Calcium Revisited: New Insights Into the Molecular Basis of Long-QT Syndrome.

Abstract

The first clinical description of long-QT syndrome (LQTS) occurred in 1957 when Drs Anton Jervell and Fred Lange-Nielsen postulated that syncopal/seizure episodes and high propensity for sudden cardiac death (SCD) observed in a subset of children with sensorineural deafness and otherwise unexplained heart rate–corrected QT interval prolongation on ECG stemmed from a novel congenital disorder.1 This was followed by independent descriptions of a syndrome characterized by a cardiac-only phenotype consisting of prolonged QT intervals and an increased risk for syncope, seizures, and SCD in the absence of sensorineural deafness by Drs Cesarino Romano and Owen Ward, in 1963 and 1964, respectively.2,3 During the past 5 decades, insights gleamed from a multitude of clinical, epidemiological, and molecular studies have demonstrated that LQTS is a collection of not only genetically and phenotypically diverse disorders of cardiac repolarization that encompasses the aforementioned predominantly autosomal-dominant, nonsyndromic Romano–Ward syndrome now simply referred to as LQTS4 and autosomal-recessive, multisystem, Jervell–Lange Nielsen syndrome but also exceedingly rare multisystem LQTS subtypes such as Timothy syndrome (TS) characterized by QT prolongation and an increased risk of SCD along with an array of extracardiac manifestations. Although mutations in calcium (Ca2+)-handling proteins, including the CACNA1C -encoded L-type Ca2+ channel (LTCC), RYR2 -encoded ryanodine receptor-2 intracellular calcium release channel (RyR2), and many other auxiliary interacting proteins, are central to the pathogenesis of inherited cardiac arrhythmia syndromes, such as catecholaminergic ventricular tachycardia and Brugada syndrome, until recently, the contribution of dysfunctional Ca2+ handling to the pathogenesis of LQTS was limited to the extremely rare and highly lethal multisystem TS. However, the unexpected recent discoveries of multiple nonsyndromic LQTS-causative mutations in CACNA1C ,5–7 syndromic LQTS-causative mutations in CALM1-3 -encoded Calmodulin8,9 and TRDN -encoded Triadin,10 and common genetic variation at …