Hereditary Retinal Degeneration Research Articles

Mutation of SPATA7 in a family with autosomal recessive early-onset retinitis pigmentosa

Mutation of SPATA7 in a family with autosomal recessive early-onset retinitis pigmentosa

Spatial Resolution and Perception of Patterns Mediated by a Subretinal 16-Electrode Array in Patients Blinded by Hereditary Retinal Dystrophies

The perception of 11 persons blinded by hereditary retinal degeneration elicited by a subretinally implanted 16-electrode array used for light-independent direct stimulation of the retina is described. This device is part of the Tübingen retina implant, which also employs a light-sensitive, multiphotodiode array (MPDA). The ability to reliably recognize complex spatial percepts was investigated. Eleven blind volunteers received implants and participated in standardized psychophysical tests investigating the size and shape of perceptions elicited by single-electrode activation, multiple-electrode activation, and activation of compound patterns such as simplified letters. Visual percepts were elicited reliably in 8 of 11 patients. On single-electrode activation, percepts were generally described as round spots of light of distinguishable localization in the visual field. On activation of a pattern of electrodes, percepts matched that pattern when electrodes were activated sequentially. Patterns such as horizontal or vertical bars were identified reliably; the most recent participant was able to recognize simplified letters presented on the 16-electrode array. The smallest distance between sites of concurrent retinal stimulation still yielding discernible spots of light was assessed to be 280 μm, corresponding to a logMAR of 1.78. Subretinal electric stimulation can yield reliable, predictable percepts. Patterned perception is feasible, enabling blind persons to recognize shapes and discriminate different letters. Stimulation paradigms must be optimized, to further increase spatial resolution, demanding a better understanding of physical and biological effects of single versus repetitive stimulation (ClinicalTrials.gov number, NCT00515814).

Switching on the Lights: The Use of Optogenetics to Advance Retinal Gene Therapy

Photoreceptors carry a high number of mitochondria necessary to maintain their high metabolic rate. This allows them to respond rapidly to small changes in illumination. However, the metabolically demanding role of light reception appears to render photoreceptors particularly vulnerable to mutations; this is manifested in the many clinical forms of hereditary retinal degeneration (RD).1 Remarkably, in many cases the remainder of the retinal circuitry remains capable of firing despite the death of the photoreceptor cells.2,3 In this issue of Molecular Therapy, Caporale et al. exploit this residual capacity for signal transmission so as to endow retinal ganglion cells with the ability to take over the task of light detection from the photoreceptors in conditions of RD.4

Identification of CYP4V2 mutation in 21 families and overview of mutation spectrum in Bietti crystalline corneoretinal dystrophy

Bietti crystalline corneoretinal dystrophy (BCD, MIM 210370) is a common form of hereditary retinal degeneration in the Chinese population. BCD is caused by CYP4V2 mutations. Understanding the CYP4V2 mutational spectrum and associated phenotypes is of value for clinical practice. In this study, nine CYP4V2 mutations, including four novel ones (c.215-2A>G, c.761A>G, c.958C>T, and c.1169G>A), were detected in all 21 families with BCD. All patients with CYP4V2 mutations had phenotypes typical for BCD. As of now, 34 CYP4V2 mutations have been identified in 104 of 109 families (95.4%), affecting 204 of the 218 alleles (93.6%). Of the 34 mutations, c.802-8_810del17insGC, c.992A>C, and c.1091-2A>G are the most common mutations, accounting for 62.7%, 7.4%, and 6.4% of the 204 mutant alleles, respectively. The remaining 31 mutations were only detected in 1–6 alleles. Mutations in exons 7, 8, and 9 account for 83.3% of mutant alleles (64.7%, 9.3%, and 10.3%, respectively). Our results expand the mutation spectrum of CYP4V2 and demonstrate an overview of the CYP4V2 mutation spectrum and its frequency in families with BCD. BCD is a clinically and genetically homogenous disease.

