MAPK8 and obesity due to melanocortin 4 receptor deficiency: Recent studies identified JNK-1 as the major isoform contributing to the development of obesity-associated insulin resistance, since mouse mutants deficient for JNK-1 but not those for JNK-2 are largely protected from the development of obesity and obesity-associated insulin resistance in both diet- and genetically-induced obesity models [12], [13].