Author’s reply: link of SCN5A SNP R1193Q to long QT syndrome: Table 1

Chen et al identified R1193Q, a single nucleotide polymorphism (SNP), in the cardiac sodium channel gene SCN5A , in a group of Han Chinese individuals. The frequency of SNP R1193Q in this Chinese population is high, reaching 12% (11/94).1 The results confirm our earlier report that SNP R1193Q is present in the general population.2 SNP R1193Q occurs within the context of a CpG dimer. Because most methylation in human DNA occurs at the C in the CpG dimer, it will interfere with efficient correction of C to T transitions resulting from 5-methyl cytosine deamination, making R1193 a potential hotspot for mutation.3 SCN5A is one of the disease causing genes for long QT syndrome (LQTS), a cardiac disorder characterised by a prolonged QT interval on electrocardiogram (ECG).4,5 LQTS patients have a high risk of syncope and sudden death due to a specific ventricular tachyarrhythmia, torsade de pointes. LQTS can be classified into two types, congenital LQTS or acquired LQTS. Congenital LQTS is uncommon, but acquired LQTS is common and may be present in more than 8% of the general population.2 Congenital LQTS is caused by genetic defects. To date, more than 250 different …