3. Risk of developing dementia
People with learning disabilities are at increased risk of developing dementia as they age, compared with others without a learning disability, although the figures vary according to how the diagnosis is made. About 1 in 5 people with a learning disability who are over the age of 65 will develop dementia. People with learning disabilities who develop dementia generally do so at a younger age. This is particularly the case for people with Down's syndrome: a third of people with Down's syndrome develop dementia in their 50s.
Down's syndrome and dementia
When people with Down's syndrome develop dementia, it is usually due to Alzheimer's disease. Studies have estimated that 1 in 50 people with Down's syndrome develop dementia in their 30s, rising sharply to more than half of those who live to 60 or over. By comparison, the number of people among the population without learning disability aged 60-69 years who develop dementia is about 1 in 75. These studies, therefore, show a greatly increased risk of developing dementia among people with Down's syndrome, compared with the general population without a learning disability.
Studies have also shown that by the age of about 40, almost all people with Down's syndrome develop changes in the brain associated with Alzheimer's disease. However, not all go on to develop clinical symptoms of dementia. The reason for this increased risk has not been fully identified, however it is thought to be linked to the extra copy of chromosome 21 which most people with Down's syndrome have. This chromosome carries the amyloid gene thought to play a role in Alzheimer's disease.
Other learning disabilities and dementia
Studies suggest that approximately 1 in 10 people aged 50 to 65 with learning disabilities other than Down's syndrome have dementia. This rises to more than half of those aged 85 or over. This suggests the risk is less than for people with Down's syndrome but still between two and three times greater than for the general population.
At present we do not know why this is the case, and more research is needed. Genetic factors may be involved, or a particular type of brain damage associated with a learning disability could be a cause.