Their search focused on abnormalities in a gene called SCN5A, which has been associated with abnormal heart rhythms. Overall, the team found common and rare changes in this gene in five percent of SIDS deaths in African Americans. One specific variation, known as Y1103, was known to confer an eight-fold risk of cardiac arrhythmia in African-American adults with one copy.
In this study, the researchers found that having two copies of Y1103 was more common in infants who died from SIDS than in controls. Three out of the 133 African-American SIDS cases (2.3%) had two copies of Y1103, compared to only one individual out of 1,056 controls (0.1%). Four other SIDS cases had other damaging mutations in one copy of the gene.
How, they asked, might this variation contribute to SIDS?
The SCN5A gene codes for a sodium channel, a pore found in cardiac muscle cells that controls the passage of sodium ions in and out of the cell.
"This seemed like a good candidate for a genetic difference that could contribute to SIDS," said Goldstein, "but we had no clear idea how it increased risk since the Y1103 variant did not affect channel operation under normal conditions."
Cellular activity, particularly that of nerve and muscle cells, is controlled by the flow of ions like sodium and potassium. A change in an ion channel, if it disrupts ion flow, can alter the cell's activity. So Goldstein's team concentrated on how Y1103 might change a cell's behavior.
On first look, it made no difference. Cells with the normal or Y1103 channels "were found to function indistinguishably," the authors wrote.
But SIDS is not purely genetic; it appears to require multiple "hits," some from altered genes and some from the environment.
The environment's role was demonstrated by the "Back to Sleep" campaign, begun in 1994, which cut the prevalence of SIDS in half by teaching parents to put babies to sleep lying on their bac
Source:University of Chicago Medical Center