Calcium release channel deficiency syndrome in patients diagnosed with idiopathic ventricular fibrillation and decedents classified as sudden unexplained death in the young.
AIMS: Calcium release channel deficiency syndrome (CRCDS) results from loss-of-function (LOF) variants in the RYR2-encoded type 2 ryanodine receptor (RyR2), predisposing patients to sudden cardiac arrest/death (SCA/SCD) without abnormalities on a stress electrocardiogram (ECG). Undetected CRCDS may underlie idiopathic ventricular fibrillation (IVF) and sudden unexplained death in the young (SUDY). We aimed to determine the prevalence of potential CRCDS-causative RYR2 variants in IVF and SUDY. METHODS AND RESULTS: We reviewed clinical evaluation and RYR2 genetic analysis of 169 IVF patients and 279 SUDY victims. Only ultra-rare (<0.005% in gnomAD) nonsynonymous RYR2 variants were considered potentially pathogenic. Among IVF patients, 6/169 (3%) overall-and 6/67 (9%) with exertion-related SCA-harboured an RYR2 variant and represent potential CRCDS cases. All exhibited normal resting and stress ECGs. Genetic analysis revealed six distinct RYR2 variants, two previously characterized as LOF. In SUDY, 31/279 victims (11%) had a RYR2 variant (30 unique variants), predominantly observed in exertion-related SCD 20/83 (24%) vs. rest-related 11/196 (6%). Of the 14 SUDY victims with functionally characterized RYR2 variants, five (2% of total cohort) had a LOF variant; among the 56 exertion-related SUDY cases, four (7%) had a LOF variant. CONCLUSION: CRCDS may account for 3% of IVF overall and 9% of exertion-related SCA in IVF. Ultra-rare RYR2 variants may underlie up to 11% of SUDY, with 65% of RYR2-positive cases occurring during exertion. LOF-RYR2 variants may contribute to ≥7% of exercise-associated SUDY. Accurate identification of the underlying ryanodinopathy is essential for clinical management of affected patients.