For example, transferrin receptor (TFRC), hemochromatosis (HFE), and heme oxygenase 1 (HMOX1) are associated with an increased risk of diabetes, while transmembrane protease, serine (TMPRS), and mothers against decapentaplegic homolog 7 (SMAD7) are associated with a decreased risk [21]. This evidence concerns the gene TFRC and diabetes mellitus.