MT-RNR1 and obesity due to melanocortin 4 receptor deficiency: Mitochondrial open reading frame of the 12S ribosomal RNA type-c (MOTS-c) is a mitochondrially-encoded 16-amino-acid biopeptide that functions as an exercise-induced regulator of metabolic homeostasis [1, 2] and a modulator of obesity-, diet-, and aging-dependent metabolic function by acting as a systemic, endocrine-acting mitokine [3, 4].