Pro-347-Arg mutation of the rhodopsin gene in autosomal dominant retinitis pigmentosa.

It has been shown recently that autosomal dominant retinitis pigmentosa may be caused by point mutations of the rhodopsin gene in a portion of families. In this communication, a large six-generation family with autosomal dominant RP is described. Molecular analysis by PCR amplification followed by restriction digestion or heteroduplex analysis suggested a point mutation in codon 347, in which two different mutations (Pro-347-Ser and Pro-347-Leu) have already been reported. Direct sequencing of the patients' DNA revealed a previously undescribed CCG----CGG transversion in codon 347 predicting a Pro----Arg substitution. Ophthalmological data of the patients are summarized and compared to those of patients with other mutations in the rhodopsin gene.     

A 3-bp deletion in the rhodopsin gene in a family with autosomal dominant retinitis pigmentosa.

Autosomal dominant retinitis pigmentosa (ADRP) has recently been linked to locus D3S47 (probe C17), with no recombination, in a single large Irish family. Other ADRP pedigrees have shown linkage at zero recombination, linkage with recombination, and no linkage, demonstrating genetic heterogeneity. The gene encoding rhodopsin, the rod photoreceptor pigment, is closely linked to locus D3S47 on chromosome 3q. A point mutation changing a conserved proline to histidine in the 23d codon of the gene has been demonstrated in affected members of one ADRP family and in 17 of 148 unrelated ADRP patients. We have sequenced the rhodopsin gene in a C17-linked ADRP family and have identified in the 4th exon and in-frame 3-bp deletion which deletes one of the two isoleucine monomers at codons 255 and 256. This mutation was not found in 30 other unrelated ADRP families. The deletion has arisen in the sequence TCATCATCAT, deleting one of a run of three x 3-bp repeats. The mechanism by which this occurred may be similar to that which creates length variation in so-called mini- and microsatellites. Thus ADRP is an extremely heterogeneous disorder which can result from a range of defects in rhodopsin and which can have a locus or loci elsewhere in the genome.     

Suppression of wild-type rhodopsin maturation by mutants linked to autosomal dominant retinitis pigmentosa

Autosomal dominant retinitis pigmentosa (ADRP) has been linked to mutations in the gene encoding rhodopsin. Most RP-linked rhodopsin mutants are unable to fold correctly in the endoplasmic reticulum, are degraded by the ubiquitin proteasome system, and are highly prone to forming detergent-insoluble high molecular weight aggregates. Here we have reported that coexpression of folding-deficient, but not folding-proficient, ADRP-linked rhodopsin mutants impairs delivery of the wild-type protein to the plasma membrane. Fluorescence resonance energy transfer and co-precipitation studies revealed that mutant and wild-type rhodopsins form a high molecular weight, detergent-insoluble complex in which the two proteins are in close (<70 A) proximity. Co-expression of ARDP-linked rhodopsin folding-deficient mutants resulted in enhanced proteasome-mediated degradation and steady-state ubiquitination of the wild-type protein. These data suggested a dominant negative effect on conformational maturation that may underlie the dominant inheritance of ARDP.     

Molecular genetic study of autosomal dominant retinitis pigmentosa in Lithuanian patients

Lithuanian patients with visual problems were clinically examined for retinitis pigmentosa (RP). A total of 33 unrelated families with autosomal dominant RP (adRP) were identified. Screening for mutations in the rhodopsin (RHO) and peripherin/RDS (RDS) genes was performed using DNA heteroduplex analysis. Direct DNA sequencing in the cases of heteroduplex formation showed the presence of the following mutations and polymorphisms in 14 adRP patients: RHO gene - Lys248Arg (1 case), and Pro347Leu (2 cases); RDS gene - Glu304Gln (12 cases), Lys310Arg (5 cases), and Gly338Asp (12 cases). The presence of these mutations (except Lys248Arg in the RHO gene) was confirmed by relevant restriction enzyme digestion. The frequency of the RDS gene mutations Glu304Gln and Gly338Asp was estimated to be 36.4%, while mutation Lys310Arg was less frequent (15.2%). These 3 RDS gene mutations appear to be polypeptide polymorphisms not related to adRP.     

Transgenic mice with a rhodopsin mutation (Pro23His): a mouse model of autosomal dominant retinitis pigmentosa.

