The overall goal of our research program is to unravel the pathogenic mechanisms in human hereditary retinal degenerations, contribute to the design of mechanism-appropriate therapies, and develop means to test their safety and efficacy. In the current proposal, we focus on recessive retinal degenerations (RD) caused by mutations in the ABCA4 gene, diseases which have attracted recent interest as potential candidates for gene replacement therapy. Patients with ABCA4-RD commonly have diagnoses of Stargardt disease or cone-rod dystrophy but show very wide phenotypic heterogeneity. Our recent findings elucidated the source of this heterogeneity by estimating disease severity caused by each individual ABCA4 allele. Unexpectedly, a substantial fraction of non-truncating alleles were shown to cause greater disease severity than truncating alleles. This finding cannot be explained by a pure loss-of-function pathogenic mechanism and suggests the existence of an additional gain-of-function mechanism in this recessive disease.
Aims 1 and 2 test this hypothesis in order to define genotypes not amenable to gene replacement therapy.
In Aim 1, we use an independent cohort of patients to validate the severity estimates of disease-causing ABCA4 alleles.
In Aim 2, we test the ability of gene therapy to arrest photoreceptor degeneration in models of complete loss of function and combined loss- and gain-of-function. A recently developed abca4-/-rdh8-/- mouse with severe photoreceptor degeneration will be used as the first model. As for the second model, we will use the human allele severity data to generate a knockin mouse with complex pathogenesis. Lastly, in Aim 3 we evaluate hypotheses about the disease stage to include in future gene therapy trials such that there is an optimal combination of remaining photoreceptors to treat and rapid progression of disease to detect. The studies proposed in this application are not only prerequisites for the safe conduct of ABCA4 gene therapy trials but also define a path to follow for other recessive retinal degenerations.

Public Health Relevance

/PUBLIC HEALTH RELEVANCE Incurable vision loss is the result of most inherited retinal degenerations with one exception: patients with a rare molecular form caused by RPE65 mutations were recently treated with gene therapy and they showed substantial restoration of vision. It is likely that this promising treatment approach will soon be applied to more common conditions. Mutations in ABCA4 gene cause one of the most common forms of retinal degeneration, and the goal of the proposed research is to define the subset of patients with ABCA4 disease who are likely to benefit from gene replacement therapy.

National Institute of Health (NIH)
National Eye Institute (NEI)
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Special Emphasis Panel (ZRG1-CB-G (90))
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Shen, Grace L
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University of Pennsylvania
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Huang, Wei Chieh; Cideciyan, Artur V; Roman, Alejandro J et al. (2014) Inner and outer retinal changes in retinal degenerations associated with ABCA4 mutations. Invest Ophthalmol Vis Sci 55:1810-22
Beltran, William A; Cideciyan, Artur V; Guziewicz, Karina E et al. (2014) Canine retina has a primate fovea-like bouquet of cone photoreceptors which is affected by inherited macular degenerations. PLoS One 9:e90390
Cideciyan, Artur V; Swider, Malgorzata; Aleman, Tomas S et al. (2012) Macular function in macular degenerations: repeatability of microperimetry as a potential outcome measure for ABCA4-associated retinopathy trials. Invest Ophthalmol Vis Sci 53:841-52
Lopes, Vanda S; Gibbs, Daniel; Libby, Richard T et al. (2011) The Usher 1B protein, MYO7A, is required for normal localization and function of the visual retinoid cycle enzyme, RPE65. Hum Mol Genet 20:2560-70
Cideciyan, Artur V (2010) Leber congenital amaurosis due to RPE65 mutations and its treatment with gene therapy. Prog Retin Eye Res 29:398-427
Maeda, Tadao; Cideciyan, Artur V; Maeda, Akiko et al. (2009) Loss of cone photoreceptors caused by chromophore depletion is partially prevented by the artificial chromophore pro-drug, 9-cis-retinyl acetate. Hum Mol Genet 18:2277-87
Cideciyan, Artur V; Swider, Malgorzata; Aleman, Tomas S et al. (2009) ABCA4 disease progression and a proposed strategy for gene therapy. Hum Mol Genet 18:931-41
Gibbs, Daniel; Cideciyan, Artur V; Jacobson, Samuel G et al. (2009) Retinal pigment epithelium defects in humans and mice with mutations in MYO7A: imaging melanosome-specific autofluorescence. Invest Ophthalmol Vis Sci 50:4386-93
Kitiratschky, Veronique B D; Wilke, Robert; Renner, Agnes B et al. (2008) Mutation analysis identifies GUCY2D as the major gene responsible for autosomal dominant progressive cone degeneration. Invest Ophthalmol Vis Sci 49:5015-23
Kitiratschky, Veronique B D; Grau, Tanja; Bernd, Antje et al. (2008) ABCA4 gene analysis in patients with autosomal recessive cone and cone rod dystrophies. Eur J Hum Genet 16:812-9

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