Insight and Advancement in Hereditary Retinal Degenerations

Hereditary retinal degenerations comprise a diverse group of inherited genetic defects in one or more retinal or retinal pigment epithelial cellular proteins. Traditionally, anatomic classification based on clinical and histopathologic phenotype has been used to organize these disorders. In the modern era of advanced molecular biological techniques and genetic screening the current classification system may soon become obsolete, due to the fact that significant overlap between different retinal degenerations has been observed, resulting from variation in gene expression, common genetic pathways, and variable inheritance patterns. In this article, we review the various clinical disease entities, emphasize a genetic classification system, and give special attention to recent advances in molecular biology and gene therapy.

Insight and Advancement in Hereditary Retinal Degenerations

Hereditary retinal degenerations comprise a diverse group of inherited genetic defects in one or more retinal or retinal pigment epithelial cellular proteins. Traditionally, anatomic classification based on clinical and histopathological phenotype has been used to organise these disorders. In the modern era of advanced molecular biological techniques and genetic screening the current classification system may soon become obsolete, due to the fact that significant overlap between different retinal degenerations has been observed, resulting from variation in gene expression, common genetic pathways and variable inheritance patterns. In this article, we review the various clinical disease entities, emphasise a genetic classification system and give special attention to recent advances in molecular biology and gene therapy.

Gene-Based Therapies for Dominant Retinopathies

Over the past two decades, significant progress has been made in defining the molecular pathogenesis of hereditary retinal degenerations. Many of these are characterised by immense genetic heterogeneity. For example, in retinitis pigmentosa (RP), the most common form of this group of disorders, over 50 disease causing genes have been implicated, 20 of which are inherited in an autosomal dominant manner. Knowledge of the underlying genetic pathogenesis together with the availability of animal models and vectors for delivery has enabled exploration of gene-based therapies for inherited retinopathies. Notably, many studies have focused on treatment of recessive forms of these disorders and significant progress including ongoing clinical trials have been achieved. Progress in developing gene therapies for dominant retinopathies has been slower. One reason for this is that gene therapies for many dominant diseases, which are targeted to correcting the primary genetic defect, are likely to require suppression of the mutant gene. Alternative therapeutic approaches, which involve modulating secondary features associated with the disease pathology (such as ER stress or apoptosis) are also being explored. This review is focused on the development of gene-based therapies for dominantly inherited retinopathies. The main topics discussed are suppression technologies, preclinical animal models, retinal gene delivery and therapeutic strategies.

Exonic SINE insertion in STK38L causes canine early retinal degeneration ( erd)

Fine mapping followed by candidate gene analysis of erd — a canine hereditary retinal degeneration characterized by aberrant photoreceptor development — established that the disease cosegregates with a SINE insertion in exon 4 of the canine STK38L/NDR2 gene. The mutation removes exon 4 from STK38L transcripts and is predicted to remove much of the N terminus from the translated protein, including binding sites for S100B and Mob proteins, part of the protein kinase domain, and a Thr-75 residue critical for autophosphorylation. Although known to have roles in neuronal cell function, the STK38L pathway has not previously been implicated in normal or abnormal photoreceptor development. Loss of STK38L function in erd provides novel potential insights into the role of the STK38L pathway in neuronal and photoreceptor cell function, and suggests that genes in this pathway need to be considered as candidate genes for hereditary retinal degenerations.

Autosomal-Recessive Early-Onset Retinitis Pigmentosa Caused by a Mutation in PDE6G, the Gene Encoding the Gamma Subunit of Rod cGMP Phosphodiesterase

