SCN5A and overlapping connective tissue disease: Moreover, SCN5A mutant gene is also responsible for dilated cardiomyopathy, atrial fibrillation, and sudden infant death syndrome.[5, 13] If more than one mutations of SCN5A co-exist, mixed or "overlap syndrome" clinical phenotypes may occur.[13] Hence, identifying causative genes and understanding the basis for ion channel functional abnormalities as well as the genotype-phenotype relationship is critical for explaining clinical phenomena and formulating appropriate therapeutic strategies.