Alzheimer's disease is a type of dementia that damages parts of the brain and severely affects memory and thinking.
The first signs are usually forgetfulness and confusion.
A person with Alzheimer's disease finds it progressively more difficult to remember events, communicate, think, learn and reason.
Unfortunately the disease is very common – 650 000 people in the UK have Alzheimer’s or other dementia, and it affects one in 5 people over the age of 80.
We all occasionally forget a name or lose our keys, but people with Alzheimer's will do these things regularly. They may get lost in their own street, not knowing how they came to be there, have difficulties with language and get very confused in day-to-day life.
Alzheimer's disease damages brain cells including those that go to the frontal cortex - the area of the brain responsible for thinking.
Scientists know that people with Alzheimer's have abnormalities in and around their brain cells but they are not sure what causes them, or if they are responsible for the disease.
No one knows why some people get Alzheimer's and others don't. The most common type does not seem to run in families.
Many of the current treatments replace a brain chemical called acetylcholine which is very low in the brains of people with Alzheimer’s disease. Some drugs relieve other symptoms of Alzheimer's for example anxiety, depression and unpredictable behaviour. However, these do not prevent brain cells being killed by the disease.
Scientists know that people with Alzheimer’s have aggregations of a protein called Amyloid in their brains. They are now investigating new treatments to stop brain cells being killed by this apparently harmful protein.
For advice and information, go to the Alzheimer's Society website.