A genome-wide DNA methylation and gene ontology analysis of leukocytes identified four differentially methylated sites in individuals who had a previous MI as compared to the rest of a population without MI; in the same study, a significant correlation between differences in DNA methylation in blood cells and the myocardial expression of Growth Differentiation Factor 15 (GDF-15) (a cytokine involved in regulating apoptosis, cell repair and cell growth) was discovered in MI patients [44]. Here, GDF15 is linked to myocardial infarction.