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According to a new study, the most likely cause of sudden infant death syndrome (SIDS) is a brain-stem abnormality that makes infants vulnerable to the known "big three" risk factors for SIDS: side or prone sleeping, face-down sleeping, and bed sharing (Paterson et al: JAMA 2006;296:2124). A case comparison of medullary tissue from 31 infants who died of SIDS and 10 infants who died of other causes showed extensive pathology involving the 5-HT neurons that regulate the serotoninergic system in the SIDS infants. These neurons are known to influence a range of physiologic processes including breathing, cardiovascular function, thermoregulation, and the sleep-wake cycle. The study strengthens the hypothesis that medullary 5-HT dysfunction is associated with SIDS and may lead to death by a failure of respiratory and autonomic responses to homeostatic stressors during sleep.
The abnormalities the investigators found occurred in infants who died from 1997 to 2005, a time when the "Back to Sleep" campaign was in full swing and had achieved a marked overall reduction in the number of SIDS deaths recorded annually. Despite the publicity, however, 65% of the infants in the study who died of SIDS were sleeping prone or on their side at the time of death. The abnormalities uncovered, the authors hypothesize, may make it difficult or impossible for babies sleeping on their belly or side to arouse or turn their head when they're not getting enough oxygen.
The study is preliminary and small-scale, but the results are an important addition to our knowledge about SIDS. The authors urge pediatricians to intensify their efforts to promote supine sleeping and encourage parents coping with a SIDS death to make their infant's brain tissue available for study.