We inserted into the germline of mice either a mutant or wild-type allele from a patient with retinitis pigmentosa and a missense mutation (P23H) in the rhodopsin gene. All three lines of transgenic mice with the mutant allele developed photoreceptor degeneration; the one with the least severe retinal photoreceptor degeneration had the lowest transgene expression, which was one-sixth the level of endogenous murine rod opsin. Of two lines of mice with the wild-type allele, one expressed approximately equal amounts of transgenic and murine opsin and maintained normal retinal function and structure. The other expressed approximately 5 times more transgenic than murine opsin and developed a retinal degeneration similar to that found in mice carrying a mutant allele, presumably due to the overexpression of this protein. Our findings help to establish the pathogenicity of mutant human P23H rod opsin and suggest that overexpression of wild-type human rod opsin leads to a remarkably similar photoreceptor degeneration.     

A rhodopsin mutant linked to autosomal dominant retinitis pigmentosa is prone to aggregate and interacts with the ubiquitin proteasome system

The inherited retinal degenerations are typified by retinitis pigmentosa (RP), a heterogeneous group of inherited disorders that causes the destruction of photoreceptor cells, the retinal pigmented epithelium, and choroid. This group of blinding conditions affects over 1.5 million persons worldwide. Approximately 30-40% of human autosomal dominant (AD) RP is caused by dominantly inherited missense mutations in the rhodopsin gene. Here we show that P23H, the most frequent RP mutation in American patients, renders rhodopsin extremely prone to form high molecular weight oligomeric species in the cytoplasm of transfected cells. Aggregated P23H accumulates in aggresomes, which are pericentriolar inclusion bodies that require an intact microtubule cytoskeleton to form. Using fluorescence resonance energy transfer (FRET), we observe that P23H aggregates in the cytoplasm even at extremely low expression levels. Our data show that the P23H mutation destabilizes the protein and targets it for degradation by the ubiquitin proteasome system. P23H is stabilized by proteasome inhibitors and by co-expression of a dominant negative form of ubiquitin. We show that expression of P23H, but not wild-type rhodopsin, results in a generalized impairment of the ubiquitin proteasome system, suggesting a mechanism for photoreceptor degeneration that links RP to a broad class of neurodegenerative diseases.     

Autosomal dominant retinitis pigmentosa: linkage to rhodopsin and evidence for genetic heterogeneity

Retinitis pigmentosa (RP) is the most prevalent human retinopathy of genetic origin. Chromosomal locations for X-linked RP and autosomal dominant RP genes have recently been established. Multipoint analyses with ADRP and seven markers on the long arm of chromosome 3 demonstrate that the gene for rhodopsin, the pigment of the rod photoreceptors, cosegregates with the disease locus with a maximum lod score of approximately 19, implicating rhodopsin as a causative gene. Recent studies have indicated the presence of a point mutation at codon 23 in exon 1 of rhodopsin which results in the substitution of histidine for the highly conserved amino acid proline, suggesting that this mutation is a cause of rhodopsin-linked ADRP. This mutation is not present in the Irish pedigree in which ADRP has been mapped close to rhodopsin. Another mutation in the rhodopsin gene or in a gene closely linked to rhodopsin may be involved. Moreover, the gene in a second ADRP pedigree, with Type II late onset ADRP, does not segregate with chromosome 3q markers, indicating that nonallelic as well as perhaps allelic genetic heterogeneity exists in the autosomal dominant form of this disease.     

Gene mapping and mutation screening in candidate genes in a Chinese family of autosomal dominant retinitis pigmentosa

We wanted to find the gene defect in a Chinese pedigree with autosomal dominant form of retinitis pigmentosa (ADRP). A small Chinese family with retinitis pigmentosa was collected. The genetic analysis of the family suggested an autosomal dominant pattern. Microsatellite (STR) markers tightly linked to candidate genes for ADRP were selected for linkage analysis. We got a maximum LOD score of 0.87 between markers D19S210 and D19S418. Precursor mRNA-processing factor (PRPF) 31, 3, 8, rhodopsin (RHO), peripherin 2 (PRPH2 or RDS), rod outer segment protein 1 (ROM1), neural retina leucine zipper (NRL), cone-rod homeobox-containing (CRX), inosine-5-prime-monophosphate dehydrogenase, type I (IMPDH1) and retinitis pigmentosa 1 (RPI) were amplified by polymerase chain reaction (PCR) and screened by direct sequencing. One new sequence variation was found. It was the missence mutation c.148G > C (D50H) occurred in exon 1 of RDS gene which existed in all the effected individuals and one unaffected family member. The DNA sequence variation didn't cosegregate with the RP disease. We considered this transition was one new polymorphism which we speculate involved in the pathogenesis of ADRP and increased the risk of ADRP. Further study should be conducted to confirm the causative gene of this family.     

