Gene therapy for Leber congenital amaurosis: advances and future directions

CRISPR-Cas9 correction of a nonsense mutation in LCA5 rescues lebercilin expression and localization in human retinal organoids

Mutations in the lebercilin-encoding gene LCA5 cause one of the most severe forms of Leber congenital amaurosis, an early-onset retinal disease that results in severe visual impairment. Here, we report on the generation of a patient-specific cellular model to study LCA5-associated retinal disease. CRISPR-Cas9 technology was used to correct a homozygous nonsense variant in LCA5 (c.835C>T; p.Q279∗) in patient-derived induced pluripotent stem cells (iPSCs). The absence of off-target editing in gene-corrected (isogenic) control iPSCs was demonstrated by whole-genome sequencing. We differentiated the patient, gene-corrected, and unrelated control iPSCs into three-dimensional retina-like cells, so-called retinal organoids. We observed opsin and rhodopsin mislocalization to the outer nuclear layer in patient-derived but not in the gene-corrected or unrelated control organoids. We also confirmed the rescue of lebercilin expression and localization along the ciliary axoneme within the gene-corrected organoids. Here, we show the potential of combining precise single-nucleotide gene editing with the iPSC-derived retinal organoid system for the generation of a cellular model of early-onset retinal disease.

RPE65 c.393T>A, p.(Asn131Lys): Novel Sequence Variant Detected

Background

Leber congenital amaurosis (LCA) is a monogenic, but genetically heterogenous disease, and at least 27 genes are implicated. This case report is aimed at providing evidence to link the novel variant RPE65 c.393T>A, p.(Asn131Lys), variant of uncertain significance (VUS), to clinical phenotype and to set the ground for objective assignment of pathogenicity confidence. Case Presentation. A case report of a female patient with LCA who manifested with nystagmus, night blindness, profound visual deficiency, and peripheral involvement of the retina consistent with RPE65 dystrophy. A thorough clinical examination, diagnostic evaluation, and genetic testing were performed. The patient was a compound heterozygote in trans form: RPE65 c.304G>T, p.(Glu102∗) pathogenic, and RPE65 c.393T>A, p.(Asn131Lys), VUS. The latter variant is absent in healthy controls and is considered harmful on in silico prediction.

Conclusions

We conclude that RPE65 c.393T>A, p.(Asn131Lys) contributed to the pathologic phenotype, demonstrating its significance clearly in the case presented, and should be reclassified according to the criteria of evidence as likely pathogenic. This being the case, patients with this specific variant are likely candidates for genetic treatment.

RPE65 and retinal dystrophy: Report of new and recurrent mutations

BACHGROUND

Leber congenital amaurosis (LCA) is a severe and congenital or early onset form of inherited retinitis pigmentosa (RP). To date, approximately 25 genes have been introduced in relation to LCA. In this regard, retinal pigment epithelium-specific 65 kDa (RPE65) is a well-known gene mutation that plays a role in the pathogenesis of 5-10% of LCA cases.

METHOS

Two individuals fromseparate families were subjected to ehole exome sequencing (WES). Causativevariants were searched further assessed using Sanger sequencing.

RESULTS

Here, two families with mutations in the RPE65 gene show severe and early onset LCA, as expected. In addition to the characterization of the phenotype, by reporting a new mutation (c.1451-1G>A), we further expand the mutation spectrum of RPE65. Likewise, as an interesting aspect of our study, we report on a previously reported RP-linked mutation associated with severe early onset LCA (c.T200G:p.L67R).

CONCLUSIONS

Considering this variant in different populations, it is likely that it represents a hotspot and affects the function of the coded protein. The variable expressivity of the phenotype can be assumed by the presence of the modifier allele(s) as a result of a different genetic background or the effect of different environments on phenotype expression.

The Progress of Gene Therapy for Leber's Optic Hereditary Neuropathy

Introduction:

Leber’s Optic Hereditary Neuropathy (LHON) is a common cause of teenaged blindness in both eyes for which there is currently no effective treatment. In 1871, the German ophthal-mologist Theodor Leber was the first to describe the clinical characteristics of his namesake disease, and through unremitting efforts over the past 100 years, researchers have continued to increase their under-standing of LHON. In recent years, using gene therapy, several groups have obtained breakthroughs in the treatment of the disease.

