Notably, obesity is simultaneously caused by internal (genetic) and external factors (dietary or lifestyle) in some cases, and it was reported that ob/ob mice, a hereditary obesity model caused by genetic mutation, had hepatic steatosis related to the increase of SREBP-1c level and the decrease of PGC1α and CPT1α levels in the liver (46–48). The gene discussed is PPARGC1A; the disease is obesity due to melanocortin 4 receptor deficiency.