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Genetic Double Hit May Explain Crib Death

By Meagan White
ScienceNOW Daily News
1 February 2006

Infants with two copies of a gene variant associated with irregular heartbeat are 24 times more likely to die suddenly in their cribs, a new study shows. The variant does not cause sudden infant death syndrome (SIDS) on its own; rather, it makes infants more vulnerable to environmental stresses that healthy children can easily tolerate.

SIDS is the leading cause of mortality in the United States among infants between 1 and 12 months of age. Research suggests that environmental factors--such as sleeping on the stomach or exposure to second-hand smoke--are partly to blame. Yet the fact that African Americans are 3 times more likely than Caucasians, and 6 times more likely than Hispanics or Asians, to succumb to SIDS indicates genetics also plays a role.

To tease out this connection, biophysicist Steve Goldstein and colleagues at the University of Chicago in Illinois studied genes in the heart tissue of 133 African-American infants diagnosed, after autopsy, with SIDS. The team's search focused on abnormalities in one gene in particular: SCN5A, which codes for a sodium ion channel in the heart. When the researchers compared tissue from SIDS patients with that from healthy individuals, they found that one particular genetic variant--called Y1103--was 24 times more likely to occur in both alleles of SCN5A in SIDS victims than it was in those without SIDS.

So the team examined heart cells with a double dose of Y1103. But, curiously, ion channel operation appeared to be normal. So Goldstein and colleagues then simulated some environmental stress. Because SIDS often occurs when infants sleep on their stomachs--which interrupts breathing, deprives cells of oxygen, and increases blood acid levels--the team simulated this acidic environment in cultured cells. Cells with two copies of the Y1103 variation could not regulate sodium ion levels, the researchers report online 1 February in the Journal of Clinical Investigation. In the heart, inability to regulate sodium ion levels throws the heart's rhythm out of whack, a common occurrence in infants who experience sudden death, says Goldstein. Two copies of Y1103 are present in over 10% of blacks, which may explain the high rate of SIDS in this population, he says.

That's doesn't mean Y1103 is the only genetic factor in SIDS, cautions geneticist Alfred George of Vanderbilt University in Nashville, Tennessee. But the study does support the idea that particular gene variants coupled with certain stresses may trigger sudden death. The findings pave the way for identifying at-risk infants through genetic screening, he says.

Related site

  • CDC site on SIDS