Variant interleukin 1 receptor antagonist gene alleles in sudden infant death syndrome

To investigate if carriage of interleukin 1 (IL-1) receptor antagonist gene variants are associated with sudden infant death syndrome (SIDS) in a large cohort of case-control demographically matched infants.

118 SIDS and 233 control infants, who were matched to each SIDS infant by date of birth, sex, birth weight (±500 g), gestational age and ethnicity, were genotyped for an IL-1RN 89 bp tandem repeat polymorphism and analysed for significant associations.

No significant difference in genotype frequencies was observed between low and normal birthweight infants and year of birth (1987-1994, when the SIDS incidence was higher). In infants born between 1987 and 1994, an association was observed with SIDS and allele 2 where 18% of SIDS infants carried the 2/2 genotype compared with 9% of controls (χ(2) p=0.026, OR 2.46). Allele 3 was found at a low frequency, but was significantly more common in SIDS infants (3.1%) compared with controls (0.9%, Fisher's exact p=0.04, OR 3.76).

The higher prevalence of IL-1RN allele 2, which predisposes to poor outcomes from infection, in SIDS infants born between 1987 and 1994 (ie, prior to the dramatic decrease in SIDS incidence) suggests that the high incidence during this period could point to infection playing a role in aetiology. An association of IL-1RN allele 3 with SIDS was also found, but should be interpreted with caution due to the low frequency of this variant. The consequence of allele 3 carriage is currently unknown in the absence of functionality studies for this isoform.