Elevated fetal hemoglobin levels in sudden infant death syndrome

The cause of sudden infant death syndrome (SIDS) is unknown, although deficits in cardiopulmonary function and central respiratory control have been suggested as possible mechanisms of the disorder. In this study, we tested the hypothesis that SIDS is associated with a delay in the maturation of hematopoiesis. Prolonged elevation in the levels of fetal hemoglobin (hemoglobin F) in infants with SIDS could denote a compromised delivery of oxygen to sensitive tissue sites. Normally, hemoglobin F (alpha 2 gamma 2) is largely replaced by adult hemoglobin, hemoglobin A (alpha 2 beta 2), during the first six months after birth. Using an isoelectric-focusing procedure for measuring stable hemoglobin subunits, we quantitated the levels of hemoglobin F in blood samples from 59 patients with SIDS and 40 controls (32 living and 8 dead) matched for postconceptional age. The level of hemoglobin F in the population with SIDS was significantly higher than that in the controls in the age range tested (39 to 75 weeks); the mean (+/- SEM) proportion of hemoglobin F was 63.2 +/- 3.6 percent in the group with SIDS, as compared with 48.1 +/- 5.0 percent in the controls (P less than 0.025). The difference in hemoglobin F levels was most pronounced 50 weeks after conception: the proportion of hemoglobin F in the 37 patients with SIDS with a postconceptional age of more than 50 weeks was 47.4 +/- 3.6 percent, as compared with 18.8 +/- 3.1 percent in the 19 controls of that age (P less than 0.0005). We conclude that hemoglobin F is a useful postmortem marker for the population with SIDS that we studied and that it may have value as a prospective marker for some infants at risk for SIDS.