Likewise, genetic testing in long QT syndromes might lead to specification of therapy, because treatment with a beta-blocker is highly effective in patients with long QT syndrome 1, caused by mutations in KCNQ1, but not as effective in those with long QT syndrome 3 due to pathogenic variants in the SCN5A gene (reviewed in Schwartz et al. The gene discussed is KCNQ1; the disease is familial long QT syndrome.