This study evaluated the association of timing of lipid levels and lipid genetic risk score (GRS) with subclinical atherosclerosis.
Atherosclerosis is a slowly progressive disorder influenced by suboptimal lipid levels. Long-term versus contemporary lipid levels may more strongly impact the development of coronary artery calcium (CAC).
Framingham Heart Study (FHS) Offspring Cohort participants (n=1156, 44%M, 63±9 years) underwent serial fasting lipids [low-density lipoprotein (LDL-C), high-density lipoprotein, and triglycerides], Exam 1 (1971–1975) – Exam 7 (1998–2001). FHS Third Generation Cohort participants (n=1954, 55%M, 45±6 years) had fasting lipid profiles assessed, 2002–2005. Computed tomography (2002–2005) measured CAC. Lipid GRSs were computed from significantly associated single nucleotide polymorphisms. The association between early, long-term average, and contemporary lipids, and lipid GRS, with elevated CAC was assessed using logistic regression.
In FHS Offspring, Exam 1 and long-term average versus Exam 7 lipid measurements, including untreated lipid levels, were strongly associated with elevated CAC. In the FHS Third Generation, contemporary lipids were associated with CAC. The LDL-C GRS was associated with CAC (age/sex-adjusted OR 1.14, 95%CI 1.00–1.29, p=0.04). However, addition of the GRS to the lipid models did not result in a significant increase in the OR or C-statistic for any lipid measure.
Early and long-term average lipid levels, as compared with contemporary measures, are more strongly associated with elevated CAC. Lipid GRS was associated with lipid levels but did not predict elevated CAC. Adult early and long-term average lipid levels provide important information when assessing subclinical atherosclerosis and cardiovascular risk.
Lipids; Genetic risk score; Coronary artery calcium
Procollagen type III N-terminal peptide (P3NP) is released during collagen synthesis in muscle. Increased circulating P3NP is a marker not only of muscle growth, but also of muscle repair and fibrosis. Thus, P3NP may be a potential biomarker for sarcopenia.
To determine the association between plasma P3NP and lean mass and strength
Design, Setting, and Participants
A cross-sectional study of men and women from the Framingham Offspring Study. Participants included a convenience sample of 687 members with a measure of plasma P3NP and lean mass, and 806 members with P3NP and quadriceps strength assessment.
Linear regression was used to estimate the association between total and appendicular lean mass and plasma P3NP, and quadriceps strength and P3NP
Mean age was 58 years. Median plasma P3NP was similar in men (3.4 mg/L), premenopausal women (3.1 mg/L), and postmenopausal women (3.0 mg/L). In adjusted models, higher P3NP was associated with a modest decrease in total and appendicular lean mass in postmenopausal women [β= −0.13 unit P3NP/kg total lean mass; p=0.003]. A similar trend was found among premenopausal women, although results were not statistically significant [β=−0.10 unit P3NP/kg total lean mass; p=0.41]. No association between P3NP and lean mass was observed in men. P3NP was not associated with strength in men or women.
Our results suggest that plasma P3NP might be a useful biomarker of muscle mass in postmenopausal women if longitudinal studies demonstrate that it has adequate sensitivity and specificity to predict muscle loss.
procollagen type III N-telopeptide; P3NP; lean mass
Alzheimer disease (AD) is highly prevalent in Wadi Ara, despite the low frequency of APOE ε4 in this genetically isolated Arab community in northern Israel. We hypothesized that the reduced genetic variability in combination with increased homozygosity would facilitate identification of genetic variants that contribute to the high rate of AD in this community. AD cases (N=124) and controls (N=142) from Wadi Ara were genotyped for a a genome-wide set of more than 300,000 single nucleotides polymorphisms (SNPs) which were used to calculate measures of population stratification and inbreeding, and to identify regions of autozygosity. Although a high degree of relatedness was evident in both cases and controls, controls were significantly more related and contained more autozygous regions than cases (P = 0.004). Eight autozygous regions on seven different chromosomes were more frequent in controls than cases, and 105 SNPs in these regions, primarily on chromosomes 6 and 9, were nominally associated with AD. Associations with SNPs in NOTCH4 and AGPAT1 (both on chromosome 6) were confirmed in a meta analysis of four genome-wide association study (GWAS) datasets. Analysis of the full Wadi Ara GWAS dataset revealed 99 SNP associations with AD at P ≤ 10−5, however none of these were confirmed in the replication GWAS datasets. The unique population structure of Wadi Ara enhanced efforts to identify genetic variants that might partially explain the high prevalence of AD in the region. Several of these variants show modest evidence for association in other Caucasian populations.
