FNDC5 and obesity due to melanocortin 4 receptor deficiency: Subsequent studies have investigated the association of circulating irisin with disease type and condition such as obesity [10,11,12,21], MS [14], diabetes mellitus [9,11,22,23,24,25,26,27,28,29], coronary artery disease (CAD) [30,31], and cerebral ischemia stroke [18] in both human and mouse models.