In addition, in both genotypes we observed that nicotine treatment increased phospho-stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) (pJNK) (Figure 1C,D), a member of the MAPK family that has been extensively linked to the development of obesity, type-2 diabetes, and related comorbidities [13,26,27]. Here, MAPK9 is linked to obesity due to melanocortin 4 receptor deficiency.