Conclusion:

In this article, we will review the challenging journey that researchers faced towards our current understanding of LHON, and describe the transition of gene therapy research for LHON from the bench to bedside.

Laboratory and clinical reliability of conformally coated subretinal implants

Despite recent developments and new treatments in ophthalmology there is nothing available to cure retinal degenerations like Retinitis Pigmentosa (RP) yet. One of the most advanced approaches to treat people that have gone blind due to RP is to replace the function of the degenerated photoreceptors by a microelectronic neuroprosthetic device. Basically, this subretinal active implant transforms the incoming light into electric pulses to stimulate the remaining cells of the retina. The functional time of such devices is a crucial aspect. In this paper the laboratory and clinical reliability of the two active subretinal implants Alpha IMS and Alpha AMS is presented. Based on clinical data the median operating life of the Alpha AMS is estimated to be 3.3 years with a one-sided lower 75 % confidence level of 2.0 years. This data shows a significant improvement of the device lifetime compared to the previous device Alpha IMS which shows a median lifetime of 0.6 years with a lower confidence bound (75 %) of 0.5 years. The results are in good agreement with laboratory data from accelerated aging tests of the implant components, showing an estimated median lifetime for Alpha IMS components of 0.7 years compared to the improved lifetime of Alpha AMS of 4.7 years.

Applications of CRISPR/Cas9 in retinal degenerative diseases

Gene therapy is a potentially effective treatment for retinal degenerative diseases. Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) system has been developed as a new genome-editing tool in ophthalmic studies. Recent advances in researches showed that CRISPR/Cas9 has been applied in generating animal models as well as gene therapy in vivo of retinitis pigmentosa (RP) and leber congenital amaurosis (LCA). It has also been shown as a potential attempt for clinic by combining with other technologies such as adeno-associated virus (AAV) and induced pluripotent stem cells (iPSCs). In this review, we highlight the main points of further prospect of using CRISPR/Cas9 in targeting retinal degeneration. We also emphasize the potential applications of this technique in treating retinal degenerative diseases.

Targeted Multifunctional Lipid ECO Plasmid DNA Nanoparticles as Efficient Non-viral Gene Therapy for Leber's Congenital Amaurosis

Development of a gene delivery system with high efficiency and a good safety profile is essential for successful gene therapy. Here we developed a targeted non-viral delivery system using a multifunctional lipid ECO for treating Leber’s congenital amaurosis type 2 (LCA2) and tested this in a mouse model. ECO formed stable nanoparticles with plasmid DNA (pDNA) at a low amine to phosphate (N/P) ratio and mediated high gene transfection efficiency in ARPE-19 cells because of their intrinsic properties of pH-sensitive amphiphilic endosomal escape and reductive cytosolic release (PERC). All-trans-retinylamine, which binds to interphotoreceptor retinoid-binding protein (IRBP), was incorporated into the nanoparticles via a polyethylene glycol (PEG) spacer for targeted delivery of pDNA into the retinal pigmented epithelium. The targeted ECO/pDNA nanoparticles provided high GFP expression in the RPE of 1-month-old Rpe65^−/− mice after subretinal injection. Such mice also exhibited a significant increase in electroretinographic activity, and this therapeutic effect continued for at least 120 days. A safety study in wild-type BALB/c mice indicated no irreversible retinal damage following subretinal injection of these targeted nanoparticles. All-trans-retinylamine-modified ECO/pDNA nanoparticles provide a promising non-viral platform for safe and effective treatment of RPE-specific monogenic eye diseases such as LCA2.

Retinol Dehydrogenases Regulate Vitamin A Metabolism for Visual Function

The visual system produces visual chromophore, 11-cis-retinal from dietary vitamin A, all-trans-retinol making this vitamin essential for retinal health and function. These metabolic events are mediated by a sequential biochemical process called the visual cycle. Retinol dehydrogenases (RDHs) are responsible for two reactions in the visual cycle performed in retinal pigmented epithelial (RPE) cells, photoreceptor cells and Müller cells in the retina. RDHs in the RPE function as 11-cis-RDHs, which oxidize 11-cis-retinol to 11-cis-retinal in vivo. RDHs in rod photoreceptor cells in the retina work as all-trans-RDHs, which reduce all-trans-retinal to all-trans-retinol. Dysfunction of RDHs can cause inherited retinal diseases in humans. To facilitate further understanding of human diseases, mouse models of RDHs-related diseases have been carefully examined and have revealed the physiological contribution of specific RDHs to visual cycle function and overall retinal health. Herein we describe the function of RDHs in the RPE and the retina, particularly in rod photoreceptor cells, their regulatory properties for retinoid homeostasis and future therapeutic strategy for treatment of retinal diseases.

