Abstract 2737: Ryanodine Receptor (RYR2) Mutations In Sudden Unexplained Death: Studies In Extended Pedigrees And Phenotypic Characterization In Vitro
Background - Up to 35% of victims of sudden unexplained death (SUD) feature morphologically normal hearts in the autopsy, suggestive of an ion channel disorder as a cause for sudden death. Catecholaminergic polymorphic ventricular tachycardia caused by mutations in the RYR2 gene manifests as severe arrhythmias, and may provide a candidate for otherwise autopsy-negative sudden deaths.
Materials and Methods - We screened 19 victims of SUD for mutations in the RYR2 gene by direct sequencing, and analyzed DNAs from available family members. A total of 300 blood donors served as controls for DNA analysis. Medico-legal investigations were conducted by experienced pathologists. We performed resting ECG, cardiac ultrasonography, exercise stress test, epinephrine test and 24-hour ambulatory ECG recording to available mutation carriers (n=18). The single channel recordings of the mutant RYR2s were conducted in planar lipid bilayers, and the open probabilities (Po) were determined by sequential addition of CaCl2 to the cis-side.
Results - Genetic analyses revealed two novel RYR2 missense mutations (G2145R and R3570W) unidentifiable in the controls in three (16%) victims of SUD. None of the living mutation carriers showed exercise-provoked premature ventricular complexes (PVCs), but two carriers of R3570W exhibited PVCs predominantly at rest. The two deceased carriers of R3570W featured dilated hearts and left ventricle wall up to 12–15 mm in the autopsy, and two surviving carriers of R3570W showed minor dilatations of the left ventricle. The living carrier of G2145R exhibited no cardiac abnormalities. The open probabilities (Po) of the R3570W appeared statistically significantly higher compared to the wild type channels (Po of 6.0 ± 2.7 % at 350 nM, 15.6 ± 4.2 % at 700 nM and 30.1 ± 6.3 % at 1 μM [Ca2+]cis for R3570W vs. Po of 0.1 ± 0.1 % at 350 nM, 2.6 ± 1.9 % at 700 nM and 10.6 ± 6.4 % at 1 μM [Ca2+]cis for wild-type, p<0.05). The mean Po of G2145R was statistically significantly higher than the wild-type at 1μM [Ca2+]cis (Po of 30.3 ± 6.6 % for G2145R vs. 10.6 ± 6.4 % for wild-type, p<0.05).
Conclusion - RYR2 mutations manifesting as a gain-of-function defect in vitro may underlie some cases of SUD. Not all the mutations of RYR2 result in a phenotype typical of CPVT.