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     

A new locus (RP31) for autosomal dominant retinitis pigmentosa maps to chromosome 9p

Retinitis pigmentosa (RP) is a debilitating disease of the retina affecting ∼1.5 million people worldwide. RP shows remarkable heterogeneity both clinically and genetically, with more than 40 genetic loci implicated, 12 of which account for the autosomal dominant form (adRP) of inheritance. We have recently identified a French Canadian family that presents with early onset adRP. After exclusion of all known loci for adRP, a genome-wide search established firm linkage with a marker from the short arm of chromosome 9 (LOD score of 6.3 at recombination fraction θ=0). The linked region is flanked by markers D9S285 and D9S1874, corresponding to a genetic distance of 31 cM, in the region 9p22-p13.     

Further refinement of the location for autosomal dominant retinitis pigmentosa on chromosome 7p (RP9).

A form of autosomal dominant retinitis pigmentosa (adRP) mapping to chromosome 7p was recently reported by this laboratory, in a single large family from southeastern England. Further sampling of the family and the use a number of genetic markers from 7p have facilitated the construction of a series of multipoint linkage maps of the region with the most likely disease gene location. From this and haplotype data, the locus can now be placed between the markers D7S484 and D7S526, in an interval estimated to be 1.6-4 cM. Genetic distances between the markers previously reported to be linked to this region and those described in the recent whole-genome poly-CA map were estimated from data in this and other families. These data should assist in the construction of a physical map of the region and will help to identify candidate genes for the 7p adRP locus.     

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.     

Evidence for a major gene (RP10) for autosomal dominant retinitis pigmentosa on chromosome 7q: linkage mapping in a second,unrelated family

Retinitis pigmentosa is a genetically heterogeneous form of retinal degeneration, which has X-linked, autosomal recessive and autosomal dominant forms. The disease genes in families with autosomal dominant retinitis pigmentosa (adRP) have been linked to six loci, on 3q, 6p, 7p, 7q, 8q and 19q. In a large American family with late-onset adRP, microsatellite markers were used to test for linkage to the loci on 3q, 6p, 7p, 7q and 8q. Linkage was found to 7q using the marker D7S480. Additional microsatellite markers from 7q were then tested. In total, five markers, D7S480, D7S514, D7S633, D7S650 and D7S677, show statistically significant evidence for link-age in this family, with a maximum two-point lod score of 5.3 at 0% recombination from D7S514. These results confirm an earlier report of linkage to an adRP locus (RP10) in an unrelated family of Spanish origin and indicate that RP10 may be a significant gene for inherited retinal degeneration. In addition, we used recently reported microsatellite markers from 7q to refine the linkage map of the RP10 locus.     

Linkage mapping of autosomal dominant retinitis pigmentosa (RP1) to the pericentric region of human chromosome 8.

Linkage mapping in a large, seven-generation family with type 2 autosomal dominant retinitis pigmentosa (ADRP) demonstrates linkage between the disease locus (RP1) and DNA markers on the short arm of human chromosome 8. Five markers were most informative for mapping ADRP in this family using two-point linkage analysis. The markers, their maximum lod scores, and recombination distances were ANK1 (ankyrin)--2.0 at 16%; D8S5 (TL11)--5.3 at 17%; D8S87 [a(CA)n repeat]--7.2 at 14%; LPL (lipoprotein lipase)--1.5 at 26%; and PLAT (plasminigen activator, tissue)--10.6 at 7%. Multipoint linkage analysis, using a simplified pedigree structure for the family (which contains 192 individuals and two inbreeding loops), gave a maximum lod score of 12.2 for RP1 at a distance 8.1 cM proximal to PLAT in the pericentric region of the chromosome. Based on linkage data from the CEPH (Paris) reference families and physical mapping information from a somatic cell hybrid panel of chromosome 8 fragments, the most likely order for four of these five loci and the diseases locus is 8pter-LPL-D8S5-D8S87-PLAT-RP1. (The precise location of ANK1 relative to PLAT in this map is not established). The most likely location for RP1 is in the pericentric region of the chromosome. Recently, several families with ADRP with tight linkage to the rhodopsin locus at 3q21-q24 were reported and a number of specific rhodopsin mutations in families with ADRP have since been reported. In other ADRP families, including the one in this study, linkage to rhodopsin has been excluded. Thus mutations at two different loci, at least, have been shown to cause ADRP. There is no remarkable clinical disparity in the expression of disease caused by these different loci.     

