家族性腺瘤样息肉病中APC基因的胚系突变分析

目的 探索有效的突变检测技术，系统分析家族性腺瘤样息肉病(familial adenomatous polyposis，FAP)相关基因结肠腺瘤病(adenomatous polyposis coli，APC)基因的胚系突变，及其与疾病表型的关系。方法 从22例临床确诊的FAP患者，外周静脉血中提取基因组DNA。变性高效液相色谱、蛋白截短检测、测序技术结合应用进行全基因分析。根据患者临床资料，进行基因型-表型分析。结果 22例FAP患者中13例检出APC基因胚系突变，均为无义或移码突变。基因型-表型关系的初步分析表明，在基因5′端或3′端发生突变的患者临床症状较轻，在基因中段发生突变的患者临床症状典型或严重。结论 本研究中所采用的技术体系可敏感、高效地检出APC基因突变，APC基因的突变型与FAP患者的临床表型存在关联，所采用的技术体系适用于FAP症状出现前的基因诊断。     

家族性腺瘤性息肉病一家系调查及APC基因胚系突变分析

目的 探讨家族性腺瘤性息肉病(familial adenomatous polyposis,FAP)家系调查及高危亲属基因筛查的意义,报道云南省一FAP家系发病相关基因APC基因的胚系突变结果.方法 查阅对2001年昆明医学院第一附属医院1例FAP患者病例,电话联系及登门随访进行其家系调查,绘制家系图谱.抽取该家系成员外周静脉血提取DNA,利用PCR方法扩增APC基因,应用DNA自动测序仪进行测序.结果 该家系三代共计9人,成员Ⅰ1、Ⅱ1、Ⅱ2、Ⅱ3、Ⅱ4、Ⅲ2、Ⅲ3、Ⅲ48人检出APC基因胚系突变c.3587C>A(S1196X),其中Ⅱ2、Ⅱ2、Ⅱ4、Ⅲ2、Ⅲ3经肠镜检查证实有结直肠多发息肉,Ⅲ4未检出息肉,为基因突变携带者.结论 通过家系调查对高危亲属进行基因筛查可以发现早期患者,尤其是无临床表现的FAP基因突变携带者,以早期进行医学干预及预防性手术治疗,降低FAP的癌变率、病死率;APC基因c.3587C>A(S1196X)胚系突变是引起该家系FAP患者发病的原因.     

家族性腺瘤性息肉病家系中一种新的APC基因的胚系突变

目的研究1个家族性腺瘤性息肉病家系的腺瘤样息肉病基因（adenomatous polyposis coli，APC）的胚系突变。方法经结肠镜、组织病理学检查和家族史的调查，确定了1例家族性腺瘤性息肉病（familial adenomatous polyposis，FAP）患者。应用多重连接依赖性探针扩增（multiplex ligation-dependent probe amplification，MLPA）、变性高效液相色谱（denaturing high-performance liquid chromatography，DHPLC）测序等技术对这一家系的成员进行系统的APC全基因筛查。结果在此家系中发现一个新的APC基因的胚系突变c。1999 C〉T（Q667X），这一突变造成了APC基因终止密码子的形成，从而形成有功能障碍的截短蛋白。临床上，此突变可引起严重的FAP症状，早发结直肠腺瘤和腺癌。结论Q667X胚系突变是引起该家系临床表型的原因，受累成员可考虑大肠预防性切除手术。     

近代人类胚系突变：从乙型血友病患者的推断

编码第Ⅸ因子的基因，对于研究人类胚系突变具有一些独特的有利条件。对所观察的这种基因的详细分析，特别注意数据中的偏倚，为突变的一些热点（包括隐蔽的双核苷酸的重复），每个碱基对每代的突变和突变的性比率提供了信息。证据有力地提示，大多数胚系突变起因于内源过程，而不是起因于外源诱变剂。可能自然不允许环境控制这个重要过程。代之以胚系突变率处于选择压力下，在选择压力下早期发生癌可能是一个重要的调节者。     

