Digenic inheritance novel mutations in SCN5a and SNTA1 increase late I_Na contributing to LQT syndrome

Abstract

are reported susceptible genes for long QT syndrome (LQTS). This study was designed to elucidate a plausible pathogenic arrhythmia mechanism for the combined novel mutations R800L-SCN5A and A261V-SNTA1 on cardiac sodium channels. A Caucasian family with syncope and marginally prolonged QT interval was screened for LQTS-susceptibility genes and found to harbor the R800L mutation in SCN5A and A261V mutation in SNTA1, and those with both mutations had the strongest clinical phenotype. The mutations were engineered into the most common splice variant of human SCN5A and SNTA1 cDNA, respectively, and sodium current (INa) was characterized in human embryonic kidney 293 cells cotransfected with neuronal nitric oxide synthase (nNOS) and the cardiac isoform of the plasma membrane Ca-ATPase (PMCA4b). Peak INa densities were unchanged for wild-type (WT) and for mutant channels containing R800L-SCN5A, A261V-SNTA1, or R800L-SCN5A plus A261V-SNTA1. However, late INa for either single mutant was moderately increased two-to threefold compared with WT. The combined mutations of R800L-SCN5A plus A261V-SNTA1 significantly enhanced the I Na late/peak ratio by 5.6-fold compared with WT. The time constants of current decay of combined mutant channel were markedly increased. The gain-of-function effect could be blocked by the N G -monomethyl-L-arginine, a nNOS inhibitor. We conclude that novel mutations in SCN5A and SNTA1 jointly exert a nNOS-dependent gain-of-function on SCN5A channels, which may consequently prolong the action potential duration and lead to LQTS phenotype.

Mexiletine rescues a mixed biophysical phenotype of the cardiac sodium channel arising from the SCN5A mutation, N406K, found in LQT3 patients

“…Membrane current data were digitized at 100 kHz, low-pass filtered at 5 kHz, and then normalized to membrane capacitance. The standard voltage clamp protocols are presented with the data and have been previously described [16]. …”

Diseases Caused by Mutations in Nav1.5 Interacting Proteins

“…When these were co-expressed with Na V 1.5, PMCA4b, and nNOS the results for S287R, T372M and G460S were similar to A390V-SNTA showing increased late I Na that was blocked by nNOS inhibitors, thereby establishing mutations in SNTA1 as a plausible cause of SIDS. Missense mutations in both SNTA1 and Na V 1.5 (A261V-SNTA and R800L-Na V 1.5) were found in a three generation family with LQTS 24 . Co-expression of both mutations showed increased late I Na that was the sum of each mutation expressed alone, suggesting additive effects to produce the phenotype.…”

Disease Caused by Mutations in NaV-β Subunit Genes

“…[61][62][63] Additionally, other sodium channel interacting protein variations might be able to augment or attenuate the clinical phenotype. [64][65][66] Moreover, interaction of Na V -b subunits with the main a subunit isoform depends on other conditions as shown recently with b2, which modulates Na V 1.5 mainly in the presence of sialic acids, whereas modulation of Na V 1.2 by b2 is sialic acid independent. 61 All these conditions might contribute to the development of the phenotype in Na V -b subunit mutations.…”