Evidence for a major retinitis pigmentosa locus on 19q13.4 (RP11) and association with a unique bimodal expressivity phenotype.

Retinitis pigmentosa (RP) is the name given to a heterogeneous group of retinal degenerations mapping to at least 16 loci. The autosomal dominant form (ARP), accounting for approximately 25% of cases, can be caused by mutations in two genes, rhodopsin and peripherin/RDS, and by at least six other loci identified by linkage analysis. The RP11 locus for adRP has previously been mapped to chromosome 19q13.4 in a large English family. This linkage has been independently confirmed in a Japanese family, and we now report three additional unrelated linked U.K. families, suggesting that this is a major locus for RP. Linkage analysis in the U.K. families refines the RP11 interval to 5 cM between markers D19S180 and AFMc001yb1. All linked families exhibit incomplete penetrance; some obligate gene carriers remain asymptomatic throughout their lives, whereas symptomatic individuals experience night blindness and visual field loss in their teens and are generally registered as blind by their 30s. This "bimodal expressivity" contrasts with the variable-expressivity RP mapping to chromosome 7p (RP9) in another family, which has implications for diagnosis and counseling of RP11 families. These results may also imply that a proportion of sporadic RP, previously assumed to be recessive, might result from mutations at this locus.     

A study of the nuclear trafficking of the splicing factor protein PRPF31 linked to autosomal dominant retinitis pigmentosa (ADRP)

In this study the mechanism of nuclear importation of the splicing factor PRPF31 is examined and the impact of two disease-linked mutations, A194E and A216P, assessed. Using pull-down assays with GST-tagged importin proteins, we demonstrate that His-tagged PRPF31 interacts with importin beta1 for translocation to the nucleus, with no requirement for importin alpha1. The A194E and A216P mutations have no affect on this interaction. Fluorescence recovery after photobleaching (FRAP) was used to estimate the rate of movement of EGFP-tagged PRPF31 into the nuclei of live cells. The kinetics indicated a two-component recovery process; a fast component with tau approximately 6 s and a slow component with tau approximately 80 s. The mutations affected neither component. We conclude that the two mutations have no negative effect on interaction with the nuclear importation machinery. Reduced mutant protein solubility resulting in an insufficiency of splicing activity in cells with a very high metabolic demand remains the most likely explanation for the disease pathology in ADRP patients.     

PAP-1, the mutated gene underlying the RP9 form of dominant retinitis pigmentosa, is a splicing factor

PAP-1 is an in vitro phosphorylation target of the Pim-1 oncogene. Although PAP-1 binds to Pim-1, it is not a substrate for phosphorylation by Pim-1 in vivo. PAP-1 has recently been implicated as the defective gene in RP9, one type of autosomal dominant retinitis pigmentosa (adRP). However, RP9 is a rare disease and only two missense mutations have been described, so the report of a link between PAP-1 and RP9 was tentative. The precise cellular role of PAP-1 was also unknown at that time. We now report that PAP-1 localizes in nuclear speckles containing the splicing factor SC35 and interacts directly with another splicing factor, U2AF35. Furthermore, we used in vitro and in vivo splicing assays to show that PAP-1 has an activity, which alters the pattern of pre-mRNA splicing and that this activity is dependent on the phosphorylation state of PAP-1. We used the same splicing assay to examine the activities of two mutant forms of PAP-1 found in RP9 patients. The results showed that while one of the mutations, H137L, had no effect on splicing activity compared with that of wild-type PAP-1, the other, D170G, resulted in both a defect in splicing activity and a decreased proportion of phosphorylated PAP-1. The D170G mutation may therefore cause RP by altering splicing of retinal genes through a decrease in PAP-1 phosphorylation. These results demonstrate that PAP-1 has a role in pre-mRNA splicing and, given that three other splicing factors have been implicated in adRP, this finding provides compelling further evidence that PAP-1 is indeed the RP9 gene.     