Alzheimer Disease; Genome-Wide Association Study; Population Groups; Meta-Analysis
A direct assay for small dense low density lipoprotein cholesterol (sdLDL-C) has been developed. Our goal was to establish normal ranges for this assay as well as to measure values in patients with established coronary heart disease (CHD) versus control subjects.
Direct LDL-C and sdLDL-C analyses were carried out on samples from 3,188 male and female participants of the Framingham Offspring Study, which included 173 male and 74 female CHD cases.
Male gender and female postmenopausal status were both associated with significantly (p<0.0001) higher sdLDL-C values. Use of cholesterol-lowering medications was significantly (p<0.0001) higher in CHD cases than in controls (46.8% versus 11.4% in men, and 35.1% versus 8.8% in women). Direct LDL-C levels were significantly lower in male CHD patients than in male controls (3.22 versus 3.51 mmol/L, p<0.0001), but their mean sdLDL-C levels were similar to those in controls (0.83 versus 0.84 mmol/L, p=0.609). Female CHD patients had similar LDL-C values to female controls (3.53 versus 3.46 mmol/L, p=0.543), but had significantly higher sdLDL-C values (0.83 versus 0.68 mmol/L, p=0.0015). Both male and female cases also had significantly (p<0.01) higher percentages of LDL-C as sdLDLC than controls.
Despite four fold greater cholesterol lowering therapy use, CHD patients had mean LDL-C values well above the LDL-C goal of < 2.6 mmol/L or 100 mg/dl, and male CHD cases had similar sdLDL C values and female CHD cases had significantly higher values than controls. These findings may explain some of the high residual risk of future CHD events in CHD patients.
small dense LDL-cholesterol; coronary heart disease; risk factor; Framingham Offspring Study; obesity
Phenotypic heterogeneity complicates detection of genomic loci predisposing to type 2 diabetes, potentially obscuring or unmasking specific loci. We conducted ordered subsets linkage analyses (OSA) for diabetes-related quantitative traits (fasting insulin and glucose, HbA1c and 28-year time averaged fasting plasma glucose (tFPG)) from 330 families of the Framingham Offspring Study. We calculated mean body mass index (BMI), waist circumference (WC), and a diabetes ‘age-of-onset score’ for each family. We constructed subsets by adding one family at a time in increasing (lean family to obese) or decreasing (obese to lean) adiposity order or increasing or decreasing propensity to develop diabetes at a younger age, with the OSA LOD reported as the maximum LOD observed in any subset. Permutation p-values tested the hypothesis that phenotypic ordering showed stronger linkage than random ordering. On chromosome 1, ordering by increasing family mean WC increased linkage to tFPG at 256 cM from LOD = 2.4 to 3.5 (permuted p=0.02) and to HbA1c at 180 cM from LOD = 2.0 to 3.3 (p=0.01). On chromosome 19, ordering by decreasing WC increased linkage to fasting insulin at 68 cM from LOD = 2.7 to 4.6 (p=0.002), and ordering by decreasing propensity to develop diabetes at a young age increased linkage to fasting insulin at 73 cM from LOD = 2.7 to 4.0 (p=0.046). We conclude that chromosomes 1 and 19 could harbor adiposity-interacting diabetes susceptibility genes. Such interactions might also influence trait-locus associations and may be useful to consider in diabetes genome-wide association studies.