Novel rhodopsin mutation in an autosomal dominant retinitis pigmentosa family: phenotypic variation in both heterozygote and homozygote Val137Met mutant patients

A family affected with autosomal dominant retinitis pigmentosa (RP) is presented. Two clinically affected patients (mother and daughter) were heterozygous for the same novel missense mutation (Val137Met) of the rhodopsin gene (RHO). Both heterozygous and homozygous cases were observed among their few symptomatic relatives. Wide clinical variation was exhibited among the individuals with mutations in this family. None of the controls showed this change in RHO, nor has it been previously reported in other RP families. No other RHO mutation was observed. Additional genetic or environmental factors could play a role in modulating the penetrance and clinical expression of this RHO mutation. Received: 20 February 1995 / Revised: 1 September 1995, 27 November 1995, 3 February 1996     

Gene mapping and mutation screeneng in candidate genes in a Chinese family of autosomal dominant retinitis pigmentosa

We wanted to find the gene defect in a Chinese pedigree with autosomal dominant form of retinitis pigmentosa (ADRP). A small Chinese family with retinitis pigmentosa was collected. The genetic analysis of the family suggested an autosomal dominant pattern. Microsatellite (STR) markers tightly linked to candidate genes for ADRP were selected for linkage analysis. We got a maximum LOD score of 0.87 between markers D19S210 and D19S418. Precursor mRNA-processing factor (PRPF) 31, 3, 8, rhodopsin (RHO), peripherin 2 (PRPH2 or RDS), rod outer segment protein 1 (ROM1), neural retina leucine zipper (NRL), cone-rod homeobox-containing (CRX), inosine-5-prime-monophosphate dehydrogenase, type I (IMPDH1) and retinitis pigmentosa 1 (RP1) were amplified by polymerase chain reaction (PCR) and screened by direct sequencing. One new sequence variation was found. It was the missence mutation c.148G > C (D50H) occurred in exon 1 of RDS gene which existed in all the effected individuals and one unaffected family member. The DNA sequence variation didn’t cosegregate with the RP disease. We considered this transition was one new polymorphism which we speculate involved in the pathogenesis of ADRP and increased the risk of ADRP. Further study should be conducted to confirm the causative gene of this family.     

A novel Cys-214-Ser mutation in the peripherin/RDS gene in a Japanese family with autosomal dominant retinitis pigmentosa

We have screened for possible disease-causing mutations in the peripherin/retinal degeneration slow (RDS) gene in 13 Japanese families with autosomal dominant retinitis pigmentosa (ADRP). Using polymerase chain reaction-single strand conformation polymorphism analysis, a novel mutation at codon 214 was found in which the highly conserved cysteine was replaced with a serine in one family. The mutation at codon 214 was found in all three affected siblings of this family, but none of the 40 normal control individuals had this mutation. These results strongly suggest, that the mutation is pathogenic for RP in this family. The clinical phenotype for this family is a late-onset form of ADRP.     

Mapping of locus for autosomal dominant retinitis pigmentosa on chromosome 6q23

Retinitis pigmentosa (RP) is a genetically heterogeneous group of retinal degenerative disorders resulting in severe visual loss and blindness that have remained incurable till date. We report the mapping of the disease locus in a 3-generation family of Indian origin with autosomal dominant RP (ADRP). Diagnosis of RP and recruitment was made after a complete clinical evaluation of all members. Manifestations of the disease included night blindness with blurred central vision in some cases, loss of peripheral vision, and diffuse degeneration of the retinal pigment epithelium. Linkage analysis using microsatellite markers was carried out on 34 members (14 affected). After testing for linkage to known retinal dystrophy loci as well as a subsequent genome-wide analysis, we detected linkage to markers on chromosome 6q23: D6S262 at 130 cM, D6S457 (130 cM) and D6S1656 (131 cM) gave significant 2-point LOD scores of 3.0–3.8. Multipoint LOD scores of ≥3.0 were obtained for markers between 121 and 130 cM. Haplotype analysis with several markers in the same region on chromosome 6 shows a disease-cosegregating region of about 25 Mb between 109 and 135 Mb. There are no known RP genes in this interval, which contains >100 genes. This study provides evidence for a novel ADRP locus on chromosome 6q23.     

