Identification of pathogenic mutations in the human rapsyn gene

Rapsyn, a complex postsynaptic protein of the striated muscle, assembles acetylcholine receptors (AChR) at high density at the motor endplate (EP). Neuromuscular junctions of mice lacking rapsyn show no clusters of AChRs or other structural postsynaptic proteins such as β-dystroglycan and utrophin. Humans with mutations in the rapsyn gene (RAPSN) are affected with a postsynaptic form of congenital myasthenic syndrome (CMS) characterized by impairment of the morphologic development of the postsynaptic region. We have identified four patients from four different families with RAPSN mutations and CMS, confirmed in two cases by microelectrode and electron microscopy studies. The N88K mutation was present in all patients. One patient who was homozygous for N88K was only mildly affected, while the other three patients who were heterozygous for N88K and a second mutation (either L14P, 46insC, or Y269X) were severely affected. Mutations 46insC and Y269X predicts truncation of the protein. L14P predicts a conformational change at the N-terminus that may disrupt membrane association. N88K occurs within the putative leucine zipper motif potentially important for AChR clustering. These findings may explain the severe clinical involvement of compound heterozygous patients. Electronic Publication     

Overexpression of rapsyn inhibits agrin-induced acetylcholine receptor clustering in muscle cells

Rapsyn is a protein on the cytoplasmic face of the postsynaptic membrane of skeletal muscle that is essential for clustering acetylcholine receptors (AChR). Here we show that transfection of rapsyn cDNA can restore AChR clustering function to muscle cells cultured from rapsyn deficient (KORAP) mice. KORAP myotubes displayed no AChR aggregates before or after treatment with neural agrin. After transfection with rapsyn expression plasmid, some KORAP myotubes expressed rapsyn at physiological levels. These formed large AChR-rapsyn clusters in response to agrin, just like wild-type myotubes. KORAP myotubes that overexpressed rapsyn formed only scattered AChR-rapsyn microaggregates, irrespective of agrin treatment. KORAP cells were then transfected with mutant forms of rapsyn. A deletion mutant lacking residues 16–254 formed rapsyn microaggregates, but failed to aggregate AChRs. Substitution mutation to the C-terminal serine phosphorylation site of rapsyn (M43^D405,D406) did not impair the response to agrin, showing that differential phosphorylation of this site is unlikely to mediate agrin-induced clustering. The results indicate that rapsyn expression is essential for agrin-induced AChR clustering but that its overexpression inhibits this pathway. The approach of using rapsyn-deficient muscle cells opens the way for defining the role of rapsyn in agrin-induced AChR clustering.     

广东客家人 G6PD基因突变型研究

目的　研究广东客家人葡萄糖 - 6 -磷酸脱氢酶缺乏症 (glucose- 6 - phosphate dehydrogenase,G6 PD)遗传多样性。方法　应用突变特异性扩增系统法 ,聚合酶链反应 -单链构象多态性并结合 DNA测序技术 ,确定客家人 G6 PD基因突变型的类型及频率。结果　在客家人中发现 G6 PD c DNA1388(G→ A)、1376 (G→ T)、95 (A→ G)、392 (G→ T)、10 2 4 (C→ T)及 1311(C→ T)复合 11内含子 93位 (T→ C)的突变。结论　 G6 PD基因 c DNA1388(G→A)、1376 (G→T)、95 (A→ G)、392 (G→ T)、10 2 4 (C→ T)、1311(C→T)复合 11内含子 93位 (T→C)突变是共同存在于中国人群中的 G6 PD基因突变型。c DNA1388(G→A)、c DNA 1376 (G→ T)是客家人群中最常见的 G6 PD基因突变型。在广东客家人群中未发现新的 G6 PD基因突变型。     

