The common polymorphism SCN5A-S1103Y (∼13% allelic frequency in African Americans) is a risk factor for arrhythmia, sudden unexplained death (SUD), and sudden infant death syndrome.
Our data provide evidence that SCN5A allelic expression imbalance occurs in African-Americans heterozygous for p.Ser1103Tyr, but this phenomenon alone does not appear to be a marker for risk of SIDS.
Targeted mutational analysis of exon 18 in SCN5A of the African-American SIDS cohort (n = 71) revealed the S1103Y polymorphism in 16 (22.5%) of 71 African-American cases of SIDS compared to 135 (11.6%) of 1,161 ostensibly healthy adult African Americans (P = .01).
Wild-type and mutant SCN5A channels both functioned typically under normal conditions in vitro, but exposure to acidic intracellular pH levels such as those found in respiratory acidosis--a known risk factor for SIDS--produced abnormal gain-of-function late reopenings of S1103Y channels, behavior that is often associated with cardiac arrhythmias.