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The presence of functionally significant human interleukin-4 receptor sequence variants, GIn551Arg and 11e50Val, was examined in four anonymous New York State populations defined by ethnic origin. These variants were studied because they are associated with atopy or atopic asthma whose prevalence varies in different populations. Methods: PCR/RFLP (11e50Val) and PCR/allele-specific oligonucleotide hybridization (GIn551Arg) assays were developed to detect both polymorphisms in 855 newborn screening specimens. Results: Arg551 was most frequently found in Blacks (allele frequency of 68|X%). However, the 11e50 allele was most common in Whites (allele frequency, 87|X%). Significantly more Blacks had chromosomes bearing both of the “enhanced signaling” variants (11e50/Arg551). Conclusions: Enhanced IL-4R signaling is associated with increased IgE production (atopy). Therefore, our data suggest that the African American population may be at increased risk for diseases, including asthma, which are associated with atopy. These data also emphasize the importance of determining the frequencies of single nucleotide polymorphisms in different populations before drawing conclusions from allele association studies, since the background allele frequencies may be disparate between different populations.