The Etiological Study of Three Hunter Syndrome Families in Southern China / 中山大学学报(医学科学版)

ObjectiveTo reveal the molecular pathogenesis of Hunter syndrome in three families in southern China and to clarify the correlation between phenotype and genotype， so as to lay a foundation for future prenatal or preimplantation genetic diagnosis. MethodsOn the basis of initial clinical diagnosis and pedigree analysis， qualitative detection of glycosaminoglycans in urine was performed first， and then anticoagulant blood samples were collected from the children and their relatives. DNA was extracted and the IDS gene sequence was analyzed by PCR and Sanger sequencing. Various methods such as RT-PCR and bioinformatics analysis were used to identify the pathogenicity of the new variants. ResultsThe urine test results of the patients in the three families were all strongly positive（++）. Probands were all male， with hemizygous mutations in IDS gene from their mothers， and the mutation sites were c.615_622delCATACAGT， c.847_848delGT and IVS7 ds+1 G>A， respectively. The cross-species conservation analysis showed that the amino acid of IDS gene mutation site was highly conserved during species evolution. Compared with the normal protein， mutant proteins exhibited significant differences in the predicted results of advanced structure. The variants identified in the three families were classified as pathogenic by ACMG criteria. ConclusionsThe three probands were diagnosed with Hunter syndrome. The c.615_622del（p.Il206Valfs*18）， c.847_848del（p.Val283Alafs*57） and IVS7 ds+1 G>A （p.G336Dfs*12） of IDS gene are all novel pathogenic mutations， which are the underlying causes of morbidity in children. This study has further enriched the mutation spectrum of IDS gene.

Characterization of an IDS pathogenic variant in a family with mucopolysaccharidosis type Ⅱ / 中华内分泌代谢杂志

Objective:To identify the genetic variation in a mucopolysaccharidosis type Ⅱ(MPS Ⅱ)family, and conduct a functional study of iduronate-2-sulfatase(IDS): c.323A>C.Methods:A five-generation MPS Ⅱ family of 83 individuals including 4 patients from northern China was collected. Urine mucopolysaccharide and Alder-Reilly body were tested to assist the clinical diagnosis of MPS Ⅱ. IDS enzyme activity was detected on core family members. By the whole exome sequencing of a MPS Ⅱ patient in this family and bioinformatics analysis, the variant was screened and further identified by PCR-Sanger sequencing. Finally, to validate the function of the variant in vitro, the wild-type IDS overexpression plasmid(pCMV-hIDS-WT)and the IDS overexpression plasmid carrying the mutation site(pCMV-hIDS-c.323A>C)were transfected into COS-7 cells and the IDS activity was detected. Results:The proband(Ⅳ3)and Ⅳ4 were diagnosed as MPS Ⅱ by urine mucopolysaccharide, Alder-Reilly body, and IDS enzyme activity tests. Ⅳ3, Ⅳ4, Ⅲ19, and Ⅲ32 were determined to carry IDS: c.323A>C missense variant through the whole-exome sequencing, and diagnosed as MPS Ⅱ. Meanwhile, Ⅱ2, Ⅱ4, Ⅱ8, Ⅱ12, Ⅱ14, Ⅲ5, Ⅲ7, Ⅳ14 in the MPS Ⅱ family carried IDS: c.323A>C missense variant, and were excluded as MPS Ⅱ. The in vitro experiment in COS-7 cells showed that the missense mutation led to a significant decrease in IDS enzyme activity. Conclusion:The variant IDS: c.323A>C: p.Y108S significantly decreases the activity of IDS enzyme in vivo and in vitro, and it is identified as a pathogenic variant for MPS Ⅱ.

Quantification of the iduronate-2-sulfatase activity in prenatal diagnosis of mucopolysaccharidosis type Ⅱ / 中华实用儿科临床杂志

