In particular, genome-wide association studies have recently identified multiple genetic variants associated with WMH in community-dwelling individuals9 and have been used to show that common variants in COL4A2, a gene associated with monogenic SVD, influence sporadic SVD.10 In addition, genome-wide association studies provide a means of interrogating the relationship between complex traits and assessing whether such traits share pathogenesis. The gene discussed is COL4A2; the disease is snowflake vitreoretinal degeneration.