type 2 diabetes mellitus; insulin resistance; genetics; risk factors; longitudinal study; linkage study; genetics; genomics
Association analyses may follow an initial linkage analysis for mapping and identifying genes underlying complex quantitative traits and may be conducted on unrelated subsets of individuals where only one member of a family is included. We evaluate two methods to select one sibling per sibship when multiple siblings are available: 1) one sibling with the most extreme trait value; and 2) one sibling using a combination score statistic based on extreme trait values and identity-by-descent sharing information. We compare the type I error and power. Furthermore, we compare these selection strategies with a strategy that randomly selects one sibling per sibship and with an approach that includes all siblings, using both simulation study and an application to fasting blood glucose in the Framingham Heart Study. When genetic effect is homogeneous, we find that using the combination score can increase power by 30 to 40% compared to a random selection strategy, and loses only 8 ~ 13% of power compared to the full sibship analysis, across all additive models considered, but offers at least 50% genotyping cost saving. In the presence of genetic heterogeneity, the score offers a 50% increase in power over a random selection strategy, but there is substantial loss compared to the full sibship analysis. In application to fasting blood sample, two SNPs are found in common for the selection strategies and the full sample among the 10 highest ranked SNPs. The EV strategy tends to agree with the IBD-EV strategy and the analysis of the full sample.
linkage analysis; association study; linkage disequilibrium; identity-by-descent (IBD)
The ω-hydroxylase CYP4A11 catalyzes the transformation of epoxyeicosatrienoic acids to omega-hydroxylated-epoxyeicosatrienoic acids, endogenous peroxisome proliferator-activated receptor α (PPARα) agonists. PPARα activation increases high-density lipoprotein-cholesterol (HDL-C). A cytosine-for-thymidine (T8590C) variant of CYP4A11 encodes for a ω-hydroxylase with reduced activity. This study examined the relationship between CYP4A11 T8590C genotype and metabolic parameters in the Framingham Offspring Study and in a clinical practice-based biobank, BioVU. In women in the Framingham Offspring Study, the CYP4A11 8590C allele was associated with reduced HDL-C concentrations (54.2±0.9 mg/dL in CYP4A11 CC or CT genotype women versus 56.7±0.5 mg/dL in TT women, p=0.02), and with an increased prevalence of low HDL-C, defined categorically as ≤50mg/dL [odds ratio 1.39 (95% CI 1.02-1.90), p=0.04]. In the BioVU cohort, the CYP4A11 8590C allele was also associated with low HDL-C in women [odds ratio 1.69 (95% CI 1.03-2.77, p=0.04)]. There was no relationship between genotype and HDL-C in men in either cohort.
We evaluated direct low density lipoprotein (LDL) cholesterol (C) and high density lipoprotein (HDL) cholesterol (C) versus standard methods using fasting plasma samples from participants in cycle 6 of the Framingham Offspring Study.
Direct LDL-C and HDL-C measurements were performed on fasting plasma from male (1335 controls, 173 CHD cases) and female (1606 controls, 74 cases) participants, and compared with LDL-C, as calculated with the Friedewald formula, and HDL-C, as measured after dextran-Mg2+ precipitation.
Values for direct LDL-C and HDL-C correlated well with standard methods (both about r2=0.94, p<0.001) with similar absolute values. Biases of > 10% were present for 7.7% of samples for LDL-C, while for HDL-C this value was 8.5%. Despite higher use of cholesterol lowering medication in CHD cases, calculated or direct LDL-C values were still well above recommended values [< 2.6 mmol/L, (100 mg/dl)] in CHD cases, especially in females.
Direct assays for both LDL-C and HDL-C provide an acceptable guide for lipid treatment. In the Framingham Offspring Study participants, most CHD cases have LDL-C levels above the recommended target.
cholesterol; LDL; HDL; coronary heart disease; Framingham Offspring Study
Our aim was to determine whether a low plasma adiponectin level is an independent predictor of coronary heart disease (CHD).
Methods and Results
We measured adiponectin levels in frozen plasma samples (−80°C) in a total of 3,188 male and female participants in cycle 6 of the Framingham Offspring Study, using a novel full-automated assay. CHD cases at baseline were excluded, and participants were followed for a mean of 7.5 years (mean age was 57 years in both men and women, and mean BMI 28.5 kg/m2 in men and 27.3 kg/m2 in women). Plasma adiponectin levels (median [25percentile, 75percentile]) were significantly higher in female than male controls (14.8 [10.7, 20.5] μg/mL versus 9.0 [7.0, 12.2] μg/mL, p< 0.001). After adjustment for age, body mass index, smoking status, systolic blood pressure, treatment for hypertension, diabetes status, use of cholesterol-lowering medication, total cholesterol level, and high-density lipoprotein cholesterol level. A decreased plasma adiponectin level was a highly significant predictor of future CHD events (n =117) in men, with a hazards ratio of 0.4728 (p=0.0024). A bottom-quartile value of < 7.0 μg/mL doubled the risk of CHD in men. The identical trend was observed in women; however, the statistical significance of these associations disappeared after multivariate adjustments, possibly due to a low number of female CHD cases (n=60).
