MLH1、MSH2基因 mRNA突变分析与遗传性非息肉性结直肠癌的基因诊断

目的检测胚系MLH1和MSH2基因mRNA突变，确立遗传性非息肉性结直肠癌（hereditary nonpolyposis colorectal cancer，HNPCC）家系。方法收集符合Amsterdam标准Ⅱ的12个家系14名家庭成员外周血，用特异引物和耐热性逆转录酶特异地逆转录MLH1和MSH2的RNA；利用长模板PCR扩增酶扩增逆转录产物（cDNA）；测序分析扩增产物。提取外周血的DNA，设计与利用上述方法检测出突变对应外显子的特异性引物，利用Taq DNA聚合酶扩增测序，以检测上述方法的有效性。结果利用基于外周血mRNA的方法，在6个家系中检出6个胚系突变，4个MLH1突变和2个MSH2突变，MLH1突变分别位于第8、12、16和第19外显子；MSH2突变分别位于第1和第2外显子。利用基于外周血DNA的方法，上述突变均在MLH1和MSH2相应的外显子中得到验证。突变类型为4个错义突变、1个同义突变和1个非编码区突变；其中5个突变国际上尚未报道；6个突变中有5个为病理性，分布于5个不同家系，该5个家系被确诊为HNPCC家系。结论基于外周血MLH1和MSH2 mRNA异常的检测能确诊HNPCC家系；该方法敏感、省时、节约成本。     

卵巢浆液性交界及恶性肿瘤K-ras基因突变分析

目的探讨K-ras基因在卵巢浆液性交界及恶性肿瘤发生发展过程中的作用。方法收集51例卵巢浆液性肿瘤标本,包括经典型交界性浆液性肿瘤18例,微乳头型交界性浆液性肿瘤11例,浸润性微乳头型浆液性癌12例,经典型浆液性癌10例。采用显微切割技术获取肿瘤细胞后,提取基因组DNA、PCR技术扩增K—ras基因第一外显子,通过直接测序的方法鉴定K—ras基因第12、13密码子的突变情况。结果1例经典型交界性浆液性肿瘤K—ras基因第12密码子发生突变,突变类型为GGT→GTT即甘氨酸→缬氨酸,余50例标本未见突变;所有标本K—ras基因第13密码子均为野生型。结论K—ras基因第12、13密码子在被检患者中卵巢浆液性交界及恶性肿瘤中的突变频率很低,其在该肿瘤发生发展过程中可能不起主要作用。     

一个表皮松解性掌跖角化病家系的KRT9基因突变分析

目的明确一个伴随有类似关节指垫样病损和指甲病变的表皮松解性掌跖角化病的中国家系中角蛋白9(keratin9,KRT9)基因突变情况。方法用聚合酶链反应技术扩增家系成员及家系外50名正常人KRT9基因的编码区及外显子与内含子交界处,DNA序列分析寻找突变位点,然后经限制性内切酶Dde分析验证。结果患者KRT9基因第1外显子第160位密码子发生AAT→AGT的突变(N160S),而家系正常成员及家系外50个正常人中均不存在此突变。结论KRT9基因的第1外显子第160位密码子发生AAT→AGT突变(N160S)导致该家系患者发生表皮松解性掌跖角化病。     

EXT2基因IVS2+1G>A突变致遗传性多发性外生性骨疣

目的　确定一个遗传性外生性骨疣家系的致病基因。方法　应用基因组扫描方法 ,利用 8、11和 19号染色体上的微卫星标记对该家系进行连锁分析 ,确定候选基因 ,然后对候选基因的编码区及外显子与内含子交界处进行测序分析寻找突变 ,并行逆转录 - PCR扩增 m RNA加以证实。结果　该家系致病基因被定位在 11号染色体的 EXT2基因区 ,在 EXT2基因中检测到 1个 IVS2 1G>A(5 36 1G>A)突变 ,该突变与疾病共分离。逆转录 - PCR证实 ,该突变导致编码区的第 316～ 5 36位共 2 2 1个碱基的缺失 ,使 10 6位密码子至 178位密码子及紧随的两个核苷酸的缺失 ,造成移码 ,形成 12 5个氨基酸的截短蛋白。结论　EXT2基因的 IVS2 1G>A突变是导致这个家系发生外生性骨疣的原因。     