中国人家族性腺瘤性患肉病患者结肠腺瘤性患肉病基因的胚系突变

目的 探讨中国人家族性腺瘤性息肉病(familial adenomatous polyposis,FAr)患者的结肠腺瘤性息肉病(adenomatous polyposis coli,APC)基因的胚系突变类型.方法 对9个FAP家系18名成员进行多重连接依赖性探针扩增(multiplex ligation-dependent probe amplification,MLPA)检测APC基因有无大片段缺失.再应用PCR扩增APC基因的15个外显子区域,经变性高效液相色谱(denaturing high performance liquid chromatography,DHPLC)对每个扩增片段进行筛查,流出峰异常的片段,经DNA测序验证小片段的改变.结果 9个家系中有3个家系发现有APC基因的胚系突变:家系2为c.3184-3187 del CAhA,家系4为c.5432C＞T,家系9为c.3925-3929 del AAAAG.3种突变中c.5432C＞T在数据库中未见报道.结论 中国人不同的APC基因的胚系突变可引起FAP;无APC胚系突变的FAP患者的发病可能存在其他的机制.     

Peutz-Jeghers综合征临床病理分析

目的提高对Peutz-Jeghers综合征胃肠道息肉恶变风险的认识及诊断治疗水平.方法分析了13例患者的诊治过程,并对其家系进行调查及追踪.结果发现黑色素斑12例,胃肠道息肉11例,其中结肠息肉6例,1例癌变.8例有家族聚集现象.因肠套叠急症手术3例.结论该病存在不完全外显现象及恶变风险,对家系成员应长期跟踪随访;肠套叠发生发展隐袭,应早诊断早治疗.     

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。     

Peutz-Jeghers综合征及其分子遗传学研究进展

ＰｅｕｔｚＪｅｇｈｅｒｓ 综合征（ＰＪＳ）是一种常染色体显性遗传性疾病，以口周皮肤、唇颊粘膜和指（趾）端的咖啡色素斑点以及发生消化道粘膜的错构性息肉为临床特征。它与肿瘤发生关系密切，有研究表明，ＰＪＳ患者一生中发展为恶性肿瘤的可能性为５０％ 。其致病基因大多数病例定位在１９ｐ１３．３，少数例外。最近，有人采用定位候选克隆的方法在１９ｐ１３．３ 区域克隆了ＰＪＳ基因，预期编码一种新的苏丝氨激酶（ｓｅｒｉｎｅ ｔｈｒｅｏｎｉｎｅ ｋｉｎａｓｅ）命名为ＳＴＫ１１，并在ＰＪＳ患者中检测出多种突变。ＰＪＳ基因克隆为我们研究ＰＪＳ的发病机制奠定了基础，同时为研究肿瘤的发生机制提供了一个新的领域和视角。     

先天性长QT综合征一家系的突变分析

目的对1个先天性长QT综合征(long QT syndrome，LQTS)家系的突变进行检测与分析。方法根据先证者的临床表现及心电图先对其致病基因初步判断，然后采用聚合酶链反应以及直接测序法对其进行KCNQ1基因检测以发现致病突变。结果根据先证者的临床表现及心电图将其致病基因初步定位于KCNQ1基因上，且在KCNQ1基因上发现一错义突变940(G—A)(G314S)，此突变在欧美及日本人群中均有发现，为长QT综合征的突变热点。结论在中国长QT综合征患者中有与国外患者同样的突变热点。     

遗传性非息肉性结直肠癌家系的MLH1基因两个胚系新突变

目的初步评价遗传性非息肉性结直肠癌（HNPCC）胚系MLH1基因突变中新突变的病理性。方法收集符合AmsterdamⅡ标准的12个不同家系的12例患者外周血,用特异引物和耐热性逆转录酶特异地逆转录MLH1的mRNA;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;利用PCR-Genescan技术和免疫组织化学染色分别检测有新突变患者肿瘤组织的5个微卫星位点（BAT26,BAT25,D5S346,D2S123和Mfd15）和MLH1蛋白的表达。结果在4例患者中检出4个MLH1突变,其中2个突变为第12外显子的第384密码子（1151bp处）GTT→GAT的突变,该突变是已报道的病理性突变;另外2个突变分别是第8外显子的第217密码子（649bp处）CGC→TGC突变和第16外显子的第581密码子（1742bp处）CC→CTG突变;后两者为尚未报道的新突变。2个新突变的患者肿瘤组织均呈高度微卫星不稳定性,两者的瘤组织MLH1蛋白均失表达。结论MLH1第8外显子的第217密码子突变和第16外显子的第581密码子的两个新突变很可能为病理性突变。     

