The Importance Of Snps
Genomic medicine will be applied to patients through several mechanisms. The primary tool will be the detection of single nucleotide polymorphisms (SNPs). These are small variations in DNA sequences that are found in every person. These normal polymorphisms are very frequent, occurring in approximately one out of every 1,000 base pairs. The majority of these SNPs occurs in regions of the genome that do not code for proteins, and usually do not contribute to a person's disease susceptibility. However, they may serve as "markers" for a disease, lying close to an important susceptibility gene. When they occur directly in a protein-coding area of a gene (exon), they can cause the protein variation that helps make each of us unique. This variation in proteins is one of the primary reasons that each of us differs in our risk for disease, infections, and drug tolerance.
It is important to realize that these SNPs are not mutations. The term "mutation" suggests a nucleotide change that prevents a protein from performing its normal function. These mutation-caused changes are rare, occurring in less than 1 percent of the population. This type of genetic mutation is almost always severe enough that its presence alone is enough to cause the disease. In contrast, SNPs are much more common, certainly occurring in more than 1 percent of the population. Their presence may make it easier for a person to get a specific disease, but they do not cause the disease by themselves. Instead, disease can occur only in the presence of the correct environment, other gene combinations, drugs, and other such factors. This is very important, for it suggests that by knowing that an individual is at risk for a disease, a doctor can take actions to prevent it. These actions may be as simple as a dietary or lifestyle change, or taking a medicine or vaccine.
Doctors will be able to use this same identification of SNPs to screen patients prior to prescribing drugs. Drug side effects are usually due to a specific, uncommon polymorphism in a gene that produces a protein that interacts with the drug. These gene interactions may not have anything to do with how the drug helps the patient. More likely, the gene is involved in how the body metabolizes the drug. This field of studying genes and their interaction with drugs is called pharmacogenetics. And pharmacogenetics does not just study drug side effects. Every doctor knows that some drugs work better for some patients than others. This difference is also likely due to normal polymorphisms, or different genetic forms of the disease.