Diplotype analysis of the human cardiac sodium channel regulatory region in Japanese cases of sudden death by unknown causes

Inherited mutations in the human cardiac sodium channel (SCN5A) gene cause arrhythmogenic diseases such as tachyarrhythmia and bradyarrhythmia. Moreover, mutation subsets in the coding region impair SCN5A function, potentially leading to sudden cardiac death (SCD). In the present study, we performed diplotype analysis of the regulatory region of the SCN5A gene in Japanese people who died suddenly because of an unknown cause (sudden death group; n = 70) and controls (n = 112). There were no significant differences at six polymorphic loci between the groups. However, 38 diplotypes of 6-nucleotide polymorphism variants were identified. One of these diplotypes-Dip.D (CTG-TC/CCG-TC)-occurred significantly more frequently in the sudden death group than in the controls (p < 0.01, OR = 5.18, 95% CI: 1.38-19.45). Dip.D has two variants (T-1062C and T-847G), and while it is unclear whether these directly affect mRNA expression, a common polymorphism in this region modulates SCN5A expression in vitro. Our results thus suggest that the transcription of the SCN5A Dip.D variant may be associated with arrhythmogenic diseases that can induce sudden death.