Identification of 9 novel IDS gene mutations in 19 unrelated Hunter syndrome (mucopolysaccharidosis Type II) patients. Mutations in brief no. 202. Online

Hunter syndrome is an X-linked lysosomal storage disorder caused by a deficiency of the lysosomal enzyme iduronate-2-sulfatase (IDS). The IDS deficiency can be caused by several different types of mutations in the IDS gene. We have performed a molecular and mutation analysis of a total 19 unrelated MPS II patients of different ethnic origin and identified 19 different IDS mutations, 9 of which were novel and unique. SSCP analysis followed by DNA sequencing revealed four novel missense mutations: S143F, associated with the 562C-->T polymorphism, C184W, D269V and Y348H. Two novel nonsense mutations were found: Y103X (433C-->A) and Y234X (826C-->G). In two patients two novel minor insertions (42linsA and 499insA) were identified. In one patient a complete IDS deletion was found, extending from locus DXS1185 to locus DXS466).     

Identification of 9 novel IDS gene mutations in 19 unrelated Hunter syndrome (Mucopolysaccharidosis type II) patients

Hunter syndrome is an X-linked lysosomal storage disorder caused by a deficiency of the lysosomal enzyme iduronate-2-sulfatase (IDS). The IDS deficiency can be caused by several different types of mutations in the IDS gene. We have performed a molecular and mutation analysis of a total of 19 unrelated MPS II patients of different ethnic origin and identified 19 different IDS mutations, 9 of which were novel and unique. SSCP analysis followed by DNA sequencing revealed four novel missense mutations: S143F, associated with the 562C→T polymorphism, C184W, D269V and Y348H. Two novel nonsense mutations were found: Y103X (433C→A) and Y234X (826C→G). In two patients two novel minor insertions (421insA and 499insA) were identified. In one patient a complete IDS deletion was found, extending from locus DXS1185 to locus DXS466. © 1998 Wiley-Liss, Inc.     

Hunter综合征患者IDS基因的一个新突变

目的研究Hunter综合征患者的艾杜糖-2-硫酸酯酶（iduronate-2-sulfatase,IDS）基因的突变情况,为产前基因诊断等打下基础。方法应用尿粘多糖含量检测、聚合酶链反应-变性高效液相色谱（polymerase chain reaction—denaturing high—perfommnce liquid chromatography,PCR-DHPLC）分析对1例Hunter综合征患者及其父母的IDS基因的突变热点第9、3、8外显子进行突变检测,并对PCR-DHPLC检出的突变样品进行直接测序。结果经PCR-DHPLC分析发现该患者的IDS基因第9外显子有明显异常峰形;DNA序列分析进一步发现该外显子发生一新的移码突变,突变部位在第482位密码子（TTA）内,即cDNA第1569bp的T后插入了2个T,致使新肽链提前在第483位遇上终止密码TAA,导致新肽链从原来的550个氨基酸缩短至482个。该患儿为这一突变的半合子,而其母为这一突变的杂合子。结论PCR-DHPLC和DNA序列分析是诊断Hunter综合征的有效方法,发现的移码突变（1569＋TT）导致肽链比正常的少了68个氨基酸,从而引起IDS酶活性明显降低,可能是该Hunter综合征患者的致病原因。     

Differences in methylation patterns in the methylation boundary region of IDS gene in Hunter syndrome patients: implications for CpG hot spot mutations

Hunter syndrome, an X-linked disorder, results from deficiency of iduronate-2-sulfatase (IDS). Around 40% of independent point mutations at IDS were found at CpG sites as transitional events. The 15 CpG sites in the coding sequences of exons 1 and 2, which are normally hypomethylated, account for very few of transitional mutations. By contrast, the CpG sites in the coding sequences of exon 3, though also normally hypomethylated, account for much higher fraction of transitional mutations. To better understand relationship between methylation status and CpG transitional mutations in this region, the methylation patterns of 11 Hunter patients with transitional mutations at CpG sites were investigated using bisulfite genomic sequencing. The patient cohort mutation spectrum is composed of one mutation in exon 1 (one patient) and three different mutations in exon 3 (10 patients). We confirmed that in normal males, cytosines at the CpG sites from the promoter region to a portion of intron 3 were hypomethylated. However, specific CpG sites in this area were more highly methylated in patients. The patients with p.R8X (exon 1), p.P86L (exon 3), and p.R88H (exon 3) mutations had a hypermethylated condition in exon 2 to intron 3 but retained hypomethylation in exon 1. The same trend was found in four patients with p.A85T (exon 3), although the degree of hypermethylation was less. These findings suggest methylation patterns in the beginning of IDS genomic region are polymorphic in humans and that hypermethylation in this region in some individuals predisposes them to CpG mutations resulting in Hunter syndrome.     

