ADRP With Choroidal Involvement Associated With Asp477gly Mutation Within The Rpe65 Gene

Abstract

 

Purpose:

 

to provide a clinical analysis of members of a family displaying adRP with choroidal involvement with a mutation in exon 13 (Asp477Gly) of the RPE65 gene and a preliminary analysis of the properties of the mutated protein.

 

Methods:

 

Clinical workup included Goldman perimetry, fundus examination, analyses of rod-isolated and mixed rod and cone electroretinographic responses. Normal and mutant RPE65 genes were cloned in vector pcDNA3.1+. Proteins were expressed in HeLa cells and cytostolic and membrane fractions analyzed by western blotting. Predicted ß-sheet distortions were analyzed using a Swiss-Model program.

 

Results:

 

Diagnosis in all cases was RP. However, in most advanced cases, extensive diffuse chorioretinal atrophy was evident, particularly in the macula region. Nummular intraretinal pigmentary deposits were also visible, the fundus picture bearing similarities to that seen in choroideremia. Following expression in HeLa cells, the mutant RPE65 protein migrated marginally faster than wild type, probably indicative of aberrant secondary covalent modification. Computer modeling using the Swiss-Model program, predicted mutant protein to exhibit several ß-sheet distortions around the area of the amino acid substitution, indicative of altered structure, and possibly function.

 

Conclusions:

 

Over 70 mutations have been found in RPE65 in LCA and arRP. However, Asp477Gly is the first mutation to exhibit autosomal dominant transmission. Of the 20% of choroideremia cases in which no mutations in the CHM gene have been identified, a proportion could harbor RPE65 mutations. Gene and/or molecular therapies will be directed toward the RPE, a much more robust cellular target than photoreceptors of the neural retina.

 

Keywords: retinal degenerations: hereditary • genetics • mutations