Retinitis pigmentosa (RP) is the most common form of hereditary retinal degeneration, with a worldwide prevalence of 1 in 4000. Over 30 genes and loci have been implicated in nonsyndromic autosomal-recessive (ar) RP. Genome-wide homozygosity mapping was conducted in two sibships from an extended consanguineous Muslim Arab Israeli family segregating ar severe early-onset RP. A shared homozygous region on chromosome 17q25.3 was identified in both sibships, with an overlap of 4.7 Mb. One of the genes located in this interval is PDE6G, encoding for the inhibitory gamma subunit of rod photoreceptor cyclic GMP-phosphodiesterase. Mutations in the genes encoding for the catalytic subunits of this holoenzyme, PDE6A and PDE6B, cause arRP. Sequencing of all coding exons, including exon-intron boundaries, revealed a homozygous single base change (c.187+1G>T) located in the conserved intron 3 donor splice site of PDE6G. This mutation cosegregated with the disease in the extended family. We used an in vitro splicing assay to demonstrate that this mutation leads to incorrect splicing. Affected individuals had markedly constricted visual fields. Both scotopic and photopic electroretinograms were severely reduced or completely extinct. Funduscopy showed typical bone spicule-type pigment deposits spread mainly at the midperiphery, as well as pallor of the optic disk. Macular involvement was indicated by the lack of foveal reflex and typical cystoid macular edema, proved by optical coherence tomography. These findings demonstrate the positive role of the gamma subunit in maintaining phosphodiesterase activity and confirm the contribution of PDE6G to the etiology of RP in humans.

Identification of a prevalent founder mutation in an Israeli Muslim Arab village confirms the role of PRCD in the aetiology of retinitis pigmentosa in humans

BackgroundRetinitis pigmentosa (RP) is the most common form of hereditary retinal degeneration. At least 32 genes and loci have been implicated in non-syndromic autosomal recessive RP. Progressive rod–cone degeneration is...

Effects of hereditary retinal degeneration due to a CEP290 mutation on the feline pupillary light reflex

To understand how progressive rod cone degeneration due to a mutation in CEP290 affects the pupillary light reflex (PLR) in domestic cats. Domestic cats identified as either normal wildtype (WT; n = 6), or homozygous for the rdAc mutation in CEP290 and having early stage retinal degeneration (stage 2, S2; n = 4), or advanced retinal degeneration (S4; n = 6). The effect of light on pupil size was measured over a series of 10-s pulses of white and chromatic light in cats lightly sedated with medetomidine. In WT cats, the PLR was characterized by a pronounced initial constriction that rapidly re-dilated during the stimulus (pupil escape), to a stable or sustained constriction. There was then a marked constriction at stimulus offset. Each component of the PLR was retained in affected cats, but with progressively reduced irradiance sensitivity from early to advanced retinal disease. The PLR of cats had multiple phases, with a remarkably high-amplitude 'paradoxical' off-constriction even in the absence of retinal disease. In rdAc cats, reduced irradiance sensitivity was consistent with progressive loss of rod and cone function. Based on previously characterized retinal pathology, this suggests the visual streak of the retina has a proportionally large contribution to PLR input. These findings support the hypothesis that the efficacy of planned therapeutic trials can be determined by careful evaluation of the PLR in cats.

Leber congenital amaurosis due to RPE65 mutations and its treatment with gene therapy

Leber congenital amaurosis (LCA) is a rare hereditary retinal degeneration caused by mutations in more than a dozen genes. RPE65, one of these mutated genes, is highly expressed in the retinal pigment epithelium where it encodes the retinoid isomerase enzyme essential for the production of chromophore which forms the visual pigment in rod and cone photoreceptors of the retina. Congenital loss of chromophore production due to RPE65-deficiency together with progressive photoreceptor degeneration cause severe and progressive loss of vision. RPE65-associated LCA recently gained recognition outside of specialty ophthalmic circles due to early success achieved by three clinical trials of gene therapy using recombinant adeno-associated virus (AAV) vectors. The trials were built on multitude of basic, pre-clinical and clinical research defining the pathophysiology of the disease in human subjects and animal models, and demonstrating the proof-of-concept of gene (augmentation) therapy. Substantial gains in visual function of clinical trial participants provided evidence for physiologically relevant biological activity resulting from a newly introduced gene. This article reviews the current knowledge on retinal degeneration and visual dysfunction in animal models and human patients with RPE65 disease, and examines the consequences of gene therapy in terms of improvement of vision reported.

