NPC1 and obesity due to melanocortin 4 receptor deficiency: To further investigate the Npc1 gene-diet interaction in relation to weight gain and associated metabolic features, BALB/cJ Npc1+/- mice were interbred with wild-type C57BL/6J mice; the latter mouse strain commonly used to study aspects of diet-induced obesity and T2DM [74, 75].