https://www.biospace.com/article/researchers-answer-how-and-why-infants-die-from-sids/

“SIDS refers to the unexplained deaths of infants under a year old, and it usually occurs while the child is sleeping. According to Mayo Clinic, many in the medical community suspected this phenomenon could be caused by a defect in the part of the brain that controls arousal from sleep and breathing. The theory was that if the infant stopped breathing during sleep, the defect would keep them from startling or waking up. “