It is a leading cause of death in children under a year old, yet the mechanism underlying sudden infant death syndrome, or cot death, remains a mystery. Now a genetic study of babies who died of SIDS suggests that abnormal lung development could be responsible in at least some cases.
David Drucker at the University of Manchester, UK, and his colleagues analysed DNA from 25 babies who died of SIDS, looking for abnormalities in five genes, including those for immune system signalling molecules called cytokines, and VEGF, a growth factor critical for the development of the lungs.
They found significant differences in the VEGF gene between SIDS babies and controls. They also found differences in the gene for IL-6, a cytokine that promotes inflammation (Human Immunology, vol 67, p 627). Previous studies have implicated abnormalities in the gene for a different cytokine, called IL-10.
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One theory is that SIDS is the result of babies being unable to produce a proper immune response to bacteria living in their upper airways, particularly when their immune systems are at their most vulnerable, between the ages of 2 and 4 months. Drucker proposes that a combination of impaired lung function and immune system reaction during this time may put a baby at increased risk under certain conditions. 鈥淭here are now three genes that are very strongly associated with SIDS,鈥� he says. 鈥淭hese may make the baby less able to cope with infection at a time when its immunity is low.鈥�
He calculates that a baby with all three unfavourable forms of the genes would be about 14 times as likely to succumb to SIDS as a baby with the alternative versions. If other known risk factors are present 鈥� such as being exposed to cigarette smoke or being placed in the 鈥渨rong鈥� position in their cot 鈥� the risk becomes greater.
鈥淭he finding is interesting, given that the final event in cot death is thought to be termination of breathing, and VEGF is important in lung development,鈥� says George Haycock, scientific director of UK-based research organisation the Foundation for the Study of Infant Deaths. 鈥淏ut you would probably need some kind of environmental trigger as well.鈥�
