Background: A novel familial arrhythmia syndrome, RyR2 calcium release deficiency syndrome (CRDS), has recently been described. We evaluated a large and well characterized family to assess provocation testing, risk factor stratification and response to therapy in CRDS. Methods: We present a family with multiple unheralded sudden cardiac deaths and aborted cardiac arrests, primarily in children and young adults, with no clear phenotype on standard clinical testing. Results: Genetic analysis, including whole genome sequencing, firmly established that a missense mutation in RYR2 , Ala4142Thr, was the underlying cause of disease in the family. Functional study of the variant in a cell model showed RyR2 loss-of-function, indicating that the family was affected by CRDS. EPS (Electrophysiological Study) was undertaken in 9 subjects known to carry the mutation, including a survivor of aborted sudden cardiac death, and the effects of flecainide alone and in combination with metoprolol were tested. There was a clear gradation in inducibility of nonsustained and sustained ventricular arrhythmia between subjects at EPS, with the survivor of aborted sudden cardiac death being the most inducible subject. Administration of flecainide substantially reduced arrhythmia inducibility in this subject and abolished arrhythmia in all others. Finally, the effects of additional metoprolol were tested; it increased inducibility in 4/9 subjects. Conclusions: The Ala4142Thr mutation of RYR2 causes the novel heritable arrhythmia syndrome CRDS, which is characterized by familial sudden death in the absence of prior symptoms or a recognizable phenotype on ambulatory monitoring or exercise stress testing. We increase the experience of a specific EPS protocol in human subjects and show that it is helpful in establishing the clinical status of gene carriers, with potential utility for risk stratification. Our data provide evidence that flecainide is protective in human subjects with CRDS, consistent with the effect previously shown in a mouse model.

BACKGROUND: A loss-of-function cardiac ryanodine receptor (RyR2) mutation, I4855M +/– , has recently been linked to a new cardiac disorder termed RyR2 Ca 2+ release deficiency syndrome (CRDS) as well as left ventricular noncompaction (LVNC). The mechanism by which RyR2 loss-of-function causes CRDS has been extensively studied, but the mechanism underlying RyR2 loss-of-function-associated LVNC is unknown. Here, we determined the impact of a CRDS-LVNC-associated RyR2-I4855M +/– loss-of-function mutation on cardiac structure and function. METHODS: We generated a mouse model expressing the CRDS-LVNC-associated RyR2-I4855M +/– mutation. Histological analysis, echocardiography, ECG recording, and intact heart Ca 2+ imaging were performed to characterize the structural and functional consequences of the RyR2-I4855M +/– mutation. RESULTS: As in humans, RyR2-I4855M +/– mice displayed LVNC characterized by cardiac hypertrabeculation and noncompaction. RyR2-I4855M +/– mice were highly susceptible to electrical stimulation–induced ventricular arrhythmias but protected from stress-induced ventricular arrhythmias. Unexpectedly, the RyR2-I4855M +/– mutation increased the peak Ca 2+ transient but did not alter the L-type Ca 2+ current, suggesting an increase in Ca 2+ -induced Ca 2+ release gain. The RyR2-I4855M +/– mutation abolished sarcoplasmic reticulum store overload–induced Ca 2+ release or Ca 2+ leak, elevated sarcoplasmic reticulum Ca 2+ load, prolonged Ca 2+ transient decay, and elevated end-diastolic Ca 2+ level upon rapid pacing. Immunoblotting revealed increased level of phosphorylated CaMKII (Ca 2+ -calmodulin dependent protein kinases II) but unchanged levels of CaMKII, calcineurin, and other Ca 2+ handling proteins in the RyR2-I4855M +/– mutant compared with wild type. CONCLUSIONS: The RyR2-I4855M +/– mutant mice represent the first RyR2-associated LVNC animal model that recapitulates the CRDS-LVNC overlapping phenotype in humans. The RyR2-I4855M +/– mutation increases the peak Ca 2+ transient by increasing the Ca 2+ -induced Ca 2+ release gain and the end-diastolic Ca 2+ level by prolonging Ca 2+ transient decay. Our data suggest that the increased peak-systolic and end-diastolic Ca 2+ levels may underlie RyR2-associated LVNC.