An adiponectin level of < 7.0 μg/mL is a powerful independent predictor of CHD in men in the United States.
adiponectin; coronary heart disease; risk factor; Framingham Offspring Study; obesity
Previous studies have shown association of single nucleotide polymorphisms (SNPs) in three contiguous genes (PON1, PON2 and PON3) encoding paraoxonase with risk of Alzheimer disease (AD). We evaluated the association of serum paraoxonase activity measured by phenyl acetate (PA) and thiobutyl butyrolactone (TBBL) with risk of AD and with 26 SNPs spanning the PON gene cluster in 266 AD cases and 306 sibling controls from the MIRAGE Study. The odds of AD (adjusted for age, gender and ethnicity) increased 20% for each standard deviation decrease in PA or TBBL activity. There were association signals with activity in all three genes. Haplotypes including SNPs spanning the PON genes were generally more significant than haplotypes comprising SNPs from one gene. Significant interactions were observed between SNP pairs located across the PON cluster with either serum activity measure as the outcome, and between several PON SNPs and PA activity with AD status as the outcome. Our results suggest that low serum paraoxonase activity is a risk factor for AD. Furthermore, multiple variants in PON influence serum paraoxonase activity and their effects may be synergistic.
Trps1 has been proposed as a candidate gene for a mouse bone mineral density (BMD) QTL on Chromosome (Chr) 15, but it remained unclear if this gene was associated with BMD in humans. We used newly available data and advanced bioinformatics techniques to confirm that Trps1 is the most likely candidate gene for the mouse QTL. In short, by combining the raw genetic mapping data from two F2 generation crosses of inbred strains of mice, we narrowed the 95% confidence interval of this QTL down to the Chr 15 region spanning from 6 to 24 cM. This region contains 131 annotated genes. Using block haplotyping, all other genes except Trps1 were eliminated as candidates for this QTL. We then examined associations of 208 SNPs within 10kb of TRPS1 with BMD and hip geometry, using human genome-wide association study (GWAS) data from the GEFOS consortium. After correction for multiple testing, six TRPS1 SNPs were significantly associated with femoral neck BMD (P=0.0015–0.0019; adjusted P=0.038–0.048). We also found that three SNPs were highly associated with femoral neck width in women (rs10505257, P = 8.6x10−5, adjusted P=2.15x10−3; rs7002384, P = 5.5x10−4, adjusted P=01.38x10−2). In conclusion, we demonstrated that combining association studies in humans with murine models provides an efficient strategy to identify new candidate genes for bone phenotypes.
Trichorhinophalangeal syndrome I; mouse models; human genetic association study; bone mineral density
Genetic factors likely contribute to the risk for vertebral fractures; however, there are few studies on the genetic contributions to vertebral fracture (VFrx), vertebral volumetric bone mineral density (vBMD) and geometry. Also the heritability (h2) for VFrx and its genetic correlation with phenotypes contributing to VFrx risk have not been established. This study aims to estimate the h2 of vertebral fracture, vBMD and cross-sectional-area (CSA) derived from quantitative computed tomography (QCT) scans, and to estimate the extent to which they share common genetic association in adults of European ancestry from three generations of Framingham Heart Study (FHS) families. Members of the FHS families were assessed for VFrx by lateral radiographs or QCT lateral scout views at 13 vertebral levels (T4-L4) using Genant’s semi-quantitative (SQ) scale (grades 0–3). Vertebral fracture was defined as having at least 25% reduction in height of any vertebra. We also analyzed QCT scans at the L3 level for integral (In.BMD) and trabecular (Tb.BMD) vBMD and cross-sectional area (CSA). Heritability estimates were calculated, and bivariate genetic correlation analysis was performed, adjusting for various covariates. For VFrx, we analyzed 4,099 individuals (148 VFrx cases) including 2,082 women and 2,017 men from 3 generations. Estimates of crude and multivariable-adjusted h2 were 0.43 to 0.69 (P< 1.1×10−2). 3,333 individuals including 1,737 men and 1,596 women from 2 generations had VFrx status and QCT-derived vBMD and CSA information. Estimates of crude and multivariable-adjusted h2 for vBMD and CSA ranged from 0.27 to 0.51. In a bivariate analysis, there was a moderate genetic correlation between VFrx and multivariable-adjusted In.BMD (−0.22) and Tb.BMD (−0.29). Our study suggests vertebral fracture, vertebral vBMD and CSA in adults of European ancestry are heritable, underscoring the importance of further work to identify the specific variants underlying genetic susceptibility to vertebral fracture, bone density and geometry.
