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Studying Down syndrome might help us understand Alzheimer’s disease better

Alzheimer’s disease is the most common form of dementia in older adults. At the moment there is no cure, but many clinicians feel that the earlier one is diagnosed, the better the possibilities are for treatment or slowing the disease.

But developing treatments or prevention approaches for Alzheimer’s disease is difficult. There is no biomarker (for example a blood test) or definitive medical test for it and there is no set age where people develop memory impairments and dementia.

Indeed, people can develop Alzheimer’s disease as young as 30 or well into old age. This is a real challenge for diagnosing Alzheimer’s in its early stages.

But in people with Down syndrome there is an age-dependent progression of changes associated with Alzheimer’s disease. This makes it much easier to map when and what kinds of changes happen in the brain in the early stages of the disease.

If we can understand how and when changes in the brain start to happen in people with Down syndrome, that could help us find ways to slow or prevent Alzheimer’s disease in this vulnerable group and for others with Alzheimer’s.

Adults with Down syndrome may provide insights for Alzheimer’s

The lifespan of people with Down syndrome has dramatically improved from 25 years in 1983 to over 60 years today although some minority groups still have lower lifespans.

Although many people with Down syndrome remain healthy as they get older, most are vulnerable to the development of Alzheimer’s disease.

Virtually all people with Down syndrome over 40 years old develop Alzheimer’s disease. It is estimated that over 70% in their 60’s and older also have dementia. This is a much higher rate than people without Down syndrome.

Over 95% of people with Down syndrome have a full extra copy of chromosome 21. There are two other causes of Down syndrome that include partial trisomy 21 where only a piece of chromosome 21 and associated genes are triplicated. The third type of Down syndrome is called mosaicism, where not all of the cells in the body have a fully extra copy of chromosome 21.

The gene for amyloid precursor protein, which is thought to be important for Alzheimer’s disease, is located on chromosome 21.

This amyloid precursor protein is cut into smaller pieces and the smaller protein, called beta-amyloid, is toxic to the cells in our brain or neurons. It collects into structures called beta-amyloid plaques, which are a hallmark of Alzheimer’s in all people. The plaques make it hard for neurons to communicate.

In people without Down syndrome there are normally two copies of this gene. In people with Down syndrome there are three copies of the gene because of the extra copy of chromosome 21. That means from an early age people with Down syndrome are making more of the beta-amyloid protein.

Beta-amyloid plaques are consistently observed in the brains of those with Down syndrome in their 30s, but they have also been reported in people eight- to 15 years old.

How does the brain change in people with Down syndrome as they get older?






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