For example, a longitudinal population-based study by Hur et al. indicated that higher circulating irisin levels were related to the development of T2D during a 2.6-year period and circulating irisin levels may be a potential biomarker for the incidence of T2D, regardless of body mass index (BMI) and systemic insulin resistance in Korean adults [13]. This evidence concerns the gene FNDC5 and type 2 diabetes mellitus.