Effective delivery of large genes to the retina by dual AAV vectors

Retinal gene therapy with adeno-associated viral (AAV) vectors is safe and effective in humans. However, AAV's limited cargo capacity prevents its application to therapies of inherited retinal diseases due to mutations of genes over 5 kb, like Stargardt's disease (STGD) and Usher syndrome type IB (USH1B). Previous methods based on 'forced' packaging of large genes into AAV capsids may not be easily translated to the clinic due to the generation of genomes of heterogeneous size which raise safety concerns. Taking advantage of AAV's ability to concatemerize, we generated dual AAV vectors which reconstitute a large gene by either splicing (trans-splicing), homologous recombination (overlapping), or a combination of the two (hybrid). We found that dual trans-splicing and hybrid vectors transduce efficiently mouse and pig photoreceptors to levels that, albeit lower than those achieved with a single AAV, resulted in significant improvement of the retinal phenotype of mouse models of STGD and USH1B. Thus, dual AAV trans-splicing or hybrid vectors are an attractive strategy for gene therapy of retinal diseases that require delivery of large genes.

Ribozyme-based therapeutic approaches for autosomal dominant retinitis pigmentosa

PURPOSE

To design, generate, and compare in vitro a range of hammerhead ribozymes targeting retinal transcripts implicated in autosomal dominant retinitis pigmentosa (adRP) and thereby identify ribozymes that may be valuable as therapeutic agents for adRP. To address mutational heterogeneity in rhodopsin and peripherin-linked adRP using mutation-independent ribozyme-based therapeutic approaches.

METHODS

Ribozyme and cDNAs constructs were cloned into pcDNA3 and expressed in vitro from the T7 promoter. Cleavage reactions were separated on polyacrylamide gels, visualized by autoradiography, and quantified using an instant imager. Ribozymes targeting rhodopsin and peripherin transcripts in a mutation-independent manner (Rz9, Rz10, and Rz40) and a multimeric ribozyme (RzMM) targeting rhodopsin transcripts were evaluated for in vitro activity. Parameters such as V:(max), K:(m), k(2) and k(-1) were established for each ribozyme.

RESULTS

Four ribozymes targeting retinal transcripts were evaluated. Mutation-independent ribozymes targeting degenerate sites or untranslated regions in retinal transcripts resulted in cleavage products of predicted size, whereas transcripts from modified replacement genes remained intact. Detailed kinetic evaluation of ribozymes revealed substantial differences in cleavage rates between ribozymes.

CONCLUSIONS

Mutation-independent hammerhead ribozymes targeting rhodopsin and peripherin have been screened in vitro, and a number of extremely efficient ribozymes identified subsequent to detailed kinetic analyses, suggesting that these ribozymes may provide mutation-independent methods of treating adRP. These are the first ribozymes reported that potentially will provide benefit for inherited retinopathies.

Apoptotic photoreceptor death in the rhodopsin knockout mouse in the presence and absence of c-fos

A combined total of approximately 100 mutations have been encountered within the rhodopsin gene in retinitis pigmentosa (RP) and congenital night blindness. Mice carrying a targeted disruption of the rhodopsin gene phenotypically mimic RP, losing their photoreceptors over a period of 3 months and having no recordable rod electroretinogram. These animals will serve as a model for both recessive and dominant disease (in the latter case, the presence of normal and mutant human rod opsin transgenes on the murine Rho(-/-)background). Precise knowledge of apoptotic photoreceptor cell death, together with factors which may influence apoptosis will be required for optimum utility of Rho(-/-)mice as a model for therapeutic genetic intervention. A peak phase of apoptosis of the photoreceptors of Rho(-/-)mice was shown to occur at 24 days post-birth. The extent of apoptosis appeared to be similar, irrespective of whether or not the rod opsin knockout was present on a c-fos(+/+)or c-fos(-/-)genetic background, the latter known to favor survival of photoreceptors following exposure of mouse retinas to excessive light. These data clearly support the existence in animals of distinct apoptotic pathways in light-induced, as opposed to mutation-induced apoptosis, and together with similar observations recently reported in studies of the naturally occurring rd mouse, may assist in focusing future research on precisely defining the distinct molecular pathways giving rise to such dichotomy.

