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Page 4
SNPs are variations in the DNA due to substitution of one base for other, for example; Thymine for Cytosine. You can think of them as road markers and scientists hope to find enough SNPs to make a detailed map of the human genome.
The significant SNP might or not be located within a gene. If located within a gene it could indicate that the protein it codes for is responsible for the disease. If not located within a gene it could be used as a marker. That is, scientists will know that near this particular SNP is the gene whose malfunction is the cause of the pathology. In this case they will need to find it, identify the protein it codes for and design drugs to stop the development of the disease. It could also be that the defect is due to a gene that is over expressed, that is, the protein it codes for is made in excess. Or that the protein is not expressed at all. In those cases they should design drugs that inhibit or activate the expression of the gene. Using this approach a research team at Glaxo Wellcome, claim that they are close to identifying the genes that cause adult-onset diabetes, migraines, and psoriasis. Once they have pinpointed those genes and identified the proteins they code for, therapies for each could quickly follow. As you can see they are close to establishing clear connections between SNPs, disease pathways, and therapeutic interventions. It has been estimated that there are between 200,000 and 400,000 SNPs and the question is: Will there be an SNP near every gene relevant to a particular disease? We will have to wait and see. Meanwhile the spectacular benefits of pharmacogenomics can be appreciated through the following examples: a.- A drug called azathioprine, is used in autoimmune disorders, and childhood leukemia is metabolized, that is, degraded by a particular enzyme called TMPT. Well, less than .5 % of Caucasians carry a gene variant on both chromosomes that produces an inactive protein and so cannot metabolize the drug. When patients with that gene variant are treated with azathioprine, its blood levels built up to toxic levels, leading to acute bone marrow failure. This happened to a boy who was started on the drug and had to be rushed to the Mayo Clinic for a marrow transplant, which saved his life. A pharmacogenomic genetic test has been developed to identify patients with this deficiency, which permits the use of an alternative therapy. The benefit of this test cannot be overemphasized these patients.
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