100例视网膜色素变性患者中视紫红质基因突变的筛选与检测

目的 研究视紫红质（rhodopsin,RHO）基因在中国人视网膜色素变性（retinitis pigmentosa,RP）患者中的突变频率，特征及其在RP发病机理中的作用。方法 运用构象敏感凝胶电泳和DNA直接测序方法对100例香港地区中国RP中层得RHO基因全编码区进行突变的筛选与检测。结果 共发现种碱基变异，其中3种为沉默型突变，两种为错义突变，1种为缺失突变。P347L在1例55岁女性患者及其同样患RP的3名子女 中检出。327（1－bp del）首次在1例53岁的晚发型RP患者中发现。其26岁的女儿同样携带该突变，但目前除眼底色素上皮出现斑点外，还没有RP的任何症状。上述两种突变均未在对照组中发现。结论 100例RP患者中检出两例携带RHO基因突变，由此可预测香港地区约为2．0％（95％的可信区间为0．2％－7．0％）的RP是由RHO基因突变所致。P347L突变改变了RHO基因C末端一段高度保守的氨基酸序列，致使视紫红质蛋白在细胞P内的运输发生障碍。P327（1 bp del）使突变蛋白的羧基末端失去了原有的磷酸化位点及一段高度保守的功能区，其可能的致病机理有待在今后的研究中通过建立相应的转基因模型或细胞培养系统来阐明。     

常染色体显性遗传视网膜色素变性家系的基因筛查

目的：确定一个常染色体显性遗传视网膜色素变性(autosomal dominant retinitis pigmentosa,ADRP）家系的致病基因及其突变位点和类型。方法：应用聚合酶链反应－单链构象多态性结合DNA测序技术，对来自同一家系的4例RP患者及4名正常人外周血DNA进行分子遗传学分析，筛查3个候选基因共8个外显子。结果：来自同一家系的4例RP患者均发现有视紫红质基因（rhodopsin,RHO)第1外显子第52密码子存在TTC→TAC的点突变（Phe52Tyr），而4名正常人未发现这种突变。结论：在这个中国ADRP大家系中，发现RHO基因的致病突变，表明ADRP存在明显遗传异质性。     

视网膜色素变性隐性遗传致病基因PDE6B的突变分析

目的 了解常染色体隐性遗传视网膜色素变性(autosomal recessive retinitis pigmentosa，ARRP)致病基因磷酸二酯酶β亚单位(phosphodiesterase β subunit,PDE6B)基因在中国视网膜色素变性(retinitis pigmentosa，RP)患者中的突变谱及突变率。方法 应用聚合酶链反应—单链构象多态性，对收集的35个常染色体隐性RP家系38例患者和55例散发RP患者进行PDE6B基因的22个外显子和5’端非翻译区突变筛选；对有变异条带者进行DNA序列分析。结果 测得一个常染色体隐性家系患者PDE6B基因第11外显子5’端上游第19位碱基(第10内含子内)发生G→A转换。1例散发RP患者同时检测到第6外显子第2492位点碱基T颠换为C和第10外显子5’端上游(第9内含子内)第27—28碱基之间有两个碱基TG插入。另两例散发RP患者分别发现第4外显子5’端上游30—31碱基处两个碱基GT插入和第18外显子3’端下游第15个碱基发生G→C颠换。结论 发现1名中国人的散发RP患者携带RP致病基因PDE6B基因的一种复合杂合突变。中国人的PDE6B基因内含子有多种变异。     

显性遗传视网膜色素变性一家系的遗传分析

目的 对一个视网膜色素变性(retinitis pigmentosa,RP)家系进行基因诊断.方法 选取已知基因附近及覆盖X染色体的微卫星标记,对该家系进行了连锁分析.PCR扩增了包括ORF15在内的GTP酶调节因子基因(retinitis pigmentosa GTPase regulator,RPGR)所有外显子及外显子内含子交界区,对家系先证者进行了序列分析,找到突变之后,直接对家系成员及101个正常对照进行测序分析,以确定该突变是否和RP共分离.结果 连锁分析排除了已知的常染色体显性RP位点,对X染色体的连锁分析发现RP和胆GR所在位置的DXS993和DXS1068连锁,直接对RPGR测序发现缺失突变,g.ORF15+1166delA(c.2919delA).该缺失造成移码突变及提前终止.该突变为de novo,并和该家系所有患者共分离,而在家系正常个体及101个对照中不存在该突变.结论 RPGR新突变g.ORF15+1166delA引起X连锁视网膜色素变性.这一研究结果揭示RPGR突变的可以引起不同的临床表型.     

