The Severe Forms of Retinal Dystrophies Are Frequently Caused by a New Class of Mutations Affecting ABCA4 Localization

Abstract

Abstract: : Purpose: ABCA4 (ABCR) is a photoreceptor–specific member of the ATP–binding cassette (ABC) family, and mutations of ABCA4 are associated with many retinal phenotypes including Stargardt disease, Fundus Flavimaculatus, combined cone–rod dystrophy and retinitis pigmentosa. Our purpose was to investigate the impact of clinically detected ABCA4 mutations on cellular localization. Methods: We analyzed a cohort of 29 arRP families for mutations in ABCA4 using a commercial microarray, ABCR400, in addition to direct sequencing and segregation analysis. For in vivo expression studies, ABCA4 constructs with clinically identified missense mutations ([L541P; A1038V], R602W and C1490Y) were used to generate transgenic X. laevis tadpoles. The retinas of 2–4 week old animals were studied for the expression and localization of transgenic ABCA4 using immunofluorescence methods. Results: Disease associated mutations [L541P; A1038V], R602W, and C1490Y cause retention of ABCA4 in the photoreceptor inner segment, likely by impairing correct folding. Conclusions: Human ABCA4 can be expressed from a transgene in Xenopus photoreceptors with appropriate localization to the ROS. We have identified a new class of ABCA4 mutations, which leads to improper protein localization in the photoreceptor – thus, rendering a null effect. Clinically, these mutations have been identified in patients with severe STGD, CRD and RP.

Keywords: photoreceptors • retinal degenerations: cell biology • retinal degenerations: hereditary