A comprehensive evaluation of IL4 variants in ethnically diverse populations:: Association of total serum IgE levels and asthma in white subjects

Background: The role of variation in the IL4 gene in asthma and allergy susceptibility is controversial. This cytokine is important in IgE isotype switching and the regulation of allergic inflammation; however, published studies have not delineated the specific role of variation in this gene in allergic disorders. Objective: We sought to identify single nucleotide polymorphisms (SNPs) in IL4 and to evaluate the association of SNPs and haplotypes with asthma and allergic phenotypes (total serum IgE) in white, African American, and Hispanic asthmatic populations. Methods: Sixteen individuals were resequenced, and 19 SNPs were identified; 2 novel and 17 SNPs were previously reported. Eleven of the SNPs were used to evaluate association in the 3 groups. Results: Nine polymorphisms were associated with total serum IgE levels in white subjects (.0012 less than or equal to P less than or equal to .034), and 5 of these were also associated with asthma in this population (.010 less than or equal to P less than or equal to .031). Three common haplotypes were observed, and all were associated with either high or low serum IgE levels in white subjects (.00008 less than or equal to P less than or equal to .004). Inspection of the haplotypes revealed that 3017 G/T in intron 2 was the only SNP concordant with serum IgE levels (G allele with lower levels and T allele with higher levels). Conclusions: After a comprehensive genetic evaluation, our data suggest that the 3017 G/T variant or the haplotype it identifies influences IL4's ability to modulate total serum IgE levels. Inconsistencies with previously reported IL4 associations might be due to population differences in allele frequencies, the extent of linkage disequilibrium with this SNP or haplotype, or both.