Mutations within the rhodopsin gene in patients with autosomal dominant retinitis pigmentosa

BACKGROUND. Night blindness is an early symptom of retinitis pigmentosa. The rod photoreceptors are responsible for night vision and use rhodopsin as the photosensitive pigment. METHODS AND RESULTS. We found three mutations in the human rhodopsin gene; each occurred exclusively in the affected members of some families with autosomal dominant retinitis pigmentosa. Two mutations were C-to-T transitions involving separate nucleotides of codon 347; the third was a C-to-G transversion in codon 58. Each mutation corresponded to a change in one amino acid residue in the rhodopsin molecule. None of these mutations were found in 106 unrelated normal subjects who served as controls. When the incidence of these three mutations was added to that of a previously reported mutation involving codon 23, 27 of 150 unrelated patients with autosomal dominant retinitis pigmentosa (18 percent) were found to carry one of these four defects in the rhodopsin gene. All 27 patients had abnormal rod function on monitoring of their electroretinograms. It appears that patients with the mutation involving codon 23 probably descend from a single ancestor. CONCLUSIONS. In some patients with autosomal dominant retinitis pigmentosa, the disease is caused by one of a variety of mutations of the rhodopsin gene.     

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。     

A completed screen for mutations of the rhodopsin gene in a panel of patients with autosomal dominant retinitis pigmentosa.

Recently it has been demonstrated that some families with autosomal dominant retinitis pigmentosa (adRP) have mutations in the rhodopsin gene while others do not. Previously we have identified six such mutations in seven adRP families in this laboratory, one of which was previously described in US patients. We now present a completed screen of the rhodopsin gene in a panel of 39 adRP families, by a rapid screening technique which will be of use for routine diagnosis. Nine different mutations were ultimately found, in a total of twelve of the 39 families. These include the six previously identified mutations, in codons 68-71, 190, 211, 255, 296 and 347, two new ones in codons 53 and 106, and another mutation first identified in a single US patient, in codon 58. Thus approximately 30% of adRP families have 'Rhodopsin RP' while the remainder probably have a defect elsewhere in the genome. Of those families in which rhodopsin mutations have been found, four have been classified D type, three as sectorial RP and the remainder are of uncertain classification. All families excluded from chromosome 3q by linkage have been classified R type. These data suggest a correlation between clinical sub-classification and the underlying rhodopsin/non-rhodopsin heterogeneity.     

Missense mutation of rhodopsin gene codon 15 found in Japanese autosomal dominant retinitis pigmentosa

Summary Heterozygous missense mutation in codon 15 of the rhodopsin gene was detected in a patient with autosomal dominant retinitis pigmentosa (ADRP), where a transition of adenine to guanine at the second nucleotide in codon 15 (AATAGT), corresponding to a substitution of serine residue for asparagine residue (Asn-15-Ser) was detected. None of the remaining unrelated 42 ADRP, 24 autosomal recessive RP (ARRP) and 34 normal individuals had this alteration. Her funduscopic findings were sectorial in type similar to that of the patients with the same mutation found in an Australian pedigree (Sullivanet al., 1993). This study shows phenotypic similarities in patients with the same mutation of a different ancestry.     

视网膜色素变性患者中视网膜色素变性1基因点突变的研究

目的 研究中国视网膜色素变性（retinitis pigmentosa，RP)患者RP1基因的突变频率、特征及其在RP发病机理中所起的作用。方法 运用构象敏感凝胶电泳（conformation sensitive gel electrophoresis,CSGE)和DNA直接测序方法对101例香港地区RP患者的RP1基因全编码区进行突变的筛选与检测。结果 101例RP患者中检出1例患者携带常见的RP1致病突变－R677X，另外在3名正常个体及1例Stargardt患者中检出非致病的无义突变－R1933X。RP1基因在所有RP患者中的突变检出率为1／101。突变最终导致RP1蛋白严重截短。此外，在本研究人群中还发现10个错义突变，除M479I的病理意义未确定之外，其余均系RP1基因的多态现象。结论 R1933X无致病意义，提示羧基端224个氨基酸的区域可能为RP1蛋白非功能区，结合最近发现的RP1羧基端的移码突变－Y1053（1bp del)的病理意义，推测RP1蛋白中相应片段（密码子1052－1933）的缺失会导致RP的发生。为证实这种推测，大范围的RP1基因分型工作是有必要的，并且可同时发现更多的RP致病突变以及不同于其他种族人群的RP1基因多态变化。     

