LQT3

Long QT Syndrome Microchapters
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [2]

LQT3 Subtype

The LQT3 type of long QT syndrome accounts for 5-10% of cases, and cardiac events can occur during sleep. This variant involves a mutation of the gene that encodes the alpha subunit of the Na⁺ ion channel. This gene is located on chromosome 3p21-24, and is known as SCN5A (also hH1 and Na_V1.5). The mutations involved in LQT3 slow the inactivation of the Na⁺ channel, resulting in prolongation of the Na⁺ influx during depolarization. Paradoxically, the mutant sodium channels inactivate more quickly, and may open repetitively during the action potential.

A large number of mutations have been characterized as leading to or predisposing LQT3. Calcium has been suggested as a regulator of SCN5A, and the effects of calcium on SCN5A may begin to explain the mechanism by which some these mutations cause LQT3. Furthermore mutations in SCN5A can cause Brugada syndrome, Cardiac Conduction disease anddilated cardiomyopathy. Rarely some affected individuals can have combinations of these diseases.