海南汉族、黎族人葡萄糖-6-磷酸脱氢酶缺乏症的基因突变型分析及一种新的G6PD基因突变型的鉴定

目的 阐明海南汉族、黎族人群中葡萄糖－6－磷酸脱氢酶缺乏症的分子基础。方法 用聚合酶链反应、限制性内切酶消化筛查了1388G→A、1360C→T、1024C→T、517T→C、493A→G、487G→A、392G→T和95A→G突变。用单链构象多态性分析筛查其它突变;用核苷酸顺序分析鉴定具有SSCP异常区带样品的突变;。结果 在59例汉族G6PD缺乏症患者中,发现1388G→A14例（23．7％）、871G→A3例（5．1％）、835A→T1例（1．7％）517T→C1例（1．7％）、392G→T3例（5．1％）95A→G4例（6．8％）;在32例黎族G6PD缺乏症患者中,发现1388G→A6例（18．8％）、871G→A3例（9．4％）和95A→G2例（6．3％）;在1例汉族患者中发现了一种新的G6PD基因突变－835A→G突变,此突变导致第279位的苏氨酸被丙氨酸取代,将此突变型命名为G6PD－海口,其酶活性约是正常的10％,此835A→T突变的活性低,后者的酶活性约是正常的40％。分析人G6PD的三维结构模型表明,第279位苏氨酸残基的羟基是维持G6PD亚基相互作用的基团。结论 海南汉族、黎族人群中具有共同的常见G6PD基因突变型;与中国其它地区人群的G6PD基因突变谱比较,结果表明某些G6PD基因突变广泛分布于中国南方不同地区人群中;G6PD第279位苏氨酸残基的可能是维持G6PD亚基相互作用及酶活性的必需基团。     

A previously undescribed nonsense mutation of the HFE gene

A patient with clinically manifest hereditary hemochromatosis was found to be heterozygous for the c.845 A-->G (C282Y) mutation. As simple heterozygotes for this mutation do not develop the hemochromatosis phenotype, the coding region of the patient's HFE gene was sequenced and a previously undescribed nonsense mutation was identified at c.211 C-->T (R74X). The patient's brother who also had the hemochromatosis phenotype shared his HFE genotype. To determine how common such mutations might be, the coding and 5' region of the HFE genes of 11 subjects who had been found in a large population survey to be heterozygous for the C282Y mutation and had elevated ferritin levels were sequenced. No mutations were found. Sequencing of the HFE gene also revealed two polymorphisms that had not previously been noted, -467 C-->G and -970 T-->G. Neither of these mutations appear to cause an abnormality in iron metabolism.     

中国汉族人HIV-1协同受体CXCR4基因编码区新的突变位点研究

目的 对中国汉族人群HIV—1协同受体CXCR4编码区的基因多态性进行研究，为中国的获得性免疫缺陷综合征(AIDS)防治提供依据。方法 CXCR4(cDNA编号AFl47204)编码区用2对引物进行PCR扩增，然后分别测序，测序样本数为48例。用DNAstar分析测序结果，寻找SNP位点。结果 在编码区发现了7个SNP位点，其中3个同义突变(129位C→T、426位C→T，968C→T)，3个有义突变(38位C→T、90位A→T、712位A→C)，1个终止突变(106位C→T使谷氨酸密码子变成终止密码子)。其中38位C→T、90位A→T、712位A→C、106位C→T，基因突变频率为4．2％、4．2％、9、4％和3．1％。结论 在CXCR4编码区找到的7个SNP位点中，4个引起氨基酸改变，1个已有报道，对HIV—1感染和AIDS病程的影响值得研究。     

Identification of three genomic haplotypes 5' to the human CD1D gene and their distribution in four ethnic groups

CD1d presents lipid antigen to a conserved population of natural killer (NK) T cells, which participate in host immune defense, tumor cell rejection and suppression of autoimmunity. The levels of human CD1d expression vary significantly between individuals. To understand such variation, we sequenced the region up to 1.7 kb 5' upstream of the translation start site and partially through exon 2 in 44 white Americans. We also studied two tagged single nucleotide polymorphisms (SNP) in 112 white Americans, 60 African-Americans, 88 Europeans, and 84 Chinese people from the region. Six SNP present in the region (-836C-->T, -773C-->T, -764C-->G, -713A-->T, -365A-->G and +363A-->G) were found to be in a complete linkage disequilibrium and comprised three haplotypes. Haplotype 1 had -836C, -773C, -764C, -713A, -365A and +363A. Haplotype 2 had -836C, -773T, -764C, -713A, -365A and +363A. Haplotype 3 had -836T, -773C, -764G, -713T, -365G and +363G. -773C-->T and -764C-->G can serve as the tagged SNP to differentiate the three haplotypes. The frequency of haplotype 1 was significantly higher in African Americans than in the other three ethnic groups, whereas the frequency of haplotype 3 was significantly higher in the Chinese people than those in the other three groups. The finding of the three haplotypes provides a genetic marker for CD1d and facilitates the study of the functional role of the genetic variations in human CD1d expression and regulation.     

