COL4A1 and snowflake vitreoretinal degeneration: The association of arterial collagen-IV with radiological SVD provides insight into genetic risk of sporadic SVD.10,11 In human genome-wide association studies data, SVD phenotypes (diffuse WML, lacunar infarcts, and deep hemorrhage) were associated with intronic SNPs in the COL4A1/COL4A2 locus.10–12 As these SNPs do not change the amino acid sequence, their likely impact is on the degree, or cellular location, of COL4A1/COL4A2 expression.