A novel mutation within the rhodopsin gene (Thr-94-Ile) causing autosomal dominant congenital stationary night blindness

More than 100 mutations within the rhodopsin gene have been found to be responsible for some forms of retinitis pigmentosa, a progressive retinal degeneration characterized by night blindness and subsequent disturbance of day vision that may eventually result in total blindness. Congenital stationary night blindness (CSNB) is an uncommon inherited retinal dysfunction in which patients complain of night vision difficulties of a nonprogressive nature only and in which generally there is no involvement of day vision. We report the results of molecular genetic analysis of an Irish family segregating an autosomal dominant form of CSNB in which a previously unreported threonine-to-isoleucine substitution at codon 94 in the rhodopsin gene was found to segregate with the disease. Computer modeling suggests that constitutive activation of transducin by the altered rhodopsin protein may be a mechanism for disease causation in this family. Only two mutations within the rhodopsin gene have been previously reported in patients with congenital stationary night blindness, constitutive activation also having been proposed as a possible disease mechanism.

Novel mutations in the TIGR gene in early and late onset open angle glaucoma

A gene for juvenile onset, open angle glaucoma (JOAG) has been localized to chromosome 1q21-31 in several families. Mutations in the trabecular meshwork-induced glucocorticoid response protein (TIGR) gene, which maps to this region, recently have been found in families segregating both JOAG and a later onset form of primary open angle glaucoma (POAG). We have analysed the TIGR gene in two families; one Spanish family segregating autosomal dominant JOAG and an Irish family with a later onset form of autosomal dominant POAG. We have found a G-T transversion in the first base of codon 426 in all affected members of the Spanish family, which results in a valine to phenylalanine amino acid substitution. We have also found a G-A transition at the first base of codon 367 that segregates through all but one branch of the Irish family and results in a glycine to arginine amino acid substitution. Members of this family that carry the Gly367Arg change also share a common haplotype that is neither present in any of the unaffected members of the family, nor in the branch that does not segregate the mutation. Identification of further mutations in the TIGR gene increases its importance in the etiology of open angle glaucoma.

A mutation-independent therapeutic strategem for osteogenesis imperfecta

Given the genetically heterogeneous nature of many dominantly inherited disorders, it will be imperative to design mutation-independent therapeutic strategies to circumvent such heterogeneity. Intragenic polymorphism represents a genomic resource that may be harnessed in the development of allele-specific mutation-independent therapeutics. A hammerhead ribozyme, Rzpol1a1, selectively cleaves a common single-nucleotide polymorphism (SNP) of the human COL1A1 transcript (heterozygosity frequency of 2 pq = 0.4032, from Hardy-Weinberg equilibrium). One SNP variant contains a hammerhead ribozyme cleavage site, and the other does not. Kinetic evaluation shows Rzpol1a1 to be both specific and extremely efficient in vitro. Thus, a single efficient ribozyme has been characterized that should be valuable in the development of a gene therapy suitable for up to 1 in 5 dominant-negative osteogenesis imperfecta (OI) patients, where over 150 different mutations have been identified to date. Given the increasing characterization of intragenic SNP, it is predicted that such a mutation-independent strategy, based on selective silencing of mutant alleles at SNP, may become increasingly important in future genomics-driven drug development for many heterogeneous dominant disorders and complex traits.

Structural and functional rescue of murine rod photoreceptors by human rhodopsin transgene

Mice carrying a targeted disruption of the rhodopsin gene develop a severe degenerative retinopathy, failing to elaborate rod photoreceptor outer segments (ROS), having no recordable rod electroretinogram (ERG) and losing all of their rod cells over a period of approximately 12 weeks. Murine and human rhodopsins differ in their amino acid sequences. Whether, or to what extent, such variability might influence the ability of human rhodopsin to serve as an adequate structural and functional substitute for the endogenous protein in mouse rod cells bears direct relevance to exploiting the full utility of Rho-/-animals as a model of degenerative retinal disease in man. We crossed Rho-/-mice with mice expressing a wild-type human rhodopsin transgene at levels approximating to those of the endogenous protein. Immunohistological examination of retinal selections from such animals demonstrated ROS of normal number and length and temporal expression of rhodopsin similar to that observed in wild-type animals; that is, immunoreactivity to an anti-rhodopsin antibody became clearly evident by day 3 post-partum. Whereas Rho-/-mice never display a rod ERG response, and even lose cone responses by 12 weeks of age, rescued mice showed 75% normal maximum amplitudes and had ERG b-wave thresholds (based on a 50 microV criterion) within 0.1 log unit of normal wild-type at 20 weeks, and cone amplitudes remained normal at this age. These data demonstrate very substantial structural and functional rescue of the rod photoreceptors of Rho-/-mice and long-term preservation by the human rhodopsin transgene.

