AKR1B1 and obesity due to melanocortin 4 receptor deficiency: The polyol pathway, its key enzyme, aldose reductase (AR; AKR1B1), and its over expression has been implicated in many disease states, including diabetes and its complications, diet-induced obesity and metabolic disease, neurological disorders including dementia, behavioral disorders and multiple sclerosis, certain cancers, and other conditions such as tissue ischemia [3,6].