Abstract 4400: Comprehensive Open Reading Frame Mutational Analysis of the RYR2-Encoded Ryanodine Receptor/Calcium Channel in Patients Diagnosed Previously with Either Catecholaminergic Polymorphic Ventricular Tachycardia or Genotype Negative, Exercise-Induced Long QT Syndrome
Pathogenic mutations in the RYR2-encoded cardiac ryanodine receptor cause type 1 catecholaminergic polymorphic ventricular tachycardia (CPVT1), a cardiac channelopathy with increased propensity for lethal ventricular dysrhythmias. Most RYR2 mutational analyses target three canonical domains encoded by < 40% of the translated exons. The extent of mutations localizing outside of these domains remains unknown as RYR2 has not been examined comprehensively in most patient cohorts. Mutational analysis of all 105 RYR2 exons was performed using PCR, DHPLC, and DNA sequencing on 108 unrelated patients (57% females, 96% white, age at diagnosis 18 ± 13 years, mean QTc 424 ± 26 ms) with either an explicit referral diagnosis of CPVT (N = 60) or an initial diagnosis of exercise-induced long QT syndrome (LQTS) but with QTc < 480 ms and a subsequent negative LQTS genetic test (N = 48). Two hundred healthy individuals from the Human Genetic Cell Repository were examined to assess allelic frequency for all non-synonymous variants detected. Thirty-eight (15 novel) possible CPVT1-associated mutations absent in 400 reference alleles, were detected in 44 unrelated patients (41%). Three cases (7%) had >1 RYR2 mutation. Besides the 25 exons known previously to contain causative mutations, eight new mutation-containing exons were identified: 10, 12, 13, 21, 26, 40, 42, and 48. Nearly two-thirds of the CPVT1-positive patients had mutations that localized to one of only 7 exons: 8, 14, 47, 90, 93, 100, and 101. In addition, 5 (2 novel) common non-synonymous single nucleotide polymorphisms were identified. This study represents one of the largest cohorts of patients for which RYR2 was examined in its entirety. Possible CPVT1 mutations in RYR2 were identified in approximately 41% of both CPVT referrals and LQTS gene-negative patients with exercise-induced syncope and QTc <480 ms. Including the eight new exons hosting mutations in this study, 33 of the 105 translated exons are now known to host possible mutations. Considering that two-thirds of CPVT1-positive cases would be discovered by selective analysis of <10 exons, a tiered targeting strategy for mutation discovery may afford a more cost-effective approach to CPVT genetic testing.