vertebral fracture; bone mineral density; heritability; QCT
Polyunsaturated fatty acids (PUFAs) may influence bone health. The objective of this work was to examine associations between plasma phosphatidylcholine (PC) PUFA concentrations and hip measures: (1) femoral neck bone mineral density (FN-BMD) (n = 765); (2) 4-year change in FN-BMD (n = 556); and (3) hip fracture risk (n = 765) over 17-year follow-up among older adults in the Framingham Osteoporosis Study. BMD measures were regressed on quintile of plasma PC PUFAs (docosahexaenoic acid [DHA], linoleic acid [LA], and arachidonic acid [AA]), adjusted for covariates. Hazard ratios (HR) and 95% confidence interval (CI) for hip fracture were estimated by quintile of plasma PC PUFAs, adjusted for covariates. Higher concentrations of PC DHA were associated with loss of FN-BMD over 4 years in women (p-trend = 0.04), but was protective in men in the uppermost quintile compared to men grouped in the lower four quintiles, in post hoc analysis (p = 0.01). PC LA concentrations were inversely associated with baseline FN-BMD in women (p-trend = 0.02), and increased hip fracture risk in women and men (p-trend = 0.05), but body mass index (BMI) adjustment attenuated these associations (p-trend = 0.12 and p-trend = 0.14, respectively). A trend toward a protective association was observed between PC AA and baseline FN-BMD in men (p-trend = 0.06). Women and men with the highest PC AA concentrations had 51% lower hip fracture risk than those with the lowest (HR = 0.49, 95% CI = 0.24–1.00). Opposing effects of PC DHA on FN-BMD loss observed in women and men need further clarification. Bone loss associated with PC LA may be confounded by BMI. High PC AA concentrations may be associated with reduced hip fracture risk.
DOCOSAHEXAENOIC ACID; LINOLEIC ACID; ARACHIDONIC ACID; BMD; FRACTURE
Background and purpose
Our objective was to investigate the associations between polymorphisms in representative genes of the renin angiotensin system with measures of cerebral blood flow regulation in older adults.
Participants in this analysis were white subjects (n=335) in the MOBILIZE Boston study, an observational study of community-dwelling elders who underwent transcranial Doppler while sitting and standing and during hypercapnea and hypocapnea. Autoregulation phenotype was the change in cerebrovascular resistance from sit to stand. Vasoreactivity (VR) phenotype was the slope of the change in cerebrovascular conductance vs change in end-tidal CO2. Total of 33 tagged single nucleotide polymorphisms (SNP) were selected in the angiotensinogen gene (AGT), the angiotensin converting enzyme (ACE) gene and the angiotensin receptor gene (AGTR). Regression analyses adjusted for age, gender, body mass index, mean arterial blood pressure, stroke and use of antihypertensives were conducted for each SNP and outcome. Bonferroni corrections were used to adjust p-values for multiple testing.
In the AGT gene, only the rs699 SNP was associated with VR after Bonferroni correction (p=0.00028). Homozygous carriers of the CC genotype of this SNP had lower VR compared to the CT or TT genotypes. There were no significant associations with autoregulation measures. None of the SNP’s in the other genes was associated with our phenotypes.
This analysis suggests that the AGT gene may be involved in vasoreactivity independent of blood pressure. Larger studies are needed to confirm the role of this gene in cerebrovascular health and aging.
Angiotensin; cerebral blood flow; vasoreactivity
Limited data exist regarding the use of a genetic risk score for predicting risk of incident cardiovascular disease (CVD) in US based samples.
