Long QT Syndrome
What is Long QT Syndrome?
Long QT syndrome (LQTS) is a condition that affects the ability of the heart to beat (contract) regularly and efficiently.
The length of a heartbeat is divided in five waves that are labelled P, Q, R, S and T, and the time between the Q and T wave – also known as the QT interval – is the time where your heart contracts and fills with blood, before the next heartbeat. When the QT interval is longer than normal, you are considered to have LQTS.
It is estimated that LQTS occurs in at least one in 3000 people, with both men and women of all ethnic backgrounds equally at risk. While the genetic form of LQTS is rare, only occurring in one out of 2000 people, it is an important cause of sudden death in children, adolescents and young adults. Sudden death is also the first and only symptom in 10 to 15 percent of fatal LQTS events.
What causes Long QT Syndrome?
Genetic causes have been found in at least 75 percent of individuals diagnosed with LQTS, and mutations in more than 12 different genes have been linked to the condition. The disorder is usually inherited as an autosomal dominant trait, so there is a 50 percent chance of passing the genetic defect down to children.
Why test for Long QT Syndrome?
Genetic testing is a diagnostic tool that may be considered for patients who clinically manifest with symptoms of LQTS and for asymptomatic family members of patients with a known mutation. It is most useful if a member of the family has been clinically diagnosed with the condition.
If the mutation causing LQTS is identified in one person, testing can help to identify other at-risk family members who will benefit from cardiac treatment and surveillance. And if a gene mutation is not found, there will be no need for further cardiac evaluations.
How does the test work?
The LQTS genetic test is a blood test ordered by your physician. Your DNA is extracted from the blood and analyzed by searching specifically for mutations in any genes that are associated with LQTS. The test takes approximately four weeks to complete, and the results will be sent to your physician, who will explain the test results to you.
We will need two tubes of blood (about 7 to 10ml) and a signed consent form from you to send to the laboratory. We recommend genetic counselling before genetic tests are ordered to discuss the implications of the testing and potential results.