Clinical Perspective: Treating RPE65-Associated Retinal Dystrophy
Authors: Albert M. Maguire, Jean Bennett, Elena M. Aleman, Bart P. Leroy, Tomas S. Aleman
Journal: Molecular Therapy (2020)

Until recently, there was no approved treatment for a retinal degenerative disease. Subretinal injection of a recombinant adeno-associated virus (AAV) delivering the normal copy of the human RPE65 cDNA led to reversal of blindness first in animal models and then in humans. This led to the first US Food and Drug Administration (FDA)-approved gene therapy product for a genetic disease, voretigene neparvovec-rzyl (Luxturna). Luxturna was then approved by the European Medicines Association and is now available in the US through Spark Therapeutics and worldwide through Novartis. Not only has treatment with Luxturna changed the lives of people previously destined to live a life of blindness, but it has fueled interest in developing additional gene therapy reagents targeting numerous other genetic forms of inherited retinal disease. This review describes many of the considerations for administration of Luxturna and describes how lessons from experience with Luxturna could lead to additional gene-based treatments of blindness. Until recently, there was no approved treatment for a retinal degenerative disease. Subretinal injection of a recombinant adeno-associated virus (AAV) delivering the normal copy of the human RPE65 cDNA led to reversal of blindness first in animal models and then in humans. This led to the first US Food and Drug Administration (FDA)-approved gene therapy product for a genetic disease, voretigene neparvovec-rzyl (Luxturna). Luxturna was then approved by the European Medicines Association and is now available in the US through Spark Therapeutics and worldwide through Novartis. Not only has treatment with Luxturna changed the lives of people previously destined to live a life of blindness, but it has fueled interest in developing additional gene therapy reagents targeting numerous other genetic forms of inherited retinal disease. This review describes many of the considerations for administration of Luxturna and describes how lessons from experience with Luxturna could lead to additional gene-based treatments of blindness. Inherited retinal degenerations (IRDs) are a large group of molecularly and phenotypically heterogeneous diseases. Disease behavior and severity, which often modulate common phenotypic features are used to clinically subclassify these conditions. Leber congenital amaurosis (LCA) is a subgroup of IRDs (∼5% of all IRDs, prevalence ∼1:80,000–1:200,000) characterized by severe vision loss occurring during the first year of life.1Stone E.M. Andorf J.L. Whitmore S.S. DeLuca A.P. Giacalone J.C. Streb L.M. Braun T.A. Mullins R.F. Scheetz T.E. 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Nystagmus, sluggish pupillary reflexes or amaurotic pupils, and a severely reduced or non-detectable electroretinogram (ERG) are sufficient to confirm this diagnosis.5den Hollander A.I. Roepman R. Koenekoop R.K. Cremers F.P. Leber congenital amaurosis: genes, proteins and disease mechanisms.Prog. Retin. Eye Res. 2008; 27: 391-419Crossref PubMed Scopus (559) Google Scholar Presentations later in life but before the age of 5–10 are grouped under the name early-onset severe retinal dystrophy (EOSRD), severe early childhood onset retinal dystrophy (SECORD), early-onset retinal degeneration (EORD), or juvenile/early-onset retinitis pigmentosa, overlapping terms intended to distinguish these presentations from LCA.6Chao D.L. Burr A. Pennesi M. RPE65-related Leber congenital amaurosis / early-onset severe retinal dystrophy.in: Adam M.P. Ardinger H.H. Pagon R.A. GeneReviews. University of Washington, 1993https://www.ncbi.nim.nih.books/NBK549574/Google Scholar,7Weleber R.G. Michaelides M. 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The RPE65 gene, which is expressed in the RPE, plays a key role in the retinoid cycle as it encodes retinoid isomerohydrolase.9Hamel C.P. Tsilou E. Pfeffer B.A. Hooks J.J. Detrick B. Redmond T.M. Molecular cloning and expression of RPE65, a novel retinal pigment epithelium-specific microsomal protein that is post-transcriptionally regulated in vitro.J. Biol. Chem. 1993; 268: 15751-15757Abstract Full Text PDF PubMed Google Scholar, 10Hamel C.P. Jenkins N.A. Gilbert D.J. Copeland N.G. Redmond T.M. The gene for the retinal pigment epithelium-specific protein RPE65 is localized to human 1p31 and mouse 3.Genomics. 