Leber Congenital Amaurosis (LCA) affects 2 to 3 in 100,000 births, accounts for 20% of childhood blindness, and poses a substantial social and financial burden. Although several target genes (fifteen: localized to retina photoreceptor neurons or retina pigment epithelium (RPE) cells) are routinely screened for LCA, the affected gene in 6% of LCA patients is still not identified. Translational studies to develop novel therapy will require an understanding of how these mutations alter cellular function in ways that lead to severe vision loss in children. Rationale: This proposal is based on the recent discovery that several mutations of the RPE inwardly rectifying potassium channel gene KCNJ13 (which encodes Kir7.1 protein) cause LCA, making it the 16th gene prioritized for routine LCA screening. Through our collaborations, we have recently discovered a novel KCNJ13 nonsense mutation c.158G>A in a young LCA patient that results in a 52 amino acid (aa) truncated product (p.W53X) compared to 360 aa full length Kir7.1 protein. We have previously characterized a Kir7.1 cytoplasmic mutation (p.R162W) that results in abnormal channel function and is a likely contributor to autosomal dominant Snowflake Vitreoretinal Degeneration, a rare vision defect that is allelic to LCA at the KCNJ13 locus. We hypothesize that the nonsense mutations, three of the four patients identified, of KCNJ13 gene result in dysfunctional Kir7.1-channel leading to LCA by altering RPE function. Specifically, we propose that there is a defect in potassium homeostasis that results in failure of the adjacent retinal neurons to perceive light. Our immediate goal is to determine the function of the mutant Kir7.1 channel and then test how RPE physiology is altered by LCA mutations.
Research Aims : In this proposal, our focus in Aim 1 will be to characterize patient derived iPSC-RPE and control human iPSC-RPE cells to model LCA16 in a dish.
In Aim 2, we will determine if agents for nonsense read-through will sufficiently rescue Kir7.1 function.
In Aim 3, we will develop a suitable gene therapy option to overcome Kir7.1 channelopathy. We are hopeful that clinical phenotype in the patient derived iPSC-RPE will be rescued using our novel therapeutic approach resulting in a normal RPE cell. The use of patient derived iPSC-RPE cells in this LCA16 drug discovery pathway will bypass the traditional use of animal disease models before clinical trials are attempted. Since ion channels like Kir7.1 are specialized, membrane proteins that regulate a wide range of physiological responses, we would have generated novel therapeutic strategies to improve the clinical outcomes of ion channelopathies.
Leber congenital Amaurosis (LCA) is a severe form of congenital retina dystrophy affecting 2-3 in 100,000 new born babies. Children with this disorder lose their ability to detect light and color. So far at least 17 gene defects are discovered that ae associated with light detection and transmission pathway. The disease is caused by transmission of defective gene by both father and mother. This project focuses on the use of existing knowledge to develop novel therapeutics as a viable option for the treatment of blindness in LCA patients.
