How are Down syndrome and Alzheimer’s Disease connected?
It is an interesting and surprising finding that every person with Down syndrome develops by age 40 the brain pathological changes of people with Alzheimer’s disease. Moreover, most people with Down syndrome in old age – i.e., beyond age 60 – show further cognitive decline. This is a devastating aspect of Down syndrome and one that is quite disconcerting for those that care for elderly individuals with Down syndrome.
The question is how to explain the link between Down syndrome and Alzheimer’s disease. There is no certain view at this time, however, some recent findings are very exciting. They point to a specific gene that is present in three copies in Down syndrome, which is known to be linked to Alzheimer’s disease. In ongoing studies, researchers are testing how this gene might contribute to the development of Alzheimer’s disease in people with Down syndrome.
How can research in Alzheimer’s disease help us understand and treat Down syndrome?
Because people with Alzheimer’s disease and elderly people with Down syndrome have the same pattern of brain pathology, it is reasonable to suppose that advances in understanding Alzheimer’s disease and new therapies to treat Alzheimer’s disease can be applied to people with Down syndrome. Indeed, this is already happening.
A number of studies are underway to test a role for cholinesterase inhibitors in people with Down syndrome. Cholinergic neurons are important for learning and memory and they are sick in both Alzheimer’s disease and Down syndrome. They release a neurotransmitter called acetylcholine. The breakdown of acetylcholine is under the control of molecules called cholinesterases. Drugs that decrease the activity of these enzymes increase the level of acetylcholine. This helps increase memory in people with Alzheimer’s disease, if only for a short time. Recent studies suggest that these drugs may also be used to treat Down syndrome. One can readily imagine that other therapies directed at Alzheimer’s disease might be made available to people with Down syndrome.
Conversely, studies on mouse models of Down syndrome may well provide new insights into how best to treat people with Alzheimer’s disease. Indeed, the research strategy for Down syndrome differs in some important ways from the typical strategy used to understand Alzheimer’s disease. Work on Down syndrome might provide an important new way of thinking about what causes degeneration of neurons in Alzheimer’s disease and how to treat or prevent it.