COL4A2 and snowflake vitreoretinal degeneration: These familial mutations lead to BM dysfunction, manifesting with early onset SVD of variable severity.5–7 Recent analysis also identified rare coding variants occurring in patients with sporadic intracerebral hemorrhage.9 In addition to monogenic SVDs, the COL4A1-COL4A2 locus is associated with the much more-common sporadic SVD.