Multiexon deletions account for 15% of congenital myasthenic syndromes with RAPSN mutations after negative DNA sequencing

Congenital myasthenic syndromes (CMS) are a heterogeneous group of genetic disorders that give rise to a defect in neuromuscular transmission. We described here three patients with a characteristic phenotype of recessive CMS and presenting mutation in the gene encoding rapsyn (RAPSN). Familial analysis showed that one allelic mutation failed to be detected by direct sequencing. An allelic quantification on patient's DNA identified three novel multi-exon deletions of RAPSN. These three genomic rearrangements in RAPSN represent 15% of our CMS patients with RAPSN mutations and we emphasize that single-nucleotide polymorphism markers and a gene dosage method should be performed in addition to DNA direct sequencing analysis particularly when there is a genetic counselling issue.     

Genetic mutation profile of isovaleric acidemia patients in Taiwan

Isovaleric acidemia (IVA), a rare recessive autosomal disorder, is caused by isovaleryl-CoA dehydrogenase (IVD) deficiency. IVA may present with symptoms during the acute stage of severe metabolic acidosis, ketosis, vomiting, and altered mental status. With the help of newborn screening (NBS) by tandem mass spectrometry (MS/MS), IVA can now be diagnosed presymptomatically. According to statistic data, the incidence of IVA in Taiwan was about 1/365,000. In this study, six IVA patients from five families were investigated and followed-up clinically. As for the timing, two patients were found before MS technique introduced to Taiwan, the others were identified after MS/MS applied to NBS. The blood level of C5-carnitine in our patients was 7.43-18.96 microM (with upper limit in our laboratory <0.51 microM) and all of their urines contained raised amounts of 3-hydroxyisovaleric acid and isovalerylglycine. Molecular analysis of their IVD gene revealed six mutation profiles, among which the 149G-->A (Arg21His) and 1174 C-->T (Arg363Cys) mutations have been reported previously, while the other four mutations, 386A-->G (His100Arg), 347C-->T (Ser87Phe), 1007G-->A (Cys307Tyr) and 1199A-->G (Tyr371Cys), were first reported. Specially, we found 1199A-->G (Tyr371Cys) mutated was a common recurring missense mutation in our population (4 in 10 mutant alleles).     

Association of polymorphisms of ABCA1 and ROS1 with hypertension in Japanese individuals

Although various environmental factors, such as a high-salt diet, a smoking habit, excessive alcohol intake, and physical inactivity, influence the development of hypertension, genetic variation also contributes to an individual's susceptibility to this condition. The purpose of the present study was to identify gene polymorphisms that confer susceptibility or resistance to hypertension, and thereby contribute to the prediction of the genetic risk for this condition. The study population comprised 2752 unrelated Japanese individuals (1370 men, 1382 women), including 1276 subjects with hypertension (774 men, 502 women) and 1476 controls (596 men, 880 women). The genotypes for 50 polymorphisms of 35 candidate genes were determined by a method that combines polymerase chain reaction and sequence-specific oligonucleotide probes with suspension array technology. Evaluation of genotype distributions by the Chi-square test and subsequent multivariable logistic regression analysis with adjustment for age, sex, body mass index, smoking status, and the prevalence of diabetes mellitus and hypercholesterolemia revealed that the -14C-->T polymorphism of ABCA1, the C-->G (Ser2229Cys) polymorphism of ROS1, the C-->T (Asn591Asn) polymorphism of LDLR, the 13989A-->G (Ile118Val) polymorphism of CYP3A4, the C-->G and A-->C polymorphisms of ADIPOR1, and the -519A-->G polymorphism of MMP1 were significantly (P<0.05) associated with the prevalence of hypertension. Systolic and diastolic blood pressure differed significantly among genotypes for the -14C-->T polymorphism of ABCA1 and the C-->G (Ser2229Cys) polymorphism of ROS1, with the variant T and G alleles, respectively, being related to increased blood pressure. These results suggest that polymorphisms of ABCA1 and ROS1 are determinants of blood pressure and the development of hypertension in Japanese individuals. Determination of genotypes for ABCA1 and ROS1 may thus prove informative for the prediction of the genetic risk for hypertension.     

A second common variant in the methylenetetrahydrofolate reductase (MTHFR) gene and its relationship to MTHFR enzyme activity, homocysteine, and cardiovascular disease risk

