Compared with the most common haplotype within each locus, 1 ARG1 haplotype was associated with reduced risk (odds ratio [OR] per haplotype copy, 0.55; 95% CI, 0.36-0.84), and 1 ARG2 haplotype was associated with increased risk (OR per haplotype copy, 1.35; 95% CI, 1.04-1.76) of asthma.