Map refinement of locus RP13 to human chromosome 17p13.3 in a second family with autosomal dominant retinitis pigmentosa.

In order to elucidate the genetic basis of autosomal dominant retinitis pigmentosa (adRP) in a large eight-generation family (UCLA-RP09) of British descent, we assessed linkage between the UCLA-RP09 adRP gene and numerous genetic loci, including eight adRP candidate genes, five anonymous adRP-linked DNA loci, and 20 phenotypic markers. Linkage to the UCLA-RP09 disease gene was excluded for all eight candidate genes analyzed, including rhodopsin (RP4) and peripherin/RDS (RP7), for the four adRP loci RP1, RP9, RP10 and RP11, as well as for 17 phenotypic markers. The anonymous DNA marker locus D17S938, linked to adRP locus RP13 on chromosome 17p13.1, yielded a suggestive but not statistically significant positive lod score. Linkage was confirmed between the UCLA-RP09 adRP gene and markers distal to D17S938 in the chromosomal region 17p13.3. A reanalysis of the original RP13 data from a South African adRP family of British descent, in conjunction with our UCLA-RP09 data, suggests that only one adRP locus exists on 17p but that it maps to a more telomeric position, at band 17p13.3, than previously reported. Confirmation of the involvement of RP13 in two presumably unrelated adRP families, both of British descent, suggests that this locus is a distinct adRP gene in a proportion of British, and possibly other, adRP families.     

Probable genetic linkage between autosomal dominant retinitis pigmentosa (RP) and amylase (AMY2): evidence of an RP locus on chromosome 1.

A linkage analysis is reported for three branches of a single family segregating for autosomal dominant retinitis pigmentosa. A statistically significant lod score of 3.9 is obtained for the RP locus and AMY2 at a recombination frequency of 1%. This linkage indicates that the RP locus is on the no. 1 chromosome since the AMY2 locus has been placed on the short arm of 1. Lod scores are reported for four other loci on chromosome 1; none of these achieve statistical significance. Analyses are reported for 23 additional autosomal markers and close linkage with RP can be excluded for a number of these.     

Mutation of CERKL, a novel human ceramide kinase gene, causes autosomal recessive retinitis pigmentosa (RP26)

Retinitis pigmentosa (RP), the main cause of adult blindness, is a genetically heterogeneous disorder characterized by progressive loss of photoreceptors through apoptosis. Up to now, 39 genes and loci have been implicated in nonsyndromic RP, yet the genetic bases of >50% of the cases, particularly of the recessive forms, remain unknown. Previous linkage analysis in a Spanish consanguineous family allowed us to define a novel autosomal recessive RP (arRP) locus, RP26, within an 11-cM interval (17.4 Mb) on 2q31.2-q32.3. In the present study, we further refine the RP26 locus down to 2.5 Mb, by microsatellite and single-nucleotide polymorphism (SNP) homozygosity mapping. After unsuccessful mutational analysis of the nine genes initially reported in this region, a detailed gene search based on expressed-sequence-tag data was undertaken. We finally identified a novel gene encoding a ceramide kinase (CERKL), which encompassed 13 exons. All of the patients from the RP26 family bear a homozygous mutation in exon 5, which generates a premature termination codon. The same mutation was also characterized in another, unrelated, Spanish pedigree with arRP. Human CERKL is expressed in the retina, among other adult and fetal tissues. A more detailed analysis by in situ hybridization on adult murine retina sections shows expression of Cerkl in the ganglion cell layer. Ceramide kinases convert the sphingolipid metabolite ceramide into ceramide-1-phosphate, both key mediators of cellular apoptosis and survival. Ceramide metabolism plays an essential role in the viability of neuronal cells, the membranes of which are particularly rich in sphingolipids. Therefore, CERKL deficiency could shift the relative levels of the signaling sphingolipid metabolites and increase sensitivity of photoreceptor and other retinal cells to apoptotic stimuli. This is the first genetic report suggesting a direct link between retinal neurodegeneration in RP and sphingolipid-mediated apoptosis.     

