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Genetic Testing for Long QT Syndrome

Long QT syndrome, or LQTS, is a condition of the heart which causes dangerous and uncontrollable heart beat patterns known as arrhythmias, which can be fatal. The disorder derives its name from the irregular pattern seen on an electrocardiogram or ECG. These arrhythmias may occur in response to stress or exercise, although in some patients no underlying trigger can be found. Long QT syndrome may be asymptomatic for some people, meaning that they do not regularly experience arrhythmias but are at risk of developing them at any time. Genetic testing is available for some types of LQTS.

  1. Frequency

    • The National Heart Lung and Blood Institute states that approximately one in 7,000 people have Long QT syndrome, although it is stipulated that this is likely an underestimate as many cases of LQTS go undiagnosed. It is responsible for the sudden death of 3,000 to 4,000 children in the United States annually. LQTS affects more women than men, although this statistic may be skewed by the fact that many boys seem to outgrow the condition following puberty.

    Causes

    • LQTS may be either inherited or acquired. Acquired LQTS may be caused by side effects from certain medications, thyroid problems, conditions causing electrolyte imbalances or may result from anorexia nervosa. There are seven known inherited forms of LQTS, according to the National Heart Lung and Blood Institute. Genetic diagnostic testing is currently available for LQTS types 1-5.

    Symptoms and Diagnosis

    • Patients may present with symptoms of unexplained fainting, seizures or death; although many people with LQTS do not experience any symptoms at all. To diagnose LQTS, doctors may order ECGs, stress tests and genetic testing, which is performed on a blood sample. According to the National Heart Blood and Lung Institute, people with inherited forms of LQTS types 1-7 have a 50 percent chance of passing the defective gene on to their children; as such, for those identified with a defect it is recommended that their children undergo genetic testing as well.

    Advantages of Genetic Testing

    • News-Medical.net reports that up to 50 percent of patients with the inherited form LQTS 1 have a normal ECG pattern, thus making the condition difficult to detect. However, if a patient is known to have a family history of LQTS it is possible to detect and treat it due to the advent of genetic testing. Also useful is determining which genetic subtype of LQTS a patient has, as different types of inherited LQTS are known to have different triggers for arrhythmias. Knowing the genetic subtype allows physicians to tailor both lifestyle and medical treatments accordingly.

    Limitations

    • While genetic testing is available for five of the most common inherited forms of LQTS, there are at least two more types for which tests are not currently available. Another limiting factor of LQTS genetic testing is cost. According to theheart.org, as of 2010, individuals with suspected heritable LQTS can expect to pay upwards of $5,400 USD for comprehensive testing. Additionally, if a genetic variant of LQTS is found, it will cost $900 to test each of the patient's children for that one specific variant. As insurance often does not cover the costs of these tests, many people find the procedure prohibitive and opt out of screening.

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