By Nancy Deutsch

NEW YORK (Reuters Health)- A significant number of infants who die of sudden infant death syndrome (SIDS) appear to have a gene that causes a life-threatening congenital heart problem known as long-QT syndrome, according to a report in the July 27th issue of The New England Journal of Medicine. This disorder is treatable and easily detected on electrocardiograms (ECGs)--which suggests that using ECGs to screen young infants for the problem may save some babies' lives.

For the first time, the mutated gene that causes these life-threatening arrhythmias has been identified, said co-author Dr. Charles Antzelevitch of the Masonic Medical Research Laboratory in Utica, New York. ``This is really the first definitive evidence that sudden infant death syndrome (SIDS) is related to long-QT syndrome,'' he said. ``This really pins it down.''

In 1998, lead author of this paper, Dr. Peter J. Schwartz of the University of Pavia in Italy, reported on a 19-year prospective study of more than 34,000 infants. Twenty-four of those 34,000 died of SIDS and 12 were found to have long-QT intervals on ECG.

In the new report, a 44-day-old baby boy was discovered pulseless and not breathing, an apparent case of SIDS, and rushed to an emergency room. An ECG showed ventricular fibrillation--an often fatal heart arrhythmia-- and he was treated to restore a regular heart rhythm. A marked prolongation of the QT interval was noted on the baby's ECG tracings. His parents were found to have normal QT intervals, but study of the infant's genes showed that he had a spontaneous mutation of the cardiac sodium-channel gene (SCN5A). With drug treatment, the boy is now 5 years old and free of heart symptoms.

More work needs to be done to study the gene, but it seems that the long-QT syndrome can be passed on genetically or may be due to a spontaneous mutation, Antzelevitch said.

It's difficult to say what percentage of infants have this mutation, but Schwartz estimates that as many as 20% to 30% of SIDS may be attributable to long-QT syndrome, Antzelevitch said. ``We believe there are other arrhythmic syndromes that (also) contribute to SIDS,'' he told Reuters Health.

An ECG is widely available and relatively inexpensive screening test at roughly $15 to $25 (US), Antzelevitch said. The controversy now is whether widespread screening of all infants, at age of 2-3 weeks when the abnormality could be seen on ECG, should be implemented, he said. ``This is a disease that is diagnosable and treatable,'' he asserted.

The long-QT syndrome may also manifest itself in the teenage years, and is responsible for many deaths of teenagers who die while playing sports, Antzelevitch added. The Japanese perform ECGs on children at ages 3, 7, and 10 for this reason, he noted. ``In (the US), we don't do widespread screening at any age.'' He recommends screening all youth, but particularly athletes, in addition to widespread screening of babies at two to three weeks of age.

``As a father, I would want to know what the ECG of my baby is at two to three weeks, and in later years,'' said the researcher.

SOURCE: The New England Journal of Medicine 2000;343:262-267

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