一个X-连锁视网膜色素变性中国家系的RPGR基因的新突变

目的 对中国人X-连锁视网膜色素变性一家系进行分子遗传学检测，报告RPGR基因突变。方法 首先对该家系X染色体进行致病基因的连锁分析，然后用单链构象多态性技术和直接DNA测序方法进行基因突变分析。结果 连锁分析在多态性微卫星遗传标记DXSS012和DXS8025产生正的Lod值分别为2．41（Zmax=2．40，θ=0）和1．26。进一步单倍型分析确定该家系致病基因位于Xp21．1，与RP3连锁。用RPGR基因突变分析，在外显子ORF15＋483－484发现GA缺失，引起阅读框架的改变，该基因缺失突变在家系中共分离。结论 报告了中国人X-连锁视网膜色素变性RPGR基因外显子ORF15＋483-484的GA缺失突变，丰富了中国人RPGR基闪突变谱，为今后研究X-连锁视网膜色素变性的基因奠定基础。     

视网膜色素变性的分子遗传学研究进展

视网膜色素变性（retinitis pigmentosa,RP)是眼科常见的遗传性致盲眼病之一。具有明显的遗传异质性，有不同的遗传方式与不同表型。病人常有夜盲和进行性视野缩小。随着分子遗传学的迅速发展，人们对于其分子病理有了一定的了解和认识，至少发现有24个疾病位点，其中已有12个致病基因被克隆。     

一个视网膜色素变性家系致病基因定位和CA4基因突变分析

目的通过对一个常染色体显性视网膜色素变性(autosomal dominant retinitis pigmentosa,adRP)家系致病基因的定位和基因突变分析,以确定该家系的致病基因及其突变形式。方法对15个已知的常染色体显性视网膜色素变性致病基因所在染色体位点进行连锁分析,以确定该家系与疾病连锁的染色体区域,对该区域附近候选基因进行直接序列分析。结果连锁分析提示在D17S701和D17S1604为正的连锁值(logofodds,LOD),分别为Zmax=2.107和Zmax=1.806。其余14个adRP染色体位点的微卫星标记两点LOD值均为负数。单倍型分析进一步将该家系致病基因定位于微卫星标记D17S916和D17S794之间的RP17位点,该位点adRP候选基因碳酸酐酶Ⅳ(carbonic anhydrase4,CA4)直接序列分析在其编码区未发现基因突变。结论将一个中国人常染色体显性视网膜色素变性家系的致病基因定位于RP17位点,但未发现该位点内的CA4基因突变,该家系是否存在CA4基因复杂突变或RP17位点是否存在新的视网膜色素变性致病基因有待于进一步研究。     

一例视网膜色素变性患者 C2ORF71基因的变异分析

目的:分析1例视网膜色素变性(retinitis pigmentosa, RP)患者的基因变异,明确其可能的遗传学病因。方法:应用全外显子测序技术对先证者进行致病基因筛查,结合临床表型确定可疑变异,应用Sanger测序法验证检出的变异,分析双亲携带变异位点的情况。采用多种软件对所检出的变异进行致病性分析。结果:全外显子...     

