To prove that one or all of them are the MI cause you must find out how the mutations affect the proteins or their production. And finally, and the most complicated step, you have to determine how those changes lead to MI. In my opinion, since the gene sequences obtained by the HGP is an average of several normal human beings it would be wise to find out if those variants are, or not, present in a representative sample of the normal population.
On the other hand, knowing the defect, even without understanding its effect, is important because a test for the variant can be designed so that by detecting it early you can suggest to the carriers to change those habits in their lifestyle that are also risk factors for MI. Also the defect could be corrected by gene therapy, which is in its infancy and deserves an article of its own.
What I have described is the best case situation because it might happen that the variants that you found are not common to all the patients but to a portion of them or that are also found in a good proportion of the normal population. In which case it will be necessary to study the interactions of the genes under study with other genes and/or with the environment.
You might also find that the genes you started with are not a risk for MI and you will need to study other gene (s) involved in cholesterol or other metabolisms.
Just to give you an example of how complicated it can be, the gene defect that is linked to the mortal disease, with no known cure, the Huntington chorea was discovered in 1993 and the function of the protein it codes for is not yet known. As a matter of fact the gene is known as IT15, where IT stands for interesting transcript.
Before finishing, I want to emphasize that because of all the research that has been done up to now in Biochemistry and Physiology, a lot is known about the metabolic processes that are relevant to many diseases, which means that in some cases scientists know what genes to look for. What is missing, in general, are the gene defects and the connection between the defect and the disease. Also, some genes have already been linked to some diseases. In particular are those known as by Mendelian diseases in which having the mutation implies that the person has the disease or is a carrier. In the first case we talk about a dominant gene and in the second, the gene is said to be recessive. A dominant gene is responsible for the a Huntington chorea and a recessive one is the one that causes retinoblastoma.
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