Background: Long QT syndrome is characterised by inherited long QT interval on the ECG and increased risk for syncope and sudden death caused by arrhythmias. For Romano-Ward syndrome and Jervell and Lange-Nielsen syndrome DNA based diagnostics are available.
Materials and methods: This paper is a summary of our experience with DNA-based diagnostics of LQTS since the autumn of 2003. The diagnostic analyses are performed by sequencing the exons of five genes, KCNQ1, HERG, SCN5A, minK and MiRP1.
Results and interpretations: As of mid-January 2005, 56 probands with long QT syndrome have been referred for genetic testing. We have identified an underlying mutation in 64% of the patients. Mutations in the KCNQ1 gene are most frequent in Norwegian long QT syndrome patients, as 61% of the patients have their mutation in this gene. The detection of a mutation in the probands has led to genetic testing of 215 relatives; 99 out of these are heterozygous for the mutation present in the family. Heterozygous patients have been referred to a cardiologist. Of the 43 that have been referred to follow up at the department of cardiology at Rikshospitalet, 35 have started treatment with beta blockers to reduce the risk of arrhythmias. Thus, DNA-based diagnostics has clinical significance leading to prophylactic treatment of long QT syndrome patients. Compared to evaluation of ECG, which is negative in 30% of mutation carriers, the sensitivity of DNA-based diagnostics of relatives of probands with a known mutation, is close to 1.