Previously reported epidemiological studies that identified numerous risk factors for AD [86], including an extra copy of the chromosome with the APP (Aβ precursor)-coding gene in Down’s syndrome [87], as well as old age [6,12], obesity [6,13], type 2 diabetes [6,14], smoking [6,15,16] and electromagnetic fields [88], failed to provide strong evidence for any association between ionizing radiation and AD. Here, APP is linked to obesity due to melanocortin 4 receptor deficiency.