Hyperleptinemia, commonly observed in obesity, promotes cell proliferation, angiogenesis, and resistance to apoptosis, largely through activation of the Janus kinase/signal transducers and activators of transcription (JAK/STAT), phosphatidyl inositol 3 kinase (PI3K)/AKT, and mitogen-activated protein kinase (MAPK) signaling pathways [37,38]. The gene discussed is PIK3CA; the disease is obesity due to melanocortin 4 receptor deficiency.