Germline mutations of the LKB1 (STK11) gene in Peutz-Jeghers patients

Germline mutations of the LKB1 (STK11) serine/threonine kinase gene (chromosome 19p13.3) cause Peutz-Jeghers syndrome, which is characterised by hamartomas of the gastrointestinal tract and typical pigmentation. Peutz-Jeghers syndrome carries an overall risk of cancer that may be up to 20 times that of the general population. Here, we report the results of a screen for germline LKB1 mutations by DNA sequencing in 12 Peutz-Jeghers patients (three sporadic and nine familial cases). Mutations were found in seven (58%) cases, in exons 1, 2, 4, 6, and 9. Five of these mutations, two of which are identical, are predicted to lead to a truncated protein (three frameshifts, two nonsense changes). A further mutation is an in frame deletion of 6 bp, resulting in a deletion of lysine and asparagine; the second of these amino acids is conserved between species. The seventh mutation is a missense change in exon 2, converting lysine to arginine, affecting non-conserved amino acids and of uncertain functional significance. Despite the fact that Peutz-Jeghers syndrome is usually an early onset disease with characteristic clinical features, predictive and diagnostic testing for LKB1 mutations will be useful for selected patients in both familial and non-familial contexts.     

De novo germline mutation in the serine-threonine kinase STK11/LKB1 gene associated with Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is an autosomal dominant disease, characterized phenotypically by mucocutaneous pigmentation and hamartomatous polyposis. Affected patients are at an increased risk of developing gastrointestinal and other malignancies. Mutations in the STK11/LKB1 (LKB1) gene, which encodes for a serine-threonine kinase, have been identified as a genetic cause of PJS. Molecular analysis of the LKB1 gene in a simplex case of PJS revealed a substitution of cytosine (C) for guanine (G) at codon 246 in exon 6, resulting in the Tyr246X mutation. The nucleotide substitution leads to a premature stop codon at the 246 residue, predicting a truncated protein and presumed loss of kinase activity. Analysis of DNA from both parents of the PJS patient did not show this mutation, which is therefore a de novo mutation. We isolated DNA from microdissected gastrointestinal hamartomatous polyps in the PJS patient and investigated the loss of heterozygosity (LOH) at the LKB1 locus by real-time fluorescence polymerase chain reaction genotyping using a fluorescent resonance energy transfer technique. The results suggest a different mechanism from LOH in the formation of hamartomatous polyps.     

Mutation analysis of the STK11/LKB1 gene and clinical characteristics of an Australian series of Peutz-Jeghers syndrome patients

Peutz-Jeghers syndrome (PJS) is a rare cancer predisposition, which is characterized by the presence of hamartomatous polyposis and mucocutaneous pigmentation. A significant proportion of both familial and sporadic forms of this disorder are associated with mutations in the STK11 (serine/threonine kinase 11)/LKB1 gene. In this report we present a series of Australian PJS cases, which suggest that mutations in the STK11 gene do not account for many families or patients without a family history. The most likely explanation is either the presence of another susceptibility gene or genetic mosaicism in the non-familial patients.     