A novel locus (RP33) for autosomal dominant retinitis pigmentosa mapping to chromosomal region 2cen-q12.1

Retinitis pigmentosa (RP) is a heterogeneous group of progressive degenerative disorders of the retina with a strong genetic component. Here, we report the clinical and genetic findings in a Chinese family in which autosomal dominant RP (adRP) was inherited by 13 affected members in four generations. Using a genome-wide linkage screening approach, a novel disease locus (RP33) was assigned to the long arm of chromosome 2. A maximum multi-point LOD score of 4.69 was reached at marker D2S2222 in 2q11.2. Meiotic recombination events in affected members placed RP33 in a 15.5 cM region between D2S329 and D2S2229. From meiotic recombinations in two unaffected members RP33 was further refined to a 4.8 cM (9.5 Mb) interval flanked by D2S2159 and D2S1343 in chromosomal region 2cen-q12.1. No disease-associated mutations were detected in the candidate genes SEMA4C, CNGA3 or HNK1ST from within the region. MERTK, a known disease gene for autosomal recessive RP located close to RP33 was similarly excluded. Clinically, the family presented relatively late onset of night blindness, gradually decreased visual acuity, progressive loss of peripheral visual field and typical RP fundus changes in the mid-periphery of the retina. In conclusion, a novel locus for adRP has been assigned to chromosomal region 2cen-q12.1, which in the present kindred was associated with a relatively late onset form of the disease.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.Chen Zhao and Shasha Lu have contributed equally to this study     

Protein 61K, encoded by a gene (PRPF31) linked to autosomal dominant retinitis pigmentosa, is required for U4/U6*U5 tri-snRNP formation and pre-mRNA splicing

In each round of nuclear pre-mRNA splicing, the U4/U6*U5 tri-snRNP must be assembled from U4/U6 and U5 snRNPs, a reaction that is at present poorly understood. We have characterized a 61 kDa protein (61K) found in human U4/U6*U5 tri-snRNPs, which is homologous to yeast Prp31p, and show that it is required for this step. Immunodepletion of protein 61K from HeLa nuclear extracts inhibits tri-snRNP formation and subsequent spliceosome assembly and pre-mRNA splicing. Significantly, complementation with recombinant 61K protein restores each of these steps. Protein 61K is operationally defined as U4/U6 snRNP-specific as it remains bound to this particle at salt concentrations where the tri-snRNP dissociates. However, as shown by two-hybrid analysis and biochemical assays, protein 61K also interacts specifically with the U5 snRNP-associated 102K protein, indicating that it physically tethers U4/U6 to the U5 snRNP to yield the tri-snRNP. Interestingly, protein 61K is encoded by a gene (PRPF31) that has been shown to be linked to autosomal dominant retinitis pigmentosa. Thus, our studies suggest that disruptions in tri-snRNP formation and function resulting from mutations in the 61K protein may contribute to the manifestation of this disease.     

Autosomal dominant retinitis pigmentosa: Localization of a disease gene (RP6) to the short arm of chromosome 6

DNA from members of an Irish pedigree presenting with late onset autosomal dominant retinitis pigmentosa (ADRP) have been typed with a series of genetic markers from chromosome 6p. Positive two-point lod scores have been obtained with five markers (D6S89: theta = 0.10, Z = 3.338; D6S109: theta = 0.10, Z = 3.932; D6S105: theta = 0.00, Z = 6.081; HLA-DRA: theta = 0.00, Z = 4.364; and RDS: theta = 0.00, Z = 5.376). In a series of overlapping multipoint analyses a lod score of 6.6 was obtained, maximizing at HLA-DRA and hence localizing the ADRP gene (RP5) segregating in this pedigree to 6p. These data provide direct evidence for an additional autosomal dominant RP locus and strongly implicate the human equivalent of the mouse retinal degeneration slow (rds) gene, peripherin-rds, as a candidate for autosomal dominant retinitis pigmentosa.