Retinitis pigmentosa and progressive sensorineural hearing loss caused by a C12258A mutation in the mitochondrial MTTS2 gene

Family ZMK is a large Irish kindred that segregates progressive sensorineural hearing loss and retinitis pigmentosa. The symptoms in the family are almost identical to those observed in Usher syndrome type III. Unlike that in Usher syndrome type III, the inheritance pattern in this family is compatible with dominant, X-linked dominant, or maternal inheritance. Prior linkage studies had resulted in exclusion of most candidate loci and >90% of the genome. A tentative location for a causative nuclear gene had been established on 9q; however, it is notable that no markers were found at zero recombination with respect to the disease gene. The marked variability in symptoms, together with the observation of subclinical muscle abnormalities in a single muscle biopsy, stimulated sequencing of the entire mtDNA in affected and unaffected individuals. This revealed a number of previously reported polymorphisms and/or silent substitutions. However, a C-->A transversion at position 12258 in the gene encoding the second mitochondrial serine tRNA, MTTS2, was heteroplasmic and was found in family members only. This sequence change was not present in 270 normal individuals from the same ethnic background. The consensus C at this position is highly conserved and is present in species as divergent from Homo sapiens as vulture and platypus. The mutation probably disrupts the amino acid-acceptor stem of the tRNA molecule, affecting aminoacylation of the tRNA and thereby reducing the efficiency and accuracy of mitochondrial translation. In summary, the data presented provide substantial evidence that the C12258A mtDNA mutation is causative of the disease phenotype in family ZMK.

A novel Asp380Ala mutation in the GLC1A/myocilin gene in a family with juvenile onset primary open angle glaucoma

Glaucoma describes a clinically and genetically heterogeneous group of diseases that result in optic neuropathy and progressive loss of visual fields. A gene for juvenile onset primary open angle glaucoma JOAG) has recently been mapped to 1q21-31. Mutations in the trabecular meshwork induced glucocorticoid response gene (TIGR, also known as myocilin or the GLC1A locus) have been found to cause both juvenile and later onset primary open angle glaucoma. Family TCD-POAG1 is a Spanish kindred, which segregates JOAG in an autosomal dominant fashion. This family was found to be linked to the previously identified GLC1A locus on chromosome 1q. Direct sequencing of the TIGR/myocilin gene showed a heterozygous A to C transition in codon 380, resulting in the substitution of alanine for aspartic acid (Asp380Ala). This substitution created a StyI restriction site, which segregated with the JOAG phenotype and permitted rapid screening of all members of the family. This restriction site was not present in 60 controls.

Strategems in vitro for gene therapies directed to dominant mutations

A major difficulty associated with the design of gene therapies for autosomal dominant diseases is the immense intragenic heterogeneity often encountered in such conditions. In order to overcome such difficulties we have designed, and evaluated in vitro, three strategies which avoid a requirement to target individual mutations for genetic suppression. In the first, normal and mutant alleles are suppressed by targeting sequences in transcribed but untranslated regions of transcript (UTRs), enabling introduction of a replacement gene with the correct coding sequencing but altered UTRs to prevent suppression. A second approach involves suppression in coding sequence and concurrent introduction of a replacement gene by exploiting the degeneracy of the genetic code. A third strategy utilises intragenic polymorphism to suppress the disease allele specifically, the advantage being that a proportion of patients with different disease mutations have the same polymorphism. These approaches provide a wider choice of target sequence than those directed to single disease mutations and are appropriate for many mutations within a given gene. General methods for suppression may be directed towards the primary defect or a secondary effect associated with the disease process, such as apoptosis. Three general methods targeting the primary defect which circumvent problems of allelic genetic heterogeneity are explored in vitro using hammerhead ribozymes designed to target transcripts from the rhodopsin, peripherin and collagen 1A1 and 1A2 genes, extensive genetic heterogeneity being a feature of associated disease pathologies.

Clinical and molecular genetic characterisation of a family segregating autosomal dominant retinitis pigmentosa and sensorineural deafness

AIMS/BACKGROUND

To characterise clinically a large kindred segregating retinitis pigmentosa and sensorineural hearing impairment in an autosomal dominant pattern and perform genetic linkage studies in this family. Extensive linkage analysis in this family had previously excluded the majority of loci shown to be involved in the aetiologies of RP, some other forms of inherited retinal degeneration, and inherited deafness.

METHODS

Members of the family were subjected to detailed ophthalmic and audiological assessment. In addition, some family members underwent skeletal muscle biopsy, electromyography, and electrocardiography. Linkage analysis using anonymous microsatellite markers was performed on DNA samples from all living members of the pedigree.

RESULTS

Patients in this kindred have a retinopathy typical of retinitis pigmentosa in addition to a hearing impairment. Those members of the pedigree examined demonstrated a subclinical myopathy, as evidence by abnormal skeletal muscle histology, electromyography, and electrocardiography. LOD scores of Zmax = 3.75 (theta = 0.10), Zmax = 3.41 (theta = 0.10), and Zmax = 3.25 (theta = 0.15) respectively were obtained with the markers D9S118, D9S121, and ASS, located on chromosome 9q34-qter, suggesting that the causative gene in this family may lie on the long arm (q) of chromosome 9.