Hypomorphic mutations identified in the candidate Leber congenital amaurosis gene CLUAP1

PURPOSE

Leber congenital amaurosis (LCA) is an early-onset form of retinal degeneration. Six of the 22 known LCA genes encode photoreceptor ciliary proteins. Despite the identification of 22 LCA genes, the genetic basis of ~30% of LCA patients remains unknown. We sought to investigate the cause of disease in the remaining 30% by examining cilia-associated genes.

METHODS

Whole-exome sequencing was performed on an LCA cohort of 212 unsolved probands previously screened for mutations in known retinal-disease genes. Immunohistochemistry using mouse retinas was used to confirm protein localization and zebrafish were used to perform rescue experiments.

RESULTS

A homozygous nonsynonymous mutation was found in a single proband in CLUAP1, a gene required for ciliogenesis and cilia maintenance. Cluap1 knockout zebrafish exhibit photoreceptor cell death as early as 5 days after fertilization, and rescue experiments revealed that our proband's mutation is significantly hypomorphic.

CONCLUSION

Consistent with the knowledge that CLUAP1 plays an important role in cilia function and that cilia are critical to photoreceptor function, our results indicate that hypomorphic mutations in CLUAP1 can result in dysfunctional photoreceptors without systemic abnormalities. This is the first report linking mutations in CLUAP1 to human disease and establishes CLUAP1 as a candidate LCA gene.Genet Med 18 10, 1044-1051.

rAAV-compatible MiniPromoters for restricted expression in the brain and eye

BACKGROUND

Small promoters that recapitulate endogenous gene expression patterns are important for basic, preclinical, and now clinical research. Recently, there has been a promising revival of gene therapy for diseases with unmet therapeutic needs. To date, most gene therapies have used viral-based ubiquitous promoters-however, promoters that restrict expression to target cells will minimize off-target side effects, broaden the palette of deliverable therapeutics, and thereby improve safety and efficacy. Here, we take steps towards filling the need for such promoters by developing a high-throughput pipeline that goes from genome-based bioinformatic design to rapid testing in vivo.

METHODS

For much of this work, therapeutically interesting Pleiades MiniPromoters (MiniPs; ~4 kb human DNA regulatory elements), previously tested in knock-in mice, were "cut down" to ~2.5 kb and tested in recombinant adeno-associated virus (rAAV), the virus of choice for gene therapy of the central nervous system. To evaluate our methods, we generated 29 experimental rAAV2/9 viruses carrying 19 different MiniPs, which were injected intravenously into neonatal mice to allow broad unbiased distribution, and characterized in neural tissues by X-gal immunohistochemistry for icre, or immunofluorescent detection of GFP.

RESULTS

The data showed that 16 of the 19 (84 %) MiniPs recapitulated the expression pattern of their design source. This included expression of: Ple67 in brain raphe nuclei; Ple155 in Purkinje cells of the cerebellum, and retinal bipolar ON cells; Ple261 in endothelial cells of brain blood vessels; and Ple264 in retinal Müller glia.

CONCLUSIONS

Overall, the methodology and MiniPs presented here represent important advances for basic and preclinical research, and may enable a paradigm shift in gene therapy.