Mutations in C2ORF71 Cause Autosomal-Recessive Retinitis Pigmentosa

With a worldwide prevalence of 1 in 4,000, retinitis pigmentosa (RP) is the most common form of hereditary retinal degeneration. More than 30 genes and loci have been implicated in nonsyndromic autosomal-recessive (ar) RP. Genome-wide homozygosity mapping was conducted in one Dutch and one Israeli family affected by arRP. The families were found to share a 5.9 Mb homozygous region on chromosome 2p23.1-p23.3. A missense variant in one of the genes residing in this interval, C2ORF71, has recently been reported to be associated with RP. C2ORF71, encoding a putative protein of 1,288 amino acids, was found to be specifically expressed in human retina. Furthermore, RT-PCR analysis revealed that in the mouse eye, C2orf71 is expressed as early as embryonic day 14. Mutation analysis detected a 1 bp deletion (c.946 del; p.Asn237MetfsX5) segregating with RP in the Dutch family, whereas a nonsense mutation (c.556C > T; p.Gln186X) was identified in the Israeli family. Microsatellite-marker analysis in additional Israeli families revealed cosegregation of a C2ORF71-linked haplotype in one other family, in which a 13 bp deletion (c.2756_2768 del; p.Lys919ThrfsX) was identified. Clinically, patients with mutations in C2ORF71 show signs of typical RP; these signs include poor night vision and peripheral field loss, typical retinal bone-spicule-type pigment deposits, pale appearance of the optic disk, and markedly reduced or completely extinguished electroretinograms. In conclusion, truncating mutations in C2ORF71 were identified in three unrelated families, thereby confirming the involvement of this gene in the etiology of arRP.

IRD1 and IRD2 Mice, Naturally Occurring Models of Hereditary Retinal Dysfunction, Show Late-Onset and Progressive Retinal Degeneration

Purpose: To elucidate whether Institute for Cancer Research (ICR) derived retinal dysfunction (IRD) 1 and IRD2 mice, spontaneous mouse models of rod-cone and rod dysfunction, respectively, develop age-related retinal degeneration.Materials and Methods: Morphological and morphometric examinations were performed in the retinas of both mutants from 1 to 18 months of age. The rate of apoptotic cell death was determined by TUNEL techniques. Electroretinography was performed on the IRD2 mice at various ages. Age-matched ICR mice were used as controls.Results: IRD1 and IRD2 mice showed a decrease in the thickness of the outer nuclear layer and a higher frequency of TUNEL-positive photoreceptor cells at 6 months of age compared with controls, and showed almost complete absence of the outer nuclear layer at 18 months of age. Light deprivation had no effect on the severity of the retinal degeneration. There were no differences in the number of cone nuclei among ICR, IRD1, and IRD2 mice at 12 months of age and the cones of the IRD2 mice were still functional at this age.Conclusions: IRD1 and IRD2 mice showed late-onset and progressive retinal degeneration.

Retinal degeneration in the Abyssinian and Somali cat (rdAc): correlation between genotype and phenotype and rdAc allele frequency in two continents

To characterize hereditary retinal degeneration in the Abyssinian cat (rdAc) in a recently established closed colony segregating for the rdAc mutation, and evaluate possible differences in the age of onset and progression of disease phenotype since the initial description of rdAc 25 years ago. The sample size of an earlier study was increased in order to determine the allele frequency in Abyssinian and Somali cats on a worldwide basis. Twenty rdAc affected cats from the closed animal facility, 87 Abyssinian and Somali cats for study of genotype-phenotype concordance, and DNA from 131 Abyssinian and Somali cats from Scandinavia, the UK and Australia for evaluation of the rdAc allele frequency. DNA was extracted from blood and buccal swabs using commercially available kits, followed by genotyping. Ophthalmic examinations were performed in the USA and Sweden by two board-certified veterinary ophthalmologists. A greater variation in the age of onset and progression of the disease was observed compared to that previously described. An excellent correlation between genotype and phenotype was observed. A population genetic survey revealed that the rdAc allele is in moderate abundance in the Abyssinian breed in Europe and Australia. Surprisingly, homozygosity for the mutant allele was observed in a Siamese cat with ophthalmoscopic findings similar to those originally described for affected rdAc individuals. Alertness to the potential of rdAc is needed on the part of the veterinary ophthalmology community, not only in Abyssinian and Somali cats but possibly also in other related cat breeds.

