INS and type 2 diabetes mellitus: In order to examine the tissue origin of ccfDNA in T2DM, we investigated the methylation status of five β-cell-specific genes based on previous literature findings that propose them as promising biomarkers for β-cell death (INS, IAPP and GCK), as well as their implication on β-cell physiology (INS, IAPP, GCK, KCNJ11 and ABCC8).