There are numerous theories that have been put forth to explain the causes, including the aggravation of ageing, the degeneration of cholinergic and cortico-cortical pathways, environmental factors like aluminium exposure, head injuries, malnutrition, mutations of the amyloid precursor protein (APP) and PSEN genes, allelic variation in apolipoprotein E, mitochondrial dysfunction, immune system dysfunction, and infectious agents.2 The gene discussed is APP; the disease is nutritional deficiency disease.