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E. Boobalan, L. Nichols, II, R. P. Alur, Y. V. Sergeev, R. C. Caruso, E. M. Stone, A. Swaroop, M. A. Johnson, B. P. Brooks; Two Novel CRX Mutant Proteins Causing Autosomal Dominant Leber Congenital Amaurosis (LCA) Interact Differently With NRL. Invest. Ophthalmol. Vis. Sci. 2010;51(13):4041.
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© ARVO (1962-2015); The Authors (2016-present)
To report the clinical and molecular phenotype associated with 2 novel, de novo, CRX mutations causing dominant LCA.
Patients underwent detailed ophthalmic examination, full field ERGs and retinal imaging. Mutations were detected using standard PCR and DNA sequencing. The transactivation capacity, protein expression, and subcellular localization of wild-type (WT) and mutant CRX proteins were analyzed in vitro, both in the presence and absence of Neural Retina Lucine Zipper (NRL).
Both patients showed early macular degenerative changes and unrecordable ERGs. One patient showed retinal thinning at 2.5 years of age, with possible preservation of some photoreceptors by OCT. We found two novel CRX mutations, c.G264T (p.K88N) and c.413delT (p.Il38fs48), which reduced transactivation to 10% & 30% of WT activity, respectively. Both mutants are expressed in vitro at levels comparable to WT protein, and their proteins show cytoplasmic localization as well as nuclear subcellular localization observed in WT and mutants transfected cells. NRL increased luciferase activity by 5 fold & 30 fold respectively, when expressed alone or with wild type CRX. However, activation was decreased to only 2- and 9- fold, respectively, when mutant constructs were coexpressed with NRL. Unlike WT or c.413delT constructs, coexpression of mutant c.G264T with NRL drastically reduced amounts of both the proteins.
Both mutations significantly reduce baseline CRX activity and are partially mislocalized. The c.G264T mutant acts in a dominant-negative-like fashion with NRL, whereas the c.413delT mutant allows NRL to exert its normal baseline activity. Although some photoreceptors may be present in patients early in disease, a simple gene-replacement strategy in dominant CRX-LCA is unlikely to address the pathophysiology of this condition.
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