A Novel KCNJ13 Nonsense Mutation and Loss of Kir7.1 Channel Function Causes Leber Congenital Amaurosis (LCA16)

Mutations in the KCNJ13 gene that encodes the inwardly rectifying potassium channel Kir7.1 cause snowflake vitreoretinal degeneration (SVD) and leber congenital amaurosis (LCA). Kir7.1 controls the microenvironment between the photoreceptors and the retinal pigment epithelium (RPE) and also contributes to the function of other organs such as uterus and brain. Heterologous expressions of the mutant channel have suggested a dominant-negative loss of Kir7.1 function in SVD, but parallel studies in LCA16 have been lacking. Herein, we report the identification of a novel nonsense mutation in the second exon of the KCNJ13 gene that leads to a premature stop codon in association with LCA16. We have determined that the mutation results in a severe truncation of the Kir7.1 C-terminus, alters protein localization, and disrupts potassium currents. Coexpression of the mutant and wild-type channel has no negative influence on the wild-type channel function, consistent with the normal clinical phenotype of carrier individuals. By suppressing Kir7.1 function in mice, we were able to reproduce the severe LCA electroretinogram phenotype. Thus, we have extended the observation that Kir7.1 mutations are associated with vision disorders to include novel insights into the molecular mechanism of disease pathobiology in LCA16.

Novel GUCY2D Gene Mutations in Japanese Male Twins with Leber Congenital Amaurosis

Purpose. Leber congenital amaurosis (LCA), a genetically and clinically heterogeneous disease, is the earliest onset retinitis pigmentosa (RP) and is the most severe of hereditary retinal dystrophies. This study was conducted to investigate genetic and clinical features of LCA in a set of Japanese male twins with LCA. Methods. To identify causative mutations, 74 genes known to cause RP or LCA were examined by targeted-next generation sequencing (NGS). Targeted-NGS was performed using a custom designed Agilent HaloPlex target enrichment kit with Illumina Miseq sequencer. Identified potential pathogenic mutations were confirmed using Sanger sequencing. Clinical analyses were based on ophthalmic examination, fundus photography, and electroretinography (ERG). Results. Compound heterozygous GUCY2D mutations of novel splicing mutation c.2113+2_2113+3insT and novel missense mutation p.L905P were detected in both twins. Their father and mother were heterozygous for c.2113+2_2113+3insT and p.L905P, respectively. The twins had phenotypic features similar to those previously reported in patients with GUCY2D mutations. This included early childhood onset of visual loss, nystagmus, unrecordable ERG, photophobia, and hyperopia. Conclusions. To the best of our knowledge, this is the first report of genetic and clinical features of Japanese LCA twins with GUCY2D mutation, which were detected using targeted-NGS.

Improvement in vision: a new goal for treatment of hereditary retinal degenerations

Introduction: Inherited retinal degenerations (IRDs) have long been considered untreatable and incurable. Recently, one form of early-onset autosomal recessive IRD, Leber congenital amaurosis (LCA) caused by mutations in RPE65 (retinal pigment epithelium-specific protein 65 kDa) gene, has responded with some improvement of vision to gene augmentation therapy and oral retinoid administration. This early success now requires refinement of such therapeutics to fully realize the impact of these major scientific and clinical advances.

Areas covered: Progress toward human therapy for RPE65-LCA is detailed from the understanding of molecular mechanisms to preclinical proof-of-concept research to clinical trials. Unexpected positive and complicating results in the patients receiving treatment are explained. Logical next steps to advance the clinical value of the therapeutics are suggested.

Expert opinion: The first molecularly based early-phase therapies for an IRD are remarkably successful in that vision has improved and adverse events are mainly associated with surgical delivery to the subretinal space. Yet, there are features of the gene augmentation therapeutic response, such as slowed kinetics of night vision, lack of foveal cone function improvement and relentlessly progressive retinal degeneration despite therapy, that still require research attention.

Localizing the RPGR protein along the cilium: a new method to determine efficacies to treat RPGR mutations

Retinal dystrophies constitute a group of clinically and genetically heterogeneous diseases that cause visual impairment. As treatments are not readily available, readout assays performed in patient-derived cells can aid in the development and comparative analysis of therapeutic approaches. We describe a new method with which the localization of the retinitis pigmentosa GTPase regulator (RPGR) protein along the cilium can be used as a measure for treatment efficacy. In a patient-derived fibroblast cell line, we found that the RPGR protein is mislocalized along the ciliary axoneme. The patient carried a point mutation that leads to skipping of RPGR exon 10. We confirmed that this skipping is causative for the impaired localization of RPGR using a U7 small nuclear RNA (U7snRNA)-based antisense approach in control cells. Treatment of the patient-derived fibroblasts with therapeutic U1snRNA significantly corrected the proteins' mislocalization. In this proof of principle study, we show that detecting the RPGR protein along the cilium provides a reliable and quantifiable readout assay to evaluate the efficacy of therapies intended to correct or silence RPGR gene mutations. This method opens the possibility to compare different therapeutic agents, and thus facilitate the identification of treatment options for the clinically and molecularly complex RPGR-associated diseases.

