Alzheimer's disease is a complex neurological dementia disease that is the cause of much human suffering and a great cost to society. According to the World Health Organisation, dementia is the fastest growing global health epidemic of our age. The prevailing hypothesis about its cause involves APP (amyloid precursor protein), a protein that resides in the outer membrane of nerve cells and that, instead of being broken down, form a harmful substance called beta-amyloid, which accumulates as plaques and kills brain cells.