How Efficient Are Genetic Tests in Medicine?

How Efficient Are Genetic Tests in Medicine?

Saturday, February 18th, 2017, Ask the Doctor

Genetic testing has been in the news a lot over the last several years. You can order a genetic test that may help you learn about your family ancestry or your yet-to-be diagnosed medical condition.

What may be less newsworthy are the genetic tests that your doctor uses. Doctors may use genetic testing to determine if you have a specific medical condition, what your risk factors might be if diagnosed with an illness, or even whether you may respond to a particular drug treatment.

The last 30 years have been revolutionary in our ability to understand the genetic make-up of many diseases, for example, Genetic Sucrase-Isomaltase Deficiency or GSID. GSID is a condition where the individual lacks or only has a limited amount of a fully functioning protein to digest sucrose or table sugar. The DNA (deoxyribonucleic acid) that codes or creates the blueprint for this sucrose digesting protein in a person with GSID is damaged (called a mutation), preventing it from working as it should. The sucrose does not get digested, so it passes untouched in the gut. The problem with GSID is that the bacteria in your gut eats the sucrose (everyone has bacteria and it is normal). Normally, gut bacteria do not get a chance to eat sucrose. In GSID, the bacteria eat the sucrose and cause a variety of symptoms such as abdominal pain, diarrhea, gassiness or a combination of these symptoms.

So how do you find out if you have GSID? You may be thinking, “If this is a genetic condition, then a simple genetic test should be able to identify GSID.” Surprisingly, that is not the case.

First, the test is not yet validated to be completely diagnostic so, at this point, it is just a tool your doctor can use to help diagnose the disease. Second, is there are many different DNA mutations that could cause GSID. In fact, 37 different GSID genetic mutations have already been identified and more could be discovered in the future. You need to have only one of those mutations to experience stomach problems. Out of ten people with GSID, all ten could have a different mutation, even though everyone’s stomach problems look the same.

So if your doctor orders a GSID genetic test and it comes back positive with a known GSID mutation, then this provides your doctor with some evidence that he can use as he determines if you have GSID. However, if the genetic test comes back showing no mutations, then you still might have GSID. The reason is that you may have a genetic mutation that has not yet been discovered. Researchers are still working to identify new GSID mutations. If you do not have a known mutation, your doctor will have to do other testing, one which can aid in the diagnosis (hydrogen breath test) and others that are diagnostics for GSID (upper endoscopy with biopsy and a short trial where you take a specific medicine).

In summary, genetic tests have helped to advance patient care. However, using a genetic test for a condition with many different mutations may not give the complete picture. If you think you may have GSID, then consider a consult with a gastroenterologist experienced in diagnosing and managing GSID. #💩

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