Molecular autopsy finds that a genetic heart condition may be the cause of many unexplained drownings
ROCHESTER, MINN. -- According to a study by Mayo Clinic pediatric cardiology and pathology specialists published in this week's edition of New England Journal of Medicine, a genetic defect known as long-QT syndrome may be the cause of many unexplained drownings.
Drowning kills more than 4,000 children and young adults each year. Drowning is second only to motor vehicle accidents as the leading causes of accidental death in children and young adults. Many drownings are attributed to lack of supervision, alcohol or drug abuse, trauma and seizures. However, each year, more than 400 drownings involving children and young adults have no explanation.
"The study proves for the first time that an unexplained drowning could be caused by a genetic defect that affects the heart's rhythm," says Michael Ackerman, M.D., Ph.D., a Mayo Clinic pediatric cardiologist and principal investigator of the study. "In a case study of a 19-year-old woman who died after a near-drowning, we were able to prove through molecular testing, that she had long-QT syndrome. And since the genetic defect runs in families, we were able to test family members and offer preventive treatment to other family members who also have the defect."
Long-QT syndrome is a genetic condition that affects the heart's electrical system. In patients with long-QT syndrome, the heart takes longer to reset, or re-charge itself between each beat. Usually, patients have no problem with this condition, but certain triggers like swimming, intense physical exertion, or being suddenly startled or frightened can set it off, causing fainting spells, seizures or even death from a fatal heart rhythm called ventricular fibrillation.
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Dr. Ackerman and his colleagues investigated the cause of death of the 19-year-old woman because her death followed a near-drowning that had no satisfactory explanation. She was athletic and a good swimmer, yet she drowned while swimming laps in four feet of water. Molecular testing of the woman's heart tissue identified the genetic mutation. Subsequent testing revealed that the mother and a sister also had inherited long-QT syndrome. The sister is now controlling the disease with daily doses of a beta-blocker, a common drug.
"Our study shows that molecular testing can play a vital role in the way we treat and identify individuals who are at risk for the condition" says Dr. Ackerman. "We will be able to diagnose family members who may be at risk even though they've never had symptoms." "If we identify the problem, we can intervene and hopefully prevent such tragedies."
Dr. Ackerman states that those at risk for long-QT syndrome include: those who experience fainting spells due to emotion, exercise or exertion; some relatives of those with long-QT syndrome; those with a family history of seizures, SIDS and sudden death; and those who experience an unexplained near-drowning. These individuals should get an electrocardiogram because the prolonged QT interval is often detected by the test. Patients with long-QT syndrome can lead normal lives with some restrictions. Those restrictions include: no swimming without a buddy, no competitive sports and taking medication daily.
Dr. Ackerman says additional research is required before widespread genetic screening for long-QT syndrome is possible.
"Most families have a different and unique mutation that causes the disease," says Dr. Ackerman. "However, the importance of genetic testing is evident in the case of the 19-year-old woman's sister's diagnosis of long-QT syndrome. Her mutation did not show up on a standard electrocardiogram, but it was apparent through molecular testing of a blood sample."
Those at risk for long-QT syndrome include those who experience fainting spells due to emotion, exercise or exertion; some relatives of those with long-QT syndrome; those with a family history of seizures, SIDS and sudden death; and those who experience an unexplained near-drowning.
Based on this finding, Mayo Clinic has established a national registry for unexplained drownings and near-drownings. The registry will help determine the prevalence of drownings caused by a genetic defect and associated family members who are at risk. For further information, go to www.mayo.edu/drowning .
Contact:
Chris Gade
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507-284-2511 (evenings)
e-mail: newsbureau@mayo.edu
Journal
New England Journal of Medicine