X-连锁和双基因型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、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。X－连锁RP和双基因型RP是视网膜色素变性的不同类型，在遗传和临床上各具特点。目前，X－连锁RP已定位6个致病基因，并克隆了2个基因（RP2和RP3）；双基因型RP是由2种不同基因（peripherin/RDS和ROM1基因）的杂合子突变导致的。     

常染色体显性遗传视网膜色素变性患者视紫红质基因和视网膜变性慢基因突变检测分析

视网膜色素变性(RP)是一组常见的视网膜感光细胞和色素上皮细胞变性导致夜盲和进行性视野缺损的遗传性眼底病,其发病机制尚未完全明确.RP具有高度的遗传异质性,其遗传方式非常复杂,分为常染色体显性遗传(ADRP)、常染色体隐性遗传(ARRP)、X-连锁遗传(XLRP)和双基因型遗传(Digenic RP),最近报道还有线粒体遗传方式(mitochondrial RP)[1].视紫红质基因(RHO)是最早被识别的RP基因,在ADRP中发病率占30%～40%[2],而盘膜周边蛋白/视网膜变性慢基因(peripherin/RDS)在ADRP中占5%[3].我们对13个ADRP家系进行了RHO和视网膜变性慢基因(RDS)检测分析,观察其突变特征,现将其结果报道如下.     

视网膜色素变性与基因突变

视网膜色素变性 (RP)是常见的致盲性遗传疾病 ,目前已发现有数十个基因的 15 0多个突变位点与其有关。与常染色体显性遗传、常染色体隐性遗传和性连锁遗传相对应的最常见的突变基因分别是视红紫质基因、杆体环鸟苷酸磷酸二脂酶基因和三磷酸鸟苷酸酶调节因子基因 ,其他的突变基因还有盘膜边缘蛋白基因 (常染色体显性遗传 )、杆体环鸟苷酸离子通道基因、RPE6 5基因、视黄醛结合蛋白基因和酪氨酸激酶受体基因 (常染色体隐性遗传 ) ,RP2基因(性连锁遗传 ) ,线粒体DNA细胞色素b基因等 ,每个突变基因对应于人群中不同的RP患者。基因治疗将成为治疗RP的根本方法 ,而对RP突变基因的定位、基因的生物学功能、突变所造成的分子病理机制的深入认识 ,是进行基因治疗的关键。     

视网膜色素变性分子遗传学研究现状

视网膜色素变性是由于视网膜感光细胞和色素上皮细胞变性导致夜盲和进行性视野缺损的最常见的遗传性眼底病 ,具有大的临床和遗传异质性。其遗传方式可为常染色体显性、常染色体隐性、X染色体连锁遗传和散发型。目前已发现RP相关基因 1 4种 ,其中常染色体显性遗传 4种 ,常染色体隐性遗传 8种 (包括视紫质 ) ,X染色体连锁遗传 2种。本文着重阐述了已知RP相关基因的研究现状。     

第六届视网膜色素变性国际会议综述

第六届视网膜色素变性国际会议于1990年7月19～22日在爱尔兰都柏林大学召开。这次盛会充分反映了近2年来世界各国对视网膜色素变性(RP)及其它变性视网膜疾病的基础和临床研究的动态和最新进展。内容包括各遗传型RP的基因定位、RP患者视紫红质基因点突变的研究、性连锁遗传型RP和无脉络膜病的基因克隆;RP动物模型发病机理的生化研究及分子遗传学研究;RP的基因治疗与细胞移植的实验研究;Refsum综合征患者的生化缺陷和临床治疗;以及RP的其它临床问题等。本文对这些内容进行了简要综述。     

视网膜色素变性的相关基因研究进展

视网膜色素变性(RP)是由于视网膜感光细胞和色素上皮细胞变性导致夜盲和进行性视野缺损的一种常见的、遗传性、致盲性眼底病,具有较大的临床和遗传异质性。迄今通过连锁分析和侯选基因筛查,已有14个常染色体显性遗传ADRP;20个常染色体隐性遗传ARRP和5个X-染色体连锁遗传型XLRP位点被定位,其中32个基因已被克隆,每种遗传方式都有多个基因被克隆。对于这些致病基因的结构、突变及其功能目前已经有了新的研究进展。     

