Following are answers to some of our research-focused Frequently Asked Questions:
Isn't Down syndrome too complex to treat?
For many years, scientists believed that Down syndrome was too complex to understand, and they believed that there was no way to reverse or reduce the severity of cognitive impairment. However, via two distinct approaches, over the last decade scientists have made unprecedented progress towards identifying a treatment to ameliorate the cognitive impairment associated with Down syndrome. The first approach is based on genetics. Scientific advances have made it possible to understand how specific genes are linked to specific abnormalities in the structure and function of the brain. Although the 21st chromosome has hundreds of genes, researchers believe that there may be only a handful that significantly impact cognition. Using advanced techniques and methods, researchers believe they will be able to isolate the effects of these specific genes and determine how their expression in the brain can cause problems with cognition. The second approach is to study the endpoints of brain structure and function in mouse models. By investigating the physical differences and the resulting functional impacts, researchers are able to define specific mechanisms responsible for cognitive dysfunction. Once these are established, they can begin the process of discovering treatments that enhance brain function, including cognition. Today we can boldly predict that Down syndrome is not too complex to understand and it is not too difficult or too late to treat.
Is a treatment a cure?
No. Once a baby is born with Down syndrome, he or she will always have an extra chromosome. However, research may be able to reverse or ameliorate the affects of the extra chromosome, particularly with regard to the degree of mental retardation. No one can say for sure how much cognition could be improved. However, even a modest improvement of 15 IQ points could have enormous impact on the life of a person with Down syndrome. Because the majority of individuals with Down syndrome fall into the mild to moderate range of cognitive impairment, an extra 15 IQ points would enable most persons with Down syndrome to function much more independently in school and the workplace.
What is DSRTF's research focus?
DSRTF believes that the most promising and cutting-edge Down syndrome research today involves understanding the underlying genetic, biological and neurological processes in Down syndrome and how they relate to one another to cause cognitive dysfunction. The area of the brain of most interest to researchers is the hippocampus, which is essential for learning and memory. Of particular interest in this region of the brain are the areas between brain cells, where information is transferred between neurons. These areas are called synapses, and evidence suggests that the structure and function of synapses in a Down syndrome brain are abnormal, causing cognitive deficits. Defining these brain abnormalities, documenting the time of their occurrence, and developing methods to evaluate them are an important focus of current Down syndrome research.
The underlying genetic and biological causes of the brain abnormalities are another focus of current research. Researchers hypothesize that the activity of one or more genes on chromosome 21 causes the structure and function of the hippocampus to be abnormal. They have begun to identify the genes responsible for certain critical brain abnormalities and to study how an over-expression in the brain can affect cognition. The next step is to identify pharmaceutical agents that can turn down or turn off the expression of these genes in critical areas of the brain with the hope of restoring the brain to normal function.
DSRTF also recognizes, that in order for successful clinical trials of potential treatments to take place, there needs to be a generally accepted cognitive benchmark. To this end DSRTF funded Drs. Lynn Nadel and Jamie Edgin of the Univeristy of Arizona in the development of the Arizona Cognitive Test Battery.
What are our research objectives for the near term?
Future research objectives focus on defining in detail the abnormalities in brain structure and function that could be responsible for cognitive problems in Down syndrome and explaining their genetic and cellular basis. Current studies are carried out in mouse models of Down syndrome, but in the future researchers hope to have access to brain tissue from people with Down syndrome so that ideas can be tested and refined.
In the near term, scientists will continue to define abnormalities in synaptic structure and function that are relevant in Down syndrome. They will develop as much information as to when and where these abnormalities occur.
In parallel, investigations are taking place to identify specific gene(s) responsible for particular abnormalities and cognitive deficits. As these are found scientists then turn their attention to identifying compounds that can regulate the expression of the targeted gene(s). The goal is for researchers to design treatments that enhance cognition.
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.
Would possible treatments be just for children?
No. Researchers believe that effective treatments could be developed for any person with Down syndrome - no matter what age they are.
Why are mice important for our research?
The progress of Down syndrome research on cognition is due largely to our ability to explore in great detail the abnormalities in the structure and function of the nervous system using mouse models. The mouse that researchers use for much of the research on Down syndrome is the Ts65Dn mouse. This mouse model is designed to have an extra copy of mouse chromosome that is very similar to chromosome 21 in humans. It has been very helpful in confirming that there are structural and functional changes in the synapses of hippocampus cells.
Unfortunately, the Ts65Dn mouse is difficult and expensive to breed. DSRTF has been working with Congress and the National Institutes of Health to increase the supply of these mice by increasing federal funding. The NIH approved more funding for production of the Ts65Dn mouse over a two-year period. It is hoped that this increased funding will lead to a greater supply of these mice for the research community.
Some exciting news is that researchers in the UK have developed a new mouse model of DS. Where the Ts65Dn mouse has an extra copy of chromosome 16, because that is the mouse chromosome that contains a significant number of the genes that are found on human chromosome 21, the new mouse model has a copy of the entire human chromosome 21. This mouse is expected to be a very powerful tool in helping researchers associate the specific genes that, by being present in a third copy, are responsible for impaired cognition in DS.