smokers (Table 1). The mean age (± SD) of study participants was 72.3 ± 7.5 years and mean BMI was 28.0 ± 4.1 kg/m2. Average SBP and DBP were 132 ± 18.4 mmHg and 76.8 ± 10.9 mmHg, respectively. We evaluated the association of SBP and DBP with ambient BC and expressed the results as the mmHg change associated with a 1-SD increase in BC (equivalent to 0.415 µg/m3) (Table 2). In our fully adjusted models (model 2), we found that a 1-SD increase in BC concentration was associated with 3.04-mmHg higher SBP (95% CI, 2.29–3.79; p = 0.003) and a 2.28- mmHg higher DBP (95% CI, 1.88–2.67; p < 0.001). These associations were attenuated compared with our model 1 analyses, which were adjusted for a subset of potential con- founders. In model 1 analyses, we observed that a 1-SD change in BC was associated with 3.52-mmHg (95% CI, 2.77–4.26) and 2.72-mmHg (95% CI, 2.31–3.12) changes in SBP and DBP, respectively. The complete list of the 19 SNPs ana- lyzed is described in Table 3. We genotyped 24 SNPs and excluded those SNPs that, in fewer than 10 study participants, were homozygous carriers of the variant allele (rg1106042 in HIWI, rs3742330 in DICER, rs417309 in DGCR8, rs636832 in AGO1) and those in which Hardy–Weinberg equilib- rium was not met at the 0.05 level (rs10719 in DROSHA), leaving a total of 19 SNPs in 10 genes. First, we examined the main effects of the SNPs of interest within this popula- tion. In our fully adjusted models, none of these SNPs were associated with BP at the 0.05 level. We examined BC-by-SNP inter- actions, and results are reported in Table 4. In models of SBP, interactions with BC were observed for two SNPs. For homozygous vari- ant carriers of rs197414, a 1-SD change in BC was associated with 9.82-mmHg lower Genea Gem-associated protein 3 (GEMIN3) (DDX20) AGO1 (EIF2C1) DROSHA (RNASEN) Exportin 5 (XPO5) AGO2 (EIF2C2) Tar-RNA binding protein 2 (TARBP) DICER (DICER1) Gem-associated protein 4 (GEMIN4) Table 3. SNPs in miRNA processing genes included in analysis. Black carbon, blood pressure, and miRNA-related SNPs DBP (95% CI, –18.68 to –0.95), whereas in wild-type individuals and heterozygous car- riers, we observed a 3.07-mmHg increase in BP (95% CI, 2.32–3.82); however, there were only 10 homozygous carriers of this variant, and the CI of these carriers is very wide. We also observed 5.58-mmHg higher BP (95% CI, 3.01–8.14) among GEMIN4 rs1062923 homozygous recessive carriers in response to a 1-SD change in BC, but only 2.87 (95% CI, 2.10–3.65) in heterozygotes and homozygous wild-type carriers. Because this SNP had a Hardy–Weinberg p-value of 0.05, we approach interpretation of these results with caution. We observed statistically significant inter- actions for four SNP-by-BC interactions pre- dicting DBP. In all of these analyses, smaller changes in BP were observed for carriers of the homozygous variant genotype. A 1-SD change in BC was associated with 1.48-mmHg higher DBP (95% CI, 0.78–2.18) for homozygous variant carriers and 2.57 mmHg (95% CI, 2.12– 3.02) in others. The rs13078 DICER SNP was associated with 0.13-mmHg higher Table 4. Effect modification of the association between a 1-SDa increase in BC concentrations and BP by gene variants related to miRNA processing under recessive models.b Sensitivity analyses Model 2 Model 1 IPW p-interactionc p-interaction p-interactiond 0.006 0.017 0.02 0.024 0.005 0.045 0.002 0.03 0.04 0.04 0.01 0.04 Amino acid change Arginine/serine Isoleucine/threonine Cysteine/arginine Isoleucine/threonine Arginine/glutamine Valine/glutamic acid Glycine/alanine Glutamic acid/glutamine 0.004 0.008 0.006 0.006 0.01 0.027 MAF (%) 0.12 0.18 0.38 0.15 0.18 0.40 0.18 0.49 0.18 0.43 0.19 0.11 0.27 0.42 0.15 0.27 0.25 0.48 0.28 945 DBP DGCR8 rs1640299 Wild-type and heterozygotes Homozygous carriers DICER rs13078 Wild-type and heterozygotes Homozygous carriers GEMIN4 rs7813 Wild-type and heterozygotes Homozygous carriers GEMIN4 rs910925 Wild-type and heterozygotes Homozygous carriers SBP GEMIN3 rs197414 Wild-type and heterozygotes Homozygous carriers GEMIN4 rs1062923 Wild-type and heterozygotes Homozygous carriers 590 189 738 25 638 136 647 134 769 10 739 37 Results Δ mmHg (95% CI) 2.57 (2.12 to 3.02) 1.48 (0.78–2.18) 2.32 (1.91 to 2.72) 0.13 (–1.65 to 1.91) 2.44 (2.00 to 2.87) 1.40 (0.60 to 2.21) 2.44 (2.02 to 2.87) 1.43 (0.61 to 2.25) 3.07 (2.32 to 3.82) –9.82 (–18.68 to –0.95) 2.87 (2.10 to 3.65) 5.58 (3.01 to 8.14) RS number rs197414 rs197388 rs197412 rs595961 rs6877842 rs11077 rs4961280 rs784567b rs13078 rs7813 rs1062923c rs3744741 rs4968104 rs910925 rs2740348 rs910924 rs3757 rs1640299 rs14035 SNP position chr1:112110646 chr1:112099005 chr1:112110476 chr1:36140367 chr5:31568395 chr6:43598925 chr8:141716596 chr12:52180732 chr14:94626500 chr17:594936 chr17:595817 chr17:595982 chr17:596255 chr17:596297 chr17:596685 chr17:602670 chr22:18479331 chr22:18478359 chr12:129927194 Alleles C/A T/A T/C A/G G/C C/A C/A C/T T/A T/C T/C C/T T/A G/C G/C C/T G/A G/T C/T Role Coding exon Promoter Coding exon Intron Promoter 3´ UTR Promoter Promoter 3´ UTR Coding exon Coding exon Coding exon Coding exon Coding exon Coding exon Promoter 3´ UTR 3´ UTR 3´ UTR aA 1-SD increment in BC concentration is equal to 0.415 µg/m3. bAdjusted for age (years), BMI, cigarette smoking status (never, current, former), pack-years smoked, blood urea nitrate, type 2 diabetes diagnosis, two or more alcoholic drinks per day, and current antihypertensive medication use (including angiotensin II receptor-, alpha-adrenoceptor, beta- or calcium channel blockers, diuretics, or ACE inhibitors) as well as apparent temperature, and season of clinical visit (spring: March–May; summer: June–August; autumn: September–November; winter: December–February). cTwo-sided p-value for interaction from SNP-by-BC coefficient. dp-Value for interaction from SNP-by-BC coefficient for sensitivity analysis using IPW. DiGeorge syndrome critical region gene 8 (DGCR8) Ras-related nuclear protein (RAN) Abbreviations: HWE, Hardy–Weinberg equilibrium; MAF, minor allele frequency; RS, reference SNP. aGene name (abbreviation), official gene symbol. bHWE p = 0.08. cHWE p = 0.05. Environmental Health Perspectives • volume 118 | number 7 | July 2010