Friday, July 22, 2011

Genetic testing for heart disease

Source: Patrick J. Lynch

Genetic testing opens the doors to personalized medicine - before receiving treatment a doctor can determine if you will respond to the treatment, if you are even at risk for particular diseases the treatment will try to prevent, and whether you might have side effects worth avoiding.

Cardiovascular disease affects tens of millions of people in the U.S. alone - as coronary artery disease, hypertension, and angina, atherosclerotic plaques and miscommunicating hormones wreak havoc on the body, leading to heart attack, stroke, and other potentially fatal consequences.

In recent years, the door to genetic testing to aid in the treatment and prevention of these disorders has made its way to public use. Tests are being fine-tuned to determine a person's genetic risk for cardiovascular disease, genome-wide screening is highlighting susceptibility and treatment options, and a test can tell if chest pain is caused by current heart disease - allowing doctors to better decide who needs an angiogram, avoiding the invasive test in those who may have other reasons for the pain.

Cardiovascular disease affects more than 81 million people according to the American Heart Association. The majority of these cases are hypertension, but another cardiovascular disease, coronary artery disease, is the leading cause of death in the United States. Coronary artery disease is caused by atherosclerosis, which often develops in the presence of excess blood cholesterol levels. Coronary artery disease can cause heart attack and chest pain (angina pectoris) due to decreased blood supply to the heart muscle. Other forms of cardiovascular disease include stroke and heart failure.

In 2009, USNews reported on the international groundwork being laid for a genetics test to determine susceptibility for heart attack. Heart disease tends to run in families, indicating the role of genetics in its course. Several research studies have identified more than a dozen genetic variants that increase a person’s risk of heart attack, some via effects on cholesterol. The genetic tests could also help pinpoint the best treatment options. That same year, a genomics company in Iceland, Decode Genetics, launched a genetic test that detects eight single nucleotide polymorphisms associated with heart attack and various blood vessel disorders. However, the test was criticized for not being highly specific for actual disease risk.

Due to the vast number of variants involved in the different cardiovascular diseases, some patients opt for genome-wide analysis. This is much more expensive (costing tens of thousands of dollars), but could potentially indicate preventative treatment. The Wall Street Journal in early 2010 discussed the case of an engineer whose genome-wide results prompted his doctor to put him on pharmaceutical therapy for heart disease he did not yet have, or may never have. This raises the question of whether the small possibility of actually developing the disease is worth the trade off for drug side effects, which can sometimes be severe or lethal.

A better use of genetic testing for cardiovascular disease was highlighted in USAToday in October 2010. In individuals with chronic chest pain, a genetic test could help doctors determine who requires an angiogram – a diagnostic procedure used to visualize the flow of blood in the coronary arteries via catheterization and X-ray imaging. Avoiding the procedure in those who are not suffering from coronary artery disease can increase clinical efficiency and diagnosis while reducing health care costs. The test looks at the activity of 23 different genes to determine whether a person currently has heart disease, which would then lead to an angiogram to plan appropriate treatment. Many doctors feel it is not yet sensitive enough for full-scale clinical application, and research is ongoing.

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