Characterization of mutations in severe methylenetetrahydrofolate reductase deficiency reveals an FAD-responsive mutation

Methylenetetrahydrofolate reductase (MTHFR) synthesizes 5-methyltetrahydrofolate, a major methyl donor for homocysteine remethylation to methionine. Severe MTHFR deficiency results in marked hyperhomocysteinemia and homocystinuria. Patients display developmental delay and a variety of neurological and vascular symptoms. Cloning of the human cDNA and gene has enabled the identification of 29 rare mutations in homocystinuric patients and two common variants [677C>T (A222V) and 1298A>C (E429A)] with mild enzymatic deficiency. Homozygosity for 677C>T or combined heterozygosity for both polymorphisms is associated with mild hyperhomocysteinemia. In this communication, we describe four novel mutations in patients with homocystinuria: two missense mutations (471C>G, I153M; 1025T>C, M338T), a nonsense mutation (1274G>A, W421X), and a 2-bp deletion (1553delAG). We expressed the 1025T>C mutation as well as two previously reported amino acid substitutions [983A>G (N324S) and 1027T>G (W339G)] and observed decreased enzyme activity at 10%, 36%, and 21% of control levels, respectively, with little or no effect on affinity for 5-methyltetrahydrofolate. One of these mutations, 983A>G (N324S), showed flavin adenine dinucleotide (FAD) responsiveness in vitro. Expression of these mutations in cis with the 677C>T polymorphism, as observed in the patients, resulted in an additional 50% decrease in enzyme activity. This report brings the total to 33 severe mutations identified in patients with severe MTHFR deficiency.     

Identification of 11 novel mutations in 49 Korean patients with mucopolysaccharidosis type II

Mucopolysaccharidosis type II (MPS II) or Hunter syndrome is a rare lysosomal storage disorder caused by a deficiency of iduronate-2-sulfatase (IDS). As MPS II is X-linked, patients are usually males with heterogeneous mutations ranging from point mutations to gross deletions and recombination. In 2003, we reported a mutation analysis of 25 patients with MPS II. In this study, 31 mutations in another 49 Korean patients (45 families) with MPS II are reported: 12 missense, nine deletions, four splicing, two nonsense, two insertions, one deletion/insertion, and IDS-IDS2 recombination mutations. Among these mutations, 11 were novel ones (4 missense mutations: Ser61Pro, Pro97Arg, Pro228Ala, and Pro261Ala; 5 deletions: c.344delA, c.420delG, c.768delT, c.1112delC and c.1402delC; 1 deletion/insertion: c.1222delinsTA; and 1 insertion mutation: c.359_360insATCC). The IDS-IDS2 recombination mutations were most frequently observed; all patients with this mutation had the severe MPS II phenotype. However, most of the patients (5/7) with the G374G splicing mutation had an attenuated phenotype, except for two sibling cases with the severe phenotype. Except for a few recurrent mutations such as the G374G, R443X, L522P, and recombination mutations, each patient had a unique individual mutation. Therefore, careful interpretation of genotype-phenotype correlations is warranted.     

Mutations of the iduronate-2-sulfatase (IDS) gene in patients with hunter syndrome (mucopolysaccharidosis II)

Genomic DNA and cDNA from fibroblasts from nine unrelated German patients with X-linked iduronate-2-sulfatase (IDS) deficiency showing variable clinical manifestation were screened for point mutations and small structural aberrations. Direct sequencing revealed a splice mutation skipping exon A, one nonsense mutation, and five missense mutations concerning the exons B, F and I of the IDS gene. Several novel missense mutations were found: A68E, S426X, I485R, Q293H, and D478G. One of the point mutations eliminating a recognition site for the restriction enzyme MspI was used as a direct marker for a prenatal diagnosis. A relationship between type of mutation and clinical picture could not be recognized. © 1994 Wiley-Liss, Inc.     