PCR-ACRS方法筛查CYP21基因P459H的突变位点

目的：研究21-羟化酶基因（CYP21）第10外显子P459H突变（CCC→CAC）在正常人群中的发生率,分析P459H是点突变还是基因多态。方法:设计特异性引物扩增CYP21基因3-10外显子,PstⅠ限制性内切酶消化验证PCR产物为特异性扩增,在此基础上,应用PCR结合扩增引进限制性酶切位点方法(PCR-ACRS)扩增首次PCR产物,FspⅠ限制性内切酶酶切后用10%聚丙烯酰胺凝胶电泳筛查第10外显子P459H的发生率。 结果:100例正常人CYP21基因第10外显子密码子459均为CCC,即均未出现P459H变异。 结论:CYP21基因P459H为点突变,排除基因多态的可能;另外,PCR-ACRS是一种快速、可靠的检测基因点突变的有效途径。     

中国人遗传性非息肉病性结直肠癌MSH6基因胚系突变的测序研究

目的探讨中国人遗传性非息肉病性结直肠癌(hereditary nonpolyposis colorectal cancer,HNPCC)家系中MSH6基因胚系突变。方法采用PCR-直接测序的方法检测39个无胚系MSH2及MLH1基因突变、符合不同临床标准的中国人HNPCC家系先证者MSH6基因各外显子胚系突变;对137名正常人胚系基因组DNA进行错义突变相应外显子的测序分析。应用Envision二步法检测有突变的先证者肿瘤组织MSH6蛋白表达。结果在39个HNPCC先证者中共发现6个MSH6基因的胚系突变,分别位于第4、6、9和第10外显子;突变类型为4个错义突变、1个无义突变、1个剪接区的插入突变;对4个错义突变的相应外显子的测序分析显示:137名正常人胚系基因组DNA5例具有第6外显子1163密码子处的c.3488A>T的错义突变,约占3.65%(5/137),为单核苷酸多态性(single nucleotide polymorphism,SNP);其余错义突变在正常人群中均未发现。在6例有MSH6基因胚系突变家系的肿瘤组织中免疫组化染色除1例为SNP的肿瘤组织MSH6蛋白阳性表达外,其余均为阴性表达。经过查询国际HNPCC突变数据库及SNP数据库证实上述突变中5个为国际上尚未报道的病理性突变,1个为新发现的SNP。结论MSH6基因胚系突变在符合不同临床标准的中国人HNPCC中均起一定作用,对无MSH2及MLH1基因胚系突变的先证者行MSH6基因胚系突变的测序分析对确诊HNPCC家系是必要的。     

3个肾上腺脑白质营养不良家系的基因突变分析

目的　对 3个肾上腺脑白质营养不良 ( adrenoleukodystrophy,AL D) ( MIM# 30 0 10 0 )家系进行基因突变分析。方法　从 3个 AL D患儿及其主要家系成员的外周血白细胞 ,提取总 RNA和基因组 DNA。应用逆转录聚合酶链反应技术 ,对 3个家系的 ABCD1基因编码区 ,分 4个片段进行 PCR扩增并对 PCR产物直接测序。同时应用 PCR-限制性酶切或扩增阻滞突变系统分析相应的基因组 DNA,进一步确证ABCD1基因的突变位点。结果　 3名患儿的 ABCD1基因上均存在错义突变 ,其中患儿 1的 ABCD1基因第 5 34位密码子发生 CCC→ CGC改变 ,使脯氨酸被精氨酸取代 ( P5 34R) ;患儿 2的 ABCD1基因第 2 6 6位密码子发生 GGG→AGG改变 ,使甘氨酸被精氨酸取代 ( G2 6 6 R) ;患儿 3母亲的 ABCD1上一个等位基因第 6 17位密码子发生 CGC→ GGC改变 ,使精氨酸被甘氨酸取代 ( R6 17G) ,另一个等位基因未发生突变。结论　在中国人 AL D患者中发现 1个新的 ABCD1基因突变 ( P5 34R) ,并首次在中国人 AL D患者中检测到G2 6 6 R、R6 17G突变     

