Objective To analyze two identical novel MOCS1 gene variant sequences in the same family⁃ with different clinical features，and to provide reliable clinical data for future research on this correlation study. Method The pathogenic gene of the proband′ s family was detected by high ⁃throughput sequencing technology， and clinical features and gene variation sequences of the two patients with type A molybdenum cofactor deficiency from the same familywere retrospectively analyzed. Result The proband was a full⁃term infant with no history of asphyxia，who had difficulty feeding after birth，and had convulsions on the second day. Head MRI showed bilateral basal ganglia hypoxic⁃ischemic damage and softening lesions. His 5⁃year⁃old sibling sister had no abnormal psycho⁃ motor development after birth，but at 10 months，sudden fever and convulsions，feeding difficulties，and progres⁃ sive overall neurodevelopmental regression were observed. Head MRI also showed hypoxic ⁃ischemic in the basal ganglia. Therefore，the whole exon high⁃throughput sequencing of 5 members of the family were performed. The pro⁃ band and his affected sister were NM of MOCS1 gene_ 001358530.2，c.1275delA（p.Gly426Aspfs Ter10）homozy⁃ gous variant，but the parents and another healthy sister all heterozygous variants. This variant site had not been reported. Conclusion The proband and his affected sister have the same MOCS1 gene mutation sequence but dif⁃ ferent clinical processes.It is speculated that the mild phenotype of the proband may result in the residual function of sulfite oxidase activity 

"> molybdenum cofactor deficiency, MOCS1 gene, new variants, clinical phenotype