But the leading SIDS theory suggests that affected babies have subtle brain-stem abnormalities that block normal arousal or alarm reflexes. Dr. Hannah Kinney, a neuropathologist at Harvard and at Children s Hospital in Boston, developed his theory during several years of research on animals and infants. Kinney says certain babies are born with chemical defects in the lower portion of the brain stem called the ventral medulla, which is involved in alarm reflexes. It regulates blood pressure and breathing during sleep, and controls how the baby responds to low oxygen blood levels and high amounts of carbon dioxide. Lack of oxygen and excessive carbon dioxide can occur when a baby is sleeping on his or her stomach, or face down.
Normal babies rouse and turn their heads.
Kinney says many SIDS babies can t respond to the challenge. She suspects the problem may arise during fetal development. The defect has no symptoms. Kinney hopes sophisticated tests that detect it will eventually become part of routine autopsies. Her ultimate goal, which will take years, is to devise a blood test that detects the abnormality before it kills, and to learn whether factors such as nutritional deficiency during pregnancy are a cause.