Genetic deletion of S-opsin prevents rapid cone degeneration in a mouse model of Leber congenital amaurosis

Mutations in RPE65 or lecithin-retinol acyltransferase (LRAT) disrupt 11-cis-retinal synthesis and cause Leber congenital amaurosis (LCA), a severe hereditary blindness occurring in early childhood. The pathology is attributed to a combination of 11-cis-retinal deficiency and photoreceptor degeneration. The mistrafficking of cone membrane-associated proteins including cone opsins (M- and S-opsins), cone transducin (Gαt2), G-protein-coupled receptor kinase 1 (GRK1) and guanylate cyclase 1 (GC1) has been suggested to play a role in cone degeneration. However, their precise role in cone degeneration is unclear. Here we investigated the role of S-opsin (Opn1sw) in cone degeneration in Lrat(-) (/-), a murine model for LCA, by genetic ablation of S-opsin. We show that deletion of just one allele of S-opsin from Lrat(-) (/-) mice is sufficient to prevent the rapid cone degeneration for at least 1 month. Deletion of both alleles of S-opsin prevents cone degeneration for an extended period (at least 12 months). This genetic prevention is accompanied by a reduction of endoplasmic reticulum (ER) stress in Lrat(-) (/-) photoreceptors. Despite cone survival in Opn1sw(-/-)Lrat(-) (/-) mice, cone membrane-associated proteins (e.g. Gαt2, GRK1 and GC1) continue to have trafficking problems. Our results suggest that cone opsins are the 'culprit' linking 11-cis-retinal deficiency to cone degeneration in LCA. This result has important implications for the current gene therapy strategy that emphasizes the need for a combinatorial therapy to both improve vision and slow photoreceptor degeneration.

A novel mutation in the RPE65 gene causing Leber congenital amaurosis and its transcriptional expression in vitro

The retinal pigment epithelium-specific 65 kDa protein is an isomerase encoded by the RPE65 gene (MIM 180069) that is responsible for an essential enzymatic step required for the function of the visual cycle. Mutations in the RPE65 gene cause not only subtype II of Leber congenital amaurosis (LCA) but also early-onset severe retinal dystrophy (EOSRD). This study aims to investigate a Chinese case diagnosed as EOSRD and to characterize the polymorphisms of the RPE65 gene. A seven-year-old girl with clinical symptoms of EOSRD and her parents were recruited into this study. Ophthalmologic examinations, including best-corrected visual acuity, slit-lamp, Optical coherence tomography (OCT), and fundus examination with dilated pupils, were performed to determine the clinical characteristics of the whole family. We amplified and sequenced the entire coding region and adjacent intronic sequences of the coding regions of the RPE65 gene for the whole family to explore the possible mutation. Our results demonstrate that the patient exhibited the typical clinically features of EOSRD. Her bilateral decimal visual acuity was 0.3 and 0.4 in the left and right eyes, respectively. Spectral-domain optical coherence tomography (SD-OCT) was used to assess the retinal stratification for the whole family. All together, we identified four mutations within the RPE65 gene (c.1056G>A, c.1243+2T>A, c.1338+20A>C and c.1590C>A) in the patient. Among the four mutations, c.1056G>A and c.1338+20A>C had been reported previously and another two were found for the first time in this study. Her mother also carried the novel mutation (c.1243+2T>A). Either a single or a compound heterozygous or a homozygous one mutation is expected to cause EOSRD because mutations of RPE65 gene usually cause an autosomal recessive disease. Therefore, we speculate that the c.1590C>A mutation together with the c.1243+2T>A mutation may cause the patient’s phenotype.