汉族常染色体显性视网膜色素变性一家系的连锁分析及突变筛查

背景 原发性视网膜色素变性(RP)有明显的遗传异质性和表型异质性,目前已确定的致病基因较多,确定患病家系的致病基因是进行基因治疗的基础. 目的 对患常染色体显性遗传性RP(ADRP)的一个汉族家系进行致病基因的定位和基因突变分析.方法 此家系的5代21名成员纳入研究,包括12例ADRP患者和9名表型正常者.12例患者进一步接受中心视野、间接检眼镜、眼电图(EOG)、视网膜电图(ERG)检查.对22个已知的ADRP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,随后对该区域附近的候选基因视紫红质(RHO)进行直接测序评估其突变情况. 结果 间接检眼镜检查该家系先证者眼底表现符合原发性RP表现,EOG和ERG表现为波形记录不到,视野呈向心性缩小.两点连锁分析结果显示,该家系致病基因位点与遗传标记D3S1292连锁,在θ=0.0时得到最大优势对数(LOD)值为3.6671.候选的RHO基因直接测序结果发现,该家系所有患者第53位密码子的第2个核苷酸均出现了C→G的突变,致其氨基酸由脯氨酸变为精氨酸(Pro53Arg),而该家系正常成员中未发现此突变. 结论 RHO基因的错义突变Pro53Arg与RP疾病出现共分离现象,可确定为该ADRP家系的致病基因.     

中国人一个显性视网膜色素变性家系8号染色体连锁分析

目的用连锁分析法对中国人一个显性视网膜色素变性家系8号染色体进行分析，确定致病基因。方法随机选取8号染色体RP1基因上下约10厘摩(cm)范围内的10对微卫星标记(marker)，确立单倍体型，用两点法计算最大优势对数(LOD SCORE)值。结果所选微卫星标记与该家系表型间最大LOD值小于1。结论RP1基因可能为该家系的非致病性基因，用连锁分析法进行致病基因排除对最终确立致病基因所在染色体的范围具有重要的价值。     

原发性视网膜色素变性家系的RDS基因Pro216Leu突变及其表型研究

目的　研究原发性视网膜色素变性 (retinitispigmentosa ,RP)家系中缓慢型视网膜变性(retinaldegenerationslow ,RDS)患者的RDS基因突变与临床表型的关联 ,以探讨RP的发病机制。方法对来自同一家系的 2例RP患者及 2例正常人外周血DNA进行分子遗传学分析 ,采用聚合酶链反应(polymerasechainreaction ,PCR)及限制性片段长度多态性 (restrictionfragmentlengthpolymorphism ,RFLP)技术 ,筛查RDS基因突变 ,对有突变的RDS基因片段进行克隆测序及分析 ,同时进行家系分析及眼部临床检查。结果　来自同一家系的 2例RP患者均查出有RDS基因 2 16密码突变 ,而 2例正常人未查出上述突变。经测序证实RDS基因 2 16密码子的第 2个核苷酸出现了C→T的突变 (Pro2 16Leu)。RDS基因Pro2 16Leu突变的眼部临床表型为视力损害严重的弥漫型RP ,伴有黄斑部病变。结论　中国人RP患者存在RDS基因Pro2 16Leu突变 ;其眼部表型为弥漫型RP伴有黄斑部病变。     

视网膜色素变性1基因在常染色体显性遗传视网膜色素变性家系中的突变分析

目的:研究常染色体显性遗传视网膜色素变性(autosomal dominant retinitis pigmentosa,ADRP)家系中视网膜色素变性1(retinitis pigmentosa-1,RP1)基因的突变特征及其在RP发病机制中的作用。方法:运用聚合酶链反应和直接测序方法,对6个ADRP家系的47例成员和50例对照者进行了RP1基因全编码区和邻近剪切位点的内含子区域序列突变的筛选与检测。运用单因素分析、多因素Logistic回归分析研究RP1基因点突变在RP发病中的作用。结果:ADRP家系成员和对照组RP1基因第4外显子上检测出2个变异位点。在1691和1725密码子存在杂合的两种类型的密码子(S1691P,Ser-Pro,TCT→CCT;Q1725Q,Gln-Gln,CAA→CAG)。ADRP家系成员中Ser-1691-Pro及Gln-1725-Gln位点突变率显著高于正常对照组(χ2=11.202,P<0.05)。结论:RP1基因Ser-1691-Pro及Gln-1725-Gln位点多态性可增高RP的危险性,具有潜在的致病性,考虑为ADRP家系的易感基因。     