Molecular defects in genes encoding enzymes involved in homocysteine metabolism may account for mild hyperhomocysteinemia, an independent and graded risk factor for cardiovascular disease (CVD). We examined the relationship of two polymorphisms in the methylenetetrahydrofolate reductase (MTHFR) gene, the 677C-->T and 1298A-->C variants, to MTHFR activity, homocysteine concentrations, and risk of CVD in a population of 190 vascular disease patients and 601 apparently healthy controls. The mean specific and residual MTHFR activities were significantly lower in 677CT and 677TT individuals (both P<0.001). The 1298A-->C mutation alone showed no effect on MTHFR activities. However, when the 677C-->T genotype was taken into account, the 1298A-->C mutation also caused a significant decrease in MTHFR activities, which was observed in both the homozygous 1298CC (P<0.001) and the heterozygous 1298AC states (P=0.005). Both the 677TT as the 677CT genotypes were associated with significantly higher fasting and postload homocysteine levels than 677CC (P<0.001 and P=0.003, respectively). The 1298A-->C mutation had no effect on fasting or postload homocysteine levels. Since homocysteine itself is considered to be positively associated with the risk of CVD, these findings indicate that the 1298A-->C mutation cannot be considered a major risk factor for CVD.     

Evidence for association between novel polymorphisms in the PRODH gene and schizophrenia in a Chinese population.

Haploinsufficiency for or mutation in at least one gene from the velocardiofacial syndrome (VCFS) region at chromosome 22q11 is implicated in psychosis. Linkage disequilibrium mapping of the region in patients identified a segment containing two genes, proline dehydrogenase (PRODH) and DGCR6, as candidates [Liu et al., 2002a] and by analysis of additional polymorphisms the PRODH gene was associated with schizophrenia in adult and early onset patients. In the present study we provide additional evidence in support of genetic association between PRODH and schizophrenia in a Chinese population. We analyzed the PRODH gene in a samples of schizophrenic patients and their families from Sichuan, SW China consisting of 528 family trios and sibling pairs. We genotyped six SNPs, PRODH*1195C-->T, PRODH*1482C-->T, PRODH*1483A-->G, PRODH*1766A-->G, PRODH*1852G-->A PRODH*1945T-->C, two of which (PRODH*1483A-->G and PRODH*1852G-->A) have not been previously reported. We found association with schizophrenia for two haplotypes consisting of PRODH*1945T-->C and PRODH*1852G-->A (Global P = 0.006), and PRODH*1852G-->A and PRODH*1766A-->G (Global P = 0.01) which include one of the newly identified markers. After six-fold Bonferroni correction for multiple testing the PRODH*1945T-C/PRODH*1852G-A haplotypes remained significant. This is a sub-haplotype of the PRODH haplotype previously associated with schizophrenia and it also maps to the 3' region of the gene, indicating that this is the region most likely to contain the underlying risk alleles. Overall this finding supports a role for the PRODH locus in schizophrenia.     

母系遗传耳聋大家系的线粒体基因组全序列分析

目的 在江苏淮阴一母系遗传非综合征型耳聋大家系中，寻找线粒体基因组上可能影响1555（A→G）突变表型的其他位点突变。方法 采用聚合酶链反应-限制性片段长度多态性分析（PCR-restriction fragment length polymorphism，PCR-RFLP）和测序技术。检测了核心分支家系中27名母系成员的线粒体DNA上1555位点和7445位点的碱基变化，进而对该家系2名母系成员的线粒体全基因组和其他25名母系成员线粒体12S rRNA基因MTRNR1和tRNA-Ser^（UCN）基因MTTS1进行了全长测序。结果 再次证明了1555（A→G）突变是该家系成员致聋的分子生物学基础之一；并发现该家系27名母系成员的线粒体基因组中除1555（A→G）突变外，还同时存在有955-960（insC）同质型突变，两突变共分离。另外，新发现一个线粒体DNA突变——7449（insG），但该突变仅在2名母系成员中存在。结论 推测955-960（insC）突变可能通过改变12S rRNA基因的高级结构，并与1555（A→G）突变协同作用，提高了突变携带者对氨基糖甙类药物的敏感性；同时该突变可能也会导致线粒体蛋白质的合成缺陷。从而提高1555（A→G）突变致聋的外显率。     

Wilson病ATP7B基因启动子区突变对基因表达的影响

目的 探讨Wilson病ATP7B基因启动子区突变与Wilson发病的关系。方法 在48例患者中发现2例存在-183（C→T）突变，对发现存在突变的样本的DNA片段进行分离，克隆入pGL2荧光素酶报告基因，转染细胞，测定荧光素酶的活性，以野生型的ATP7B基因启动子作为对照，分析ATP7B基因启动子点突变对转录活性的影响。结果 含正常与含突变ATP7B启动子区序列的pGL2载体的荧光素酶转录活性相比较差异无统计学意义（n=3，P〉0．05）。结论 启动子区-183（C→T）突变不影响基因转录活性。提示该突变的意义有待进一步的探讨。     

Spontaneous mutant frequency and mutation spectrum for gene A of phiX174 grown in E. coli