AAV2 delivery of Flt23k intraceptors inhibits murine choroidal neovascularization

Long-term inhibition of extracellular vascular endothelial growth factor (VEGF) in the treatment of age-related macular degeneration (AMD) may induce retinal neuronal toxicity and risk other side effects. We developed a novel strategy which inhibits retinal pigment epithelium (RPE)-derived VEGF, sparing other highly sensitive retinal tissues. Flt23k, an intraceptor inhibitor of VEGF, was able to inhibit VEGF in vitro. Adeno-associated virus type 2 (AAV2)-mediated expression of Flt23k was maintained for up to 6 months postsubretinal injection in mice. Flt23k was able to effectively inhibit laser-induced murine choroidal neovascularization (CNV). VEGF levels in the RPE/choroid complex decreased significantly in AAV2.Flt23k treated eyes. Neither retinal structure detected by Heidelberg Spectralis nor function measured by electroretinography (ERG) was adversely affected by treatment with AAV2.Flt23k. Hence AAV2.Flt23k can effectively maintain long-term expression and inhibit laser-induced CNV in mice through downregulation of VEGF while maintaining a sound retinal safety profile. These findings suggest a promising novel approach for the treatment of CNV.

Dog as a model in studies on human hereditary diseases and their gene therapy

During the last 15 years spectacular progress has been achieved in knowledge on the dog genome organization and the molecular background of hereditary diseases in this species. A majority of canine genetic diseases have their counterparts in humans and thus dogs are considered as a very important large animal model in human biomedicine. Among canine monogenic diseases with known causative gene mutations there are two large groups classified as retinal dystrophies and lysosomal storage diseases. Specific types of these diseases are usually diagnosed in a single or several breeds. A well known disorder, restricted to a single breed, is congenital stationary night blindness described in Briards. This disease is a counterpart of Leber amaurosis in children. On the other hand, one of the most common monogenic human diseases (Duchenne muscular dystrophy), has its canine counterparts in several breeds (e.g., the Golden retriever, Beagle and German short-haired pointer). For some of the canine diseases gene therapy strategy was successfully applied, e.g., for congenital stationary night blindness, rod-cone dystrophy and muccopolysaccharydoses type I, IIIB and VII. Since phenotypic variability between the breeds is exceptionally high, the dog is an interesting model to study the molecular background of congenital malformations (e.g., dwarfism and osteoporosis imperfecta). Also disorders of sexual development (DSD), especially testicular or ovotesticular DSD (78,XX; SRY-negative), which is widely distributed across dozens of breeds, are of particular interest. Studies on the genetic background of canine cancers, a major health problem in this species, are also quite advanced. On the other hand, genetic studies on canine counterparts of major human complex diseases (e.g., obesity, the metabolic syndrome and diabetes mellitus) are still in their infancy.

The prevalence of neutralizing antibodies against adeno-associated virus capsids is reduced in young Japanese individuals

Pre-existing antibodies against adeno-associated virus (AAV), caused by natural AAV infections, interfere with recombinant AAV vector-mediated gene transfer. We studied the prevalence of neutralizing antibodies against AAV serotypes 1, 2, 5, 8, and 9 in healthy subjects (n = 85) and hemophilia patients (n = 59) in a Japanese population. For healthy subjects, the prevalence of neutralizing antibodies against AAV serotypes 1, 2, 5, 8, and 9 was 36.5%, 35.3%, 37.6%, 32.9%, and 36.5%, respectively, while that in hemophilia patients was 39.7%, 28.8%, 35.6%, 32.9%, and 27.4%, respectively. There was no difference in the prevalence of neutralizing antibody against each AAV serotype between the healthy subjects and the hemophilia patients. The prevalence of neutralizing antibodies against all AAV serotypes increased with age in both healthy subjects and hemophilia patients. High titers of neutralizing antibodies against AAV2 (≥1:224) and AAV8 (≥1:224) were more evident in older individuals (≥42 years old). Approximately 50% of all screened individuals were seronegative for neutralizing antibodies against each AAV tested, while approximately 25% of individuals were seropositive for each AAV serotype tested. The prevalence of seronegativity for all AAV serotypes was 67.0% (healthy subjects, 68.6%; hemophilia patients, 65.0%) and 18.6% (healthy subjects, 20.5%; hemophilia patients, 15.7%) in young (<42 years old) and older subjects (≥42 years old), respectively. The findings from this study suggested that young subjects are more likely to be eligible for gene therapy based on AAV vectors delivered via an intravascular route because of the low prevalence of antibodies to AAV capsids.

