CLINICAL PROGRESS IN INHERITED RETINAL DEGENERATIONS: GENE THERAPY CLINICAL TRIALS AND ADVANCES IN GENETIC SEQUENCING

Abstract

Purpose: Inherited retinal dystrophies are a significant cause of vision loss and are characterized by the loss of photoreceptors and the retinal pigment epithelium (RPE). Mutations in approximately 250 genes cause inherited retinal degenerations with a high degree of genetic heterogeneity. New techniques in next-generation sequencing are allowing the comprehensive analysis of all retinal disease genes thus changing the approach to the molecular diagnosis of inherited retinal dystrophies. This review serves to analyze clinical progress in genetic diagnostic testing and implications for retinal gene therapy.

Methods: A literature search of PubMed and OMIM was conducted to relevant articles in inherited retinal dystrophies.

Results: Next-generation genetic sequencing allows the simultaneous analysis of all the approximately 250 genes that cause inherited retinal dystrophies. Reported diagnostic rates range are high and range from 51% to 57%. These new sequencing tools are highly accurate with sensitivities of 97.9% and specificities of 100%. Retinal gene therapy clinical trials are underway for multiple genes including RPE65, ABCA4, CHM, RS1, MYO7A, CNGA3, CNGB3, ND4, and MERTK for which a molecular diagnosis may be beneficial for patients.

Conclusion: Comprehensive next-generation genetic sequencing of all retinal dystrophy genes is changing the paradigm for how retinal specialists perform genetic testing for inherited retinal degenerations. Not only are high diagnostic yields obtained, but mutations in genes with novel clinical phenotypes are also identified. In the era of retinal gene therapy clinical trials, identifying specific genetic defects will increasingly be of use to identify patients who may enroll in clinical studies and benefit from novel therapies.

Fig. 1

Variety of retinal dystrophies associated with homozygous ABCA4 mutations. Images in A and autofluorescence in D show an area of parafoveal hyperautofluorescence associated with a macular dystrophy. Images in B and autofluorescence in E show a small central area of hypoautofluorescence corresponding to RPE atrophy with surrounding flecks of hyperautofluorescence associated with a cone dystrophy. Images in C and autofluorescence in F show a central area of hypoautofluorescence in the macula with peripheral areas of punctate hyperautofluorescence and hypoautofluorescence associated with a cone–rod dystrophy.