Cardiac ryanodine receptor (RyR2) gain-of-function mutations cause catecholaminergic polymorphic ventricular tachycardia, a condition characterized by prominent ventricular ectopy in response to catecholamine stress, which can be reproduced on exercise stress testing (EST). However, reports of sudden cardiac death (SCD) have emerged in EST-negative individuals who have loss-of-function (LOF) RyR2 mutations. The clinical relevance of RyR2 LOF mutations including their pathogenic mechanism, diagnosis, and treatment are all unknowns. Here, we performed clinical and genetic evaluations of individuals who suffered from SCD and harbored an LOF RyR2 mutation. We carried out electrophysiological studies using a programed electrical stimulation protocol consisting of a long-burst, long-pause, and short-coupled (LBLPS) ventricular extra-stimulus. Linkage analysis of RyR2 LOF mutations in six families revealed a combined logarithm of the odds ratio for linkage score of 11.479 for a condition associated with SCD with negative EST. A RyR2 LOF mouse model exhibited no catecholamine-provoked ventricular arrhythmias as in humans but did have substantial cardiac electrophysiological remodeling and an increased propensity for early afterdepolarizations. The LBLPS pacing protocol reliably induced ventricular arrhythmias in mice and humans having RyR2 LOF mutations, whose phenotype is otherwise concealed before SCD. Furthermore, treatment with quinidine and flecainide abolished LBLPS-induced ventricular arrhythmias in model mice. Thus, RyR2 LOF mutations underlie a previously unknown disease entity characterized by SCD with normal EST that we have termed RyR2 Ca2+ release deficiency syndrome (CRDS). Our study provides insights into the mechanism of CRDS, reports a specific CRDS diagnostic test, and identifies potentially efficacious anti-CRDS therapies.

Hutchinson-Gilford progeria syndrome (HGPS) is a rare genetic disease caused by defective prelamin A processing, leading to nuclear lamina alterations, severe cardiovascular pathology, and premature death. Prelamin A alterations also occur in physiological aging. It remains unknown how defective prelamin A processing affects the cardiac rhythm. We show age-dependent cardiac repolarization abnormalities in HGPS patients that are also present in the Zmpste24−/− mouse model of HGPS. Challenge of Zmpste24−/− mice with the β-adrenergic agonist isoproterenol did not trigger ventricular arrhythmia but caused bradycardia-related premature ventricular complexes and slow-rate polymorphic ventricular rhythms during recovery. Patch-clamping in Zmpste24 −/− cardiomyocytes revealed prolonged calcium-transient duration and reduced sarcoplasmic reticulum calcium loading and release, consistent with the absence of isoproterenol-induced ventricular arrhythmia. Zmpste24 −/− progeroid mice also developed severe fibrosis-unrelated bradycardia and PQ interval and QRS complex prolongation. These conduction defects were accompanied by overt mislocalization of the gap junction protein connexin43 (Cx43). Remarkably, Cx43 mislocalization was also evident in autopsied left ventricle tissue from HGPS patients, suggesting intercellular connectivity alterations at late stages of the disease. The similarities between HGPS patients and progeroid mice reported here strongly suggest that defective cardiac repolarization and cardiomyocyte connectivity are important abnormalities in the HGPS pathogenesis that increase the risk of arrhythmia and premature death.Hutchinson-Gilford progeria syndrome | progerin | prelamin A | connexin43 | calcium handling T he LMNA gene encodes A-type lamins (lamin A and lamin C), key components of the mammalian nuclear envelope with important structural and regulatory functions that affect signaling, transcription, and chromatin organization among other processes (1). Mature lamin A is produced from the precursor prelamin A through a series of posttranslational modifications, consisting of sequential farnesylation at the cysteine in the Cysteine-SerineIsoleucine-Methionine motif, cleavage of the Serine-IsoleucineMethionine residues, carboxymethylation of the newly accessible cysteine, and a final proteolytic cleavage by the zinc metallopeptidase STE24 (ZMPSTE24, also called FACE-1) (2).Mutations in the human LMNA gene or defective processing of prelamin A cause a group of diseases termed laminopathies, including the premature aging disorder Hutchinson-Gilford progeria syndrome (HGPS), a very rare genetic disorder with an estimated prevalence of 1 in 21 million people (www.progeriaresearch.org). SignificanceDefective prelamin A processing causes cardiovascular alterations and premature death in Hutchinson-Gilford progeria syndrome (HGPS) patients and also occurs during physiological aging. We found overt repolarization abnormalities in HGPS patients at advanced disease stages. Similar alterations were present in proger...

Rationale Phospholamban (PLN) is an inhibitor of cardiac sarco(endo)plasmic reticulum Ca2+ ATPase (SERCA2a). PLN knockout (PLN-KO) enhances sarcoplasmic reticulum (SR) Ca2+ load and Ca2+ leak. Conversely, PLN-KO accelerates Ca2+ sequestration and aborts arrhythmogenic spontaneous Ca2+ waves (SCWs). An important question is whether these seemingly paradoxical effects of PLN-KO exacerbate or protect against Ca2+-triggered arrhythmias. Objective We investigate the impact of PLN-KO on SCWs, triggered activities, and stress-induced ventricular tachyarrhythmias (VTs) in a mouse model of cardiac ryanodine receptor (RyR2)-linked catecholaminergic polymorphic ventricular tachycardia (CPVT). Methods and Results We generated a PLN-deficient, RyR2 mutant mouse model (PLN−/−/RyR2-R4496C+/−) by crossbreeding PLN-KO mice with CPVT-associated RyR2-R4496C mutant mice. Ca2+ imaging and patch-clamp recording revealed cell-wide propagating SCWs and triggered activities in RyR2-R4496C+/− ventricular myocytes during SR Ca2+ overload. PLN-KO fragmented these cell-wide SCWs into mini-waves and Ca2+ sparks, and suppressed triggered activities evoked by SR Ca2+ overload. Importantly, these effects of PLN-KO were reverted by partially inhibiting SERCA2a with 2,5-Di-tert-butylhydroquinone (tBHQ). However, Bay K, caffeine, or Li+ failed to convert mini-waves to cell-wide SCWs in PLN−/−/RyR2-R4496C+/− ventricular myocytes. Furthermore, ECG analysis showed that PLN-KO mice are not susceptible to stress-induced VTs. On the contrary, PLN-KO protected RyR2-R4496C mutant mice from stress-induced VTs. Conclusions Our results demonstrate that despite severe SR Ca2+ leak, PLN-KO suppresses triggered activities and stress-induced VTs in a mouse model of CPVT. These data suggest that breaking up cell-wide propagating SCWs by enhancing Ca2+ sequestration represents an effective approach for suppressing Ca2+-triggered arrhythmias.