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pan> gene has been described. OBJECTIVE: We sought to examine the functional significance of this promoter SNP and its relationship to asthma. METHODS: We examined the effect of the -295 SNP on promoter activity in cell-line (HBE4-E6/E7) transfection experiments. We investigated the association of the IL16 -295 genotype with asthma among 341 affected sib-pair white families and 184 unrelated nonasthmatic control subjects. We analyzed the association between the IL16 genotype and asthma using family-based association test and case-control analyses. RESULTS: In in vitro transfection experiments the T allele in the -295 position was associated with substantially reduced promoter activity compared with the C allele. In the family study the more common T allele at the -295 position was significantly associated with all asthma phenotypes (P = .002 to P = .015). In the case-control analysis asthmatic subjects were more likely than unrelated nonasthmatic control subjects to have the -295 TT genotype, but this did not reach statistical significance (odds ratio, 1.36; 95% CI, 0.92-2.02). CONCLUSIONS: The T allele at the -295 position in the IL16 promoter region is associated with reduced promoter activity relative to the C allele and with asthma in this white population. Further investigation is needed to delineate the mechanisms underlying these findings and the relationship of the IL16 -295 genotype to asthma in other populations.