Delayed maturation of the vagus nerve in sudden infant death syndrome.

Abnormalities of the respiratory control system have been implicated in the cause of death in sudden infant death syndrome (SIDS). The vagus nerve is a major component of the neural regulation of respiration. Ultrastructural quantitative morphometry of myelinated and unmyelinated fibers was performed on cervical vagus nerves taken from 30 SIDS victims and 29 age-matched controls between 1 and 9 months of age. In SIDS infants, more small and fewer large myelinated vagal fibers were found than in controls, suggesting that the vagus nerve in SIDS is relatively immature. Delayed vagal nerve maturation, together with delays in central nervous system myelination and dendritic development, indicates a neural developmental delay in SIDS, the cause of which is undetermined.