Disease Information for QT prolongation/deafness syndrome

Long QT Syndrome by Sanjay Sharma © 2001 Medibyte-com Ltd:

Hereditary or congenital long QT syndrome (LQTS) is characterised by delayed or prolonged ventricular repolarisation on the ECG and a propensity for syncope, polymorphic tachycardia and sudden death should the tachycardia degenerate to ventricular fibrillation; The condition is familial in up to 90% of cases, the other 10% of cases result from sporadic mutations in utero. It can be inherited both as an autosomal dominant and recessive trait; The rarer autosomal recessive variant has a prevalence of 3 per million and is associated with congenital nerve deafness; It is known as the Jarvell and Lange-Neilsen syndrome; The commoner autosomal dominant form has a prevalence of 1/10,000 and is termed the the Romano Ward syndrome; Defects within transmembrane ion channels produce abnormalities in cardiac repolarisation, leading to fatal ventricular arrhythmias; Factors producing increased sympathetic activity, particularly physical exertion, intense emotion and sudden loud auditory stimuli may precipitate syncope/sudden death; Thus far abnormalities have been demonstrated in 4 genes encoding potassium or sodium ion transport channels; These are located on chromosome 11, 3, 4 and 7; On chromosome 11 there is a mutation in the gene encoding KVLQT1, a potassium ion channel (LQT1); On chromosome 7 there is a mutation in the HERG gene also encoding a potassium channel abnormality (LQT2); Other genetic mutations include the SCN5A on chromosome three which causes abnormalities in the sodium ion channel (LQT3) and minK (LQT5); Mutations within the HERG gene are responsible for the Romano-Ward syndrome; Jarvell and Lange-Neilsen syndrome is caused by mutations in both copies of LVLQT1 and minK genes, therefore off-spring and parents of patients with this syndrome and obligate heterozygotes for Long QT-associated mutations and are at increased risk of arrhythmias. Family screening with ECG is indicated in these families;

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