Long QT Syndrome pathophysiology

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

Pathophysiology

Genetics

The two most common types of LQTS are genetic and drug-induced. Genetic LQTS can arise from mutation to one of several genes. These mutations tend to prolong the duration of the ventricular action potential (APD), thus lengthening the QT interval. LQTS can be inherited in an autosomal dominant or an autosomal recessive fashion. The autosomal recessive forms of LQTS tend to have a more severephenotype, with some variants having associated syndactyly (LQT8) or congenital neural deafness (LQT1). A number of specific genes loci have been identified that are associated with LQTS.

LQT10

This novel susceptibility gene for LQT is SCN4B encoding the protein Na_Vβ4, an auxiliary subunit to the pore-forming Na_V1.5 (gene: SCN5A) subunit of the voltage-gated sodium channel of the heart. The mutation leads to a positive shift in inactivation of the sodium current, thus increasing sodium current. Only one mutation in one patient has so far been found.

Associated syndromes

A number of syndromes are associated with LQTS.

Jervell and Lange-Nielsen syndrome

The Jervell and Lange-Nielsen syndrome (JLNS) is an autosomal recessive form of LQTS with associated congenital deafness. It is caused specifically by mutation of the KCNE1 and KCNQ1 genes

In untreated individuals with JLNS, about 50 percent die by the age of 15 years due to ventricular arrhythmias.

Romano-Ward syndrome

Romano-Ward syndrome is an autosomal dominant form of LQTS that is notassociated with deafness.