The Sydney researchers were able to confirm this theory by analyzing dried blood samples taken from newborns who died from SIDS and other unknown causes. Each SIDS sample was then compared with blood taken from healthy babies. They found the activity of the enzyme butyrylcholinesterase (BChE) was significantly lower in babies who died of SIDS compared to living infants and other non-SIDS infant deaths. BChE plays a major role in the brain’s arousal pathway, explaining why SIDS typically occurs during sleep.