Novel therapeutic strategies for autosomal dominant retinitis pigmentosa

Abstract

A major difficulty associated with the design of gene therapies for autosomal dominant diseases is the immense intragenic heterogeneity often encountered in such conditions. Two strategies which circumvent the difficulties associated with developing multiple mutation-specific therapies for dominant disorders and with discriminating between disease and normal alleles have been explored in this thesis. In the first, normal and mutant alleles are suppressed by targeting sequences in transcribed but untranslated regions (UTRs) enabling introduction of a replacement gene with the correct coding sequence but altered UTRs to prevent suppression. The second approach involves suppression in the coding sequence of a gene and concurrent introduction of a replacement gene by exploiting the degeneracy of the genetic code. Both approaches provide a wider choice of target sequence than those directed to single disease mutations and are appropriate for many mutations within a given gene. The aim of this project was to examine the feasibility of both therapeutic approaches using a group of genetically heterogeneous retinopathies termed retinitis pigmentosa; for example, over 150 mutations have been identified in the genes encoding the photoreceptor-specific proteins, rhodopsin and peripherin in patients with retinal degenerations. Notably, the vast majority of these mutations are known to give rise to autosomal dominant retinitis pigmentosa. In the context of general methods for gene suppression it is of note that such methods may be directed towards the primary defect, in the case of RP for example the rhodopsin gene, or a secondary effect associated with the disease process such as apoptosis. Two general methods targeting the primary defect which overcome the problems of allelic heterogeneity are explored in this thesis using hammerhead ribozymes directed to transcripts from the rhodopsin and peripherin genes. The ribozyme technologies explored in the study could be used to develop therapies for retinopathies which are directed to therapeutic targets other than rhodopsin or peripherin.