Study finds brain stem abnormality in SIDS infants

by Ralph A. Franciosi, MD

Ralph Franciosi, MD, was medical adviser for the Infant Death Center of Wisconsin and pathologist at Children's Hospital of Wisconsin. He also was a professor of Pathology and Laboratory Medicine at the Medical College of Wisconsin.

Researchers have made a major breakthrough in understanding how SIDS babies die. A research team, directed by Hanna Kinney, MD, researcher at Boston Children's Hospital and Harvard Medical School in Boston, have found another structural abnormality in the receptors located in the arcuate nucleus - the portion of the brain stem responsible for the control of vital functions such as breathing and arousal from sleep. The study was published in the November issue of the Journal of Neuropathology and Experimental Neurology.

The arcuate nucleus consists of a group of nerve cells that communicate with each other and with other nerve cells to control breathing and arousal. Receptors, or message receivers, on the surface of the nerve cell bind to chemicals (neurotransmitters) to transmit messages. Researchers found significantly decreased binding (faulty communication) of the kainate receptor. This is the second receptor to be identified as abnormal. A prior study identified the muscarinic receptor as abnormal in infants who died of SIDS.

These observations are focusing our attention on not just the number, but the function of nerve cells.

These arcuate nucleus abnormalities help explain why the prone sleep position places infants at a higher risk for SIDS. Prone sleeping, especially on a soft sleep surface, can trap exhaled carbon dioxide and increase the level of carbon dioxide in the infant's blood and spinal fluid. If the muscarinic and kainate receptors, which are critical sensors of elevated carbon dioxide, are malfunctioning, the infant will not arouse from sleep and will rebreathe the trapped air.

One of the goals of this research is to eventually be able to screen infants for risk. Another is to create a standard measurement of kainate receptor binding, or the level of malfunction, to be used for diagnosis during an autopsy.

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