CONCLUSIONS

These data indicate that the gene responsible for the phenotype in this kindred is located on chromosome 9 q. These data, together with evidence that a murine deafness gene is located in a syntenic area of the mouse genome, should direct the research community to consider this area as a candidate region for retinopathy and/or deafness genes.

Retinopathy induced in mice by targeted disruption of the rhodopsin gene

Retinitis pigmentosa (RP) represents the most common mendelian degenerative retinopathy of man, involving death of rod photoreceptors, cone cell degeneration, retinal vessel attenuation and pigmentary deposits. The patient experiences night blindness, usually followed by progressive loss of visual field. Genetic linkage between an autosomal dominant RP locus and rhodopsin, the photoreactive pigment of the rod cells, led to the identification of mutations within the rhodopsin gene in both dominant and recessive forms of RP. To better understand the functional and structural role of rhodopsin in the normal retina and in the pathogenesis of retinal disease, we generated mice carrying a targeted disruption of the rhodopsin gene. Rho-/- mice do not elaborate rod outer segments, losing their photoreceptors over 3 months. There is no rod ERG response in 8-week-old animals. Rho+/- animals retain the majority of their photoreceptors although the inner and outer segments of these cells display some structural disorganization, the outer segments becoming shorter in older mice. These animals should provide a useful genetic background on which to express other mutant opsin transgenes, as well as a model to assess the therapeutic potential of re-introducing functional rhodopsin genes into degenerating retinal tissues.

Three keratin gene mutations account for the majority of dominant simplex epidermolysis bullosa cases within the population of Ireland

We have located three extended families in Ireland (population 3.5 million) with autosomal dominant simplex forms of Epidermolysis Bullosa (EBS). A mutation within the keratin type I (K14) gene (Met-->272-->Arg) in one family suffering from the generalized simplex (Koebner) form of the disease has been previously described (Humphries et al., Hum Mutat 2:37-42, 1993). Here we report on the identification of mutations within the remaining two families, both of whom suffer from the Weber-Cockayne form of the disease. These mutations, within the type II keratin (K5) gene, are Asn-->193-->Lys and Met-->327-->Thr. They have been shown in each case to co-segregate with the disease and are not present in the normal population. Within the three families, a total of 44 living persons with such mutations have been identified, providing a minimum prevalence estimate for the disease in the Irish population of approximately 1 in 80,000, compared to an overall estimated global incidence at birth for all forms of EB of 1 in 50,000. Therefore, these three mutations probably account for the majority of cases of EBS within this population.

Evidence for genetic heterogeneity in Best's vitelliform macular dystrophy

Best's vitelliform macular dystrophy is an early onset, autosomal dominant macular degeneration. Linkage analysis has previously mapped a disease locus in this disorder to the pericentromeric region of chromosome 11. We examined two families, one of German and one of Irish origin, both affected with this disorder. The Irish family (BTMD1) showed strong evidence for linkage to the previously reported locus on chromosome 11. Linkage of the disease locus to the same region of chromosome 11 has been significantly excluded in the German family (Fam E), thereby providing evidence of locus heterogeneity in this clinically unique condition.

Assignment of a gene for autosomal recessive retinitis pigmentosa (RP12) to chromosome 1q31-q32.1 in an inbred and genetically heterogeneous disease population

Linkage analysis was carried out in a large family segregating for autosomal recessive retinitis pigmentosa (arRP), originating from a genetically isolated population in The Netherlands. Within the family, clinical heterogeneity was observed, with a major section of the family segregating arRP with characteristic para-arteriolar preservation of the retinal pigment epithelium (PPRPE). In the remainder of the ar-RP-patients no PPRPE was found. Initially, all branches of the family were analyzed jointly, and linkage was found between the marker F13B, located on 1q31-q32.1, and RP12 (zmax = 4.99 at 8% recombination). Analysis of linkage heterogeneity between five branches of the family yielded significant evidence for nonallelic genetic heterogeneity within this family, coinciding with the observed clinical differences. Multipoint analysis, carried out in the branches that showed linkage, favored the locus order 1cen-D1S158-(F13B, RP12)-D1S53-1qter (zmax = 9.17). The finding of a single founder allele associated with the disease phenotype supports this localization. This study reveals that even in a large family, apparently segregating for a single disease entity, genetic heterogeneity can be detected and resolved successfully.