Mutations in the human LKB1/STK11 gene

The human LKB gene (official HUGO symbol, STK11) encodes a serine/threonine protein kinase that is defective in patients with Peutz-Jeghers syndrome (PJS). PJS is an autosomal dominantly inherited syndrome characterized by hamartomatous polyposis of the gastrointestinal tract and mucocutaneous pigmentation. To date, 145 different germline LKB1 mutations have been reported. The majority of the mutations lead to a truncated protein product. One mutational hotspot has been observed. A 1-bp deletion and a 1-bp insertion at the mononucleotide repeat (C6 repeat, c.837-c.842) between the codons 279-281 have been found in six and seven unrelated PJS families, respectively. However, these mutations account only for approximately 7% of all mutations identified in the PJS families (13/193). A review of the literature provides a total of 40 different somatic LKB1 mutations in 41 sporadic tumors and seven cancer cell lines. Mutations occur particularly in lung and colorectal cancer. Most of the somatic LKB1 mutations result in truncation of the protein. A mutational hotspot seems to be a C6 repeat accounting for 12.5% of all somatic mutations (6/48). These results are concordant with the germline mutation spectrum. However, the proportion of the missense mutations seems to be higher among the somatic mutations (45%) than among the germline mutations (21%), and only seven of the mutations are exactly the same in both of the mutation types.     

Mutation screening in Rett syndrome patients

Rett syndrome (RTT) was first described in 1966. Its biological and genetic foundations were not clear until recently when Amir et al reported that mutations in the MECP2 gene were detected in around 50% of RTT patients. In this study, we have screened the MECP2 gene for mutations in our RTT material, including nine familial cases (19 Rett girls) and 59 sporadic cases. A total of 27 sporadic RTT patients were found to have mutations in the MECP2 gene, but no mutations were identified in our RTT families. In order to address the possibility of further X chromosomal or autosomal genetic factors in RTT, we evaluated six candidate genes for RTT selected on clinical, pathological, and genetic grounds: UBE1 (human ubiquitin activating enzyme E1, located in chromosome Xp11.23), UBE2I (ubiquitin conjugating enzyme E2I, homologous to yeast UBC9, chromosome 16p13.3), GdX (ubiquitin-like protein, chromosome Xq28), SOX3 (SRY related HMG box gene 3, chromosome Xq26-q27), GABRA3 (gamma-aminobutyric acid type A receptor alpha3 subunit, chromosome Xq28), and CDR2 (cerebellar degeneration related autoantigen 2, chromosome 16p12-p13.1). No mutations were detected in the coding regions of these six genes in 10 affected subjects and, therefore, alterations in the amino acid sequences of the encoded proteins can be excluded as having a causative role in RTT. Furthermore, gene expression of MECP2, GdX, GABRA3, and L1CAM (L1 cell adhesion molecule) was also investigated by in situ hybridisation. No gross differences were observed in neurones of several brain regions between normal controls and Rett patients.     

PLCE1基因突变与激素耐药性肾病综合征的关系

磷脂酶Cε1(phospholipase C epsilon-1，PLCE1) 基因定位于常染色体10q23.32-q24.1,其编码蛋白为磷脂酶Cε1(phospholipase C epsilon-1, PLCε1)。PLCε1蛋白是最新发现的一种磷脂酶C(phospholipase C,PLC)同工酶，在成熟的肾小球足细胞表达,参与肾小球毛细血管袢的形成和正常发育。近来发现PLCE1 基因突变可以引起常染色体隐性遗传性肾病综合征。PLCE1基因移码或无义突变可导致婴儿早发性肾病综合征，其病理特征为弥漫性肾小球硬化(diffuse mesangial sclerosis，DMS)；而错义突变可导致局灶性节段性肾小球硬化(focal segmental glomerulosclerosis，FSGS)。但其确切发病情况及机制目前尚不清楚，本文就PLCE1基因及其编码蛋白与激素耐药性肾病综合征之间的关系作一简要综述。     

Specific pattern of LKB1 and phospho-acetyl-CoA carboxylase protein immunostaining in human normal tissues and lung carcinomas

