Abstract: 　Objective　To improve the recognition of clinical phenotype and genotype of mucopolysaccharidosis type II. Methods　The clinical data of a child with mucopolysaccharide storage type II was retrospectively analyzed and the related literatures were reviewed. Results　A 5 years and 6 months old boy presenting with developmental delay and facial dysmorphism including rough face, protruding forehead, thick eyebrows, protruding eyes, hepatomegly and splenomegaly, umbilical hernia, and progressive joint limitation. A novel hemizygous mutation of c.820dupG in IDS gene was found by whole exome sequencing which led to the change of amino acid synthesis starting from the 274 amino acid of Glu, and the 68th amino acid was terminated after the change (p.glu274glyfster68). Family verification showed that the variation was inherited from his mother, and his elder brother was found to have the same variant. Conclusion　A novel hemizygous mutation c.820dupG in IDS gene is found to cause mucopolysaccharidosis type Ⅱ.

Key words: 　mucopolysaccharidosis type II;　IDS gene;　semizygous mutation