Rett综合征MECP2基因突变分析

目的 分析我国典型的Rett综合征患儿甲基化CpG结合蛋白－2基因（methyl-CpG-binding protein 2,MECP2）突变。方法 使用PCR扩增、单链构象多态性分析、PCR产物克隆和DNA测序的方法。检测分析了26例Rett综合征患儿、其父母和其中2例患儿的妹妹MECP2基因3个外显子的基因突变。结果 26例Rett综合征患儿中发现14例有9种类型MECP2基因的杂合性突变，突变均位于第3外显子。其中7例有3种错义突变：C473T（T158M)4例,C674G(P225R)1例，C916T（R306C）2例；4例有3种无义突变：C502T（R168X）2例，C763T（R255X）1例，C880T（R294X）1例；2种由于缺失导致的突变：1例为1152del 44bp和1例1158－1167／1171－1186del 26bp；1鲍由于碱基插入导致的移码突变：874insA。1158－1167／1171－1186del 26bp和874insA突变为首次报千，突变均为新生突变。此外，新发现了一种源于你亲的错义变异1141G（P381A）。结论 我国Rett综合征患儿存在MECP2基因突变，典型的Rett综合征MECP2基因突变率大于50％。     

常染色体隐性遗传视网膜色素变性的相关基因研究进展

视网膜色素变性（retinitis pigmentosa,RP)是一组进行性的可致盲的单基因遗传性视网膜疾病，以视网膜光感受器和色素上皮功能进行性受损为主要特征。常染色体隐性视网膜色素变性（autosoma recessive RP,adRP)属视网膜色素变性的一种类型，具有遗传异质性和临床异质性。目前巳克隆了15个致病基因，包括PDEA、PDEB、CNGA1、ABCA4、RLBP1、RPE65、TULP1和CRB1等。现简介绍下。     

RP1 in Chinese: Eight novel variants and evidence that truncation of the extreme C-terminal does not cause retinitis pigmentosa

Heterozygous truncating mutations in the RP1 gene cause approximately 7% of autosomal dominant retinitis pigmentosa (RP) cases. To examine the role of RP1 mutations in RP, we screened 101 unrelated Chinese RP patients (unselected for mode of inheritance) and 190 elderly normal control subjects for sequence changes in the coding exons for the 2156 amino acid RP1 protein. One patient had a mutation, thus RP1 mutations cause about 0.0% to 5.4% (95% confidence interval) of all RP among Chinese. The mutation was R677X, the most common found in Americans. Five other known sequence changes were found. In addition, nine novel sequence alterations were identified: 746G>A (R249H), 1437G>T (M479I), 2116G>C (G706R), 3024G>A (Q1008Q), 3188G>A (Q1063R), 5797C>T (R1933X), 6423A>G (I2141M), and the variants 6542C>T and 6676T>A, both in the 3' untranslated region. One control subject and three members of a non-RP family were heterozygous for R1933X, which is therefore likely to be a non-disease-causing variant. The most C-terminal truncation previously reported was due to Tyr1053 (1-bp del) and occurred in RP patients. Thus the presence of a normal level of at least part of RP1 between amino acids 1052 and 1933 appears necessary to prevent RP. Hum Mutat 17:436, 2001.     

Mutations in the RP1 gene causing autosomal dominant retinitis pigmentosa.

Retinitis pigmentosa is a genetically heterogeneous form of retinal degeneration that affects approximately 1 in 3500 people worldwide. Recently we identified the gene responsible for the RP1 form of autosomal dominant retinitis pigmentosa (adRP) at 8q11-12 and found two different nonsense mutations in three families previously mapped to 8q. The RP1 gene is an unusually large protein, 2156 amino acids in length, but is comprised of four exons only. To determine the frequency and range of mutations in RP1 we screened probands from 56 large adRP families for mutations in the entire gene. After preliminary results indicated that mutations seem to cluster in a 442 nucleotide segment of exon 4, an additional 194 probands with adRP and 409 probands with other degenerative retinal diseases were tested for mutations in this region alone. We identified eight different disease-causing mutations in 17 of the 250 adRP probands tested. All of these mutations are either nonsense or frameshift mutations and lead to a severely truncated protein. Two of the eight different mutations, Arg677X and a 5 bp deletion of nucleotides 2280-2284, were reported previously, while the remaining six mutations are novel. We also identified two rare missense changes in two other families, one new polymorphic amino acid substitution, one silent substitution and a rare variant in the 5'-untranslated region that is not associated with disease. Based on this study, mutations in RP1 appear to cause at least 7% (17/250) of adRP. The 5 bp deletion of nucleotides 2280-2284 and the Arg677X nonsense mutation account for 59% (10/17) of these mutations. Further studies will determine whether missense changes in the RP1 gene are associated with disease, whether mutations in other regions of RP1 can cause forms of retinal disease other than adRP and whether the background variation in either the mutated or wild-type RP1 allele plays a role in the disease phenotype.     

