An abnormal gene carried by one in nine African-Americans confers a 24-fold increase in sudden infant death syndrome in infants who receive a copy from both parents, according to a report from Chicago researchers.
Blacks have a higher incidence of SIDS than other ethnic groups and the mutant gene, which also causes an increased risk of heart arrhythmias in adults, may play a role in that risk, according to the report in the Journal of Clinical Investigation.
Significantly, the effects of the gene can be mitigated in adults with drugs, and it may be possible to block its effects in at-risk children as well, the researchers said.
The mutant gene alone does not cause SIDS, said Dr. Steven Goldstein of the University of Chicago, who led the study. "Our findings suggest that it renders infants vulnerable to environmental challenges - such as a long pause in respiration - that are tolerated by children without the mutation," he said.
The gene, called SCN5A, is not the first to be associated with SIDS, but it is the first to be linked to a specific ethnic group and it seems to produce a greater increase in risk than previously discovered mutations.
Still, it appears to account for only about 5 percent of SIDS deaths in blacks.
"Anything we can find that brings us closer to understanding the deaths is a big deal," said Dr. Dorothy Kelly of the Littleton Regional Hospital in Littleton, N.H., president-elect of the American Association of SIDS Prevention Physicians. "We've been looking for 30 years and even a little ... help is important."
SIDS is the most common cause of death in infants between the ages of 1 month and 1 year, striking about 2,500 children in the United States each year. It typically strikes the infant without warning while the child is sleeping, hence its common name "crib death."
The prevalence has been halved in recent years by campaigns to encourage parents to have infants sleep on their backs, but there are other risk factors.
Genetics is one of them. African-Americans are three times as likely as whites to die from SIDS and six times as likely as Latinos and Asians.
To explore those genetic links, Goldstein and his colleagues studied DNA from 133 black infants who died of SIDS and compared it with DNA from 1,056 black adults with no known health problems.
They found two copies of a particular mutation of SCN5A in three of the infants (2.3 percent), compared with only one (0.1 percent) of the healthy adults. Four other infants had other damaging mutations in the gene.
The SCN5A gene is the blueprint for a protein that forms a pore in heart muscle cells that controls the passage of sodium ions in and out of the cells, thereby regulating heart rhythms.
In laboratory studies, the team found that the pore produced by the defective gene operated properly under normal conditions. But when the defective pore was exposed to slightly acidic conditions - as might happen, for example, when breathing is interrupted by sleep apnea - the pore stays open, producing a fluttering and ineffective heart rhythm.
Adults carrying the defective gene also develop arrhythmias under stress but previous studies have shown that the heart rate can be controlled with a drug called mexilitene.
Thomas H. Maugh II writes for the Los Angeles Times.