Exclusion of the involvement of all known retinitis pigmentosa loci in the disease present in a family of Irish origin provides evidence for a sixth autosomal dominant locus (RP8)

Retinitis Pigmentosa (RP) is the most prevalent degenerative retinal disease of mendelian origin, currently affecting approximately 1.5 million people worldwide. To date it has been established that a minimum of five different genes maybe involved in the pathogenesis of autosomal dominant forms of RP (adRP). The genes encoding two retinal specific proteins, rhodopsin and peripherin/RDS, have been implicated in causing adRP due to the observation of many different mutations in these genes in patients suffering from RP. The three remaining adRP genes have been mapped to specific regions of human chromosomes but as yet are uncharacterized. We have investigated if there is evidence for the presence of another locus in the genome which when mutated causes adRP. We have utilised polymorphic genetic markers which have previously been mapped to each of the regions known to harbour adRP genes, to test for the exclusion or linkage of the disease gene segregating in a pedigree of Irish origin and find no evidence for linkage. Hence we provide definitive evidence for the involvement of yet another locus. The implications of high levels of genetic heterogeneity inherent in adRP are discussed in relation to diagnosis, prognosis and future therapies.

Localization of an autosomal dominant retinitis pigmentosa gene to chromosome 7q

Retinitis pigmentosa is a group of clinically and genetically heterogeneous retinopathies and a significant cause of worldwide visual handicap. We have typed DNA from members of a Spanish family segregating an autosomal dominant form of retinitis pigmentosa (adRP) using a large series of simple sequence polymorphic markers. Positive two-point lod scores have been obtained with fifteen markers including D7S480 (theta max = 0.00, Zmax = 7.22). Multipoint analyses using a subset of these markers gave a lod score of 7.51 maximizing at D7S480. These data provide definitive evidence for the localisation of an adRP gene on chromosome 7q, and highlight the extensive genetic heterogeneity that exists in the autosomal dominant form of this disease.

Autosomal dominant retinitis pigmentosa: no evidence for nonallelic genetic heterogeneity on 3q

Since the initial report of linkage of autosomal dominant retinitis pigmentosa (adRP) to the long arm of chromosome 3, several mutations in the gene encoding rhodopsin, which also maps to 3q, have been reported in adRP pedigrees. However, there has been some discussion as to the possibility of a second adRP locus on 3q. This suggestion has important diagnostic and research implications and must raise doubts about the usefulness of linked markers for reliable diagnosis of RP patients. In order to address this issue we have performed an admixture test (A-test) on 10 D3S47-linked adRP pedigrees and have found a likelihood ratio of heterogeneity versus homogeneity of 4.90. We performed a second A-test, combining the data from all families with known rhodopsin mutations. In this test we obtained a reduced likelihood ratio of heterogeneity versus homogeneity, of 1.0. On the basis of these statistical analyses we have found no significant support for two adRP loci on chromosome 3q. Furthermore, using 40 CEPH families, we have localized the rhodopsin gene to the D3S47-D3S20 interval, with a maximum lod score (Zm) of 20 and have found that the order qter-D3S47-rhodopsin-D3S20-cen is significantly more likely than any other order. In addition, we have mapped (Zm = 30) the microsatellite marker D3S621 relative to other loci in this region of the genome.

A mutation (Met-->Arg) in the type I keratin (K14) gene responsible for autosomal dominant epidermolysis bullosa simplex

We have identified a single base change in exon 4 of the type I keratin gene which results in the replacement of a methionine for an arginine residue at codon 272 in an Irish family displaying an autosomal dominant simplex (Koebner) form of epidermolysis bullosa (EB). This family had previously provided tentative evidence for linkage to genetic markers on chromosome 1q. The mutation cosegregates with the disease, producing a lod score of 4.8 at theta = 0.

Evidence for further genetic heterogeneity in autosomal dominant retinitis pigmentosa

We have investigated the possible involvement of further genetic heterogeneity in autosomal dominant retinitis pigmentosa using a previously unreported large Irish family with the disease. We have utilized polymorphic microsatellite markers to exclude the disease gene segregating in this family from 3q, 6p, and the pericentric region of 8, that is, each of the three chromosomal regions to which adRP loci are known to map. Hence, we provide definitive evidence for the involvement of a fourth locus in autosomal dominant retinitis pigmentosa.

Autosomal dominant retinitis pigmentosa: a novel mutation at the peripherin/RDS locus in the original 6p-linked pedigree

Using single-strand conformation polymorphism electrophoresis, heteroduplex analysis, and direct sequencing, we have searched for possible disease-causing mutations in the adRP family in which we originally found tight linkage of the disease to 6p. We have now identified a single base change in exon 2, which results in the replacement of a serine residue at codon 212 for a glycine residue. The mutation cosegregates with the disease with a lod score of 12.1 at theta = 0.0.