A nonsense mutation in a novel gene is associated with retinitis pigmentosa in a family linked to the RP1 locus.

Retinitis pigmentosa (RP) represents a group of inherited human retinal diseases which involve degeneration of photoreceptor cells resulting in visual loss and often leading to blindness. In order to identify candidate genes for the causes of these diseases, we have been studying a pool of photoreceptor-specific cDNAs isolated by subtractive hybridization of mRNAs from normal and photoreceptorless rd mouse retinas. One of these cDNAs was of interest because it mapped to proximal mouse chromosome 1 in a region homo-logous to human 8q11-q13, the locus of autosomal dominant RP1. Therefore, using the mouse cDNA as probe, we cloned the human cDNA (hG28) and its corresponding gene and mapped it near to D8S509, which lies in the RP1 locus. This gene consists of four exons with an open reading frame of 6468 nt encoding a protein of 2156 amino acids with a predicted mass of 240 kDa. Given its chromosomal localization, we screened this gene for mutations in a large family affected with autosomal dominant RP previously linked to the RP1 locus. We found an R677X mutation that co-segregated with disease in the family and is absent from unaffected members and 100 unrelated controls. This mutation is predicted to lead to rapid degradation of hG28 mRNA or to the synthesis of a truncated protein lacking approximately 70% of its original length. Our results suggest that R677X is responsible for disease in this family and that the gene corresponding to hG28 is the RP1 gene.     

Identification of novel RP2 mutations in a subset of X‐linked retinitis pigmentosa families and prediction of new domains

X‐linked Retinitis Pigmentosa (XLRP) shows a huge genetic heterogeneity with almost five distinct loci on the X chromosome. So far, only two XLRP genes have been identified, RPGR (or RP3) and RP2, being mutated in approximately 70% and 10% of the XLRP patients. Clinically there is no clearly significative difference between RP3 and RP2 phenotypes. In the attempt to assess the degree of involvement of the RP2 gene, we performed a complete mutation analysis in a cohort of patients and we identified five novel mutations in five different XLRP families. These mutations include three missense mutations, a splice site mutation, and a single base insertion, which, because of frameshift, anticipates a stop codon. Four mutations fall in RP2 exon 2 and one in exon 3. Evidence that such mutations are different from the 21 RP2 mutations described thus far suggests that a high mutation rate occurs at the RP2 locus, and that most mutations arise independently, without a founder effect. Our mutation analysis confirms the percentage of RP2 mutations detected so far in populations of different ethnic origin. In addition to novel mutations, we report here that a deeper sequence analysis of the RP2 product predicts, in addition to cofactor C homology domain, further putative functional domains, and that some novel mutations identify RP2 amino acid residues which are evolutionary conserved, hence possibly crucial to the RP2 function. Hum Mutat 18:109–119, 2001. © 2001 Wiley‐Liss, Inc.     

Genes and mutations causing retinitis pigmentosa

Retinitis pigmentosa (RP) is a heterogeneous set of inherited retinopathies with many disease‐causing genes, many known mutations, and highly varied clinical consequences. Progress in finding treatments is dependent on determining the genes and mutations causing these diseases, which includes both gene discovery and mutation screening in affected individuals and families. Despite the complexity, substantial progress has been made in finding RP genes and mutations. Depending on the type of RP, and the technology used, it is possible to detect mutations in 30–80% of cases. One of the most powerful approaches to genetic testing is high‐throughput ‘deep sequencing’, that is, next‐generation sequencing (NGS). NGS has identified several novel RP genes but a substantial fraction of previously unsolved cases have mutations in genes that are known causes of retinal disease but not necessarily RP. Apparent discrepancy between the molecular defect and clinical findings may warrant reevaluation of patients and families. In this review, we summarize the current approaches to gene discovery and mutation detection for RP, and indicate pitfalls and unsolved problems. Similar considerations apply to other forms of inherited retinal disease.     

