What your DNA says about you

with just a saliva sample and from home


QT Intervals

Long QT syndrome

Long QT syndrome (LQTS) is a genetic disease associated with abnormal cardiac ion channel function, which affects individuals without evident cardiac structure anomalies and which manifests itself through the lengthening of the QT interval on the electrocardiogram

Congenital long QT interval is a family affectation, affecting 1/5,000 persons, and is the principal cause of sudden death in children and adolescents.

The space between the start of the Q wave and the end of the T wave (Q-T interval) corresponds to the time it takes for your heart to contract and then refill with blood before beginning the next contraction. Long QT syndrome is characterized by a prolonged repolarization. In it, your heart muscle takes longer than normal to recharge between beats. This electrical disturbance, which often can be seen on an electrocardiogram (ECG), is called a prolonged Q-T interval. Alterations can lead to syncope, ventricular tachycardia, torsade de pointes, cardiac arrest and sudden death.


Those persons affected by long QT syndrome do not always show symptoms. Where these do occur, the most common one are fainting and arrhythmia. Persons with long QT often present a prolonged QT interval during physical exercise, in moments of emotional stress or as a reaction to a loud or alarming sound.

The persons who suffer from LQTS have generally had at least one fainting episode before their 10th birthday. Other may have only one or two fainting episodes during childhood but no others afterwards.

Since LQT may produce an abnormal cardiac rhythm (arrhythmia), fainting or loss of consciousness (syncope) and even sudden death, it is important to seek medical attention for a child who has the above symptoms during physical exercise, intense emotional moments, swimming or brusque auditory stimulations.

Generally, Patients under clinical suspicion of long QT syndrome: asymptomatic subjects with serial ECGs showing QTc VALUES >460 ms (prepubescent) or > 470 ms in adult women and 450 ms in adult males. The QT interval is best measured in the II and V5 leads of the ECG.


A medical test is recommended for those subjects with

  • an ECG characteristic of the syndrome
  • a personal or family history of sudden death or suspicion of LQT
  • subjects with a history of syncope of unknown origin
  • subjects with ventricular fibrillation of unknown origin

There are no specific measures to prevent Long QT syndrome given the genetic importance but a specific study and follow-up is recommended for those persons who from young ages have had any syncope, especially when brought on by exercise, strong emotions or loud auditory stimulations.

Gene or region studied

  • NOS1AP
The DNA test you were looking for