On the molecular genetics of retinitis pigmentosa

The human retina carries specialized neurons, the rod and cone photoreceptors, which absorb and transduce light energy and transmit impulses through the optic nerve to the brain. The most prevalent group of inherited retinopathies, affecting approximately 1.5 million people, is collectively termed retinitis pigmentosa (RP). Mutations responsible for RP have now been found in two genes encoding transmembrane proteins of the rod photoreceptor outer segment disc, and a number of additional causative genes have been localized. It is likely that characterization of the majority of such genes over the next few years will lead to a substantial elucidation of the molecular pathology of this debilitating group of hereditary conditions.

Autosomal dominant retinitis pigmentosa (adRP; RP6): cosegregation of RP6 and the peripherin-RDS locus in a late-onset family of Irish origin

We recently reported the localization of a gene for late-onset autosomal dominant retinitis pigmentosa (adRP; RP6), on the short arm of chromosome 6, by linkage analysis in a large family of Irish origin. It is notable that the gene encoding peripherin-RDS, a photoreceptor-specific protein, recently has been physically mapped on 6p. In our own analysis, an intrageneic marker derived from this gene cosegregated with the adRP disease locus with zero recombination (lod score 5.46 at q = .00). Using the CEPH reference panel, we now report the mapping of the peripherin-RDS gene relative to other 6p markers in the CEPH data base. Incorporation of these data into a multipoint analysis produced a lod score for adRP of 8.21, maximizing at the peripherin-RDS locus. This study provides strong evidence suggesting a role for peripherin-RDS in the etiology of one form of adRP.

Recombination between rhodopsin and locus D3S47 (C17) in rhodopsin retinitis pigmentosa families

Autosomal dominant retinitis pigmentosa (adRP) has shown linkage to the chromosome 3q marker C17 (D3S47) in two large adRP pedigrees known as TCDM1 and adRP3. On the basis of this evidence the rhodopsin gene, which also maps to 3q, was screened for mutations which segregated with the disease in adRP patients, and several have now been identified. However, we report that, as yet, no rhodopsin mutation has been found in the families first linked to C17. Since no highly informative marker system is available in the rhodopsin gene, it has not been possible to measure the genetic distance between rhodopsin and D3S47 accurately. We now present a linkage analysis between D3S47 and the rhodopsin locus (RHO) in five proven rhodopsin-retinitis pigmentosa (rhodopsin-RP) families, using the causative mutations as highly informative polymorphic markers. The distance, between RHO and D3S47, obtained by this analysis is theta = .12, with a lod score of 4.5. This contrast with peak lod scores between D3S47 and adRP of 6.1 at theta = .05 and 16.5 at theta = 0 in families adRP3 and TCDM1, respectively. These data would be consistent with the hypothesis that TCDM1 and ADRP3 represent a second adRP locus on chromosome 3q, closer to D3S47 than is the rhodopsin locus. This result shows that care must be taken when interpreting adRP exclusion data generated with probe C17 and that it is probably not a suitable marker for predictive genetic testing in all chromosome 3q-linked adRP families.

Polymorphic variation within "conserved" sequences at the 3' end of the human RDS gene which results in amino acid substitutions

The human RDS gene, previously mapped to chromosome 6p, encodes a protein found in the outer disc membrane of the photoreceptor cells of the retina. The cDNA sequence of the human gene shows 85% identity with the bovine peripherin gene and the rds (retinal degeneration slow) genes from mouse and rat. Mutations in the RDS gene have recently been implicated in autosomal dominant retinitis pigmentosa (adRP) in some families. Here we present evidence that the third exon of this gene is subject to polymorphic variation in humans. The three sequence alterations described in this paper give rise to amino acid substitutions. However, as these missense mutations also occur in the normal population they are not implicated as causing adRP. Interestingly such sequence variation is not found within other species examined including mouse and bovine. These intragenic polymorphisms will be of future potential value in studies to locate further disease causing mutations in adRP patients in the RDS gene.

A sequence polymorphism in the human peripherin/RDS gene

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A three-base-pair deletion in the peripherin-RDS gene in one form of retinitis pigmentosa

The group of retinopathies termed retinitis pigmentosa (RP) greatly contribute to visual dysfunction in man with a frequency of roughly 1 in 4,000. We mapped the first autosomal dominant RP (adRP) gene to chromosome 3q, close to the gene encoding rhodopsin, a rod photoreceptor pigment protein. Subsequently, mutations in this gene have been implicated as responsible for some forms of adRP. Another adRP gene has been mapped to chromosome 8p. A third adRP gene in a large Irish pedigree has been mapped to chromosome 6p, showing tight linkage with the gene for peripherin, a photoreceptor cell-specific glycoprotein, which is thus a strong candidate for the defective gene. We have now identified a three-base-pair deletion which results in the loss of one of a pair of highly conserved cysteine residues in the predicted third transmembrane domain of peripherin. This deletion segregates with the disease phenotype but is not present in unaffected controls, and suggests that mutant peripherin gives rise to retinitis pigmentosa.

