INSR and obesity due to melanocortin 4 receptor deficiency: The action of this cell-surface receptor thus translates into whole-body nutrient homeostasis, and INSR malfunction in humans is linked to various disorders, such as type 2 diabetes mellitus (T2DM), obesity, metabolic syndrome, polycystic ovary syndrome (PCOS), atherosclerotic cardiovascular diseases, neurodegenerative disorders including Alzheimer’s disease (AD), and multiple cancers [44,45,46,47,48,49,50,51] (see also: Section 2.