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Background Autonomic dysfunction has been implicated in the pathophysiology of Sudden Infant Death Syndrome (SIDS). Butyrylcholinesterase (BChE) is an enzyme of the cholinergic system, a major branch of the autonomic system, and may provide a measure of autonomic (dys)function. This study was undertaken to evaluate BChE in infants and young children who had died from SIDS or Sudden Unexpected Death. Methods We measured BChE specific activity (BChEsa) in the eluate of 5μL spots punched from the dried blood spots (DBS) taken at birth as part of the newborn screening program. Results for each of 67 SUDI deaths classified by the coroner (aged 1 week – 104 weeks) = Cases, were compared to 10 date of birth - and gender-matched surviving controls (Controls), with five cases reclassified to meet criteria for SIDS. Findings Conditional logistic regression showed that in groups where cases were reported as “SIDS death” there was strong evidence that lower BChEsa was associated with death (OR=0·73 per U/mg, 95% CI 0·60 – 0·89, P=0·0014), whereas in the “Non-SIDS death” group there was no evidence of a linear association between BChEsa and death (OR=1·001 per U/mg, 95% CI 0·89 – 1·13, P=0·99). Conclusion BChEsa, measured in DBS taken 2-3 days after birth, was lower in babies who subsequently died of SIDS compared to surviving controls and other Non-SIDS deaths. We conclude that a previously unidentified cholinergic deficit, identifiable by abnormal BChEsa, is present at birth in SIDS babies and represents a measurable, specific vulnerability prior to their death.

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