Background Age-related cataract is a highly prevalent eye disorder that results in the clouding of the crystalline lens and is one of the leading causes of visual impairment and blindness. The disease is influenced by multiple factors including genetics, prolonged exposure to ultraviolet radiation (UVR), and a history of diabetes. However, the extent to which each of these factors contributes to the development of cataracts remains unclear. Further research into the genetic basis of cataracts could provide valuable insights into the disease's etiology and lead to a better understanding of biological mechanisms that are associated with its development. Methods This study presents the largest genome-wide association study of cataracts to date, using data from 127,985 cases and 837,371 controls. We performed gene enrichment analysis to identify genes and biological pathways associated with cataracts. We integrated our results with gene expression reference datasets to identify genetic variants modifying risk for cataracts through changes in the expression of specific genes. We further explored drug-gene interactions to better understand the potential impact of pharmacological interventions on cataract development. Finally, we explored whether a causal relationship underlies the known comorbidity between type 1 diabetes and cataracts using a mendelian randomization framework, and the association between UV exposure and cataract risk in adults using a polygenic risk scoring approach. Findings Our study identified 85 independent genome-wide significant loci, 37 of which are novel. Gene-based association tests identified 126 genes associated with cataracts, hinting at a potential relationship between negative regulation of lipid biosynthesis and the development of cataracts. Four of the genes identified GNL3, JAG1, METTL21A, and CREB1 are involved in drug-gene interactions. Moreover, Mendelian Randomisation analysis identified a putative causal relationship between genetic predisposition to type 1 diabetes and an increased risk of cataracts. Lastly, we found evidence indicating that early-life exposure to UVR may have an impact on the later development of cataracts. Interpretation Our findings advance our understanding of the genetic basis of cataract and provide new insights into its etiology. We identified multiple genes and biological pathways associated with the condition, including associations with four genes from which drug repurposing could be proposed. Our results suggest a causal association between type 1 diabetes and cataracts. Also, we highlighted a surrogate measure of UV light exposure as a marker of cataract risk in adults and drug-genes interactions that has the potential of informing novel therapies.