Methods and Results
Using findings from recent GWAS, we constructed genetic risk scores (GRS) comprised of 13 genetic variants associated with myocardial infarction (MI) or other manifestations of CHD and 102 genetic variants associated with CHD or its major risk factors. We also updated the 13 SNP GRS with 16 SNPs recently discovered by GWAS. We estimated the association, discrimination and risk reclassification of each GRS for incident cardiovascular events and for prevalent coronary artery calcium (CAC).
In analyses adjusted for age, sex, CVD risk factors and parental history of CVD, the 13 SNP GRS was significantly associated with incident hard CHD (HR 1.07, 95% CI 1.00-1.15, p=0.04), CVD (hazard ratio [HR] per-allele 1.05, 95% confidence interval [CI] 1.01-1.09; p=0.03), and high CAC (defined as >75th age and sex-specific percentile; odds ratio [OR] per-allele 1.18, 95% CI 1.11-1.26, p=3.4 × 10-7). The GRS did not improve discrimination for incident CHD or CVD but led to modest improvements in risk reclassification. However, significant improvements in discrimination and risk reclassification were observed for the prediction of high CAC. The addition of 16 newly discovered SNPs to the 13 SNP GRS did not significantly modify these results.
A GRS comprised of 13 SNPs associated with coronary disease is an independent predictor of cardiovascular events and of high CAC, modestly improves risk reclassification for incident CHD and significant improves discrimination for high CAC. The addition of recently discovered SNPs did not significantly improve the performance of this GRS.
Genetics; single nucleotide polymorphisms; cardiovascular disease; coronary heart disease; risk prediction; reclassification
The major histocompatibility complex (MHC) on chromosome 6p21 is a key contributor to the genetic basis of systemic lupus erythemathosus (SLE). Although SLE affects African Americans disproportionately compared to European Americans, there has been no comprehensive analysis of the MHC region in relationship to SLE in African Americans. We conducted a screening of the MHC region for 1,536 single nucleotide polymorphisms (SNPs) and the deletion of the C4A gene in a SLE case-control study (380 cases, 765 age-matched controls) nested within the prospective Black Women’s Health Study. We also genotyped 1,509 ancestral informative markers throughout the genome to estimate European ancestry in order to control for population stratification due to population admixture. The most strongly associated SNP with SLE was the rs9271366 (odds ratio, OR = 1.70, p = 5.6×10−5) near the HLA-DRB1 gene. Conditional haplotype analysis revealed three other SNPs, rs204890 (OR = 1.86, p = 1.2×10−4), rs2071349 (OR = 1.53, p = 1.0×10−3), and rs2844580 (OR = 1.43, p = 1.3×10−3) to be associated with SLE independent of the rs9271366 SNP. In univariate analysis, the OR for the C4A deletion was 1.38, p = 0.075, but after simultaneous adjustment for the other four SNPs the odds ratio was 1.01, p = 0.98. A genotype score combining the four newly identified SNPs showed an additive risk according to the number of high-risk alleles (OR = 1.67 per high-risk allele, p< 0.0001). Our strongest signal, the rs9271366 SNP, was also associated with higher risk of SLE in a previous Chinese genome-wide association study (GWAS). In addition, two SNPs found in a GWAS of European ancestry women were confirmed in our study, indicating that African Americans share some genetic risk factors for SLE with European and Chinese subjects. In summary, we found four independent signals in the MHC region associated with risk of SLE in African American women.
systemic lupus erythemathosus; African Americans; major histocompatibility complex; single nucleotide polymorphisms
HIV-infected women are at increased risk for cervical cancer; thus, adherence with Papanicolaou (Pap) testing is of particular importance. The objective of this study was to identify risk factors for inadequate Pap testing in a diverse cohort of HIV-infected women at a large urban safety net HIV clinic.
This retrospective cohort study assessed HIV-infected women aged 18–60 years in care between October 1, 2003, and March 31, 2008, for risk factors for inadequate Pap testing. Unadjusted odds ratios (OR) with confidence intervals (CI) and multivariate analyses with generalized estimating equations for correlated data were calculated.
