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Closing in on SIDS
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esearchers are closing in on the brain abnormalities thought to be responsible for the 3,000 unexplained sudden infant deaths in this country each year. Their work further supports the belief that having infants sleep on their backs dramatically reduces the risks for sudden infant death syndrome (SIDS). SIDS, the sudden, unexplained death of a n infant less than one year old, is the leading cause of death among infants one month to one year of age. N o w researchers say they have discovered that some infants who have died of SIDS show abnormalities in two receptors in the brainstem thought to be involved in the control of breathing, carbon dioxide sensitivity, and blood pressure responses. This discovery, which was published in the November 1997 issue of the lournal of Neuropathy and Experimental Neurology, confirms earlier evidence of a similar brain abnormality in another receptor and provides additional support for the theory that malfunctions in the region of the brain known as the arcuate nucleus may be a strong factor in SIDS. The team of researchers studied the brainstems of 7 9 infants whose deaths were due to SIDS and other causes. “This finding is also extremely important for the back sleeping recommendation. We think this new finding fits in with the rebreathing theory-that infants sleeping in the prone (on their stomachs) position are rebreathing trapped air and, unable to sense and respond to the excess carbon dioxide, die suddenly,” said Dr. Hannah Kinney, the study’s author and a researcher at Children’s Hospital and Harvard LMedicalSchool in Boston. Just six years ago, the American Academy of Pediatrics (AAP) first recommended that infants be placed on their backs or sides to sleep after reviewing studies that linked infant prone sleeping with an increased February 1998
risk of SIDS. In 1994, the National Institute of Child Health Development-which co-funded Dr. Kinney’s study-joined with the AAP to initiate the now well-known “Back to Sleep” campaign. Before that time, some 70 percent of babies were sleeping on their stomachs. “Now, only about 21 percent of babies are stomach sleeping-and the SIDS death rate has dropped 38 percent between 1992 and 1996,” said NICHD Director Duane Alexander, M.D., at the AAP’s annual meeting held last November. As reported in the recently published SIDS study, researchers are now noting a significant decrease in kainate binding to the kainate neurotransmitter receptors in the arcuate nucleus on the brainstem in a group of SIDS infants. “Brain and nerve cells communicate by means of molecules called neurotransmitters,” said Dr. Kinney. Neurotransmitters produced in one brain cell bind to special receptor molecules on the neighboring cells, in much the same way a key fits into a lock. In victims of SIDS, it appears that the decreased binding
faulty communication among nerve cells and may prevent them from responding to life-threatening cardiorespiratory events during sleep. Earlier reported findings suggested that a significant decrease in binding of another receptor, the muscarinic cholinergic receptor (mAChR), in the arcuate nucleus could prevent SIDS victims from responding to potentially life-threatening events that occur frequently during sleep. These events include responding to the rising levels of carbon dioxide or decreasing levels of oxygen that might occur when infants, lying face down in heavy bedding or blankets, rebreathe trapped air. “We now have a clue about the region of the brain that’s involvedand that there may be a more global, neural cell defect in the arcuate nucleus. We know two of the neurotransmitters involved. O u r next step is to find out how and why this occurs,’’ Dr. Kinney said. One of the goals of her research is to eventually develop a screening test to identify infants at risk or a standard measurement of kainate receptor binding that could be used for diagnosis a t autopsy. In the meantime, the NICHD is trying to increase back sleeping compliance among the parents of babies less than one year old and is making materials about back sleeping available to practitioners by calling (800) 505-CRIB and asking for the “Back to Sleep” materials.
Lifelines
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