Distribution of interleukin-1 receptor antagonist genotypes in sudden unexpected death in infancy (SUDI); unexplained SUDI have a higher frequency of allele 2.

AIMS: This investigation was designed to explore the role of IL-1RN genotype in unexplained infant deaths (including sudden infant death syndrome (SIDS)), non-infectious infant deaths, and infectious infant deaths, and to investigate whether IL-1RN genotype is related to the finding of organisms in normally sterile sites in infant deaths.
METHODS: IL-1RN 89bp variable number of tandem repeat polymorphism genotype was determined using polymerase chain reaction for 49 cases of unexplained sudden unexpected death in infancy (uSUDI), 13 cases of infectious sudden unexpected death in infancy, 10 cases of non-infectious sudden unexpected death in infancy, and 103 live control infants. IL-1RN genotype was then compared with the presence of bacteria in normally sterile sites in infant deaths.
RESULTS: An association was found between the homozygous A2 allele and uSUDI (P = 0.007; 95% confidence interval 1.41-17.67) where carriage of the 2/2 genotype was 4.85 times more likely to increase risk of uSUDI compared with the predominant 1/1 genotype.
CONCLUSIONS: The role of infection in uSUDI and SIDS may be via an immune response pathway where IL-1RN A2 affects interleukin (IL)-1 regulation. These results are consistent with previous research where polymorphic genotypes conferring more severe proinflammatory responses are found more frequently in uSUDI/SIDS infants than in controls.