Objective:To evaluate the activity of iduronate-2-sulfatase (IDS) in fetal villi and peripheral blood plasma of pregnant women at high risk of mucopolysaccharidosis type Ⅱ (MPS Ⅱ), and to discuss the application of gene analysis in prenatal diagnosis of MPS Ⅱ.Methods:The enzymatic testing and gene analysis results of 23 pregnant women at high risk of MPS Ⅱ, who underwent prenatal diagnosis in Guangzhou Women and Children′s Medical Center from February 2013 to December 2020, were analyzed retrospectively.The IDS activity in fetal villi (30 cases) and plasma (28 cases) was detected by artificial substrate fluorescence.The IDS activity in fetal villi (28 cases) and plasma (34 cases) of normal pregnant women was taken as control.Meanwhile, the fetal villi of both pregnant women at high risk of MPS Ⅱ and normal pregnant women were also analyzed by gene testing and for fetal sex identification.Data were compared between groups by the independent samples t test. Results:The normal reference values of the IDS activity in fetal villi and plasma of normal pregnant women were(71.2±23.4) nmol/(mg·4 h) and (611.1±114.5) nmol/(mL·4 h), respectively.Among the 30 cases of high-risk fetal villi, the IDS activity in fetal villi of 8 affected male fetuses was (1.7±0.3) nmol/(mg·4 h), which was significantly lower than that of 11 unaffected male fetuses (83.2±6.3) nmol/(mg·4 h) and that of 9 non-carrier female fetuses (80.0±7.5) nmol/(mg·4 h) ( t=10.8, 8.8; all P<0.01). Meanwhile, the IDS activity was measured in the maternal peripheral plasma of 28 pregnant women at high risk of MPS Ⅱ.Among them, the IDS activity in 8 affected male fetuses was(225.4±20.5) nmol/(mL·4 h), which was significantly lower than that in non-affected male fetuses[(451.0±15.1) nmol/(mL·4 h)] and that in non-carrier female fetuses[(467.7±45.3)nmol/(mL·4 h)]. Eight known pathogenic mutations were found in 30 cases at high risk of MPS Ⅱ of fetal villi, and the mutation types were c. 1048A>C, c.212G>A, c.514C>T, c.257C>T, c.425C>T, and c. 998C>T.Of the 8 cases, 6 affected male fetuses had significantly reduced IDS activities, and the other 2 female carriers had normal IDS enzyme activities. Conclusions:The IDS activity in fetal villi and peripheral plasma of pregnant woman is consistent with the gene analysis results.The IDS activity has an important reference value for the prenatal diagnosis of MPS Ⅱ in the first trimester.When no genetic mutations are found in the probands or the pathogenicity of the new mutation remains unclear, the IDS activity in fetal villi can be detected separately for the prenatal diagnosis of MPS Ⅱ.

Study on genetic etiology of two patients with mucopolysaccharidosis using whole-exome sequencing / 中华内分泌代谢杂志

Objective:To explore the underlying genetic cause in two patients with mucopolysaccharidosis(MPS)using the whole-exome sequencing.Methods:Genomic DNA was extracted from the peripheral blood of two patients with MPS and their family members. Sanger sequencing and pedigree verification were performed on the pathogenic variants filtered by whole-exome sequencing. The function of the mutation sites was analyzed by bioinformatics software. The effect of the splice mutation on mRNA was further determined by reverse transcription-PCR(RT-PCR).Results:The proband 1 was a 25-year-old male, who carried compound heterozygous mutations of α-L-iduronidas(IDUA) gene: p. T179R and p. S633L, and was diagnosed as MPSⅠ. His mother and sister carried heterozygous p. T179R, while his father carried heterozygous p. S633L, consistent with the autosomal recessive inheritance pattern. The proband 2 was a 3-year-old male, who was hemizygous for IVS 6-8A>G of iduronate-2-sulfatase(IDS) gene. His mother and grandmother were heterozygous for this mutation, consistent with the X-linked recessive inheritance. The proband 2 was diagnosed as MPSⅡ. Sequencing of RT-PCR products showed that the IVS 6-8A>G mutation activated an upstream cryptic splice-site in intron 6, leading to 7 nucleotide insertion in exon 7, frameshift, and shorter peptide chain.Conclusion:In this study, IDUA p. T179R and p. S633L, and IDS IVS 6-8A>G mutations were found in two patients with MPS by whole exome sequencing, which further expanded the genotypic and phenotype spectrum of MPS.

Changes in Glycogen and Glycosaminoglycan Levels in Hepatocytes of Iduronate-2-Sulfatase Knockout Mice before and after Recombinant Iduronate-2-Sulfatase Supplementation

PURPOSE: Mucopolysaccharidosis II (MPS II) is a lysosomal storage disorder caused by a deficiency of iduronate-2 sulfatase (IdS), which is involved in the degradation of glycosaminoglycan (GAG). In this study, the frequency of fasting hypoglycemia in patients with MPS II was investigated and changes in accumulation of glycogen and GAG in the hepatocytes of IdS-knockout (KO) mice were evaluated before and after recombinant IdS enzyme replacement therapy (ERT). MATERIALS AND METHODS: Plasma glucose levels were evaluated after an 8-hour fast in 50 patients with MPS II. The IdS-KO mice were divided into three groups (group 2; saline, group 3; 0.15 mg/kg of IdS, and group 4; 0.5 mg/kg of IdS); wild-type mice were included as controls (group 1). ERT was initiated intravenously at four weeks of age, and continued every week until 20 weeks of age. RESULTS: The mean glucose level after an 8-hour fast was 94.1 +/- 23.7 mg/dL in the patients with MPS II. Two (4%) out of 50 patients had fasting hypoglycemia. For the mice, GAG in the lysosomes nearly disappeared and glycogen particles in the cytoplasm were restored to the normal range in group 4. CONCLUSION: Glucose metabolism in patients with MPS II appeared to function well despite hepatocytic GAG accumulation and hypothetical glycogen depletion. A higher dose of IdS infusion in MPS II mice led to disappearance of lysosomal GAG and restoration of glycogen to the cytoplasm of hepatocytes.