Long QT syndrome (LQTS) is a hereditary cardiac disease characterized by a prolongation of the QT interval at basal ECG and by a high risk of life-threatening arrhythmias. It can be caused by mutations in several cardiac ion channel genes. There are eight types of LQT syndrome based on the gene in which causative mutations occur. The most prevalent forms are LQT1, LQT2, and LQT3. Half of individuals with LQT2 remain asymptomatic until the age of 16. Symptoms are triggered by a variety of causes including emotions, auditory experience, and exercise. Furthermore, some cases may occur during rest and sleep.
The diagnosis of LQT2 is based on electrocardiogram (ECG) abnormalities; notched T waves are most commonly seen in this type. Patients with LQT2 have symptom relief from beta-blocker therapy. Symptoms can also be improved in patients who maintain their potassium levels and modify their lifestyles. Treatment with potassium may be recommended.
pore-forming subunit of the potassium channel, are the cause of Long QT syndrome 2. These mutations result in diminution of IKr current. Therefore, IKr channels that incorporate mutated subunits carry a reduced IKr repolarizing current with abnormal ventricular repolarization.
Bhuiyan et al. (2009) described four Saudi families with long QT syndrome 2; three of them had recessive mode of inheritance and one was dominant. The first family had an affected girl, who had multiple, short attacks of syncope with seizures from the age of 12 years. The second family had a 14-year-old girl who had episodes of syncope and tonic-clonic seizures at the age of 6 and 12 years, from which she recovered within 3-4 minutes. The third family had a 3-year-old boy who was delivered at 32 weeks by Cesarean section because he had alternative episodes of brady and tachyarrhythmis from the age of 22 weeks of gestational age. The parents were consanguineous and healthy. The fourth family had a 10-week-old baby boy who, at the age of 5 days, had cardiopulmonary arrest; he was feeding poorly and suddenly stopped breathing. The third and the fourth families were diagnosed with the recessive variant of LQT2, and they both originated from the Assir region.
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