Abstract: Objective：To investigate the clinical features of urocanase deficiency caused by mutations in UROC1 gene. Methods：The clinical information and gene sequencing result of an urocanase deficiency patient that carried mutations in UROC1 gene was reported and the relative literature was reviewed. Results：The patient was a boy 1-year-1-month old, with complaint of 'unable to sit steadily without assistance or actively grasp objects'. He could hold his head up at 4.5 months, roll over at 6.5 months, actively found people at 8 months. Physical examination: slow response, internal strabismus, not good at tracking objects; hypertonia at upper limbs, hyperactive tendon reflex, cortical thumb sign. Concentration of folic acid was more than 25.2 ng·mL-1(reference value: 3.0-17.0 ng·mL-1). Head MRI scan presented increased extracerebral space and myelination development delay in bilateral temporal occipital lobe. LC–MS/MS assay of blood indicated increased concentration of histidine 116.075 μmol·L-1(reference value of 6 month - 1-year old babies is 0~79.3 μmol·L-1), with 1.464 times rate. The result of urine metabolic analysis was normal. Two mutations, one maternal missense mutation c.74G>A (p.G25E) and one paternal nonsense mutation c.74G>A (p.G25E) in UROC1 gene were discovered by gene sequencing. Both mutations are predicted to be deleterious on analysis. Searching on CNKI, Wanfang and PubMed databases, 3 English reports have been discovered, 4 cases of urocanase deficiency were reported. Including the case in our report, 5 cases have been reported till now. The diagnosis age of our patient is the youngest one, others were diagnosed at age 16, 9, 11 and 19 respectively; 2 male patients and 3 female patients have been reported; clinical features are all development delay and mental retardation with IQ less than 60. One patient was reported carrying compound heterozygous mutations c.209T>C and c.1348C>T in UROC1 gene. Conclusion：Mutations c.74G>A and c.854G>A might be novel pathogenic mutations in UROC1 gene that could cause abnormality in structure and function in urocanase. These mutations may cause urocanase deficiency.