Of 549 women, 293 (53.4%) had a Pap test during each follow-up period. Women who were older, white or Hispanic race/ethnicity, U.S. born, unemployed, drug users, and those with advanced HIV had increased odds of no Pap testing in unadjusted analyses. In multivariate analyses, U.S.-born women who were white or unemployed or had a baseline CD4 count <200 cells/mm3 had increased odds of no Pap testing (OR 2.0, 95% CI 1.3-3.1; OR 2.3, CI 1.0-5.0; OR 1.7, CI 1.0-2.9, respectively). For non-U.S.-born women, age ≥50 years (OR 3.9, CI 1.7-9.0), non-English-speaking status (OR 1.6, CI 1.0-2.4), and drug use (OR 5.8, CI 2.5-13.9) were associated with no Pap testing.
U.S.-born status and low CD4 count were associated with increased odds of inadequate Pap testing. Further study is needed to identify interventions to improve Pap testing adherence in this high-risk group.
Association studies of risk factors and complex diseases require careful assessment of potential confounding factors. Two-stage regression analysis, sometimes referred to as residual- or adjusted-outcome analysis, has been increasingly used in association studies of single nucleotide polymorphisms (SNPs) and quantitative traits. In this analysis, first, a residual-outcome is calculated from a regression of the outcome variable on covariates and then the relationship between the adjusted-outcome and the SNP is evaluated by a simple linear regression of the adjusted-outcome on the SNP. In this paper, we examine the performance of this 2-stage analysis as compared with multiple linear regression (MLR) analysis. Our findings show that when a SNP and a covariate are correlated, the 2-stage approach results in biased genotypic effect and loss of power. Bias is always toward the null and increases with the squared-correlation between the SNP and the covariate (ρSC2). For example, for ρSC2=0.0, 0.1 and 0.5, 2-stage analysis results in, respectively, 0%, 10% and 50% attenuation in the SNP effect. As expected, MLR was always unbiased. Since individual SNPs often show little or no correlation with covariates, a 2-stage analysis is expected to perform as well as MLR in many genetic studies; however, it produces considerably different results from MLR and may lead to incorrect conclusions when independent variables are highly correlated. While a useful alternative to MLR under ρSC2=0.0, the 2-stage approach has serious limitations. Its use as a simple substitute for MLR should be avoided.
confounding; conditional analysis; covariate; 2-stage regression; adjusted-outcome; adjusted-genotype
Several bone marrow-derived cell populations may possess angiogenic activity, including cells termed endothelial progenitor cells. Decreased numbers of circulating angiogenic cell populations have been associated with increased cardiovascular risk. However, few data exist from large, unselected samples, and the genetic determinants of these traits are unclear.
Methods and Results
We examined the clinical and genetic correlates of early outgrowth colony forming units (CFUs) in 1,799 participants of the Framingham Heart Study (mean age, 66 years; 54% women). Among individuals without cardiovascular disease (n=1612), CFU number was inversely related to advanced age (P=0.004), female sex (P=0.04), and triglycerides (P=0.008), and positively related to hormone replacement (P=0.008) and statin therapy (P=0.027) in stepwise multivariable analyses. Overall, CFU number was inversely related to the Framingham risk score (p=0.01) but not with prevalent cardiovascular disease. In genome-wide association analyses in the entire sample, polymorphisms were associated with CFUs at the MOSC1 locus (P=3.3×10−7) and at the SLC22A3-LPAL2-LPA locus (P=4.9×10−7), a previously replicated susceptibility locus for myocardial infarction. Furthermore, alleles at the SLC22A3-LPAL2-LPA locus that were associated with decreased CFUs were also related to increased risk of myocardial infarction (P=1.1×10−4).
In a community-based sample, early outgrowth CFUs are inversely associated with select cardiovascular risk factors. Furthermore, genetic variants at the SLC22A3-LPAL2-LPA locus are associated with both decreased CFUs and an increased risk of myocardial infarction. These findings are consistent with the hypothesis that decreased circulating angiogenic cell populations promote susceptibility to myocardial infarction.
Genetics; epidemiology; coronary disease; cardiovascular disease; cells
To evaluate the association of genetic variation with late-onset Alzheimer disease (AD) in African Americans, including genes implicated in recent genome-wide association studies of whites.
