This study identified mutations of the idumate-2-suffatase (IDS) gene in a patient with Hunter syndrome,and established a basis for the diagnosis of the prenatal gene of Hunter syndrome.Urine glyeosaminoglycan (GAG) assay was used to make the preliminary diagnosis of mucopolysaccharidosis type H.Polymerase chain reaction (PCR) from dried blood spots and DNA sequencing were applied to analyze hotspot mutations in exons 9,3 and 8 of the IDS gene in the proband and his parents.A new missense mutation (T1140C) in exon 8 of the IDS gene was found by using DNA sequencing.This mutation caused a substitution of codon 339 from CTA (leucine) to CCA (praline).The patient is a hemizygote,and his mother is a heterozygote.The new missense mutation results in a change in the primary and tertiary structure of the IDS protein.It is possible that this mutation severely impairs enzymatic activity and is the underlying basis for the pathology seen in this patient with Hunter syndrome.