Spectral Domain Optical Coherence Tomography in Mouse Models of Retinal Degeneration

Spectral domain optical coherence tomography (SD-OCT) allows cross-sectional visualization of retinal structures in vivo. Here, the authors report the efficacy of a commercially available SD-OCT device to study mouse models of retinal degeneration. C57BL/6 and BALB/c wild-type mice and three different mouse models of hereditary retinal degeneration (Rho(-/-), rd1, RPE65(-/-)) were investigated using confocal scanning laser ophthalmoscopy (cSLO) for en face visualization and SD-OCT for cross-sectional imaging of retinal structures. Histology was performed to correlate structural findings in SD-OCT with light microscopic data. In C57BL/6 and BALB/c mice, cSLO and SD-OCT imaging provided structural details of frequently used control animals (central retinal thickness, CRT(C57BL/6) = 237 +/- 2 microm and CRT(BALB/c) = 211 +/- 10 microm). RPE65(-/-) mice at 11 months of age showed a significant reduction of retinal thickness (CRT(RPE65) = 193 +/- 2 microm) with thinning of the outer nuclear layer. Rho(-/-) mice at P28 demonstrated degenerative changes mainly in the outer retinal layers (CRT(Rho) = 193 +/- 2 microm). Examining rd1 animals before and after the onset of retinal degeneration allowed monitoring of disease progression (CRT(rd1 P11) = 246 +/- 4 microm, CRT(rd1 P28) = 143 +/- 4 microm). Correlation of CRT assessed by histology and SD-OCT was high (r(2) = 0.897). The authors demonstrated cross-sectional visualization of retinal structures in wild-type mice and mouse models for retinal degeneration in vivo using a commercially available SD-OCT device. This method will help to reduce numbers of animals needed per study by allowing longitudinal study designs and will facilitate characterization of disease dynamics and evaluation of putative therapeutic effects after experimental interventions.

A single-base substitution within an intronic repetitive element causes dominant retinitis pigmentosa with reduced penetrance

We report the study of a large American family displaying autosomal dominant retinitis pigmentosa with reduced penetrance, a form of hereditary retinal degeneration. Although the inheritance pattern and previous linkage mapping pointed to the involvement of the PRPF31 gene, extensive screening of all its exons and their boundaries failed in the past to reveal any mutation. In this work, we sequenced the entire PRPF31 genomic region by both the classical Sanger method and ultrahigh throughput (UHT) sequencing. Among the many variants identified, a single-base substitution (c.1374+654C>G) located deep within intron 13 and inside a repetitive DNA element was common to all patients and obligate asymptomatic carriers. This change created a new splice donor site leading to the synthesis of two mutant PRPF31 isoforms, degraded by nonsense-mediated mRNA decay. As a consequence, amounts of PRPF31 mRNA derived from the mutant allele were very reduced, with no evidence of mutant proteins being synthesized. Our results indicate that c.1374+654C>G causes retinitis pigmentosa via haploinsufficiency, similar to the vast majority of PRPF31 mutations described so far. We discuss the potential of UHT sequencing technologies in mutation screening and the continued identification of pathogenic splicing mutations buried deep within intronic regions.

