COL4A4 and keratoconus: The genes selected in the present study can broadly be categorised as regulatory genes, such as CAST[30] and VSX1;[31] structural genes, including the collagen genes COL4A3 and COL4A4;[32] and genes involved in immune responses, such as SOD1,[33] TF[34] and RAD51,[35] IL1A[36] and IL1B.[37] The initial studies that implicated CAST, COL4A3, COL4A1, TF, RAD51, IL1A and IL1B in keratoconus showed associations at nearby or intronic SNPs.