SCN5A and familial long QT syndrome: These analyses revealed that this polymorphism was present as a heterozygous allele in all samples (Figure S3 in File S1), suggesting that if any modulation of Nav1.5 function would occur through this polymorphism the effect would be manifested in CM derived from both control and LQTS-3 iPS cells and is thus not expected to be a confounding factor in our experiments.