Abstract: 　Objective　To explore clinical features and genetic diagnosis of a family with mucopolysaccharide II (MPS II). Methods　Clinical data of the patient and his family members were collected, imaging and urine mucopolysaccharide qualitative tests were performed, DNA of patients and family members was extracted, and genetic analysis was carried out by next generation sequencing and Sanger sequencing. Enzyme activities of iduronate-2-sulfatase were performed for the proband and his mother. Results　The proband was a 15 years old male, with physical developmental disorder and hearing loss. Imaging test showed enlarged ventricle system, and vertebrae, ribs and other bone dysplasia. Urine mucopolysaccharide was positive, which lead to preliminary diagnosis of MPS II. In his family, 6 patients and 1 suspected child were all male. In addition to the proband, another patient still survived. One suspected child was diagnosed with hydrocephalus during the prenatal diagnosis at 7th month of pregnancy and terminated, the other four patients were all died. Gene tests found an IDS synonymous mutation (exon 8, C. 1122C > T) in the patient, and another 5 female carriers were identified. The enzyme activities of iduronate-2-sulfataseare were respectively 0 nmol/4hr/mg (the proband) and 6.96 nmol/4hr/mg (mother). Conclusion　The proband was diagnosed as MPS II, and several male patients and female carriers of pathogenic variant in the family members were identifies. This provided a basis for genetic counseling.

Key words: 　mucopolysaccharide II;　idurose-2-sulfatase;　variant;　gene