Characteristics of the participants genotyped in the Framingham Offspring Study are presented in . Overall, 2,531 participants were included in this analysis, 53% were women, and 10% had a diagnosis of diabetes over the 28 years of follow-up. Mean resistin levels measured at exam 7 were 14.1 ± 7.2 ng/dl. The heritability of resistin levels in the Framingham Offspring Study was estimated to be 35% (adjusted for sex, age, age2, and BMI). Other metabolic traits measured at exam 7 and the mean glucose levels over exams 3–7 are presented in . Resistin levels were modestly correlated with BMI (r = 0.16), waist circumference (r = 0.18), VAT (r = 0.15), and SAT (r = 0.13; all correlations age and sex adjusted; all P values < 0.001).
Characteristics of 2,531 Framingham Offspring Study participants genotyped for RETN variants
With 21 tag SNPs selected by a tagging approach that set an r2
> 0.8, we were able to capture 96% (26 of 27 SNPs that passed quality control in the CEU plates) of SNPs in the region of interest at an r2
> 0.8 and 100% at an r2
> 0.7 (see supplementary Table 1 for details regarding coverage [available at http://diabetes.diabetesjournals.org/cgi/content/full/db08-1339/DC1
]). Average distance between tag SNPs was 1.5 kb. The tag SNPs are shown in , with their location on chromosome 19 (NCBI B35 assembly), relation to RETN
itself (in and around the gene), and other names given in prior publications. SNP rs3745368 was not followed further due to its low MAF (0.002) in our sample.
Characteristics of SNPs genotyped in and around RETN in 2,543 participants in the Framingham Offspring Study
The LD map of the genotyped region is presented in supplementary Fig. 1 (D′ statistics). RETN is a short gene spanning only 1,369 bp. A gene coding for an open reading frame (C19orf59) also known as mast cell–expressed membrane protein 1 (MCEMP1) is located downstream of the 3′end of RETN and was fully captured by our tagging approach, with our last downstream SNP being on the 3′ side of MCEMP1. The LD map for the tagging SNPs in the Framingham population is shown in supplementary Fig. 2.
Circulating resistin levels were measured in 1,877 genotyped participants without diabetes. The associations for each tag SNP with resistin levels is illustrated in . The mean resistin level for each genotype and the nominal (uncorrected) and empirical (corrected for the number of SNPs) P values for each tag SNP are presented in . We found that the minor alleles at four tag SNPs (rs1477341, rs4804765, rs1423096, and rs10401670) in the 3′ region of RETN were associated with higher resistin levels (all Pe < 0.05). Since some of those SNPs were in moderate LD in the Framingham cohort (see supplementary Table 6 for specific D′ and r2 values), we conducted multiple SNPs models. When models were examined with various combinations of these SNPs, rs4804765 and rs1423096 had independent associations with resistin levels and rs4804765 explained the association of the two other SNPs (rs1477341 and rs10401670). The best-fitting model included rs4804765 and rs1423096 and explained 1.5% of the variance in resistin levels.
FIG. 1. Negative log base 10 of the P value for genetic associations for resistin levels under the additive model (left Y-axis), graphed versus SNPs in the RETN region arranged by chromosomal position (X-axis). The continuous line marked by the right Y-axis indicates (more ...)
Mean circulating resistin levels per genotype at SNPs in or near RETN in the Framingham Offspring Study*
One of these SNPs in the 3′ region, rs10401670, was also associated with mean glucose over follow-up (Pe = 0.02, after BMI adjustment Pe = 0.01) and FPG at exam 7 (Pe = 0.10, after BMI adjustment Pe = 0.02): its minor T allele was associated with higher glucose levels, concordant with a potential effect of its association with higher resistin levels. Two other SNPs showed associations with FPG at exam 7 (rs1423096, Pe = 0.049; and rs10413807, Pe = 0.02) but did not remain significant after adjustment for BMI. No other associations were observed in the glycemic or adiposity traits (Pe > 0.05) (see supplemental Table 3 for details).
Diabetes incidence was analyzed over the 28 years of follow-up. None of the SNPs offered convincing association with diabetes survival (all P
values ≥ 0.05) (see supplementary Table 2). Because a previous study reported that IVS2 + 181G/A was associated with diabetes when an interaction with BMI was added to the model (28
), we conducted diabetes incidence analysis with a BMI interaction term included in the model for this SNP, but even with this more refined replication attempt we did not detect a significant association. We also explored the effect of BMI on the association between rs10401670 and diabetes incidence: adding a BMI × rs10401670 term to the LME model revealed a significant interaction (P
= 0.02), and the P
value for the main effect for rs10401670 reached nominal significance (P
The promoter SNP −420C/G (rs1862513) has been investigated by many groups, some examining its association with resistin levels (9
) and a few with diabetes (29
) or adiposity (15
). The analysis of −420C/G (rs1862513) in the Framingham Offspring Study did not show an association with any of the traits measured, including resistin levels. To help attempt to discriminate low power from a true null association, we conducted a meta-analysis of the association of SNP −420C/G (rs1862513) with resistin levels. The details of each population included in the meta-analysis (9
) and our results are presented in . The minor C allele seemed to be associated with higher resistin levels; this effect was mainly driven by the largest Japanese study. Heterogeneity was highly significant (P
< 0.0001). The divergence between studies could be due to differences in ethnic background, age, sex distribution, diabetes status, or other characteristics. When we removed the diabetic subjects from the analysis, heterogeneity was still present.
Results from meta-analysis of the association between SNP −420C/G (rs1862513) and resistin levels*