The genes concerned are important in the regulation of the baby's immune system. However, even a threefold increased risk of SIDS over the average is still a tiny risk - the gene is unlikely to be the sole factor. Eight babies a week die from SIDS, and doctors still have no clear idea what happens in a cot death. Studies have suggested that parents who smoke, and babies born underweight may be at higher risk. Recent advice given by parents to place babies to sleep on their backs has drastically cut the number of deaths since 1990.
Cot deaths are more common in boys, and twins are thought to be at increased risk.
Most happen within the first six months of life. The research was funded by the Foundation for the Study of Infant Death. Dr Drucker told the BBC that he hoped the gene, combined with other factors such as the smoking habits of the parents and the birthweight of the baby, would help doctors pick out the babies who were at the highest risk. The research was published in the journal Immunology.