RYR2 and familial long QT syndrome: This frequency was also higher and more severe compared with that in genotype-unknown LQTS, while the QTc interval was shorter in patients with the RYR2 mutation than that with genotype-negative LQTS (439 ± 30 vs. 471 ± 50 ms; p-value = 0.01), strengthening the importance of RYR2 in LQTS pathogenesis.