Background-Calmodulin (CaM) mutations are associated with severe forms of long QT syndrome and catecholaminergic polymorphic ventricular tachycardia (CPVT). CaM mutations are found in 13% of genotype-negative long QT syndrome patients, but the prevalence of CaM mutations in genotype-negative CPVT patients is unknown. Here, we identify and characterize CaM mutations in 12 patients with genotype-negative but clinically diagnosed CPVT. Methods and Results-We performed mutational analysis of CALM1, CALM2, and CALM3 gene-coding regions, in vitro measurement of CaM-Ca2+ (Ca)-binding affinity, ryanodine receptor 2-CaM binding, Ca handling, L-type Ca current, and action potential duration. We identified a novel CaM mutation-A103V-in CALM3 in 1 of 12 patients (8%), a female who experienced episodes of exertion-induced syncope since age 10, had normal QT interval, and displayed ventricular ectopy during stress testing consistent with CPVT. A103V modestly lowered CaM Ca-binding affinity (3-fold reduction versus WT-CaM), but did not alter CaM binding to ryanodine receptor 2. In permeabilized cardiomyocytes, A103V-CaM (100 nmol/L) promoted spontaneous Ca wave and spark activity, a cellular phenotype of ryanodine receptor 2 activation. Even a 1:3 mixture of A103V-CaM:WT-CaM activated Ca waves, demonstrating functional dominance. Compared with long QT syndrome D96V-CaM, A103V-CaM had significantly less effects on L-type Ca current inactivation, did not alter action potential duration, and caused delayed afterdepolarizations and triggered beats in intact cardiomyocytes. Conclusions-We discovered a novel CPVT mutation in the CALM3 gene that shares functional characteristics with established CPVT-associated mutations in CALM1. A small proportion of A103V-CaM is sufficient to evoke arrhythmogenic Ca disturbances via ryanodine receptor 2 dysregulation, which explains the autosomal dominant inheritance.
Bibliographical noteFunding Information:
This work was partly supported by the United States National Institutes of Health (HL88635, HL71670, and HL108173 to B.C. Knollmann); 5 F32 HL117612-02 to C.N. Johnson; T32 HL069764 (to F.R. Nitu); HL092097 and AG26160 to R.L. Cornea; by the American Heart Association (13IRG13680003 to B.C. Knollmann, 12POST12080080 to D.O. Kryshtal, and 15GRNT25610022 to R.L. Cornea); and by the Mayo Clinic Windland Smith Rice Comprehensive Sudden Cardiac Death Program to M.J. Ackerman.
© 2016 American Heart Association, Inc.
- calcium channel
- catecholaminergic polymorphic ventricular tachycardia
- ryanodine receptor