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.

Autosomal dominant retinitis pigmentosa: a new multi-allelic marker (D3S621) genetically linked to the disease locus (RP4)

We report the characterization of a new eight-allele microsatellite (D3S621) isolated from a human chromosome 3 library. Two-point and multi-locus genetic linkage analysis have shown D3S621 to co-segregate with the previously mapped RP4 (theta m = 0.12, Zm = 4.34) and with other genetic markers on the long arm of the chromosome, including D3S14 (R208) (theta m = 0.00, Zm = 15.10), D3S47 (C17) (theta m = 0.11, Zm = 4.95), Rho (theta m = 0.07, Zm = 1.37), D3S21 (L182) (theta m = 0.07, Zm = 2.40) and D3S19 (U1) (theta m = 0.13, Zm = 2.78). This highly informative marker, with a polymorphic information content of 0.78, should be of considerable value in the extension of linkage data for autosomal dominant retinitis pigmentosa with respect to locii on the long arm of chromosome 3.

Autosomal dominant retinitis pigmentosa: absence of the rhodopsin proline----histidine substitution (codon 23) in pedigrees from Europe

In exon 1 at codon 23 of the rhodopsin gene, a mutation resulting in a proline-to-histidine substitution has previously been observed in approximately 12% of American autosomal dominant retinitis pigmentosa (ADRP) patients. The region around the site of this mutation in the rhodopsin gene has been amplified and analyzed in affected individuals from 91 European ADRP pedigrees. The codon 23 mutation has been found to be absent in all cases, including a large Irish pedigree in which the disease gene has previously been shown to be closely linked to the rhodopsin locus. This indicates the presence of either allelic or nonallelic heterogeneity in ADRP.

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.

Epidermolysis bullosa: evidence for linkage to genetic markers on chromosome 1 in a family with the autosomal dominant simplex form

DNA from members of a three-generation pedigree of Irish origin, displaying an autosomal dominant simplex form of epidermolysis bullosa of the epidermolytic, simplex, or Koebner variety (EBS2), was analyzed for linkage with a set of markers derived from the long arm of chromosome 1. Two-point analysis revealed positive lod scores for five of these markers, AT3 (Z = 2.107, theta = 0), APOA2 (Z = 1.939, theta = 0.15), D1S66 (Z = 1.204, theta = 0), D1S13 (Z = 1.026, theta = 0.15), and D1S65 (Z = 0.329, theta = 0.15). Multilocus analysis, incorporating the markers D1S19, D1S16, D1S13, APOA2, D1S66, AT3, and D1S65, resulted in a lod score of 3 maximizing at AT3. These data strongly support previous tentative indications of linkage between EBS2 and genetic markers on the long arm of chromosome 1.

Retinitis pigmentosa: genetic mapping in X-linked and autosomal forms of the disease

Retinitis pigmentosa (RP) is an hereditary degenerative disease of the retina and a major cause of visual impairment, prevalence estimates ranging from 1 in 3000 to 1 in 7000. The condition may segregate as an autosomal dominant, autosomal recessive or an X-linked recessive trait and it may also occur on a sporadic basis in up to 50% of cases. In the autosomal dominant form, close linkage to the DNA marker C17 (D3S47) was recently established in a large family of Irish origin displaying early-onset disease (McWilliam et al. 1989), multipoint analysis indicating the gene for rhodopsin as a likely candidate (Farrar et al. 1990). In that gene, a C----A transversion in codon 23, resulting in a proline----histidine substitution has now been identified in 17 of 148 unrelated ADRP patients in the United States (Dryja et al. 1990). This mutation is absent however in the original Irish pedigree (it is also absent in 21 other dominant Irish pedigrees, representing approximately 70% of the estimated ADRP population) indicating that another mutation, either in rhodopsin itself, or in a gene very closely linked to rhodopsin is responsible for the disease in that family. Analysis of other dominant pedigrees using the C17 and/or rhodopsin probes has indicated either tight linkage (Bhattacharya, Personal Communication), looser linkage, possibly indicative of a second locus on 3q (Olsson et al. 1990) or no linkage (Farrar et al. 1990, Blanton et al. 1990, Inglehearn et al. 1990). Extensive genetic heterogeneity thus exists in the autosomal dominant form of this disease, and in the light of these new observations, earlier tentative evidence for linkage of ADRP to the Rhesus locus on chromosome 1 will be re-evaluated. A locus for type II Usher syndrome (classical RP combined with congenital pedial deafness, and normal vestibular function) has now been established on the long arm of chromosome 1 (Kimberling et al. 1990). Type I Usher families, in which hearing loss is more profound and vestibular function absent, do not segregate with the same chromosome 1q markers, indicating the existence of another, as yet unlocated gene. In the X-linked form of the disease, two genes, XLRP2 and XLRP3, have been located on the proximal short arm of the X chromosome using a combination of physical and linkage mapping techniques, and there is some evidence to suggest a possible third locus more distally located.(ABSTRACT TRUNCATED AT 400 WORDS)