PCR直接测序在Wilson病基因第8外显子检出一个突变热点

目的寻找中国人Ｗｉｌｓｏｎ病（ＷＤ）基因突变热点。方法应用ＰＣＲ直接测序法对３０例Ｗｉｌｓｏｎ病患者ＷＤ基因第８外显子进行了突变筛查。结果在１４例患者中发现同一种错义突变Ａｒｇ７７８Ｌｅｕ，其中４例为这一突变的纯合，其余为杂合，突变率为３０％。结论ＷＤ基因第８外显子７７８位密码子（ＣＧＧ→ＣＴＧ）系中国人的突变热点之一。     

Alzheimer病患者早老素-1基因第5外显子突变特征分析

目的　探讨早老素-1 基因突变在散发性Alzheim er 病(sporadic Alzheim er's disease, SAD)患者发病机理中的作用。方法　应用聚合酶链反应-单链构象多态性(polym erase chain reaction-singlestrand conform ation polym orphsim ,PCR-SSCP)及DNA 直接测序技术检测68 例SAD 患者和65 名正常老年人的早老素-1 基因第5 外显子。结果　发现68 例SAD患者中有4 例患者的SSCP发生泳动异常,DNA 序列分析发现:这4 例SAD 患者的130 号密码子发生了CTG→ATG 错义突变(388 位点发生C→A突变),使氨基酸由亮氨酸变为蛋氨酸(Leu 130 Met);157 号密码子发生了GTG→CTG 错义突变(469 位点发生G→C突变),使氨基酸由缬氨酸变为亮氨酸(Val157 Leu);有11 例患者的SSCP表现为一条单链电泳迁移率明显增快,DNA 序列分析发现:这11 例SAD患者的130 号密码子发生了CTG→ATG 错义突变(388 位点发生C→A 突变),使氨基酸由亮氨酸变为蛋氨酸(Leu 130 Met);154 号密码子发生了TGC→TGT 同义突变(462 位点发生C→T)突变。结论　我们发现在SAD患者中存在早老素-1 基因第5 外显子突变,该突变点可能为中国人SAD 患者早老素基因突变点之一。     

汉族家族性中枢神经系统海绵状血管畸形致病基因的一个新突变位点

目的 探查汉族家族性中枢神经系统海绵状血管畸形(CCM)的突变基因。方法 选择经神经科确诊的2个家系(A及B)和8例散发性中枢神经系统海绵状血管畸形病例。所有受检对象临床表现有癫痫、突发头痛;2例伴有皮肤病变。候选基因为已确认的Krit-1,对该基因的16个编码外显子进行PCR扩增,扩增产物进行直接测序。结果 受检的A家系在第14外显子的第1289(从起始密码子计算,或2308即从mRNA的第一个碱基计算)位核苷酸一个拷贝有C→G的取代,出现编码改变(S430X),形成终止密码子(UGA),使翻译过程提前终止,导致的基因异常属无义点突变。同法筛查,A家族中有1名成员突变未获得遗传;散发病例发现一个正常多态性变化,未见到突变。结论 发现第1例汉族人CCM基因的点突变,也是国际上未见报道的新位点。这一点突变将会导致一种截短蛋白,是CCM发生的基本原因。研究结果可用于症状前基因诊断。     

Novel germline mutation (300-305delAGTTGA) in the human MSH2 gene in hereditary non-polyposis colorectal cancer (HNPCC)

Hereditary non-polyposis colorectal cancer (HNPCC) is a common hereditary syndrome characterized by the high incidence and early onset of colorectal cancer. The majority of the HNPCC families carry germline mutations in either the MSH2 or the MLH1 mismatch repair gene. A 46 year-old female patient whose family history fulfilled the Amsterdam criteria for HNPCC was diagnosed with undifferentiated adenocarcinoma of the transverse colon. Recognizing the Lynch 2 syndrome (the existance of multiple HNPCC related cancers in a pedigree), we used polymerase chain reaction followed by direct sequencing to screen the coding regions of both the MSH2 and the MLH1 genes for germline mutations in DNA from the patient. We detected a novel germline mutation (300-305delAGTTGA) in exon 2 of human MSH2. We noted microsatellite instability in four microsatellite loci. Immunohistochemistry showed a lack of expression of the MSH2 gene product in the tumor, suggesting that the mutation is a disease-causing mutation.     

