Novel gene variants predict serum levels of the cytokines IL-18 and IL-1ra in older adults.

Activation of inflammatory pathways measured by serum inflammatory markers such as interleukin-18 (IL-18) and interleukin-1 receptor antagonist (IL-1ra) is strongly associated with the progression of chronic disease states in older adults. Given that these serum cytokine levels are in part a heritable trait, genetic variation may predict increased serum levels. Using the Cardiovascular Health Study and InCHIANTI cohorts, a genome-wide association study was performed to identify genetic variants that influence IL-18 and IL-1ra serum levels among older adults. Multiple linear regression models characterized the association between each SNP and log-transformed cytokine values. Tests for multiple independent signals within statistically significant loci were performed using haplotype analysis and regression models conditional on lead SNP in each region. Multiple SNPs were associated with these cytokines with genome-wide significance, including SNPs in the IL-18-BCO gene region of chromosome 2 for IL-18 (top SNP rs2250417, P=1.9×10(-32)) and in the IL-1 gene family region of chromosome 2 for IL-1ra (rs6743376, P=2.3×10(-26)). Haplotype tests and conditional linear regression models showed evidence of multiple independent signals in these regions. Serum IL-18 levels were also associated with a region on chromosome 2 containing the NLRC4 gene (rs12989936, P=2.7×10(-19)). These data characterize multiple robust genetic signals that influence IL-18 and IL-1ra cytokine production. In particular, the signal for serum IL-18 located on chromosome two is novel and potentially important in inflammasome triggered chronic activation of inflammation in older adults. Replication in independent cohorts is an important next step, as well as molecular studies to better understand the role of NLRC4.

Transcobalamin-II variants, decreased vitamin B12 availability and increased risk of frailty.

OBJECTIVE: This project was designed to follow-up prior evidence that demonstrated a significant association between vitamin B12 transport and metabolism and the frailty syndrome in community-dwelling older women. The cross-sectional relationship between genetic variants within six candidate genes along this pathway with serum methylmalonic acid (MMA) levels and frailty was evaluated in this same population of older women. METHODS: Baseline measures were collected prior to folate fortification from 326 women in the Women's Health and Aging Studies I and II. Odds ratios and statistical tests were estimated for single SNP and haplotype via linear regression models for serum MMA, a marker for available vitamin B12, and in logistic regression models for frailty. RESULTS: Fifty-six SNPs from CBS, MTHFR, MTR, MTRR, TCN1 and TCN2 genes were genotyped. Several SNPs in MTHFR, MTR and MTRR demonstrated a modest association to elevated MMA, while SNPs in TCN2 showed significant association to the frailty syndrome. TCN2 polymorphisms, particularly one SNP reported to be in perfect LD with functional variant Pro259Arg, were significantly associated with increased odds of frailty, after adjustment for age, presence of cardiovascular disease and elevated MMA (OR = 2.25, p-value = 0.009). CONCLUSIONS: Using MMA as a marker for vitamin B12, these results suggest that TCN2 gene variants may lead to decreased vitamin B12 availability, leading to reduced energy metabolism, ultimately contributing to frailty pathology. Further studies to determine the biological role of functional TCN2 polymorphisms in frailty are needed.

Markers of B-vitamin deficiency and frailty in older women.

OBJECTIVE: To evaluate the association between markers of vitamins B12, B6 and folate deficiency and the geriatric syndrome of frailty. DESIGN: Cross-sectional study of baseline measures from the combined Women's Health and Aging Studies. SETTING: Baltimore, Maryland. PARTICIPANTS: Seven hundred three community-dwelling women, aged 70-79. MEASUREMENTS: Frailty was defined by five-component screening criteria that include weight, grip strength, endurance, physical activity and walking speed measurements and modeled as binary and 3-level polytomous outcomes. Independent variables serum vitamin B6, vitamin B12, methylmalonic acid, total homocysteine, cystathionine and folate were modeled continuously and as abnormal versus normal. RESULTS: Serum biomarker levels varied significantly by race. All analyses were race-stratified and results are reported only for Caucasian women due to small African American sample size. In polytomous logistic regression models of 3-level frailty, Caucasian women with increasing MMA, defined either continuously or using a predefined threshold, had 40-60% greater odds of being prefrail (p-values < 0.07) and 1.66-2.33 times greater odds of being frail (p-values < 0.02) compared to nonfrails after adjustment for age, education, low serum carotenoids, alcohol intake, cardiovascular disease and renal impairment. Both binary and polytomous frailty models evaluating vitamin B12 as the main exposure estimated odds ratios that were similar in trend yet slightly less significant than the MMA results. CONCLUSIONS: These results suggest that vitamin B12 deficiency may contribute to the frailty syndrome in community-dwelling older women. Future studies are needed to explore these relationships longitudinally.