We analyzed a genome-wide set of 2.5 million imputed markers to evaluate the genetic basis of AD in an African American population.
Five hundred thirteen well-characterized African American AD cases and 496 cognitively normal African American control subjects.
Data were collected from multiple sites as part of the Multi-Institutional Research on Alzheimer Genetic Epidemiology (MIRAGE) Study and the Henry Ford Health System as part of the Genetic and Environmental Risk Factors for Alzheimer Disease Among African Americans (GenerAAtions) Study.
Several significant single-nucleotide polymorphisms (SNPs) were observed in the region of the apolipoprotein E gene (APOE). After adjusting for the confounding effects of APOE genotype, one of these SNPs, rs6859 in PVRL2, remained significantly associated with AD (P=.0087). Association was also observed with SNPs in CLU, PICALM, BIN1, EPHA1, MS4A, ABCA7, and CD33, although the effect direction for some SNPs and the most significant SNPs differed from findings in data sets consisting of whites. Finally, using the African American genome-wide association study data set as a discovery sample, we obtained suggestive evidence of association with SNPs for several novel candidate genes.
Some genes contribute to AD pathogenesis in both white and African American cohorts, although it is unclear whether the causal variants are the same. A larger African American sample will be needed to confirm novel gene associations, which may be population specific.
Apolipoprotein E (APOE) has been studied for its potential role in osteoporosis risk. It is hypothesized that genetic variation at APOE locus, known as E2, E3, and E4, may modulate bone mineral density (BMD) through its effects on lipoproteins and vitamin K transport. The purpose of this study was to determine the association of the APOE-E4 gene polymorphism with bone-related phenotypes.
We conducted a meta-analysis that combined newly-analyzed individual data from two community-based cohorts, the Framingham Offspring Study (N=1,495) and the Vitamin K Clinical Trial (N=377), with fifteen other eligible published reports. Bone phenotypes included BMD measurements of the hip (total hip and trochanteric and femoral neck sites) and lumbar spine (from the L2 to L4 vertebrae) and prevalence or incidence of vertebral, hip and other fractures.
In sex-pooled analyses, APOE4 carriers had a 0.018 g/cm2 lower weighted mean trochanteric BMD than non carriers (p=0.0002) with no evidence for between-study heterogeneity. A significant association was also detected with lumbar spine BMD (p=0.006); however, inter-study heterogeneity was observed. Associations with lumbar spine and trochanteric BMD were observed predominantly in women and became less significant in meta-regression (p=0.055 and 0.01, respectively). There were no consistent associations of APOE4 genotype with BMD at other skeletal sites or with fracture risk.
Based on these findings, there is insufficient evidence to support a strong and consistent association of the APOE genotype with BMD and fracture incidence.
Apolipoprotein E; BMD; Fracture; meta-analysis; polymorphism
genome-wide association study; genetic epidemiology; genetics; subclinical atherosclerosis; carotid intima media thickness; cardiovascular disease; cohort study; meta-analysis; risk
Genetic discoveries are validated through the meta-analysis of genome-wide association scans in large international consortia. Because environmental variables may interact with genetic factors, investigation of differing genetic effects for distinct levels of an environmental exposure in these large consortia may yield additional susceptibility loci undetected by main effects analysis. We describe a method of joint meta-analysis of SNP and SNP by Environment (SNP×E) regression coefficients for use in gene-environment interaction studies.
In testing SNP×E interactions, one approach uses a two degree of freedom test to identify genetic variants that influence the trait of interest. This approach detects both main and interaction effects between the trait and the SNP. We propose a method to jointly meta-analyze the SNP and SNP×E coefficients using multivariate generalized least squares. This approach provides confidence intervals of the two estimates, a joint significance test for SNP and SNP×E terms, and a test of homogeneity across samples.
We present a simulation study comparing this method to four other methods of meta-analysis and demonstrate that the joint meta-analysis performs better than the others when both main and interaction effects are present. Additionally, we implemented our methods in a meta-analysis of the association between SNPs from the type 2 diabetes-associated gene PPARG and log-transformed fasting insulin levels and interaction by body mass index in a combined sample of 19,466 individuals from 5 cohorts.
2 degree of freedom meta-analysis; joint meta-analysis; PPARG; Gene-environment interaction meta-analysis