Lastly, collagen type II α-1 chain (COL2A1) is an extracellular matrix protein whose protein family members, COL4A1 and COL4A2 (collagen type-IV α-1 and α-2 chains), have been shown to play essential roles in SVD pathogenesis.40 Here, COL4A2 is linked to snowflake vitreoretinal degeneration.