Autosomal recessive retinitis pigmentosa and cone-rod dystrophy caused by splice site mutations in the Stargardt's disease gene ABCR

Ophthalmological and molecular genetic studies were performed in a consanguineous family with individuals showing either retinitis pigmentosa (RP) or cone-rod dystrophy (CRD). Assuming pseudodominant (recessive) inheritance of allelic defects, linkage analysis positioned the causal gene at 1p21-p13 (lod score 4.22), a genomic segment known to harbor the ABCR gene involved in Stargardt's disease (STGD) and age- related macular degeneration (AMD). We completed the exon-intron structure of the ABCR gene and detected a severe homozygous 5[prime] splice site mutation, IVS30+1G->T, in the four RP patients. The five CRD patients in this family are compound heterozygotes for the IVS30+1G- >T mutation and a 5[prime] splice site mutation in intron 40 (IVS40+5G- >A). Both splice site mutations were found heterozygously in two unrelated STGD patients, but not in 100 control individuals. In these patients the second mutation was either a missense mutation or unknown. Since thus far no STGD patients have been reported to carry two ABCR null alleles and taking into account that the RP phenotype is more severe than the STGD phenotype, we hypothesize that the intron 30 splice site mutation represents a true null allele. Since the intron 30 mutation is found heterozygously in the CRD patients, the IVS40+5G->A mutation probably renders the exon 40 5[prime] splice site partially functional. These results show that mutations in the ABCR gene not only result in STGD and AMD, but can also cause autosomal recessive RP and CRD. Since the heterozygote frequency for ABCR mutations is estimated at 0.02, mutations in ABCR might be an important cause of autosomal recessive and sporadic forms of RP and CRD.      

A novel mutation of RPGR gene in an X-linked Chinese family with retinitis pigmentosa

PurposeTo localize and identify the gene and mutations causing an X-linked Chinese family with retinitis pigmentosa.MethodsAn XLRP Chinese family was ascertained and patients underwent ophthalmological examinations. Blood samples were collected and genomic DNA was extracted. Linkage scan was performed on genomic DNA from affected and unaffected family members using microsatellite markers flanking 17 known autosomal dominant loci and markers covering the entire X chromosome. Mutation screening of RPGR gene was carried out by direct DNA sequence analysis.ResultsA genome wide scan yielded a lod score of 2.7 at θ = 0 with DXS1068 and 3.29 at θ = 0 with DXS993. This region harbors the RPGR gene. Direct DNA sequence analysis reveals one base pair deletion, gORF15 + 556delA, in all affected individuals. The deletion results in the frameshift change of RPGR gene and produces a truncated protein.ConclusionsWe identified a novel mutation, gORF15 + 556delA (p.Lys184fs), in a Han Chinese family with retinitis pigmentosa. This mutation expands the mutation spectrum of RPGR and helps to study molecular pathogenesis of RP further.     

Severe manifestations in carrier females in X linked retinitis pigmentosa.

Retinitis pigmentosa (RP) is a group of progressive hereditary disorders of the retina in which various modes of inheritance have been described. Here, we report on X linked RP in nine families with constant and severe expression in carrier females. In our series, however, the phenotype was milder and delayed in carrier females compared to hemizygous males. This form of X linked RP could be regarded therefore as partially dominant. The disease gene maps to chromosome Xp2.1 in the genetic interval encompassing the RP3 locus (Zmax=13.71 at the DXS1100 locus). Single strand conformation polymorphism and direct sequence analysis of the retinitis pigmentosa GTPase regulator (RPGR) gene, which accounts for RP3, failed to detect any mutation in our families. Future advances in the identification of X linked RP genes will hopefully help to elucidate the molecular basis of this X linked dominant RP.