Three new mutations in hereditary nonpolyposis colorectal cancer (Lynch syndrome II) in Uruguay

Hereditary nonpolyposis colorectal cancer (HNPCC) is the most common hereditary form of colorectal cancer (CRC). Our purpose is to describe three extended HNPCC families, each of which manifests novel germline mutations in Uruguay, a small country that is a study model for cancer investigation given its high cancer incidence and mortality rate. This is a study of three extended HNPCC families in which extensive genealogic information, medical history, and pathology findings are critically reviewed. DNA testing was performed for evidence of HNPCC mutations. The findings reveal three novel germline mutations, namely MLH1, with a deletion resulting in a frameshift and a premature stop codon (codon 228) in one of the families; in the second family, MSH2 exon 1, codon 61 at nucleotide 181, which results in immediate stop of translation; and in the third family, a mutation in MSH2 at exon 3: the amino acid at nucleotide 530, codon 117, causing a frameshift and a premature stop codon eight base pairs later. We conclude that it is important to study HNPCC mismatch repair genes because of emerging evidence for genotypic and phenotypic heterogeneity, which will harbor the potential to eventually translate this knowledge into specific screening and management protocols. Future projections for such mutations could even contribute to the emergence of molecular-based designer drugs developed through advances in genomics, proteomics, high-throughput screening, and bioinformatics, which would be effective therapeutically for these high-cancer risk patients.     

Seven novel MLH1 and MSH2 germline mutations in hereditary nonpolyposis colorectal cancer

Hereditary nonpolyposis colorectal cancer (HNPCC) is the most frequent hereditary form of colorectal cancer and is caused by germline mutations in mismatch repair (MMR) genes. The majority of mutations occur in MLH1 and MSH2. We report hereby seven novel germline mutations in these two genes (five in MLH1 and two in MSH2). All mutations have been found in families fulfilling criteria of the Bethesda guidelines and four of which also fulfilled the Amsterdam criteria. We identified three insertions or deletions of 1 bp leading to premature stop codons (MLH1: c.341delC, c.1413‐1414insA; MSH2: c.1119delG) and three nonsense mutations (MLH1: c.67G>T [E23X], c.436C>T [Q146X]; MSH2: c.1857T>G [Y619X]). The corresponding tumors showed a high level of microsatellite instability (MSI‐H) and a complete loss of expression of the affected protein. In addition, a missense mutation in MLH1 was identified (c.1984A>C [T662P]). The respective tumor also showed a high level of microsatellite instability but a reduced, rather then lost, expression of the MLH1‐protein. This missense mutation was not found in 107 healthy control individuals and in 54 HNPCC patients. © 2001 Wiley‐Liss, Inc.     

Assessing the pathogenicity of MLH1 missense mutations in patients with suspected hereditary nonpolyposis colorectal cancer: correlation with clinical, genetic and functional features

Assessing the pathogenicity of missense mutations of MLH1 and MSH2 is critical to counsel patients with suspected hereditary nonpolyposis colorectal cancer (HNPCC). Approximately 32% of all MLH1 mutations and 18% of MSH2 mutations are missense variants which often have an uncertain genetic significance. To assess the pathogenicity of four MLH1 missense mutations which were found in five patients with suspected HNPCC, P648S (CCC --> TCC), L559R (CTG --> CGG), K618A (AAG --> GCG), Y646C (TAT --> TGT), we studied their ability to disrupt MLH1 protein function and their relationship with all those clinical, genetic and pathological features which are typical of this syndrome. Our results indicated that the P648S and L559R mutations were probably pathogenic because they disrupted MLH1 protein interaction with its partner PMS2 in vitro and abolished MLH1 expression in HCT116 cells. In addition these variants were associated with features often found in HNPCC patients: in particular high microsatellite instability, occurrence of high grade tumours and, in one case, strong family history. The pathogenicity of the K618A and Y646C mutations was questionable as their correlation with features typical of HNPCC was low and the outcome of the functional analysis was ambiguous. These observations suggested that a clinically usable assessment of the pathogenicity of MLH missense variants can be achieved through the analysis of multiple mutation characteristics among which loss of protein function, occurrence of microsatellite instability and family history seemed to have a predominant role.     

