One minute, he's a strapping 40-year-old with an enviable cholesterol level, working out on his treadmill.
The next, he's dead.
That an abnormality in his heart's electrical system had managed to stay on the Q.T. until it proved lethal is characteristic of sudden cardiac death, which annually claims more than a quarter million Americans. A dearth of discernable symptoms and lack of detectable molecules circulating in the blood makes the prediction of sudden cardiac death largely dependent on genetic risk factors.
Having identified 10 common variants of genes that modify the timing of the contraction of the heart, known as the QT interval, scientists in the Johns Hopkins University School of Medicine, in collaboration with an international contingent of researchers, now provide new insight about the underpinnings of the QT interval which, when prolonged or shortened, predisposes to sudden cardiac death.
QT interval, which is determined from a standard electrocardiogram (ECG), reflects the time it takes for the heart (ventricles) to contract and then reset for the next heartbeat.
Publishing March 22 in Nature Genetics, the international team including researchers from the Technical University in Munich, Johns Hopkins and others, used DNA samples previously collected for epidemiological studies to analyze the genomes of 15,842 individuals whose QT intervals had been measured by electrocardiogram. With DNA microarray chips, each able to assess hundreds of thousands of markers in each sample, followed by bioinformatic techniques to increase the number of markers, the researchers screened approximately 2.5 million markers to detect subtle alterations in the sequences of these genomes that modify the QT interval.
By focusing on 2.5 million sites in a genome of 3 billion sites, the scientists surveyed one-one-thousandth of nearly 16,000 genomes. This relatively small but "still extremely powerful"
|Contact: Maryalice Yakutchik|
Johns Hopkins Medical Institutions