CHI3L1 and type 1 diabetes mellitus: Based on a literature search, genes with known functions in retina and eye development (BCOR, GFI1, GLRA1, HDAC4, HMGA1, HTT, KLF5, LAMA4, and SHANK1) [15], inflammation (AHRR, CCL1, CD247, CD58, CD9, CXCR5, KDM1A, and SLC9A3R1) [16], diabetic complications (ACTN4, ARG1, CHI3L1, CHN2, CNP, GIPR, GPX1, KIFC1, NFE2, PEMT, RPS6KA2, TNF, TNFAIP3, and TNFAIP8) [17], and oxidative stress (AHRR, BACH2, GPX1, OXSR1, PFKFB3, and RCAN1) [18] were among the genes that showed differential DNA methylation in blood from T1D subjects with PDR (Fig. 1c–f).