Hyperlipidemia, peroxisome proliferator-activated receptor (PPAR) alpha/delta agonist drugs, butyrate (149), and other metabolic changes in obesity reduce the function of mammalian target of rapamycin (mTOR) and NK cytotoxicity in vivo and in vitro (150). The gene discussed is MTOR; the disease is obesity due to melanocortin 4 receptor deficiency.