LEP and obesity due to melanocortin 4 receptor deficiency: Using two mouse models of partial leptin deficiency, OBHZ, which are whole-body leptin heterozygous mice, and LepHZ, which are adipocyte-specific congenital heterozygous leptin knockout mice, researchers found that when exposed to a high-fat diet (HFD), the inability to increase leptin levels due to partial leptin deficiency helped protect against diet-induced obesity and metabolic problems [42,51,52].