually presentsas lethal hyperammonemia, is a rare autosomal recessive hereditary disease.Case: We report a case of a two-day-old female neonate with lethal hyperammonemia.The newborn infant was presented with hyperammonemia. In Plasma amino acid analysis, there was a significant elevated levels ofalanine , glutamine , asparagine, glutamic acid, aspartic acid, and lysine. We cannot diagnose the urea cycle disorder (UCD) CPS1D properlyonly based on the quantity of biochemical intermediary metabolites to exclude otherUCDs with similar symptoms. Following next generation sequencing determined onehomozygous mutation in CPS1 gene and also this mutation was determined in herparents. The identified mutation was c.2758G > C; p.Asp920His, in the 23 exon ofCPS1. This novel homozygous mutation had not been reported previously.Conclusion: We applied whole exome sequencing successfully to diagnose the patientwith CPS1D in a clinical setting. This result supports the clinical applicability of wholeexome sequencing for cost-effective molecular diagnosis of UCDs.

CPS1 deficiency, Hyperammonemia, Urea cycle disorder, Whole exome sequencing