Recent discoveries at Mayo Clinic added two more cardiac genes to the list of potential links to sudden infant death syndrome (SIDS), increasing the possibility that genetic defects of the heart may cause up to 15 percent of SIDS cases. This research will be presented Friday at Heart Rhythm 2006, the 27th Annual Scientific Sessions of the Heart Rhythm Society in Boston.

In the two recent separate studies, researchers examined caveolin-3 (CAV3) and the cardiac ryanodine receptor (RyR2) and found molecular and functional evidence in both to implicate them as SIDS-susceptibility genes. Researchers examined the tissue of 135 unrelated cases of SIDS - in infants with an average age of 3 months old - that had been referred to Mayo Clinic’s Sudden Death Genomics Laboratory for molecular autopsy. In each study, two of the 135 cases possessed mutations in either CAV3 or RyR2.

SIDS - the sudden, unexplained death of an infant under 1 year old - is estimated to cause 2,500 infant deaths each year. “Combined with our previous discoveries, we now estimate that defects in genes that provide the blueprints for the critical controllers of the heart’s electrical system might have played a key role in more than 300 of those tragedies,” says Michael J. Ackerman, M.D., Ph.D., principal investigator of both studies and director of Mayo Clinic’s Long QT Syndrome Clinic and Sudden Death Genomics Laboratory.

“We are continuing to expose the causes of SIDS. So far, we have now added six genes to the SIDS most-wanted list.”

In 2001, a team of investigators led by Dr. Ackerman identified the first cardiac gene, SCN5A, linked to SIDS. In 2005, a comprehensive search of the five channel genes that cause a potentially lethal heart rhythm syndrome known as long QT syndrome (LQTS) was found in 5 percent to 10 percent of SIDS cases.

In collaboration with Baylor College of Medicine, Mayo’s sudden death investigators chose to examine CAV3 following our recent discovery of CAV3 as a novel LQTS-causing gene. RyR2 was targeted because of its involvement in a distinct genetic heart rhythm disease known as catecholaminergic polymorphic ventricular tachycardia (CPVT).

“For a parent whose infant died suddenly and mysteriously even five years ago, we were essentially unable to provide them with a cause and would often have to tell them, ‘We have no idea why your apparently healthy infant did not wake up this morning,’ ” Dr. Ackerman says. “Although so much of SIDS remains unexplained, these findings that point to the heart for 10 percent to 15 percent of SIDS provide one place to search for a possible explanation. For families that have lost an infant to SIDS, it would be reasonable for parents to talk with their physician to make sure there is no family history of other unexplained deaths, unexplained fainting episodes, unexplained seizures that might provide clues and prevent more deaths.”

Other researchers involved in the CAV3 study were from the University of Wisconsin-Madison and Baylor College of Medicine, Houston. Researchers involved in the RyR2 study were from Columbia University, New York.

Mayo Clinic