Mutational screening of LCA genes emphasizing RPE65 in South Indian cohort of patients

Background

Leber congenital amaurosis (LCA) is the most severe form of inherited retinal visual impairment in children. So far, mutations in more than 20 genes have been known to cause LCA and among them, RPE65 is a suitable candidate for gene therapy. The mutational screenings of RPE65 and other LCA genes are requisite in support of emerging gene specific therapy for LCA. Therefore, we have carried out a comprehensive LCA genes screening using a combined approach of direct sequencing and DNA microarray based Asper chip analysis.

Methodology/Principal Findings

Thirty clinically diagnosed index LCA cases from Southern India were screened for coding and flanking intronic regions of RPE65 through direct sequencing. Among thirty, 25 cases excluded from RPE65 mutations were subjected to Asper chip analysis, testing 784 known pathogenic variations in 15 major LCA genes. In RPE65 screening, four different pathogenic variations including two novel (c.361insT & c.939T>A) and two known (c.394G>A & c.361delT) mutations were identified in five index cases. In the chip analysis, seven known pathogenic mutations were identified in six index cases, involving genes GUCY2D, RPGRIP1, AIPL1, CRX and IQCB1. Overall, 11 out of 30 LCA cases (36.6%) revealed pathogenic variations with the involvement of RPE65 (16.6%), GUCY2D (10%), RPGRIP1 (3.3%), AIPL1 (3.3%) and CRX & IQCB1 (3.3%).

Conclusions/Significance

Our study suggests that such combined screening approach is productive and cost-effective for mutation detection and can be applied in Indian LCA cohort for molecular diagnosis and genetic counselling.

Persistence of non-viral vector mediated RPE65 expression: case for viability as a gene transfer therapy for RPE-based diseases

Mutations in the retinal pigment epithelium (RPE) gene RPE65 are associated with multiple blinding diseases including Leber's Congenital Amaurosis (LCA). Our goal has been to develop persistent, effective non-viral genetic therapies to treat this condition. Using precisely engineered DNA vectors and high capacity compacted DNA nanoparticles (NP), we previously demonstrated that both plasmid and NP forms of VMD2-hRPE65-S/MAR improved the disease phenotypes in an rpe65(-/-) model of LCA up to 6 months post-injection (PI), however the duration of this treatment efficacy was not established. Here, we test the ability of these vectors to sustain gene expression and phenotypic improvement for the life of the animal. NPs or naked DNA were subretinally injected in rpe65(-/-) mice at postnatal day (P) 16 and evaluated at 15 months PI. Quantitative real-time PCR (qRT-PCR) and immunofluorescence were performed at PI-15 months and demonstrated appreciable expression of transferred RPE65 (levels were 32% of wild-type [WT] for NPs and 44% of WT for naked DNA). No reduction in expression at the message level was observed from PI-6 month data. Spectral electroretinography (ERG) demonstrated significant improvement in cone ERG amplitudes in treated versus uninjected animals. Most importantly, we also observed reduced fundus autofluorescence in the eyes injected with NP and naked DNA compared to uninjected counterparts. Consistent with these observations, biochemical studies showed a reduction in the accumulation of toxic retinyl esters in treated mice, suggesting that the transferred hRPE65 was functional. These critical results indicate that both NP and uncompacted plasmid VMD2-hRPE65-S/MAR can mediate persistent, long-term improvement in an RPE-associated disease phenotype, and suggest that DNA NPs, which are non-toxic and have a large payload capacity, expand the treatment repertoire available for ocular gene therapy.

Genetic testing for inherited ocular disease: delivering on the promise at last?

Genetic testing is of increasing clinical utility for diagnosing inherited eye disease. Clarifying a clinical diagnosis is important for accurate estimation of prognosis, facilitating genetic counselling and management of families, and in the future will direct gene-specific therapeutic strategies. Often, precise diagnosis of genetic ophthalmic conditions is complicated by genetic heterogeneity, a difficulty that the so-called 'next-generation sequencing' technologies promise to overcome. Despite considerable counselling and ethical complexities, next-generation sequencing offers to revolutionize clinical practice. This will necessitate considerable adjustment to standard practice but has the power to deliver a personalized approach to genomic medicine for many more patients and enhance the potential for preventing vision loss.