CDK5 and MEKK1 mediate pro-apoptotic signalling following endoplasmic reticulum stress in an autosomal dominant retinitis pigmentosa model

Chronic stress in the endoplasmic reticulum (ER) underlies many degenerative and metabolic diseases involving apoptosis of vital cells. A well-established example is autosomal dominant retinitis pigmentosa (ADRP), an age-related retinal degenerative disease caused by mutant rhodopsins. Similar mutant alleles of Drosophila Rhodopsin-1 also impose stress on the ER and cause age-related retinal degeneration in that organism. Well-characterized signalling responses to ER stress, referred to as the unfolded protein response (UPR), induce various ER quality control genes that can suppress such retinal degeneration. However, how cells activate cell death programs after chronic ER stress remains poorly understood. Here, we report the identification of a signalling pathway mediated by cdk5 and mekk1 required for ER-stress-induced apoptosis. Inactivation of these genes specifically suppressed apoptosis, without affecting other protective branches of the UPR. CDK5 phosphorylates MEKK1, and together, they activate the JNK pathway for apoptosis. Moreover, disruption of this pathway can delay the course of age-related retinal degeneration in a Drosophila model of ADRP. These findings establish a previously unrecognized branch of ER-stress response signalling involved in degenerative diseases.     

Mutations in TOPORS cause autosomal dominant retinitis pigmentosa with perivascular retinal pigment epithelium atrophy

We report mutations in the gene for topoisomerase I-binding RS protein (TOPORS) in patients with autosomal dominant retinitis pigmentosa (adRP) linked to chromosome 9p21.1 (locus RP31). A positional-cloning approach, together with the use of bioinformatics, identified TOPORS (comprising three exons and encoding a protein of 1,045 aa) as the gene responsible for adRP. Mutations that include an insertion and a deletion have been identified in two adRP-affected families--one French Canadian and one German family, respectively. Interestingly, a distinct phenotype is noted at the earlier stages of the disease, with an unusual perivascular cuff of retinal pigment epithelium atrophy, which was found surrounding the superior and inferior arcades in the retina. TOPORS is a RING domain-containing E3 ubiquitin ligase and localizes in the nucleus in speckled loci that are associated with promyelocytic leukemia bodies. The ubiquitous nature of TOPORS expression and a lack of mutant protein in patients are highly suggestive of haploinsufficiency, rather than a dominant negative effect, as the molecular mechanism of the disease and make rescue of the clinical phenotype amenable to somatic gene therapy.     

Mice with a D190N mutation in the gene encoding rhodopsin: a model for human autosomal-dominant retinitis pigmentosa

Rhodopsin is the G protein-coupled receptor in charge of initiating signal transduction in rod photoreceptor cells upon the arrival of the photon. D190N (Rho(D190n)), a missense mutation in rhodopsin, causes autosomal-dominant retinitis pigmentosa (adRP) in humans. Affected patients present hyperfluorescent retinal rings and progressive rod photoreceptor degeneration. Studies in humans cannot reveal the molecular processes causing the earliest stages of the condition, thus necessitating the creation of an appropriate animal model. A knock-in mouse model with the D190N mutation was engineered to study the pathogenesis of the disease. Electrophysiological and histological findings in the mouse were similar to those observed in human patients, and the hyperfluorescence pattern was analogous to that seen in humans, confirming that the D190N mouse is an accurate model for the study of adRP.     

Refined mapping of the gene for autosomal dominant retinitis pigmentosa (RP17) on chromosome 17q22

Linkage analysis was performed on a large Dutch family with autosomal dominant retinitis pigmentosa. Linkage was found to the RP17 locus on chromosome 17q22, which was previously described in two South African families by Bardien et al. (1995, 1997). Assuming that the disease phenotypes in these families are caused by the same gene, the RP17 critical region is refined to a 7.7-cM interval between markers D17S1607 and D17S948. Two positional candidate genes, the retina-specific amine oxidase (RAO) gene (AOC2) and the cone transducin γ gene (GNGT2), were excluded. Received: 7 September 1998 / Accepted: 23 November 1998