Molecular analysis of the ABCA4 gene in Turkish patients with Stargardt disease and retinitis pigmentosa

The clinical importance of sequence variations in the ABCA4 gene has been extensively discussed during the last decade. Mutations in the ABCA4 gene are involved in several forms of inherited retinal degenerations. We screened all 50 exons of the ABCA4 gene in a cohort of 5 Stargardt Disease (STGD) and 35 autosomal recessive retinitis pigmentosa (arRP) patients of Turkish descent to assess the nature of ABCA4 mutant alleles in this population. Our results revealed the presence of three novel mutations: c.160T>G (p.C54G), c.2486C>T (p.T829M), and c.973-6C>A; two mutations previously reported, c.634C>T (p.R212C) and c.4253+4C>T, and several polymorphic changes in the ABCA4 gene among Turkish patients affected with Stargardt and arRP. To our knowledge this report represents the first published study of ABCA4 mutations in the Turkish population resulting in STGD.     

一个视网膜色素变性家系的视紫红质基因突变分析

目的　确定常染色体显性遗传视网膜色素变性家系的致病基因及其突变位点,并研究其临床表型。方法　对一个常染色体显性遗传视网膜色素变性(autosomal dominat retinitis pigmentosa,ADRP)家系成员进行了视力、视野及眼底镜检查,并对该家系中先证者进行了视网膜电流图分析。应用聚合酶链反应和直接测序技术,对该家系的所有现存人员的视紫红质基因的外显子进行测序分析。结果　该家系的2 5名成员中12例患者有视紫红质基因(rhodopsin,RH O)的5 12 C>T(P171L)突变,均呈杂合子,该错义突变使密码子171由CCA变成CTA。而未受累者的视紫红质基因表现为野生型。该家系患者的临床表现为5～6岁时出现夜盲,在2 0～30岁逐渐出现视力和视野损害,并先后在4 0～5 0岁前后失明,其中2例患者并发青光眼,先证者的闪烁视网膜电图呈熄灭型。结论　视紫红质基因RH O的一种已知突变5 12 C>T(P171L)是该家系的病因。与国外相同的基因突变类型相比较,该家系发病早、病情进展快、视功能损害较重。     

Pharmacological manipulation of gain-of-function and dominant-negative mechanisms in rhodopsin retinitis pigmentosa

Mutations in the dim light photoreceptor protein rod opsin cause autosomal dominant retinitis pigmentosa. The majority of these mutations (class II) lead to protein misfolding. For example, the common class II rod opsin mutation P23H misfolds and is retained in the ER, prior to retrotranslocation and degradation by the proteasome. If degradation fails then the protein can aggregate to form intracellular inclusions. Furthermore, mutant opsin exerts a dominant negative effect on the wild-type (WT) protein. Here we show that the toxic gain of function and dominant negative properties of misfolded rod opsin in cells can be alleviated by drug treatments targeted against a range of cellular pathways. P23H rod opsin aggregation, inclusion formation with associated caspase activation and cell death were reduced by kosmotropes, molecular chaperone inducers and mToR inhibition. But these treatments did not enhance mutant opsin folding or reduce the dominant negative effect of P23H rod opsin. In contrast, retinoids acted as pharmacological chaperones to enhance P23H folding and reduce the dominant negative effect on WT rod opsin processing, as well as reducing toxic gains of function. Therefore, the suppression of the dominant negative effects of protein misfolding required enhanced folding of the mutant protein, whereas suppression of toxic gain of function effects did not require improved folding per se. These studies suggest that some forms of rhodopsin RP may be treated by targeting protein folding and reducing protein aggregation.     

Point mutations of rhodopsin gene found in Japanese families with autosomal dominant retinitis pigmentosa (ADRP)

Summary The mutations of codon 17, 23, 58, and 347 of rhodopsin gene were investigated in 24 unrelated Japanese families including 33 patients with autosomal dominant retinitis pigmentosa (ADRP). A patient with codon 17 mutation (Thr-17-Met, ACGATG) and a family including 4 patients with codon 347 mutation (Pro-347-Leu, CCGCTG) were detected among them. Their clinical findings were extremely different between the two mutations. The former showed type 2 and the latter showed type 1 ADRP. No mutation of codon 23 and 58 was detected in any families so far analyzed in the present study. Clinical findings associated with the mutation in codon 17 and 347 of the rhodopsin gene show an existence of allelic heterogeneity.     

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.