Long QT and short QT syndromes (LQTS and SQTS) are cardiac repolarization 
abnormalities that are characterized by length perturbations of the QT interval 
as measured on electrocardiogram (ECG). Prolonged QT interval and a propensity 
for ventricular tachycardia of the torsades de pointes (TdP) type are 
characteristic of LQTS, while SQTS is characterized by shortened QT interval 
with tall peaked T-waves and a propensity for atrial fibrillation. Both 
syndromes represent a high risk for syncope and sudden death. LQTS exists as a 
congenital genetic disease (cLQTS) with more than 700 mutations described in 12 
genes (LQT1-12), but can also be acquired (aLQTS). The genetic forms of LQTS 
include Romano-Ward syndrome (RWS), which is characterized by isolated LQTS and 
an autosomal dominant pattern of inheritance, and syndromes with LQTS in 
association with other conditions. The latter includes Jervell and Lange-Nielsen 
syndrome (JLNS), Andersen syndrome (AS), and Timothy syndrome (TS). The genetics 
are further complicated by the occurrence of double and triple heterozygotes in 
LQTS and a considerable number of nonpathogenic rare polymorphisms in the 
involved genes. SQTS is a very rare condition, caused by mutations in five genes 
(SQTS1-5). The present mutation update is a comprehensive description of all 
known LQTS- and SQTS-associated mutations.