Clinical and genetical aspects of the long QT syndrome.

The idiopathic long QT syndrome (LQTS) is a congenital disorder characterized by a prolongation of the QT interval and by the occurrence of stress-induced syncope or cardiac arrest due to ventricular tachyarrhythmias. Such lethal events may be prevented by quite effective pharmacological or surgical antiadrenergic therapies. Two pathophysiological hypotheses have been considered: 1. A "sympathetic imbalance" caused by a lower than normal right sympathetic activity and 2. A cardiac cellular dysfunction, possibly an altered potassium channel. Although one may find clinical features of LQTS compatible with both hypotheses, there is no proof for either of them. Since a locus has been mapped for the long QT syndrome on the short arm of chromosome 11 in several families, tightly linked to the Harvey-ras-1 (H-ras-1) gene, this gene became a candidate gene for LQTS. It is an attractive hypothesis that an alteration in the H-ras-1 gene may cause LQTS by modulation of acetylcholine-activated potassium channels through guanine-nucleotide-binding RAS proteins. No mutation in the H-ras-1 gene has been found until now, so that other genes located in this region close to H-ras-1 have to be considered to cause LQTS. Moreover, the variability of the clinical picture in patients with LQTS and the absence of linkage to the H-ras-1 locus in other families make genetic heterogeneity likely. Advances in recombinant DNA technology raise the possibility to identify the abnormal gene(s). This could be the basis to understand the pathogenetic of LQTS leading to a more accurate diagnosis and possibly new therapeutic concepts.