Identification of germline MSH2 gene mutations in endometrial cancer not fulfilling the new clinical criteria for hereditary nonpolyposis colorectal cancer

Endometrial cancer is the second most common malignancy in patients with hereditary nonpolyposis colorectal cancer (HNPCC). This cancer is caused by germline mutations in one of the DNA mismatch repair (MMR) genes. The present study was undertaken to analyze the relation between microsatellite instability (MSI) and germline mutations of MMR genes. We analyzed MSI in 38 cases of endometrial cancer. MSI was present in one or more (out of 5 examined) regions in 11 (29%) cases. Furthermore, alterations in MLH1 and MSH2, two culprit genes representative of HNPCC, were examined in the 11 MSI-positive patients using polymerase chain reaction-single-strand conformation polymorphism and sequencing. Germline mutations, namely, 1) a missense mutation at codon 688 (ATG-->ATA, Met-->Ile) and 2) a missense mutation at codon 390 (CTT-->TTT, Leu-->Phe) of the MSH2 gene, were found in 2 of the 11 patients (18%). Although these two cases do not fulfill the new Amsterdam criteria, they had strong family histories of colorectal and endometrial carcinoma. Our results show that genetic testing is important in cases of endometrial cancer with a history suggestive of HNPCC even if the new Amsterdam criteria are not fulfilled.     

PAX6 gene variations associated with aniridia in south India

Background

Hereditary non-polyposis colorectal cancer (HNPCC) is an autosomal dominant disease with a high risk for colorectal and endometrial cancer caused by germline mutations in DNA mismatch-repair genes (MMR). HNPCC accounts for approximately 2 to 5% of all colorectal cancers. Here we present 6 novel mutations in the DNA mismatch-repair genes MLH1, MSH2 and MSH6.

Methods

Patients with clinical diagnosis of HNPCC were counselled. Tumor specimen were analysed for microsatellite instability and immunohistochemistry for MLH1, MSH2 and MSH6 protein was performed. If one of these proteins was not detectable in the tumor mutation analysis of the corresponding gene was carried out.

Results

We identified 6 frameshift mutations (2 in MLH1, 3 in MSH2, 1 in MSH6) resulting in a premature stop: two mutations in MLH1 (c.2198_2199insAACA [p.N733fsX745], c.2076_2077delTG [p.G693fsX702]), three mutations in MSH2 (c.810_811delGT [p.C271fsX282], c.763_766delAGTGinsTT [p.F255fsX282], c.873_876delGACT [p.L292fsX298]) and one mutation in MSH6 (c.1421_1422dupTG [p.C475fsX480]). All six tumors tested for microsatellite instability showed high levels of microsatellite instability (MSI-H).

Conclusions

HNPCC in families with MSH6 germline mutations may show an age of onset that is comparable to this of patients with MLH1 and MSH2 mutations.     

Mechanisms underlying mismatch repair deficiencies in normal cells

Hereditary nonpolyposis colon cancer (HNPCC) is an autosomal dominantly inherited cancer predisposition which is linked to heterozygous mutations in mismatch repair genes. HNPCC tumour cells, in which the remaining wild-type copy of the mismatch repair gene is inactivated, display instability of microsatellite markers reflecting a defect in mismatch repair. Recently, patients carrying either one of two distinct germline mutations in the MLH1 and PMS2 genes were reported to accumulate somatic mutations of microsatellites in untransformed cells. One of the mechanisms that might account for this phenomenon was a dominant negative effect of the mutant allele. To evaluate this possibility, we examined a different family carrying one of the mutations (deletion of codon 618K in the MLH1 gene) which has been suspected to induce genetic instability in untransformed cells. No mutations in dinucleotide repeat markers were observed in a large number of lymphoblast clones derived from a carrier. Evidence for the deletion of the wild-type allele in two different tumours suggested that the inactivation of both gene copies was required for tumour initiation. These results indicate that the MLH1 618K deletion mutation alone does not necessarily cause marked mismatch repair deficiency in the presence of a wild-type allele. Genes Chromosomes Cancer 20:305–309, 1997. © 1997 Wiley-Liss, Inc.