Long QT syndrome (LQTS) is a cardiac electrophysiologic disorder, characterized by QT prolongation and T-wave abnormalities on the EKG that are associated with tachyarrhythmias, typically 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. Such cardiac events typically occur during exercise and emotional stress, less frequently 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 untreated individuals with a pathogenic variant in one of the genes associated with LQTS have symptoms, usually one to a few syncopal events. While cardiac events may occur from infancy through middle age, they are most common from the preteen 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); hand/foot, facial, and neurodevelopmental features in Timothy syndrome (LQTS type 8); and profound sensorineural hearing loss in Jervell and Lange-Nielson syndrome.

Long QT syndrome (LQTS) is a cardiac electrophysiologic disorder, characterized by QT prolongation and T-wave abnormalities on the EKG that are associated with tachyarrhythmias, typically 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. Such cardiac events typically occur during exercise and emotional stress, less frequently 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 untreated individuals with a pathogenic variant in one of the genes associated with LQTS have symptoms, usually one to a few syncopal events. While cardiac events may occur from infancy through middle age, they are most common from the preteen 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); hand/foot, facial, and neurodevelopmental features in Timothy syndrome (LQTS type 8); and profound sensorineural hearing loss in Jervell and Lange-Nielson syndrome.

LQT16 Long QT syndrome-16 (LQT16) is characterized by a markedly prolonged corrected QT (QTc) interval and 2:1 atrioventricular (AV) block, with onset in the perinatal period. Patients experience bradycardia or ventricular tachyarrhythmias that may result in syncope, cardiac arrest, and/or sudden death (Reed et al., 2015; Wren et al., 2019). Patients with LQT14 (616247), LQT15 (616249), or LQT16, resulting from mutation in calmodulin genes CALM1 (114180), CALM2 (114182), or CALM3, respectively, typically have a more severe phenotype, with earlier onset, profound QT prolongation, and a high predilection for cardiac arrest and sudden death, than patients with mutations in other genes (Boczek et al., 2016). CPVT6 Catecholaminergic polymorphic ventricular tachycardia-6 (CPVT6) is characterized by childhood-onset syncopal episodes with exercise or stress. Electrocardiogram (ECG) shows a normal QT interval with a prominent U wave, and stress testing reveals premature ventricular contractions (PVCs) that may occur as bigeminy or couplets, and nonsustained ventricular tachycardia (Gomez-Hurtado et al., 2016).