Genetic Analysis of 17 Children with Hunter Syndrome:Identification and Functional Characterization of Four Novel Mutations in the Iduronate-2-Sulfatase Gene

Mucopolysaccharidosis type II （MPS II） is a rare X-linked disorder caused by alterations in the iduronate-2-sulfatase （IDS） gene. In this study, IDS activity in peripheral mononuclear blood monocytes （PMBCs） was measured with a fluorimetric enzyme assay. Urinary glycosaminoglycans （GAGs） were quantified using a colorimetric assay. All IDS exons and intronic flanks were bidirectionally sequenced. A total of 15 mutations （all exonic region） were found in 17 MPS II patients. In this cohort of MPS II patients, all alterations in the IDS gene were caused by point nucleotide substitutions or small deletions. Mutations p.Arg88His and p.Arg172＊ occurred twice. All mu- tations were inherited except for p.Gly489Alafs＊7, a germline mutation. We found four new mutations （p.Ser142Phe, p.Arg233Gly, p.Glu430＊, and p.Ile360Tyrfs＊31）. In Epstein-Barr virus （EBV）-immortalized PMBCs derived from the MPS II patients, no IDS protein was detected in case of the p.Ser142Phe and p.Ile360Tyrfs＊31 mutants. For p.Arg233Gly and p.Glu430＊, we observed a residual expression of IDS. The p.Arg233Gly and p.Glu430＊ mutants had a residuary enzymatic activity that was lowered by 14.3 and 76-fold, respectively, compared with healthy controls. This observation may help explain the mild disease phenotype in MPS II patients who had these two mutations whereas the p.Ser142Phe and p.Ile360Tyrfs＊31 mutations caused the severe disease manifestation.

Detection of a new mutation(T1140C)in a patient with Hunter syndrome from Guangdong,China

This study identified mutations of the idurnate-2-sulfatase(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 mucopolysac-charidosis type II.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 hemi-zygote,and his mother is a heterozygote.The new missense mutation results in a change in the primary and tertiary struc-ture 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.