Influence of genetic modifiers on sudden cardiac death cases.

Sequence variants in the ion channel genes KCNH2 and SCN5A may cause the cardiac disorder long QT syndrome (LQTS). This disorder is associated with incomplete penetrance and variable expression in KCNH2- or SCN5A-mutation carriers. Common genetic variants, if associated with a mutation, may affect the severity of this cardiac disorder. This study identified rare mutations in the cardiac ion channel genes KCNH2 and SCN5A in a SCD case, as well as in a LQTS-affected family with a history of SCD. Moreover, common variants were found to occur together within the same genes. These findings support the concept that common single-nucleotide polymorphisms (SNPs) in genes encoding cardiac ion channels can directly modulate the functional effect of mutations and therefore enhance or weaken the risk of cardiac events.