Alzheimer’s disease: Understanding how Down’s syndrome increases risk

Down’s syndrome increases the risk of Alzheimer’s disease. People with Down’s syndrome may experience health problems as they age that are similar to those experienced by older people in the general population. The presence of extra genetic material found among people with Down’s syndrome may lead to abnormalities in the immune system and a higher susceptibility to certain illnesses, such as Alzheimer’s, leukaemia, seizures, cataracts, breathing problems and heart conditions.

People with Down’s syndrome also experience premature ageing. That is, they show physical changes related to ageing about 20 to 30 years ahead of people of the same age in the general population. As a result, Alzheimer’s disease is far more common in people with Down’s syndrome than in the regular population. Adults with Down’s syndrome are often in their mid to late 40s or early 50s when Alzheimer’s symptoms first appear. People in the general population don’t usually experience symptoms until they are in their late 60s.

The symptoms of Alzheimer’s disease may be expressed differently among adults with Down’s syndrome. For example, in the early stages of the disease, memory loss is not always noted. In addition, not all symptoms ordinarily associated with Alzheimer’s disease will occur. Generally, changes in activities of daily living skills are noticed, and the person with Down’s syndrome may begin to have seizures when he or she had never had them before. Changes in mental processes - such as thinking, reasoning and judgment - may also be present, but they are often not very noticeable because of the limitation of the individual’s functioning in general.

How common is Alzheimer’s disease in people with Down’s syndrome?

Estimates suggest that 25% or more of individuals with Down’s syndrome over the age of 35 show the signs and symptoms of Alzheimer’s-type dementia. This percentage increases with age. The incidence of Alzheimer’s disease in people with Down’s syndrome is estimated to be three to five times greater than that of the general population.

Why do people with Down’s syndrome get Alzheimer’s disease?

Current research shows that the extra “gene dosage” caused by the abnormal third chromosome of Down’s syndrome may be a factor in the development of Alzheimer’s disease. The early ageing of the Down’s syndrome brain may also be a factor.