This report describes general characteristics of the group of diseases classified as long QT syndrome. Long QT syndrome is an autosomal disorder, with multiple genes and mapped loci, and is characterized by delayed repolarization of the heart following a heartbeat increases the risk of episodes of torsade de pointes (TDP, a form of irregular heartbeat that originates from the ventricles). A listing of long QT syndrome subtypes, as defined by OMIM, may be found in the table below, with links to more detailed reports for subtypes that have been investigated using fly models.
[updated May 2016 by FlyBase; FBrf0222196]
Long QT syndrome (LQTS) is a cardiac electrophysiologic disorder, characterized by QT prolongation and T-wave abnormalities on the ECG and the ventricular tachycardia torsade de pointes (TdP). TdP is usually self-terminating, thus causing a syncopal event, the most common symptom in individuals with LQTS. Syncope typically occurs during exercise and high emotions, less frequently at rest or during sleep, and usually without warning. In some instances, TdP degenerates to ventricular fibrillation and causes aborted cardiac arrest (if the individual is defibrillated) or sudden death. Approximately 50% of individuals with a pathogenic variant in one of the genes associated with LQTS have symptoms, usually one to a few syncopal spells. While cardiac events may occur from infancy through middle age, they are most common from the pre-teen years through the 20s. Some types of LQTS are associated with a phenotype extending beyond cardiac arrhythmia. In addition to the prolonged QT interval, associations include muscle weakness and facial dysmorphism in Andersen-Tawil syndrome (LQTS type 7, MIM:170390), hand/foot, facial, and neurodevelopmental features in Timothy syndrome (LQTS type 8, MIM:601005) and profound sensorineural hearing loss in Jervell and Lange-Nielson syndrome (MIM:220400, MIM:612347). [from GeneReviews, Long QT Syndrome, pubmed:20301308 2016.06.07]
Congenital long QT syndrome is electrocardiographically characterized by a prolonged QT interval and polymorphic ventricular arrhythmias (torsade de pointes). These cardiac arrhythmias may result in recurrent syncope, seizure, or sudden death (Jongbloed et al., 1999, pubmed:10220144). [From MIM:192500, 2016.06.07]
Many subtypes of long QT syndrome are associated with mutations in genes encoding ion channel subunits. Approximately 10% of LQTS patients in whom a mutation is identified in one ion channel gene carry a second mutation in the same gene or in another ion channel gene (Tester et al., 2005, pubmed:15840476).
