FGF21 and obesity due to melanocortin 4 receptor deficiency: FGF21 analogues are under investigation for metabolic diseases, such as obesity, dyslipidemia, T2DM, and MASLD/MASH (Gaich et al., 2013; Harrison et al., 2021b, 2023a, 2023b; Loomba et al., 2023b; Rader et al., 2022; Sanyal et al., 2019).