Common human SCN5A polymorphisms have altered electrophysiology when expressed in Q1077 splice variants

Background: Eight common (>0.5%) polymorphisms of SCN5A have been described in the US population. Every human also continuously generates two wild-type (WT) splice variants, one with a glutamine residue at position 1077 (Q1077) and one lacking this glutamine (Q1077del). One polymorphism (H558R) has been studied in both splice variants, five polymorphisms (R34C, R481W, S524Y, P1090L,V1951L) have not been previously studied, and two polymorphisms (S1103Y and R1193Q) have been studied in only one of the two splice variants. Objectives: The purpose of this study was to examine the electrophysiologic molecular phenotype of the eight common polymorphisms in the two human splice variants of SCN5A. Methods: Currents from 16 channels (all polymorphisms in both splice variants) were determined by voltage clamp and compared with WT after expression in HEK-293 cells. Results: Six of eight polymorphisms showed a distinct phenotype that depended upon the background splice variant used for expression. Only R34C and V1951L showed no functional differences. S524Y showed a dramatic reduction in current density in the Q1077 background similar to that previously described for H558R. Four other polymorphisms (R481W, P1090L, S1103Y, R1193Q) showed shifts in activation, inactivation, or recovery that depended upon the splice variants. Shifts of a similar magnitude have been reported for arrhythmia syndrome mutations and are thought to be pathogenic. Conclusion: The majority of common human SCN5 A polymorphisms have a distinct molecular phenotype that depends upon the splice variant background. These findings have implications for the interpretation of previous studies of arrhythmia mutations. The significance of these findings for clinical arrhythmia remains to be elucidated.