Objective  To investigate the clinical characteristics and gene mutation of delayed carbamoyl phosphate synthetase I deficiency (CPSID) in infants. 

Methods  The clinical characteristics, cranial magnetic resonance imaging(MRI) and gene detection results were analyzed retrospectively, and the related literatures were analyzed. 

Results  A 59-day old boy developed the disease with nonspecific manifestations such as spitting milk, dysphoria and poor mental response, and then the disease progressed rapidly with symptoms such as convulsion, coma, and apnea. The blood ammonia was tested two times and values were 518.6 umol/L and 952.8 umol/L respectively. Cranial magnetic resonance revealed abnormal signals in the white matter region of bilateral cerebral hemispheres. Gene detection revealed two hybrid mutations of exon 15 c.1676delA(p.E559fs) and exon 20 c.2407C>G(p.R803G) in the CPS1 pathogenic gene. Combined with the above, the final diagnosis was delayed CPSID. 

Conclusions  For infants with unexplained vomiting, feeding difficulties and consciousness disorders after the establishment of feeding, metabolic indicators such as blood ammonia should be improved as soon as possible. If the blood ammonia level is significantly increased, congenital urea circulation disorder should be considered and MRI examination of the head should be performed to evaluate the degree of brain injury.  A new mutation site c.1676delA(p.E559fs) was found in the gene detection results of this patient, which expanded the gene spectrum of CPSID to a certain extent.

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