1994; 20: 509-512Crossref PubMed Scopus (0) Google Scholar, 11Marlhens F. Bareil C. Griffoin J.M. Zrenner E. Amalric P. Eliaou C. Liu S.Y. Harris E. Redmond T.M. Arnaud B. et al.Mutations in RPE65 cause Leber's congenital amaurosis.Nat. Genet. 1997; 17: 139-141Crossref PubMed Google Scholar, 12Tsilou E. Hamel C.P. Yu S. Redmond T.M. RPE65, the major retinal pigment epithelium microsomal membrane protein, associates with phospholipid liposomes.Arch. Biochem. Biophys. 1997; 346: 21-27Crossref PubMed Scopus (0) Google Scholar, 13Redmond T.M. Hamel C.P. Genetic analysis of RPE65: from human disease to mouse model.Methods Enzymol. 2000; 316: 705-724Crossref PubMed Google Scholar This enzyme regenerates 11-cis retinal, the chromophore that plays an essential role in phototransduction in photoreceptor cells.14Redmond T.M. Yu S. Lee E. Bok D. Hamasaki D. Chen N. Goletz P. Ma J.X. Crouch R.K. Pfeifer K. Rpe65 is necessary for production of 11-cis-vitamin A in the retinal visual cycle.Nat. Genet. 1998; 20: 344-351Crossref PubMed Scopus (747) Google Scholar Bi-allelic loss-of-function mutations in RPE65 result in either a lack of RPE65 protein or protein that is non-functional. Without this protein, photoreceptors have severely impaired responses to light and ultimately degenerate. The biochemical deficit explains the early-onset symptoms of the disease.11Marlhens F. Bareil C. Griffoin J.M. Zrenner E. Amalric P. Eliaou C. Liu S.Y. Harris E. Redmond T.M. Arnaud B. et al.Mutations in RPE65 cause Leber's congenital amaurosis.Nat. Genet. 1997; 17: 139-141Crossref PubMed Google Scholar,15Kumaran N. Rubin G.S. Kalitzeos A. Fujinami K. Bainbridge J.W.B. Weleber R.G. Michaelides M. A cross-sectional and longitudinal study of retinal sensitivity in RPE65-associated Leber congenital amaurosis.Invest. Ophthalmol. Vis. Sci. 2018; 59: 3330-3339Crossref PubMed Scopus (5) Google Scholar, 16Lotery A.J. Namperumalsamy P. Jacobson S.G. Weleber R.G. Fishman G.A. Musarella M.A. Hoyt C.S. Héon E. Levin A. Jan J. et al.Mutation analysis of 3 genes in patients with Leber congenital amaurosis.Arch. Ophthalmol. 2000; 118: 538-543Crossref PubMed Google Scholar, 17Van Hooser J.P. Aleman T.S. He Y.G. Cideciyan A.V. Kuksa V. Pittler S.J. Stone E.M. Jacobson S.G. Palczewski K. Rapid restoration of visual pigment and function with oral retinoid in a mouse model of childhood blindness.Proc. Natl. Acad. Sci. USA. 2000; 97: 8623-8628Crossref PubMed Scopus (218) Google Scholar, 18Gu S.M. Thompson D.A. Srikumari C.R. Lorenz B. Finckh U. Nicoletti A. Murthy K.R. Rathmann M. Kumaramanickavel G. Denton M.J. Gal A. Mutations in RPE65 cause autosomal recessive childhood-onset severe retinal dystrophy.Nat. Genet. 1997; 17: 194-197Crossref PubMed Scopus (503) Google Scholar, 19Lorenz B. Gyürüs P. Preising M. Bremser D. Gu S. Andrassi M. Gerth C. Gal A. Early-onset severe rod-cone dystrophy in young children with RPE65 mutations.Invest. Ophthalmol. Vis. Sci. 2000; 41: 2735-2742PubMed Google Scholar, 20Jacobson S.G. Aleman T.S. Cideciyan A.V. Roman A.J. Sumaroka A. Windsor E.A. Schwartz S.B. Heon E. Stone E.M. Defining the residual vision in Leber congenital amaurosis caused by RPE65 mutations.Invest. Ophthalmol. Vis. Sci. 2009; 50: 2368-2375Crossref PubMed Scopus (89) Google Scholar RPE65-LCA became the disease model for an IRD phenotypic pattern where a relatively preserved retina is associated with a disproportionately severe vision loss.21Jacobson S.G. Aleman T.S. Cideciyan A.V. Sumaroka A. Schwartz S.B. Windsor E.A. Traboulsi E.I. Heon E. Pittler S.J. Milam A.H. et al.Identifying photoreceptors in blind eyes caused by RPE65 mutations: prerequisite for human gene therapy success.Proc. Natl. Acad. Sci. USA. 2005; 102: 6177-6182Crossref PubMed Scopus (209) Google Scholar There are individuals with bi-allelic RPE65 mutations whose disease may be diagnosed as retinitis pigmentosa (RP) later in life, presumably due to presence of a hypomorphic allele, but who share all of the key phenotypic features of patients with LCA/EOSRD.19Lorenz B. Gyürüs P. Preising M. Bremser D. Gu S. Andrassi M. Gerth C. Gal A. Early-onset severe rod-cone dystrophy in young children with RPE65 mutations.Invest. Ophthalmol. 