The use of transgenic targets for measuring mutant frequencies in mammalian tissue requires an estimate of the mutant frequency that results from recovery of the transgene in bacterial recovery systems. In this study, we have determined the spontaneous mutant frequency, estimated the mutation rate, and ascertained the mutation spectrum for gene A of phiX174 grown in E. coli strain CQ2 from 156 small independent cultures. The mutant frequency of 12 of the 156 cultures was 17 +/- 1.0 x 10(-6) and the estimated mutation rate per gene replication was 7.4 +/- 2.3 x 10(-6). The mutant frequency and spectrum from E. coli were not significantly different from that of solvent-treated embryonic mouse cells in culture, 19 +/- 0.5 x 10(-6) (Valentine CR et al. [2002]: Environ Mol Mutagen 39:55-68), indicating that those spontaneous mutants were primarily derived from E. coli. The E. coli spectrum was heavily weighted toward two major target sites (hot spots), 4225A-->G (56%) and 4218G-->A or C (20%). Four new target sites and one new mutational event were recovered by the gene A forward assay. A mutant spectrum from an expanded phage stock was also determined to assess the effects of propagating the virus. This mutant frequency was higher (6 x 10(-4)), contained more double mutants (15% compared to 0.6%), and had a significantly different spectrum from the spectrum for independent cultures (fewer A:T-->G:C and G:C-->C:G changes and more G:C-->A:T; P < 0.002). The E. coli mutation spectrum will be useful for determining the origin of gene A mutation in tissues of phiX174 transgenic mice.     

线粒体DNA变异与2型糖尿病易感性的关联研究

目的研究湖北地区2型糖尿病（type 2 diabetes mellitus，T2DM）中线粒体基因突变的发生率及其相关性。方法采用聚合酶链反应一限制性片段长度多态性及DNA测序技术，对184例2型糖尿病患者和210名糖耐量正常的健康对照进行检测，并用mfold和tRNAscan-SE软件对检出的突变位点进行二级结构分析。结果MIND1 3316（G→A）、MIND1 3394（T→C）、D环区16189（T→C）变异率分别为3．26％、2．72％、36．9％，并首次在T2DM中发现4例MTTE14693（A→G）突变（2．17％）；对照组检出3316（G→A）突变2例（0．99％）、16189（T→C）变异56例（26．6％），朱检出3394、14693的点突变；两组间3394（T→C）、14693（A→G）、16189（T→C）变异率差别均有统计学意义（P〈0．05）；且T2DM组中16189（T→C）变异阳性者的胰岛素抵抗指数（HOMA→IR）值较16189（T→C）变异阴性组升高，差异有统计学意义（P=0．028）：多元回归分析显示该变异为参与HOMA→IR的独立变量（R2=0．043，P=0．037）。RNA二级结构预测发现，3394（T→C）和14693（A→G）突变使其相应的二级结构发生变化。结论3394（T→C）、14693（A→G）突变与T2DM的易感性有一定关联，16189（T→C）变异与湖北地区汉族人T2DM胰岛素抵抗相关。     

Rapsyn对正常及实验性自身免疫性重症肌无力小鼠乙酰胆碱受体的作用

目的: 探讨突触后膜乙酰胆碱受体缔合蛋白(rapsyn)对正常小鼠及实验性自身免疫性重症肌无力(EAMG)小鼠肌肉组织内乙酰胆碱受体(AChR)的作用。方法: 将扩增的pcDNA-rapsyn质粒注入小鼠左后肢,右后肢相同部位注射等量生理盐水,2周后将实验小鼠随机分为E组和C组,E组经腹腔注射AchR单克隆抗体35 (mAb35)诱导EAMG动物模型,C组经腹腔注射相同剂量的生理盐水,模型诱导48 h后处死实验动物分离双侧后肢肌肉,注射pcDNA-rapsyn质粒的左后肢肌肉分别为LE组和LC组,注射生理盐水的右后肢肌肉分别为RE组和RC组。免疫荧光染色法观察突触后膜AChR与运动终板的结合情况,RT-PCR和Western blotting法检测AChRα mRNA和蛋白表达情况。结果: 结果表明,LC组与RC组相比AChRα蛋白表达量增多(P<0.05),LE组与RE组相比AChRα蛋白表达量增多(P<0.05); LC组与RC组相比AChRα mRNA表达变化无统计学意义(P>0.05),LE组与RE组相比AChRα mRNA表达有明显降低(P<0.01)。结论: 在肌肉组织内上调rapsyn蛋白的表达对正常及EAMG小鼠AChR受体发挥保护性作用。