Background: Several cardiac ion channel genes have been implicated in monogenic traits with a high risk of sudden cardiac death (SCD). Mutations or rare variants in these genes have been proposed as potential contributors to more common forms of SCD, but this hypothesis has not been assessed systematically.
Methods and results: We directly sequenced the entire coding region and splice junctions of 5 cardiac ion channel genes, SCN5A, KCNQ1, KCNH2, KCNE1, and KCNE2, in 113 SCD cases from 2 large prospective cohorts of women (Nurses' Health Study) and men (Health Professional Follow-Up Study). Controls from the same population were then screened for the presence of mutations or rare variants identified in cases, and sequence variants without prior functional data were expressed in Xenopus oocytes to assess their biophysical consequences. No mutations or rare variants were identified in any of the 53 subjects who were men. In contrast, in 6 of 60 women (10%), we identified 5 rare missense variants in SCN5A that either had been associated previously with long-QT syndrome (A572D and G615E), had been reported to alter sodium channel function (F2004L), or had not been reported previously in control populations (A572F and W1205C). Of the 4 variants without prior functional data, 3 variants were located in the I-II linker (A572D, A572F, and G615E), and all resulted in significantly shorter recovery times from inactivation. When compared with 733 control samples from the same population, the overall frequency of these rare variants in SCN5A was significantly higher in the SCD cases (6/60, 10.0%) than in controls (12/733, 1.6%; P=0.001).
Conclusions: Functionally significant mutations and rare variants in SCN5A may contribute to SCD risk among women.