Localizing multiple X chromosome-linked retinitis pigmentosa loci using multilocus homogeneity tests

Multilocus linkage analysis of 62 family pedigrees with X chromosome-linked retinitis pigmentosa (XLRP) was undertaken to determine the presence of possible multiple disease loci and to reliably estimate their map location. Multilocus homogeneity tests furnished convincing evidence for the presence of two XLRP loci, the likelihood ratio being 6.4 x 10(9):1 in favor of two versus a single XLRP locus and gave accurate estimates for their map location. In 60-75% of the families, location of an XLRP gene was estimated at 1 centimorgan distal to OTC, and in 25-40% of the families, an XLRP locus was located halfway between DXS14 (p58-1) and DXZ1 (Xcen), with an estimated recombination fraction of 25% between the two XLRP loci. There is also good evidence for a third XLRP locus, midway between DXS28 (C7) and DXS164 (pERT87), supported by a likelihood ratio of 293:1 for three versus two XLRP loci.

Autosomal dominant retinitis pigmentosa: exclusion of a gene from extensive regions of chromosomes 6, 13, 20, and 21

Members of a large pedigree of Irish origin presenting with early onset Type I autosomal dominant retinitis pigmentosa (ADRP) have been typed for polymorphic DNA markers from chromosomes 6, 13, 20, and 21. For each marker close linkage to ADRP has been excluded by pairwise analyses. Using distances fixed from well-established genetic maps of these chromosomes and multipoint analyses with two or three contiguous markers, exclusion of ADRP was extended to the areas between markers, resulting in the exclusion of ADRP from extensive regions of each chromosome, totaling approximately 500 cM or 15% of the genome. The study indicates the large quantity of linkage/exclusion data obtainable using well-spaced highly polymorphic markers.

Autosomal dominant retinitis pigmentosa (ADRP): localization of an ADRP gene to the long arm of chromosome 3

Members of a large pedigree of Irish origin presenting with early onset Type I autosomal dominant retinitis pigmentosa (ADRP) have been typed for D3S47 (C17), a polymorphic marker from the long arm of chromosome 3. Significant, tight linkage of ADRP to D3S47, with a lod score of 14.7 maximizing at 0.00 recombination, has been obtained, hence localizing the ADRP gene (RP1) segregating in this pedigree to 3q.

Autosomal dominant retinitis pigmentosa: exclusion of the gene from the short arm of chromosome 1 including the region surrounding the rhesus locus

Members of a large Irish pedigree exhibiting early-onset autosomal dominant retinitis pigmentosa (ADRP) were typed for the rhesus blood group and nine DNA markers on chromosome 1. Close linkage between the ADRP locus and any of the marker loci was excluded using two-point analysis. With use of the sex-averaged maps of Dracopoli et al. and Donis-Keller et al. and a strategy of rolling multipoint analyses, support was gained for the exclusion of ADRP from a 224-cM region of the chromosome, including almost the entire short arm. The disease locus was significantly excluded from within at least 50 cM of the rhesus locus and, as a loose linkage between these two genes has been suggested by other studies, this result may support the possibility of genetic heterogeneity within the autosomal dominant subgroup of retinitis pigmentosa.

Linkage analysis of X linked retinitis pigmentosa in the Irish population

There is significant evidence for genetic and phenotypic heterogeneity in X linked retinitis pigmentosa (XLRP). We have studied the linkage of XLRP in four Irish families to a number of polymorphic DNA markers. We report linkage between the DXS7 (L1.28) locus and the XLRP locus (Z = 3.445, theta = 0.00). Combined with the previously published data on British and Danish families, the genetic distance between the DXS7 and XLRP loci is now estimated at 5 cM with a maximum lod score of 13.026 and a 1-lod confidence interval of 0.75 to 9.5 cM. Linkage was also observed between 754 and XLRP (Z = 3.41, theta = 0.00) and between pERT87 and XLRP (Z = 1.37, theta = 0.1). The heterogeneity of XLRP is discussed in relation to these observations.