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Clinical phenotypes in carriers of Leber congenital amaurosis mutations.Ophthalmology. 2005; 112: 349-356Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar There are an estimated 1,000–2,000 individuals in the US with RPE65-IRDs. The true prevalence will become apparent as more individuals with IRDs are genotyped. RPE65 mutations occur in all ethnic groups, and they are thought to account for 5%–6% of LCA. The prevalence is in the range of 2–3 per 100,000 individuals.2Koenekoop R.K. An overview of Leber congenital amaurosis: a model to understand human retinal development.Surv. Ophthalmol. 2004; 49: 379-398Abstract Full Text Full Text PDF PubMed Scopus (193) Google Scholar,25Stone E.M. Leber congenital amaurosis—a model for efficient genetic testing of heterogeneous disorders: LXIV Edward Jackson Memorial Lecture.Am. J. Ophthalmol. 2007; 144: 791-811Abstract Full Text Full Text PDF PubMed Scopus (224) Google Scholar There are examples of greater frequency of RPE65 disease due to founder effects in geographically isolated populations, including in the Netherlands and in Israel, however.26Yzer S. van den Born L.I. Schuil J. Kroes H.Y. van Genderen M.M. Boonstra F.N. van den Helm B. Brunner H.G. Koenekoop R.K. Cremers F.P. A Tyr368His RPE65 founder mutation is associated with variable expression and progression of early onset retinal dystrophy in 10 families of a genetically isolated population.J. Med. Genet. 2003; 40: 709-713Crossref PubMed Google Scholar,27Banin E. Bandah-Rozenfeld D. Obolensky A. Cideciyan A.V. Aleman T.S. Marks-Ohana D. Sela M. Boye S. Sumaroka A. Roman A.J. et al.Molecular anthropology meets genetic medicine to treat blindness in the North African Jewish population: human gene therapy initiated in Israel.Hum. Gene Ther. 2010; 21: 1749-1757Crossref PubMed Scopus (55) Google Scholar As is true with other autosomal recessive conditions, there can be an increased prevalence in the disease in consanguineous populations. Much of what is known about the pathogenesis of RPE65 disease comes from studies of naturally occurring and genetically engineered animal models.28Acland G.M. Aguirre G.D. Bennett J. Aleman T.S. Cideciyan A.V. Bennicelli J. Dejneka N.S. Pearce-Kelling S.E. Maguire A.M. Palczewski K. et al.Long-term restoration of rod and cone vision by single dose rAAV-mediated gene transfer to the retina in a canine model of childhood blindness.Mol. Ther. 2005; 12: 1072-1082Abstract Full Text Full Text PDF PubMed Scopus (365) Google Scholar, 29Acland G.M. Aguirre G.D. Ray J. Zhang Q. Aleman T.S. Cideciyan A.V. Pearce-Kelling S.E. Anand V. Zeng Y. Maguire A.M. et al.Gene therapy restores vision in a canine model of childhood blindness.Nat. 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Retinal dystrophy of Swedish briard/briard-beagle dogs is due to a 4-bp deletion in RPE65.Genomics. 1999; 57: 57-61Crossref PubMed Scopus (138) Google Scholar,33Aguirre G.D. Baldwin V. Pearce-Kelling S. Narfström K. Ray K. Acland G.M. Congenital stationary night blindness in the dog: common mutation in the RPE65 gene indicates founder effect.Mol. Vis. 1998; 4: 23PubMed Google Scholar Some animals have nystagmus. The ERGs show markedly reduced to non-detectable rod- and cone-mediated responses. ERGs, however, may be clearly detectable with the use of bright stimuli, consistent with an insensitive system.28Acland G.M. Aguirre G.D. Bennett J. Aleman T.S. Cideciyan A.V. Bennicelli J. Dejneka N.S. Pearce-Kelling S.E. Maguire A.M. Palczewski K. et al.Long-term restoration of rod and cone vision by single dose rAAV-mediated gene transfer to the retina in a canine model of childhood blindness.Mol. 