Identification of 6 new mutations in the iduronate sulfatase gene. Mutation in brief no. 233. Online

Mucopolysaccharidosis type II (Hunter syndrome) is an X-linked lysosomal storage disorder caused by a deficiency of the enzyme iduronate-2-sulfatase. We sequenced genomic DNA and RT-PCR products in the iduronate sulfatase (IDS) gene in 6 unrelated patients with Hunter syndrome to assess genotype/phenotype relationships and offer carrier testing where required. Six novel mutations were identified: four missense mutations, one four-base pair deletion (596-599delAACA) and a cryptic splice site mutation. Three of the missense mutations were significant amino acid substitutions (S143F, S491F, E341K) of which the latter two involve amino acids conserved amongst sulfatase enzymes. The patients identified with these mutations all had a severe clinical phenotype. One missense mutation with a minimal amino acid substitution (H342Y), in a non-conserved region of the gene, was associated with a mild clinical phenotype. We identified a novel cryptic splice site (IVS5+934G>A) with some normal (wild type) mRNA processing. We predict that the normal mRNA product confered some residual functional enzyme, resulting in a mild phenotype associated with the absence of overt central nervous system disease.     

Mutation analysis of Jewish hunter patients in Israel

We have performed molecular and mutation analyses on 14 unrelated Israeli Hunter families and have identified the IDS mutation in 8 of them. Three unrelated Ashkenazi patients had the same previously reported mutation (1246 C→T). Based on the haplotypes of the mutation-bearing chromosomes, we concluded that this is a recurrent mutation. In two patients, we identified a deletion spanning exons V–VII. Three novel mutations were observed in different patients: L410P, 717del4, and 244del3. In addition, the silent mutation (562 C→T) was observed in one patient. © 1994 Wiley-Liss, Inc.     

Identification of 6 new mutations in the iduronate sulfatase gene

Mucopolysaccharidosis type II (Hunter syndrome) is an X‐linked lysosomal storage disorder caused by a deficiency of the enzyme iduronate‐2‐sulfatase. We sequenced genomic DNA and RT‐PCR products in the iduronate sulfatase (IDS) gene in 6 unrelated patients with Hunter syndrome to assess genotype / phenotype relationships and offer carrier testing where required. Six novel mutations were identified: four missense mutations, one four‐base pair deletion (596‐599delAACA) and a cryptic splice site mutation. Three of the missense mutations were significant amino acid substitutions (S143F, S491F, E341K) of which the latter two involve amino acids conserved amongst sulfatase enzymes. The patients identified with these mutations all had a severe clinical phenotype. One missense mutation with a minimal amino acid substitution (H342Y), in a non‐conserved region of the gene, was associated with a mild clinical phenotype. We identified a novel cryptic splice site (IVS5+934G>A) with some normal (wild type) mRNA processing. We predict that the normal mRNA product confered some residual functional enzyme, resulting in a mild phenotype associated with the absence of overt central nervous system disease. © 1999 Wiley‐Liss, Inc.     

Mutation analysis of the iduronate-2-sulfatase gene in patients with mucopolysaccharidosis type II (Hunter syndrome).

Iduronate-2-sulfatase (IDS) cDNA from fibroblasts of nine patients with Hunter syndrome (mucopolysaccharidosis type II) was screened for mutations using single strand conformation polymorphism analysis. Direct sequencing revealed a number of different mutations including missense or nonsense point mutations, deletions of one, two, or 60 base pairs, and a 22 base pair-insertion. Mutations of these types probably account for most IDS gene defects as only about 20% of Hunter patients have a complete deletion or gross structural alteration of their IDS gene. Thus the broad clinical variability amongst the Hunter patients may be due to the extensive genetic heterogeneity seen. The relationship between genotype and clinical phenotype is analysed in 12 Hunter patients.     

Carrier detection of deletions of the Hunter gene by in situ hybridization

Deficiency of the lysosomal enzyme α-iduronate sulphate sulphatase (IDS) causes the clinical manifestations of Hunter syndrome, an X-linked condition. In about 30% of male patients, the disease is due to a major deletion. Using a non-isotopic in situ hybridization (NISH) method, and a yeast artificial chromosome (YAC) probe, the Hunter gene was mapped to the terminal region of the human X chromosome, close to the Xq28 band.
The NISH procedure was then applied to investigate the carrier status of female relatives of a Hunter patient known to have a deletion of the IDS gene.
Unequivocal evidence that two female relatives were carriers of the deletion was obtained, demonstrating that the NISH method is a valuable diagnostic tool in genetic counselling of families with Hunter patients.     