Vitamin A derivatives as treatment options for retinal degenerative diseases

The visual cycle is a sequential enzymatic reaction for vitamin A, all-trans-retinol, occurring in the outer layer of the human retina and is essential for the maintenance of vision. The central source of retinol is derived from dietary intake of both retinol and pro-vitamin A carotenoids. A series of enzymatic reactions, located in both the photoreceptor outer segment and the retinal pigment epithelium, transform retinol into the visual chromophore 11-cis-retinal, regenerating visual pigments. Retina specific proteins carry out the majority of the visual cycle, and any significant interruption in this sequence of reactions is capable of causing varying degrees of blindness. Among these important proteins are Lecithin:retinol acyltransferase (LRAT) and retinal pigment epithelium-specific 65-kDa protein (RPE65) known to be responsible for esterification of retinol to all-trans-retinyl esters and isomerization of these esters to 11-cis-retinal, respectively. Deleterious mutations in these genes are identified in human retinal diseases that cause blindness, such as Leber congenital amaurosis (LCA) and retinitis pigmentosa (RP). Herein, we discuss the pathology of 11-cis-retinal deficiency caused by these mutations in both animal disease models and human patients. We also review novel therapeutic strategies employing artificial visual chromophore 9-cis-retinoids which have been employed in clinical trials involving LCA patients.

Long-term efficacy of ciliary muscle gene transfer of three sFlt-1 variants in a rat model of laser-induced choroidal neovascularization

Inhibition of vascular endothelial growth factor (VEGF) has become the standard of care for patients presenting with wet age-related macular degeneration. However, monthly intravitreal injections are required for optimal efficacy. We have previously shown that electroporation enabled ciliary muscle gene transfer results in sustained protein secretion into the vitreous for up to 9 months. Here, we evaluated the long-term efficacy of ciliary muscle gene transfer of three soluble VEGF receptor-1 (sFlt-1) variants in a rat model of laser-induced choroidal neovascularization (CNV). All three sFlt-1 variants significantly diminished vascular leakage and neovascularization as measured by fluorescein angiography (FA) and flatmount choroid at 3 weeks. FA and infracyanine angiography demonstrated that inhibition of CNV was maintained for up to 6 months after gene transfer of the two shortest sFlt-1 variants. Throughout, clinical efficacy was correlated with sustained VEGF neutralization in the ocular media. Interestingly, treatment with sFlt-1 induced a 50% downregulation of VEGF messenger RNA levels in the retinal pigment epithelium and the choroid. We demonstrate for the first time that non-viral gene transfer can achieve a long-term reduction of VEGF levels and efficacy in the treatment of CNV.

A review of therapeutic prospects of non-viral gene therapy in the retinal pigment epithelium

Ocular gene therapy has been extensively explored in recent years as a therapeutic avenue to target diseases of the cornea, retina and retinal pigment epithelium (RPE). Adeno-associated virus (AAV)-mediated gene therapy has shown promise in several RPE clinical trials but AAVs have limited payload capacity and potential immunogenicity. Traditionally however, non-viral alternatives have been plagued by low transfection efficiency, short-term expression and low expression levels. Recently, these drawbacks have begun to be overcome by the use of specialty carriers such as polylysine, liposomes, or polyethyleneimines, and by inclusion of suitable DNA elements to enhance gene expression and longevity. Recent advancements in the field have yielded non-viral vectors that have favorable safety profiles, lack immunogenicity, exhibit long-term elevated gene expression, and show efficient transfection in the retina and RPE, making them poised to transition to clinical applications. Here we discuss the advancements in nanotechnology and vector engineering that have improved the prospects for clinical application of non-viral gene therapy in the RPE.

Nucleic acid delivery: roles in biogerontological interventions

Prolongation of longevity is a history-long desire of humans. Driven by the genetic contribution to longevity and the remarkable plasticity of healthy lifespan as demonstrated in animal models, arduous efforts have been directed to aging and longevity research over the years. Today, our understanding of lifespan determination is much greater than it was in the past, but administrable interventions for longevity enhancement are still virtually absent. The aim of this article is to highlight the technical gap between basic biogerontological research and intervention development, and to explore the importance of nucleic acid (NA) delivery technologies in bridging the gap. It is hoped that this article can engender more awareness of the roles of NA delivery technologies in biogerontological interventions, particularly NA therapy.