Does circadian variation in risk factors for sudden infant death syndrome (SIDS) suggest there are two (or more) SIDS subtypes?

Sudden infant death syndrome (SIDS) is known to occur more frequently at night. In two studies it has now been shown that a prone sleep position is more strongly associated with SIDS occurring during the day, whereas night‐time deaths are more strongly associated with maternal smoking and illness. Conclusion : This variation, although unexplained, does suggest at least two SIDS subtypes: one related to sleep position and possibly a thermal mechanism, and one related to an uncontrolled inflammatory response to infection predominantly occurring at night. In addition, there are probably other mechanisms that do not show a circadian variation.