Carrier detection in X-linked retinitis pigmentosa

X-linked retinitis pigmentosa (XLRP) is manifested in affected males in their first decade and results in blindness by the third or fourth decade. Carrier detection is difficult since most carrier females show no or only equivocal signs well into or beyond their reproductive years. The genes, or the mutations causing RP have not been identified but at least two have been localised to the short arm of the X chromosome provisionally named RP2 and RP3. Identifying inheritance of one or other of these genes must be done by linkage in families using close, informative DNA markers. Here we report the localisation of a highly informative polymerase chain reaction (PCR) detectable microsatellite marker DXS538 using a previously studied family with X-linked RP3 in which recombination had occurred in the region of importance. The DXS538 dinucleotide repeat locus was previously localised to Xp21.1-p11.21 to study RP3 in one XLRP family. Using published RFLP data we narrowed the localisation of DXS538 to the region Xp21.1 - p11.23. Thus DXS538 is now a convenient diagnostic tool, aiding carrier detection of XLRP in females, as shown in the family presented here.     

Update on the molecular genetics of retinitis pigmentosa

Retinitis pigmentosa (RP) is a heterogeneous group of retinal dystrophies characterized by photoreceptor cell degeneration. RP causes night blindness, a gradual loss of peripheral visual fields, and eventual loss of central vision. Advances in molecular genetics have provided new insights into the genes responsible and the pathogenic mechanisms of RP. The genetics of RP is complex, and the disease can be inherited in autosomal dominant, recessive, X-linked, or digenic modes. Twenty-six causative genes have been identified or cloned for RP, and an additional fourteen genes have been mapped, but not yet identified. Eight autosomal dominant forms are due to mutations in RHO on chromosome 3q21-24, RDS on 6p21.1-cen, RP1 on 8p11-21, RGR on 10q23, ROM1 on 11q13, NRL on 14q11.1-11.2, CRX on 19q13.3, and PRKCG on 19q13.4. Autosomal recessive genes include RPE65 on chromosome 1p31, ABCA4 on 1p21-13, CRB1 on 1q31-32.1, USH2A on 1q41, MERTK on 2q14.1, SAG on 2q37.1, RHO on 3q21-24, PDE6B on 4p16.3, CNGA1 on 4p14-q13, PDE6A on 5q31.2-34, TULP1 on 6p21.3, RGR on 10q, NR2E3 on 15q23, and RLBP1 on 15q26. For X-linked RP, two genes, RP2 and RP3 (RPGR), have been cloned. Moreover, heterozygous mutations in ROM1 on 11q13, in combination with heterozygous mutations in RDS on 6p21.1-cen, cause digenic RP (the two-locus mechanism). These exciting molecular discoveries have defined the genetic pathways underlying the pathogenesis of retinitis pigmentosa, and have raised the hope of genetic testing for RP and the development of new avenues for therapy.     

Wilson's disease: presymptomatic patients and Kayser-Fleischer rings

Purpose: To describe new disease-causing RP2 and RPGR-ORF15 mutations and their corresponding clinical phenotypes in Swedish families with X-linked retinitis pigmentosa (XLRP) and to establish genotype-phenotype correlations by studying the clinical spectrum of disease in families with a known molecular defect. Methods: Seventeen unrelated families with RP and an apparent X-linked pattern of disease inheritance were identified from the Swedish RP registry and screened for mutations in the RP2 and RPGR (for the RP3 disease) genes. These families had been previously screened for the RPGR exons 1–19, and disease-causing mutations were identified in four of them. In the remaining 13 families, we sequenced the RP2 gene and the newly discovered RPGR-ORF exon. Detailed clinical evaluations were then obtained from individuals in the three families with identified mutations. Results: Mutations in RP2 and RPGRORF15 were identified in three of the 13 families. Clinical evaluations of affected males and carrier females demonstrated varying degrees of retinal dysfunction and visual handicap, with early onset and severe disease in the families with mutations in the ORF15 exon of the RPGR gene. Conclusions: A total of seven mutations in the RP2 and RPGR genes have been discovered so far in Swedish XLRP families. All affected individuals express a severe form of retinal degeneration with visual handicap early in life, although the degree of retinal dysfunction varies both in hemizygous male patients and in heterozygous carrier females. Retinal disease phenotypes in patients with mutations in the RPGR-ORF15 were more severe than in patients with mutations in RP2 or other regions of the RPGR .     

