The one thing that decides the colour of your hair, the texture of your skin and your intelligence is your DNA [deoxyribonucleic acid]. And it has to do with more than just your looks. It is the blueprint we are born with. DNA testing is the new tool used by people to try and read the blueprint and asses a person’s risk for an illness. Let's understand it in detail.
Why is a DNA test necessary?
DNA is a double-stranded helix and we all have two copies of each gene. One comes from the father and the other from the mother. It is nature’s way of ensuring that we get at least one good gene if something goes wrong with the other. DNA is said to have undergone 'mutation' when something goes wrong with it. Diseased people often carry a mutation in their genes. It is these changes in the DNA that lead to the initiation of a disease. Unfortunately we can't choose our genes. A DNA test then comes in handy as a precautionary measure to know our health risks and take steps to safeguard the future.
How is the test done?
A 2ml sample of your blood is collected from which the DNA is isolated in the lab. The test is done using a procedure called microarray hybridization. In this procedure, a person's DNA is hybridised with probes mounted on a special chip. The probes on the chip are sequences of DNA carrying mutations. If the DNA has mutations, then it binds to the chip and emits a fluorescent signal when the chip is scanned. If there are no mutations, then the DNA does not bind to the chip or show a signal on scanning. Usually, it takes about 10 days to get your results.
Another method that is being tested by scientists is by scraping the inner cheeks with a cotton swab to derive buccal cells. However, the method hasn't yet found acceptance in everyday practice due to its limitations.
Is my information kept secret?
When you order a DNA test, your file and sample is made anonymous and marked with a bar code. This ensures that even the lab scientist is not aware of who the sample belongs to. Once the test is over, only one person decodes it back and the report is handed over to you in full confidentiality.
What does the report tell me?
Your DNA test report shows the mutations you carry. Since not all mutations are harmful, you may be healthy even though your report shows mutations. Sometimes, a set of accumulated mutations are worse than a single mutation.
In the above example of a report, the genotype at this particular position on DNA of the interleukin 8(IL8) is AG. This means A has come from the father and G from the mother or vice-versa. Having AG genotype indicates that the person whom the report belongs is 1.5 times more likely to get gastric cancer when compared to a person who has a healthy genotype [it could be AA or GG]. Next important item in the report is the odds ratio [OR]. The OR measures the ratio of the odds of a disease or death from a specific illness happening to the odds of the disease or death not occurring. In the above example, the OR is derived from studies conducted on cancer patients and healthy subjects to find the OR for cancer.
What are the limitations of DNA testing?
One DNA test helps reveal only one disease. Also, tests are not available for every disease. Another limitation is the cost—a single test costs around Rs.20,000 – Rs.30,000. Because of the high costs, DNA tests are only asked for where threat from a certain disease is suspected.
Moreover, like any other test, even DNA testing is not foolproof. Each day, new mutations are discovered; so a DNA testing chip used five years from now will have a better detecting power than a chip used today. But that doesn’t mean we sit waiting for the ultimate chip to arrive.
The current DNA testing can predict with 90 per cent sensitivity your risk to a particular disease.
Genetic testing is in its fledgling state. But the time is not too far, when instead of horoscopes, DNA reports will be matched before marriage. By then, the test will become common and as affordable as a simple glucose test.
Below is a sample of what a DNA testing report looks like
|Gene||Genotype||SNP ID||Gene Function||Odds Ratio||Related Cancer Type|
|ILR||AG||rs2227306||Chemotaxis, Inflamatory Response||1.43||Gastric|
Know before you test
- Your genotype is not in your control. We don’t choose our genes, we are born with them. Studies have shown that by regular exercise and good
eating habits, the expression of these genes can
- If your reports don’t reveal anything, it doesn’t mean you will not be affected by any disease and life will be one big party. As the body ages, our immune mechanisms become weak. The enzymes [proteins in our body, which help in all biochemical reactions] become less productive leading to poor metabolism. They are coded by DNA. Poor metabolism leads to obesity, which is the culprit behind most diseases.
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