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Genetic testing is beginning to play an important role in personalised medicine and is indispensable for the diagnosis and therapy of many diseases. However, the preventive and diagnostic power of many genetic tests is still inferior to traditional diagnostic tests. In addition, commercial genetic tests do not always live up to the claims made about them.
The sequencing of the human genome, which was heavily publicised around the world ten years ago, was celebrated by scientists and politicians alike as the beginning of a new era of medicine and health care. It was envisaged that the sequencing of the human genome would enable doctors in the future to determine any individual's genetic predisposition to certain diseases, identify risk factors and find strategies to prevent the development of disease, or treat it, if the disease could not be prevented. Such developments would bring us towards personalised medicine, tailored to the individual requirements of a patient. The determination of an individual's genetic composition on the basis of the sequenced human genome seemed to create the conditions required for such treatment to be possible.
Ever since DNA sequencing and hybridisation methods became routine applications, many laboratory physicians and human genetics laboratories have offered predictive gene tests to assess a person’s susceptibility to disease. The example of the emerging field of nutrigenetics, a science that is focused on matching a person’s nutritional requirements to their genes, will be used to reveal the pro's and con's of such gene tests: The new techniques can be used to identify people who possess a defective, only weakly active form of the enzyme methylenetetrahydrofolate reductase (MTHFR). The MTHFR tests are used to test individuals for mutations in the MTHFR gene in order to identify a genetic aetiology for hyperhomocysteinemia. When eating normally, these people have an elevated homocysteine level, an amino acid that is suspected of increasing a person’s risk of myocardial infarction and stroke. The homocysteine level can be decreased by consuming foods rich in folic acid (vitamin B9, which is for example found in fresh vegetables and fruit). This seems like a convincing argument for a person to undergo genetic testing in order to prevent cardiovascular diseases at the same time as being excellent news for the providers of MTHFR tests and the manufacturers of vitamin preparations.
The US Food and Drug Administration now requires the addition of folic acid (folate) to enrich flour and cereals. Although there is substantial evidence that the uptake of higher folic acid levels reduces the risk of colon cancer and potentially also other types of cancer, legal regulations requiring the addition of folic acid to basic foodstuffs are still a matter of controversy in Europe due to evidence suggesting that folate is also able to promote the growth of early-stage tumours. However, agreement exists on the consumption of supplemental folic acid in addition to a healthy diet prior to and during pregnancy. It has been shown that folate-rich foods or folate supplements reduce neural tube defects in unborn children (see "Cornelia Ulrich: Cancer prevention through food and sport").
MTHFR gene tests to prevent cardiovascular diseases are now heavily contested. As discussed in the renowned Journal of the American Medical Association (for example JAMA 299, 2086-2087, 2008), some large-scale studies have shown a positive relation of diet and disease prevention, while others found that elevated vitamin B9 intake does not lead to a reduction in myocardial infarction and stroke risk. Other B vitamins (vitamin B6 and B12) have also been shown to play a role in the development/prevention of cardiovascular diseases. The relationship between homocysteine level and cardiovascular diseases seems far more complicated than initially thought. Basically, the example confirms what has been known for a long time: Cardiovascular diseases (as well as many other common diseases such as diabetes and cancer) are the result of a broad range of factors and of the interaction of many genes.
The “PROCAM Health Check” includes laboratory test results such as the LDL cholesterol blood level (generally known as ‘bad’ cholesterol), HDL cholesterol (‘good’ cholesterol), triglycerides and blood glucose levels, but also blood pressure, age, familiar predisposition and smoking. By entering patient data into the interactive website of the "International Task Force for Prevention of Coronary Heart Disease", physicians can obtain immediate results and call on their patients to change their lifestyle if necessary. The study suggests that such checks should be carried out before taking lipid-reducing drugs (statins). A PROCAM Quick Test, which does not require the entry of laboratory test results, is available from the same site to anybody who wants to find out his or her coronary risk.
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