Prevalence of disease-causing mutations in families with autosomal dominant retinitis pigmentosa: a screen of known genes in 200 families

PURPOSE: To survey families with clinical evidence of autosomal dominant retinitis pigmentosa (adRP) for mutations in genes known to cause adRP. METHODS: Two hundred adRP families, drawn from a cohort of more than 400 potential families, were selected by analysis of pedigrees. Minimum criteria for inclusion in the adRP cohort included either evidence of at least three generations of affected individuals or two generations with evidence of male-to-male transmission. Probands from each family were screened for mutations in 13 genes known to cause adRP: CA4, CRX, FSCN2, IMPDH1, NRL, PRPF3 (RP18), PRPF8 (RP13), PRPF31 (RP11), RDS, RHO, ROM1, RP1, and RP9. Families without mutations in autosomal genes and in which an X-linked mode of inheritance could not be excluded were tested for mutations in ORF 15 of X-linked RPGR. Potentially pathogenic variants were evaluated based on a variety of genetic and computational criteria, to confirm or exclude pathogenicity. RESULTS: A total of 82 distinct, rare (nonpolymorphic) variants were detected among the genes tested. Of these, 57 are clearly pathogenic based on multiple criteria, 10 are probably pathogenic, and 15 are probably benign. In the cohort of 200 families, 94 (47%) have one of the clearly pathogenic variants and 10 (5%) have one of the probably pathogenic variants. One family (0.5%) has digenic RDS-ROM1 mutations. Two families (1%) have a pathogenic RPGR mutation, indicating that families with apparent autosomal transmission of RP may actually have X-linked genetic disease. Thus, 107 families (53.5%) have mutations in known genes, leaving 93 whose underlying cause is still unknown. CONCLUSIONS: Together, the known adRP genes account for retinal disease in approximately half of the families in this survey, mostly Americans of European origin. Among the adRP genes, IMPDH1, PRPF8, PRPF31, RDS, RHO, and RP1 each accounts for more than 2% of the total; CRX, PRPF3, and RPGR each accounts for roughly 1%. Disease-causing mutations were not found in CA4, FSCN2, NRL, or RP9. Because some mutations are frequent and some regions are more likely to harbor mutations than others, more than two thirds of the detected mutations can be found by screening less than 10% of the total gene sequences. Among the remaining families, mutations may lie in regions of known genes that were not tested, mutations may not be detectable by PCR-based sequencing, or other loci may be involved.     

Studies on retinitis pigmentosa in man. I. Taurine and blood platelets.

Platelets from patients with various genetically determined forms of photoreceptor dystrophy and with the clinical manifestations of retinitis pigmentosa (RP) have been studied. Variations in protein content have been observed, with less than normal in multiplex RP (probably autosomal recessive inheritance) and more in platelets from patients with autosomal dominant RP. This may reflect variation in platelet size or in surface adsorption of plasma proteins. Several patients presented with thrombocytopenia, the mean platelet count for X-linked hemizygote patients, as a group, being significantly lower than normal. Accumulation of 3H-taurine has been studied in platelets incubated in Ca2+-free Krebs bicarbonate medium containing 1.0 microM or 60.0 microM taurine, and in autologous plasma. Although, in general, platelets from patients with RP showed normal taurine uptake, the capacity of the higher affinity carrier was increased in patients with X-linked hemizygote and multiplex disease. In contrast, plasma from patients with X-linked hemizygote RP reduced the platelet tissue to medium ratio, established for 3H-taurine uptake, by 20%. More studies are needed to ascertain whether this represents a reduced taurine uptake or is caused by an increased concentration of taurine in the plasma.     

