Over time, their mental abilities deteriorate, gradually progressing through forgetting important matters, getting confused about where they are and what day it is, to becoming lethargic and withdrawn and starting to neglect personal hygiene.

The sufferer may tend to dwell in the past and mistake friends and neighbours for long-departed family members. Conversation may become repetitive and the personality may alter as people develop odd or uncharacteristic behaviours.

In the later stages of the illness, sufferers lose insight and may not be aware of their plight, which makes the disease particularly hard for carers to bear.

Alzheimer's disease tends to progress, deteriorate and lead to death within 2 to 15 years. However, the progress of the illness varies a lot between individuals. For some, the illness may progress slowly over many years, whereas for others it may progress rapidly.

A number of other treatable medical conditions can mimic Alzheimer's disease. These include thyroid problems, infections, vitamin deficiencies, depression and anxiety. It is vital that any elderly person who is concerned about whether they may be getting Alzheimer's disease sees their family doctor and receives a full medical assessment.

Never assume that an old person who becomes forgetful will have Alzheimer's disease. For the majority of old people, forgetfulness is simply a nuisance, and some does not develop Alzheimer's disease. But this is the FIRST sign of Alzheimer's disease.