Cystathionine beta-synthase deficiency in Georgia (USA): correlation of clinical and biochemical phenotype with genotype

Cystathionine beta-synthase (CBS) deficiency is a rare autosomal recessive disorder that is the most frequent cause of clinical homocystinuria. Patients not treated in infancy have multi-systems disorders including dislocated lenses, mental deficiency, osteoporosis, premature arteriosclerosis, and thrombosis. In this paper, we examine the relationship of the clinical and biochemical phenotypes with the genotypes of 12 CBS deficient patients from 11 families from the state of Georgia, USA. By DNA sequencing of all of the coding exons we identified mutations in the CBS genes in 21 of the 22 possible mutant alleles. Ten different missense mutations were identified and one novel splice-site mutation was found. Five of the missense mutations were previously described (G307S, I278T, V320A, T353M, and L101P), while five were novel (A226T, N228S, A231L, D376N, Q526K). Each missense mutation was tested for function by expression in S. cerevisiae and all were found to cause decreased growth rate and to have significantly decreased levels of CBS enzyme activity. The I278T and T353M mutations accounted for 45% of the mutant alleles in this patient cohort. The T353M mutation, found exclusively in four African American patients, was associated with a B(6)-nonresponsive phenotype and detection by newborn screening for hypermethioninemia. The I278T mutation was found exclusively in Caucasian patients and was associated with a B(6)-responsive phenotype. We conclude that these two mutations occurred after ethnic socialization and that the CBS genotype is predictive of phenotype.     

粘多糖贮积症Ⅱ型患者IDS基因的一个新突变

目的　研究粘多糖贮积症 型 ( mucopolysaccharidosis type ,MPS )患者的艾杜糖 - 2 -硫酸酯酶 ( iduronate- 2 - sulfatase,IDS)基因的基因突变。方法　应用聚合酶链反应 -单链构象多态性( polymerase chain reaction- single strand conformation polymorphism,PCR- SSCP)对患者的 IDS基因可能的常见突变第 2、3、5、7～ 9外显子进行检测 ,并对 PCR- SSCP检出的突变进行直接测序 ,测序发现的突变进行 PCR-限制性酶切分析验证。结果　经 PCR- SSCP和 DNA序列分析发现该患者的第 7外显子发生新的点突变 ( G12 5 3T) ;聚合酶链反应 -限制性片段长度多态性 ( PCR- RFL P)电泳检测示患者和母亲出现突变导致的酶切位点 ,进一步验证了序列分析结果。结论　筛查所得的点突变 G12 5 3T可能是该 MPS 患者的致病原因     

慢性乙型肝炎患者HBV耐药模式及rtA181变异准种分析

目的分析慢性乙型肝炎患者HBV逆转录酶区耐药变异情况及rtA181变异准种的分布。方法提取患者血清中HBVDNA,PCR扩增逆转录酶区域,产物测序后经软件比对分析耐药变异情况和基因型;对部分rtA181变异标本进行克隆后测序分析准种分布。结果 489例标本中,检出明确耐药变异265例,在B、C基因型中分布比例存在差异（56.6%vs43.0%,P=0.022）。拉米夫定相关耐药138例（52.1%）,以M204I、M204I/V＋L180M±L80I/V变异为主;阿德福韦相关耐药35例（13.2%）,以N236T＋A181T/V较为多见;拉米夫定＋阿德福韦相关耐药70例（26.4%）,几乎都和A181有关。rtA181准种分析发现1例位于同一病毒株的多耐药组合,且未发现单一A181T变异的病毒准种。结论 HBV耐药变异主要表现为M204和A181相关变异,耐药模式复杂;检测HBV逆转录酶区的变异有助于临床及时发现和确认耐药情况,指导临床合理进行抗病毒用药。     

Molecular basis of recessive congenital methemoglobinemia, types I and II: Exon skipping and three novel missense mutations in the NADH-cytochrome b5 reductase (diaphorase 1) gene

Hereditary methemoglobinemia due to reduced nicotin amide adenine dinucleotide (NADH)-cytochrome b5 reductase (b5r) deficiency is classified into an erythrocyte type (I) and a generalized type (II). We investigated the b5r gene of three unrelated patients with types I and II and found four novel mutations. The patient with type I was homozygous for a c.535 G-->A exchange in exon 6 (A179T). The patients with type II were found to be homozygous for a c.757 G-->A transition in exon 9 (V253M) and compound heterozygous for two mutations, respectively. One allele presented a c.379 A-->G transition (M127V). The second allele carried a sequence difference at the invariant 3' splice-acceptor dinucleotide of intron 4 (IVS4-2A-->G) resulting in skipping of exon 5. To characterize a possible effect of this mutation on RNA metabolism, poly(A)(+) RNA was analyzed by RT-PCR and sequencing. The results show that RNA is made from the allele harboring the 3'-splice site mutation. Furthermore, western blot analysis revealed a complete absence of immunologically detectable b5r in skin fibroblasts of this patient. The compound heterozygosity for the splice site and the missense mutations apparently caused hereditary methemoglobinemia type II in this patient. Hum Mutat 17:348, 2001.