The LKB1 tumor suppressor gene codes for a serine/threonine protein kinase, and among its substrates is the adenosine monophosphate-dependent protein kinase, a sensor of intracellular energy levels. LKB1 is genetically inactivated in several types of tumors, especially lung adenocarcinomas. Here we used immunohistochemistry to evaluate the levels of LKB1 and the phosphorylated form of the acetyl-CoA carboxylase (ACC) protein in a variety of human adult normal tissues and in 159 lung carcinomas. The enzyme ACC becomes inactive upon phosphorylation by adenosine monophosphate-dependent protein kinase. Our analysis in normal tissues revealed strong LKB1 immunostaining in most epithelia, in the seminiferous tubules of the testis, in myocytes from skeletal muscle, and in glia cells. In contrast to the cytosolic location of LKB1 found in most tissues, glia cells carried mainly nuclear LKB1. Some epithelial cells showed apical accumulation of LKB1, supporting its role in cell polarity. Regarding phospho-ACC (p-ACC), strong immunostaining was observed in myocytes from the skeletal muscle and heart, and in Leydig cells of the testis. In lung tumors, LKB1 immunostaining was absent, moderate, and high in 20%, 61%, and 19% of the tumors, respectively, whereas p-ACC immunostaining was found to be absent/low, moderate, and high in 35%, 34%, and 31% of the tumors, respectively. High levels of LKB1 and p-ACC immunostaining predominated in lung adenocarcinomas compared with squamous cell carcinomas. Finally, high p-ACC was an independent marker for prediction of better survival in lung adenocarcinoma patients. Median overall survival was longer in patients with p-ACC-positive than those with p-ACC-negative tumors (96 versus 44 months, P = .04). In conclusion, our observations provide complete information about the pattern and levels of LKB1 and p-ACC immunostaining in normal tissues and in lung tumors, and highlight the special relevance of abnormalities of the LKB1 pathway in lung adenocarcinoma.     

Functional analysis of LKB1/STK11 mutants and two aberrant isoforms found in Peutz-Jeghers Syndrome patients

Peutz-Jeghers Syndrome (PJS) is thought to be caused by mutations occurring in the widely expressed serine/threonine protein kinase named LKB1/STK11. Recent work has led to the identification of four mutants (R304W, I177N, K175-D176del, L263fsX286) and two novel aberrant LKB1/STK11 cDNA isoforms (r291-464del, r485-1283del) in a group of PJS Italian patients. Three of the four mutations only change 1 or 2 amino acids in the LKB1/STK11 catalytic domain. Here we demonstrate that all six LKB1/STK11 variants analysed are completely inactive in vitro as they were unable to autophosphorylate at Thr336, the major LKB1/STK11 autophosphorylation site, and to phosphorylate the p53 tumour suppressor protein. We also show that 5 out of the 6 variants are entirely localised in the nucleus in contrast to the wild type LKB1/STK11, which is detected in both the nucleus and cytoplasm. Finally we demonstrate that all 6 LKB1/STK11 variants, in contrast to wild type LKB1/STK11, are unable to suppress the growth of melanoma G361 cells. Taken together, these results demonstrate that the LKB1 mutations investigated in this study lead to the loss of serine/threonine kinase activity and are therefore likely to be the primary cause of PJS development in the patients that they were isolated from.     

Noonan综合征患者PTPN11基因突变分析

目的 研究中国人Noonan综合征患者非受体型蛋白酪氨酸磷酸酯酶(protein-tyrosine phosphatase,nonreceptor-type 11,PTPN11)基因的突变.方法 收集遗传咨询门诊3例散发的Noonan综合征患者及其无症状父母,外周血提取基因组DNA,PCR产物直接测序法对患者PTPN11基因的全部15个编码区外显子及其邻接的内含子区域进行测序,检出突变后再对其父母的相应外显子区域进行测序,并通过限制性内切酶检测100名无亲缘关系的正常人相应碱基改变以排除多态性,利用网上ClustalW工具分析突变位点所在氨基酸在多个物种中的保守性.结果 在1例患者的第3外显子区域检出一杂合的c.181G＞A碱基取代,导致第61位的天冬氨酸改变为天冬酰胺(p.D61N),在其无症状父母和100名正常个体中无此突变;该位点在多个物种中高度保守.另外2例患者PTPN11基因的编码区未检到突变.结论 p.D61N突变在文献中已有报道,本例患者为新生突变.本研究进一步肯定了 p.D61N为Noonan综合征的致病突变,基因诊断的结果验证了该患者的临床诊断.另外两例Noonan综合征患者可能由其他基因的突变所致,反映了该病的遗传异质性.