Current mutation discovery approaches in Retinitis Pigmentosa

With a worldwide prevalence of about 1 in 3500–5000 individuals, Retinitis Pigmentosa (RP) is the most common form of hereditary retinal degeneration. It is an extremely heterogeneous group of genetically determined retinal diseases leading to progressive loss of vision due to impairment of rod and cone photoreceptors. RP can be inherited as an autosomal-recessive, autosomal-dominant, or X-linked trait. Non-Mendelian inheritance patterns such as digenic, maternal (mitochondrial) or compound heterozygosity have also been reported. To date, more than 65 genes have been implicated in syndromic and non-syndromic forms of RP, which account for only about 60% of all RP cases. Due to this high heterogeneity and diversity of inheritance patterns, the molecular diagnosis of syndromic and non-syndromic RP is very challenging, and the heritability of 40% of total RP cases worldwide remains unknown. However new sequencing methodologies, boosted by the human genome project, have contributed to exponential plummeting in sequencing costs, thereby making it feasible to include molecular testing for RP patients in routine clinical practice within the coming years. Here, we summarize the most widely used state-of-the-art technologies currently applied for the molecular diagnosis of RP, and address their strengths and weaknesses for the molecular diagnosis of such a complex genetic disease.     

Mutational screening of the RP2 and RPGR genes in Spanish families with X-linked retinitis pigmentosa

PURPOSE: The X-linked form of retinitis pigmentosa (XLRP) is the most severe type because of its early onset and rapid progression. Five XLRP loci have been mapped, although only two genes, RPGR (for RP3) and RP2, have been cloned. In this study, 30 unrelated XLRP Spanish families were screened to determine the molecular cause of the disease. METHODS: Haplotype analysis was performed, to determine whether the disease is linked to the RP3 or RP2 region. In those families in which the disease cosegregates with either locus, mutational screening was performed. The RP2 gene, the first 15 exons of RPGR at the cDNA level, and the open reading frame (ORF) 14 and 15 exons were screened at the genomic DNA level. RESULTS: Haplotype analysis ruled out the implication in the disease of RP2 in six families and of RPGR in four families. Among the 30 unrelated XLRP families, there 4 mutations were identified in RP2 (13%), 3 of which are novel, and 16 mutations in RPGR (53.3%), 7 of which are novel. CONCLUSIONS: In this cohort of XLRP families, as has happened in previous studies, RP3 also seems to be the most prevalent form of XLRP, and, based on the results, the authors propose a four-step protocol for molecular diagnosis of XLRP families.     

Refractive errors of retinitis pigmentosa patients.

A retinitis pigmentosa (RP) population (268 eyes) had predominantly myopic refractive errors. Whereas 12% of a normal population have myopic refractions, myopia was found in 75% of 268 eyes of RP patients and in 95% of 41 eyes of X-linked RP patients. The spherical errors describe a single-peaked, skewed distribution, with a mean of -1.86 dioptres that is significantly (P less than 0.001) more myopic, by -2.93 D, than that of a normal population. The X-linked genetic group has a spherical mean of -5.51 D that is significantly (P less than 0.01) more myopic than the non-X-linked RP population. This X-linked spherical error distribution may be composed of two separate subdistributions. Astigmatic refractive errors greater than 0.5 D are found in 47% of this RP population, considerably in excess of the 19% of a normal population with such astigmatic errors.     

X-linked retinitis pigmentosa: mutation spectrum of the RPGR and RP2 genes and correlation with visual function

PURPOSE: To assess the frequency of RPGR and RP2 mutations in a set of 85 patients with X-linked retinitis pigmentosa (XLRP) and to compare the visual function of patients with mutations in RPGR versus RP2. METHODS: Eighty-five unrelated patients with XLRP were ascertained, mainly from North America. The single-strand conformation polymorphism (SSCP) and a direct sequencing technique were used to screen their DNA for mutations in the coding region and splice sites of RPGR and RP2. The Snellen visual acuities, visual field areas, and 0.5-Hz and 30-Hz electroretinograms (ERGs) were measured in male patients. The visual function parameters were compared using multiple regression analysis. RESULTS: A wide spectrum of mutations was found in both genes, including missense, nonsense, splice-site, and frameshift mutations. Twenty putative pathogenic mutations in RPGR, 15 of which were novel, were found in 22 patients (26%), whereas 6 mutations in RP2, 4 of which were novel, were found in 6 patients (7%). A high fraction of the mutations in both genes affected amino acid residues within or adjacent to presumed functional domains. Comparison of visual function between comparably aged patients with mutations in RPGR versus RP2 showed that, on average, patients with RPGR mutations have lower ERG amplitudes and smaller visual field areas. CONCLUSIONS: Mutations in RPGR and RP2 genes together account for approximately 33% of cases of XLRP in North America. Patients with RPGR mutations have less overall retinal function on average than those with RP2 mutations, on the basis of measurements of visual field areas and full-field ERG amplitudes.