Alzheimer's disease is the most common cause of dementia, affecting around 496,000 people in the UK. Dementia is a brain diseases that cause long term loss of the ability to think, mood changes and reason clearly that is severe enough to affect a person's daily functioning. These symptoms occur when the brain is damaged by certain diseases and conditions, including Alzheimer's disease. Alzheimer's disease, first described by the German neurologist Alois Alzheimer, is a physical disease affecting the brain. During the course of the disease, protein 'plaques' and 'tangles' develop in the structure of the brain, leading to the death of brain cells. People with Alzheimer's also have a shortage of some important chemicals in their brain.