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Aleman T.S. Cideciyan A.V. Roman A.J. Sumaroka A. Mullins C.L. Boye S.L. Hauswirth W.W. Jacobson S.G. Retinal disease in Rpe65-deficient mice: comparison to human Leber congenital amaurosis due to RPE65 mutations.Invest. Ophthalmol. Vis. Sci. 2010; 51: 5304-5313Crossref PubMed Scopus (23) Google Scholar,37Aleman T. Cideciyan A. Bennett J. Cheung A. Glover E. Furushima M. Milam A.H. Jacobson S.G. Natural history of retinal function and structure in the Rpe65−/− murine model of Leber congenital amaurosis.Invest. Ophthalmol. Vis. Sci. 2003; 44: 4920PubMed Google Scholar,38Aleman T.S. Jacobson S.G. Chico J.D. Scott M.L. Cheung A.Y. Windsor E.A. Furushima M. Redmond T.M. Bennett J. Palczewski K. Cideciyan A.V. Impairment of the transient pupillary light reflex in Rpe65−/− mice and humans with Leber congenital amaurosis.Invest. Ophthalmol. Vis. Sci. 2004; 45: 1259-1271Crossref PubMed Scopus (0) Google Scholar RPE65-IRD generally presents before the age of 5 as LCA or an EOSRD.39Thompson D.A. Gyürüs P. Fleischer L.L. Bingham E.L. McHenry C.L. Apfelstedt-Sylla E. Zrenner E. Lorenz B. Richards J.E. Jacobson S.G. et al.Genetics and phenotypes of RPE65 mutations in inherited retinal degeneration.Invest. Ophthalmol. Vis. Sci. 2000; 41: 4293-4299PubMed Google Scholar Affected infants and young children show difficulties navigating or recognizing objects, toys, and parents' faces in dimly lit environments, but they show better functioning in brightly illuminated places.19Lorenz B. Gyürüs P. Preising M. Bremser D. Gu S. Andrassi M. Gerth C. Gal A. Early-onset severe rod-cone dystrophy in young children with RPE65 mutations.Invest. Ophthalmol. Vis. Sci. 2000; 41: 2735-2742PubMed Google Scholar Staring at brightly illuminated objects (photophilia) is common.19Lorenz B. Gyürüs P. Preising M. Bremser D. Gu S. Andrassi M. Gerth C. Gal A. Early-onset severe rod-cone dystrophy in young children with RPE65 mutations.Invest. Ophthalmol. Vis. Sci. 2000; 41: 2735-2742PubMed Google Scholar A small amplitude pendular nystagmus is also recognized by parents, less frequently a gross rotatory or wondering nystagmus, which is more commonly found in other molecular subtypes of LCA.40Chen N. Shin K. Millin R. Song Y. Kwon M. Tjan B.S. Cortical reorganization of peripheral vision induced by simulated central vision loss.J. Neurosci. 2019; 39: 3529-3536PubMed Google Scholar Unlike other molecular forms of LCA, eye rubbing or eye pocking to evoke photopsias, or Franceschetti's oculo-digital sign, is observed only in the most severely affected patients. Visual acuity is variably impaired but is on average at around 20/200 to 20/100.41Walia S. Fishman G.A. Jacobson S.G. Aleman T.S. Koenekoop R.K. Traboulsi E.I. Weleber R.G. Pennesi M.E. Heon E. 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Sci. 2013; 54: 1378-1383Crossref PubMed Scopus (0) Google Scholar Color vision is also variably impaired and when measurable can show a non-specific axis of confusion, a tritan defect, or be within normal limits, reflecting variable preservation of the foveal function in these patients.45Kumaran N. Ripamonti C. Kalitzeos A. Rubin G.S. Bainbridge J.W.B. Michaelides M. Severe loss of tritan color discrimination in RPE65 associated Leber congenital amaurosis.Invest. Ophthalmol. Vis. Sci. 2018; 59: 85-93Crossref PubMed Scopus (0) Google Scholar As noted above, most patients show a small amplitude pendular nystagmus. The amplitude of their nystagmus and the position of the preferred locus of fixation relates well to the level of visual acuity and overall foveal function. Fixation in untreated eyes occurs at the fovea or within 1° of the foveal center.46Cideciyan A.V. Aguirre G.K. Jacobson S.G. Butt O.H. Schwartz S.B. Swider M. Roman A.J. Sadigh S. Hauswirth W.W. Pseudo-fovea formation after gene therapy for RPE65-LCA.Invest. Ophthalmol. Vis. Sci. 2014; 56: 526-537Crossref PubMed Scopus (0) Google Scholar Early in life the fundus examination may appear normal or show only minor epithelial changes with white-yellow dots in the midperiphery (Figure 1, P1 and P4). More advanced disease can show waxy pallor of the nerve, often a bull's maculopathy, attenuated vessels, and pigmentary changes (Figure 1, P2).7Weleber R.G. Michaelides M. Trzupek K.M. Stover N.B. Stone E.M. The phenotype of severe early childhood onset retinal dystrophy (SECORD) from mutation of RPE65 and differentiation from Leber congenital amaurosis.Invest. Ophthalmol. Vis. Sci. 2011; 52: 292-302Crossref PubMed Scopus (42) Google Scholar,42Chung D.C. Bertelsen M. Lorenz B. Pennesi M.E. Leroy B.P. Hamel C.P. Pierce E. Sallum J. Larsen M. Stieger K. et al.The natural history of inherited retinal dystrophy due to biallelic mutations in the RPE65 gene.Am. J. 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