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See article by Huang et al. [14] (pages 670–680) in this issue. The electrophysiological basis of the congenital long QT syndrome (LQTS), including both the Romano–Ward (RW) and the Jervell and Lange–Nielsen syndrome (JLN), relates to dysfunctioning ion channels, secondary to genetic aberrancies in their encoding genes (for review see Roden and Spooner [1]). Because these ion channels have different time and voltage characteristics gene-specific elements in clinical presentation have been searched for. Indeed, a gene-differentiating potential has been demonstrated, initially in small series and later confirmed in larger patient populations, for the morphology of ST-T segments [2–4] and for symptoms-related triggers [5–7]. To some extent also the clinical course including prognosis relies on the underlying gene defect [8]. Based on these data and other, more subtle differences [9], correct prediction of the genotype of clinically affected patients is feasible with reasonable accuracy. At present this prediction only refers to the causally related gene, i.e. KCNQ1, KCNH2 (HERG) or SCN5A and not to the site of a mutation within a specific gene. Recent data suggest, however, that, for example in LQT2/KCNH2 specific ST-T segment characteristics exist for the type and localization of mutations [4].In LQT1 and LQT2 a reduction in respectively the slow and rapid component of the delayed rectifier (i.e. I Ks and I Kr) are believed to underlie the prolongation of the action potential and the QT interval. The voltage- and time-dependent characteristics of I Ks are dependent on the interaction of at least two transmembrane proteins, the pore-forming alpha subunit, encoded by KCNQ1 and a regulatory subunit IsK, encoded by KCNE1. Mutations in both genes have been demonstrated to be causally involved in RW and JLN syndrome. Homozygous mutations in either gene cause JLN syndrome and heterozygous mutations RW syndrome, LQT type … *Corresponding author. Tel.: +31-20-566-3265; fax: +31-20-697-5458 a.a.wilde{at}amc.uva.nl

LQT genotype–phenotype relationships: patients and patches