粘多糖贮积症Ⅱ型IDS基因的1343-TT新突变

Detection of a new mutation(1343-TT) in the iduronate-2-sulfatase gene from a Chinese patient with mucopolysaccharidosis type Ⅱ

目的研究中国粘多糖贮积症Ⅱ型(MPSⅡ)艾杜糖-2-硫酸酯酶(IDS)的基因突变,为产前基因诊断打下基础。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(PCR-DHPLC)对1例MPSⅡ患儿及其父母的IDS基因的突变热点exons 9,3,8,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,发现患儿的IDS基因exon 9有明显异常峰形;DNA序列分析进一步发现,患儿IDS基因的exon 9发生1343-TT新移码突变,突变部位在第407位密码子(TTT)内,即IDS基因cDNA第1343 bp的T后缺失了2个T,并在第429位提前遇上终止密码TGA,导致肽链从550个氨基酸缩短至428个。患儿为这一突变的半合子,而其母为这一突变的杂合子。结论新发现的移码突变(1343-TT)导致肽链比正常的少了122个氨基酸,极可能引起酶活性大大降低,因此可能是该MPSⅡ患儿发病的真正原因。

Objective Mutations of the iduronate-2-sulfatase （ IDS ） gene is the ultimate cause of Hunter syndrome. Clarification of the nature of mutations will create a necessary premise for prenatal gene diagnosis. A mucopolysaccharidosis （MPS） type Ⅱ patient and his parents from an ethnic minority in Yunnan province were studied to identify their possible mutation in IDS gene to establish the basis for prenatal gene diagnosis. Methods The patient was a boy, 6 years and 10 months old. Urine glycosaminoglycans （GAGs） assay was used for preliminary diagnosis of the patient and his parents with the disease. The three related persons＇ DNA was extracted and the concentration and purity of the DNA were measured after the urine test results confirmed the diagnosis. Polymerase chain reaction-denaturing high performance liquid chromatography （ PCR-DHPLC ） analysis was performed to detect the position of the mutation around the hot spots of mutation in exon 9, 3, 8 of the IDS gene. DNA bidirectional direct sequencing was applied to analyze the mutation detected by PCR-DHPLC. Results The results of GAGs test showed that in the child with MPS, dermatan sulfate （DS） was positive （ ＋＋＋ ） , heparan sulfate （HS） （ ＋＋＋ ） ,chondroitin sulfate （CS） and keratan sulfate （KS） were negative（ - ） ; while in his parents none of DS, HS, CS and KS was positive. Abnormal peaks in exon 9 of IDS gene shown by PCR-DHPLC were found in the patient. His mother had heterozygotic peaks. A new frame-mutation （ 1343-TT in exon 9 of IDS gene of this patient was confirmed by DNA sequencing. The position where mutation occurred was inside codon 407 （TTT）, that means two ＂T＂ deleted at position 1343 base pair（1343-TT） in cDNA of the IDS gene, caused a new frame-mutation. It caused elongation of the amino acid chain to a terminal codon TGA at position 429. Thus the peptide chain was shortened from 550 to 428 amino acids. The patient is a hemizygote of the mutation and his mother is a heterozygote. Conclusion A new frame-mutation （1343-TT） on the IDS gene was identified in this study. The patient is a hemizygote and his mother is a heterozygote. The mutation （1343-TT） resulted in loss of 122 amino acids, which probably caused seriously decreased enzyme activity of IDS, and the authors speculate that this mutation may be the pathological basis of the disease. So, if the mother becomes pregnant again, a prenatal gene diagnostic test for the same mutation should be performed. Furthermore, PCR-DHPLC followed by DNA sequencing are effective methods for diagnosis, including prenatal diagnosis of MPS Ⅱ.