The clinical characteristics of study participants are presented in . Mean adiponectin levels were 7.4 ± 4.5 μg/ml for men and 12.4 ± 6.4 μg/ml for women. Characteristics at exam 5, including the OGTT results, are presented in supplementary Table 1, and exam 7 adiposity measures by computed tomography are in supplementary Table 2, both of which are available in the online appendix.
Characteristics at entry and at exam 7 of 2,543 FOS participants genotyped for ADIPOQ variants
Details of the genotyped SNPs are presented in . The tag SNPs captured 100% of SNPs passing quality control with an r2 ≥0.80 and an MAF >0.05. The details of all SNPs captured by our tagging approach are available in supplementary Table 3 in the online appendix. The SNPs span 45,832 bp, with an average inter-SNP distance of 1,706 bp. A nonsynonymous coding SNP located in exon 3 (rs17366743 [Y111H]) had an MAF of 0.036 in the FOS but was reported to have an MAF of 0.075 in the HapMap CEU sample. Allele frequencies were otherwise similar to HapMap frequencies.
Characteristics of 22 SNPs genotyped in and around ADIPOQ in 2,543 men and women in the FOS
Supplementary Fig. 1, available in the online appendix, illustrates the linkage disequilibrium map of the 35 SNPs. As previously reported, ADIPOQ is composed of two regions of high linkage disequilibrium, one covering the 5′-promoter region, and the second including intron 2, exon 3, and the 3′-untranslated region (3′UTR), separated by a segment of high recombination rate.
Adiponectin levels were available in 2,018 genotyped participants. illustrates the association of SNPs with adiponectin levels and the strength of their association (expressed as −log P) adjusted for sex, age, and age2 or for sex, age, age2, and BMI. The minor A allele (MAF = 0.10) at SNP rs17300539 (−11391G/A), located in the promoter region, showed the strongest association with higher adiponectin levels under an additive model (Pn = 2.6 × 10−8; Pe = 0.0005). Also in the 5′–linkage disequilibrium region, the minor C allele at rs822387 (MAF = 0.10) was strongly associated with higher adiponectin levels (Pn = 3.8 × 10−5; Pe = 0.001) and was in strong linkage disequilibrium (r2 = 0.794 in unrelated members of the FOS) with rs17300539.
FIG. 1. Negative log base 10 of the P value for genetic associations for adiponectin levels under the additive model (left y-axis), graphed versus SNPs in the ADIPOQ region arranged by chromosomal position (x-axis). The continuous line marked by the right y-axis (more ...)
In the 3′UTR, the minor A allele at rs6773957 (MAF = 0.41) showed the strongest association with higher adiponectin levels (Pn
= 4.4 × 10−4
= 0.005). Located further downstream in the 3′ region, rs6444175 showed a nominal trend of association with adiponectin levels that did not remain significant after multiple testing correction (Pn
= 0.017; Pe
= 0.2); however, further adjustment for BMI seemed to strengthen the association (Pn
= 0.003; Pe
= 0.04). Also, in the second linkage disequilibrium region, rs1501299 (+276G/T; located in intron 2) showed a nominal association with adiponectin levels once adjusted for BMI (Pn
= 0.007), but the empiric P
value was not significant (Pe
= 0.10). The two latter SNPs (rs6444175 and rs1501299) are in strong linkage disequilibrium with each other (r2
= 0.92) and in moderate linkage disequilibrium with rs6773957 (r2
0.5). A few other SNPs had nominal associations with adiponectin levels; all of the details for each SNP association with adiponectin levels (without and with adjustment for BMI) are shown in .
Adiponectin levels for each SNP in and around ADIPOQ in the FOS
Diabetes incidence was associated with only one SNP, rs17366743 (Y111H), which is a nonsynonymous SNP coding for a Y→H change at codon 111 in exon 3 of ADIPOQ. In age-sex adjusted analysis, those carrying the minor C allele (MAF = 0.036) were associated with a hazard ratio (HR) of 1.94 for incident diabetes (95% CI 1.16–3.25; Pn = 0.01). rs17366743 also was associated with 28-year time-averaged mean FPG (Pn = 0.0004; Pe = 0.004); consistent with our diabetes survival analysis, the minor C allele was associated with higher glucose levels. We had limited power to see smaller effects (HR 1.1–1.4) on diabetes incidence, even with higher MAF (supplementary Table 9). summarizes the associations of SNPs in ADIPOQ with diabetes incidence and mean FPG. A few SNPs also showed trends of associations with other glycemic quantitative traits, but none remained statistically significant after empiric correction (supplementary Tables 4 and 5, available in the online appendix). Subsidiary analysis did not show any SNP to be significantly associated with incidence of hyperglycemia (affecting 52.7% of the FOS) (supplementary Table 10, available in the online appendix).
FIG. 2. Negative log base 10 of the P value for genetic associations with diabetes survival (circles) and mean glucose over 29 years of follow-up (diamonds) under the additive model (left y-axis), graphed versus SNPs in the ADIPOQ region arranged by chromosomal (more ...)
Concerning adiposity, we did not find an association between any SNPs in ADIPOQ and adiposity measurements, including BMI, waist circumference, or visceral and subcutaneous adipose tissue volumes (supplementary Tables 4–6). In the obesity-stratified analyses, our main findings seemed to have a similar effect on adiponectin levels in both nonobese and obese strata; whereas two SNPs (rs17366568 and rs864265) appeared to have a stronger effect in the obese population. There was no significant interaction between any of the SNPs and BMI on diabetes incidence. All of the details for each SNP association with adiponectin levels, mean glucose, and diabetes incidence stratified by obesity status and tested for interaction with BMI are presented in supplementary Table 8, available in the online appendix.
In the 5′–linkage disequilibrium region–multiple SNPs model, both rs17300539 and rs822387 remained significantly associated with adiponectin levels, indicating that despite their strong linkage disequilibrium, they may represent independent signals. In the 3′–linkage disequilibrium region, including rs6773957, rs6444175, and rs1501299 in the same model, there was a loss of significance for all three SNPs, indicating that they probably represent the same signal, with rs6773957 having the strongest individual effect. Finally, we examined a model with all SNPs associated with adiponectin levels. Only the two SNPs in the promoter region (rs17300539 and rs822387) remained significant in the model.
We performed subsidiary analyses using recessive and dominant genetic models for the main traits of interest. The results are presented in supplementary Table 7, available in the online appendix. In brief, dominant model results were very similar to the additive model, whereas recessive models showed similar direction of effect but no significant association. Some trends for SNPs other than the ones observed in the additive models were seen, but we consider those findings exploratory.