Functional and structural assessment of retinal sheet allograft transplantation in feline hereditary retinal degeneration

To investigate whether sheets of fetal retinal allografts can integrate into the dystrophic Abyssinian cat retina with progressive rod cone degeneration. Fetal retinal sheets (cat gestational day 42), incubated with BDNF microspheres, were transplanted to the subretinal space of four cats at an early disease stage. Cats were studied by fundus examinations, bilateral full-field flash ERGs, and indocyanine green and fluorescein angiograms up to 4 months following surgery. E42 donor and transplanted eyes were analyzed by histology and immunohistochemistry for retinal markers. Funduscopy and angiography showed good integration of the transplants in two of four cats, including extension of host blood vessels into the transplant and some scarring in the host. In these two, transplants were found in the subretinal space with laminated areas, with photoreceptor outer segments in normal contacts with the host retinal pigment epithelium. In some areas, transplants appeared to be well-integrated within the host neural retina. Neither of these two cats showed functional improvement in ERGs. In the other two cats, only remnants of donor tissue were left. Transplants stained for all investigated cellular markers. No PKC immunoreactivity was detected in the fetal donor retina at E42, but developed in the 4-month-old grafts. Fetal sheet transplants can integrate well within a degenerating cat retina and develop good lamination of photoreceptors. Functional improvement was not demonstrated by ERG in cats with well-laminated grafts. Transplants need to be further evaluated in cat host retinas with a more advanced retinal degeneration using longer follow-up times.

Genetic heterogeneity in two consanguineous families segregating early onset retinal degeneration: The pitfalls of homozygosity mapping

Retinitis pigmentosa is the most common form of hereditary retinal degeneration, with a worldwide prevalence of 1 in 4,000. At least 28 genes and loci have been implicated in nonsyndromic autosomal recessive retinitis pigmentosa. Here we report two extended and highly consanguineous families segregating early onset retinitis pigmentosa. Despite the consanguinity in both families, we found allelic heterogeneity in one of them, in which affected individuals were compound heterozygotes for two different mutations of the CRB1 gene. In the second family we found evidence for locus heterogeneity. A novel homozygous mutation of RDH12 was found in only 14 of 17 affected individuals in this family. Our data indicate that in the other affected individuals the disease is caused by a different gene/s. These findings demonstrate that while homozygosity mapping is an efficient tool for identification of the underlying mutated genes in inbred families, both locus and allelic heterogeneity may occur even within the same consanguineous family. These observations should be taken into account, especially when studying common and heterogeneous recessive genetic conditions.

Two trans-acting eQTLs modulate the penetrance of PRPF31 mutations

Dominant mutations in the gene encoding the ubiquitously-expressed splicing factor PRPF31 cause retinitis pigmentosa, a form of hereditary retinal degeneration, with reduced penetrance. We and others have previously shown that penetrance is tightly correlated with PRPF31 expression, as lymphoblastoid cell lines (LCLs) from affected patients produce less abundant PRPF31 transcripts than LCLs from their unaffected relatives carrying the same mutation. We have investigated the genetic elements determining the variable expression of PRPF31, and therefore possibly influencing the penetrance of its mutations, by quantifying PRPF31 mRNA levels in LCLs derived from 15 CEPH families (200 individuals), representative of the general population. We found that PRPF31 transcript abundance was a highly variable and highly heritable character. Moreover, by linkage analysis we showed that PRPF31 expression was significantly associated with at least one expression quantitative trait locus (eQTL), spanning a 8.2-Mb region on chromosome 14q21-23. We also investigated a previously mapped penetrance factor located near PRPF31 itself in LCLs from individuals belonging to selected families segregating PRPF31 mutations that displayed reduced penetrance. Our results indicate that, despite its constant association with the non-mutant allele, this factor was able to modulate the expression of both PRPF31 alleles. Furthermore, we showed that LCLs from affected patients have less PRPF31 RNA than those of asymptomatic patients, even at the pre-splicing stage. Altogether, these data demonstrate that PRPF31 mRNA expression and consequently the penetrance of PRPF31 mutations is managed by diffusible compounds encoded by at least two modifiers, acting in a co-regulatory system on both PRPF31 alleles during transcription.