Abstract: 　Objective　To explore the clinical characteristics, diagnosis and treatment of carbamoyl phosphate synthetase 1 deficiency (CPS1D) caused by CPS1 gene mutation. Methods　The clinical data and gene detection results of CPS1D caused by CPS1 gene mutation in a child were analyzed retrospectively. Related literature was reviewed. Results　The patient was male, born prematurely at 36 weeks and weighed 2500 g. After birth, the patient had poor reaction, milk rejection and low muscle tone in the limbs. The blood ammonia was significantly elevated, and tandem mass spectrometry showed that blood citrulline levels were reduced and there was a urea cycle disorder. The whole exon sequencing showed a complex heterozygous mutation of CPS1 gene, which came from the missense mutations of mother [c.2876a > G (p.y959c)] and father [c.2429a > C (p.q810p)]. Parents were not close relatives, and the phenotype is normal. Conclusion　Early detection of genes can help diagnose CPS1D.

Key words: 　CPS1 gene;　carbamoyl phosphate synthetase 1 deficiency;　gene mutation;　urea cycle disorder