Changes in lung surfactant lipids associated with the sudden infant death syndrome

The lipid composition of lung surfactant obtained by lung lavage at autopsy in 40 infants dying from Sudden Infant Death Syndrome (SIDS) was compared with that obtained from 12 infants dying from other causes (control group). Analysis of the total lipids extracted from the surfactant of the SIDS and the control groups showed no major differences in the proportion of the various phospholipids including the major phospholipid, phosphatidylcholine (PC). However, a significantly reduced proportion of the PC was in the form of the biologically active species, disaturated phosphatidylcholine (DSPC) (P less than 0.005). In surfactant from SIDS infants, mean DSPC amounted to 65.8% (s.e.m. = 1.6) compared with normal surfactant 77.4% (s.e.m. = 3.5). A functional consequence of such a reduction in DSPC content of lung surfactant of SIDS infants could be a greater degree of fluidity of surfactant, particularly at exhalation. Such a biophysical change in surfactant properties could have a profound influence on lung function and, perhaps in response to external or internal stimuli, could be a causative factor in sudden infant death.