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Currently, one of the most important topics in medical research is to track down the gene or genes responsible for a disease. The pages of newspapers and scientific journals are filled on an almost daily basis with reports of the location of a particular gene that causes a disease. It doesn't actually mean that there is a gene for said disease i.e. a gene for Parkinson's disease or a gene for cancer; what these reports refer to are malfunctions in a gene that lead to the development of the condition.
Finding the location of the gene is a good first base, and should ultimately lead to swifter diagnosis and ultimately treatment. At the very least it will tell researchers more about a specific disease. Locating a particular disease gene is like finding a meter long section on a highway that spans the entire planet. So where do scientists start their journey?
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Search for a gene
To find the genes that may be responsible for a particular disorder scientists study families with a history of the condition. They compare the DNA of affected family members with each other and with unaffected family members.
If you think of the human genome as a map, what scientists are first looking for are some landmarks that tell them they are in the right neighbourhood. So they search for markers on a chromosome; specific regions of DNA that are shared by members of the family who have the condition. Some markers can be 'seen' by chemicals, others can affect a way a cell behaves.
All the while the scientists are zooming in, getting closer and closer to the gene or genes that may cause the disorder. What they want, and need to see is a common pattern of DNA changes in a gene that is shared only by the family members who have the condition. That is a very big indicator that the gene has been located. The results here are then compared with other studies of families who have the condition, and a pattern of gene variants that lead to the disease is gradually built up.
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Benefits of locating a gene
Once a disease gene is located the next step is functional studies, to try and find out how the gene is causing the problem; what happens to make a protein malfunction or appear misshaped, for example. Of immediate benefit will be swifter diagnosis, as once a gene is known about, a simple blood test can determine whether a person has the gene in question. Further down the road will be treatment, and perhaps one day, a cure.