Statistical and experimental analysis of genetic and non-genetic markers associated with risk and progression of age-related macular degeneration (AMD)

Age-related macular degeneration (AMD) is a degenerative disease of the central retina and a leading cause of severe vision impairment in industrialized countries. AMD is a complex disease caused by genetic predisposition and environmental factors. Early stages of the disease usually do not lead to visual impairment. In contrast, the late stage forms of AMD can result in profound vision loss, eventually leading to blindness. Two distinct forms of late stage AMD have been described: geographic atrophy (GA) and neovascular AMD (NV). In this thesis, four main projects were pursued: (i) In the first project, a genetic risk model for AMD should be computed and evaluated. This model was based on a genetic risk score (GRS) calculated from twelve known, common genetic risk factors in a large cohort of late stage AMD cases and AMD-free controls. The computed model presented to have a decent classification accuracy with an area under the receiver operating characteristics curve (AUC) value of 0.82, which is sufficient to classify individuals as having a high or low risk for AMD. Furthermore, we computed absolute risk estimates for several risk groups to develop AMD in the next five years. In addition, we showed that individuals that were affected with AMD before the age of 75 had a statistically significantly higher genetic risk score than those individuals that got AMD after the age of 75. (ii) In order to improve the classification scheme, circulating microRNAs were investigated as potential biomarkers for AMD. We showed that three circulating microRNAs (hsa-mir-301a-3p, hsa-mir-424-5p and hsa-mir-361-5p) as well as a combined profile are significantly associated with neovascular AMD. With pathway enrichment analyses performed on predicted target genes of these microRNAs, inflammatory as well as angiogenc pathways were implicated in AMD. In addition, hsa-mir-361-5p was shown to influence the rate of neovascularization in an in vitro angiogenesis assay. (iii) The third project investigated a potential involvement of the genetic risk score and single genetic variants as well as clinical factors on the growth rate of geographic atrophy lesions. By analyzing the largest dataset available on geographic atrophy lesion growth, we showed that two genetic risk variants (C3_rs2230199 and ARMS2_rs10490924) are significanlty correlated with the growth rate of GA lesions. Furthermore, the presence of GA in the fellow eye (bilateral GA) was shown to be significantly correlated with increased GA growth. We computed multivariate linear regression models and showed that these factors are independently correlated with GA growth and jointly explain around 7% of the disease variability. (iv) In a candidate gene approach, novel genetic risk variants associated with AMD risk were investigated. We found a statistically significant association of two variants in the DAPL1 gene with late stage AMD. Interestingly, the observed associations were confined to females, thus identifying the first gender specific locus associated with AMD. By further functional characterization of these risk variants and DAPL1 transcript levels, we showed that the presence of risk alleles correlated with reduced levels of retinal and RPE specific isoforms of DAPL1. In conclusion, this thesis provided further insights into AMD pathology by: (i) implicating novel genetic factors associated with AMD risk; (ii) computing a genetic risk model, effectively summarizing the genetic risk for AMD of an individual; (iii) implicating factors correlated with geographic atrophy lesion growth and thus disease severity and (iv) identification of a biomarker for neovascular AMD based on circulating microRNAs.