Candace M. Kammerer

Genetic and environmental contributions to cardiovascular risk factors in Mexican Americans: The San Antonio Family Heart Study

BACKGROUND The familial aggregation of coronary heart disease can be in large part accounted for by a clustering of cardiovascular disease risk factors. To elucidate the determinants of cardiovascular disease, many epidemiological studies have focused on the behavioral and lifestyle determinants of these risk factors, whereas others have examined whether specific candidate genes influence quantitative variation in these phenotypes. METHODS AND RESULTS Among Mexican Americans from San Antonio (Tex), we quantified the relative contributions of both genetic and environmental influences to a large panel of cardiovascular risk factors, including serum levels of lipids, lipoproteins, glucose, hormones, adiposity, and blood pressure. Members of 42 extended families were studied, including 1236 first-, second-, and third-degree relatives of randomly ascertained probands and their spouses. In addition to the phenotypic assessments, information was obtained regarding usual dietary and physical activity patterns, medication use, smoking habits, alcohol consumption, and other lifestyle behaviors and medical factors. Maximum likelihood methods were used to partition the variance of each phenotype into components attributable to the measured covariates, additive genetic effects (heritability), household effects, and an unmeasured environmental residual. For the lipid and lipoprotein phenotypes, age, gender, and other environmental covariates accounted in general for < 15% of the total phenotypic variance, whereas genes accounted for 30% to 45% of the phenotypic variation. Similarly, genes accounted for 15% to 30% of the phenotypic variation in measures of glucose, hormones, adiposity, and blood pressure. CONCLUSIONS These results highlight the importance of considering genetic factors in studies of risk factors for cardiovascular disease.

Accelerated Loss of Skeletal Muscle Strength in Older Adults With Type 2 Diabetes The Health, Aging, and Body Composition Study

OBJECTIVE—It has been shown that adults with either long-standing type 1 or type 2 diabetes had lower skeletal muscle strength than nondiabetic adults in cross-sectional studies. The aim of the study was to investigate longitudinal changes of muscle mass and strength in community-dwelling older adults with and without type 2 diabetes. RESEARCH DESIGN AND METHODS—We examined leg and arm muscle mass and strength at baseline and 3 years later in 1,840 older adults aged 70–79 years in the Health, Aging, and Body Composition Study. Regional muscle mass was measured by dual energy X-ray absorptiometry, and muscle strength was measured using isokinetic and isometric dynamometers. RESULTS—Older adults with type 2 diabetes (n = 305) showed greater declines in the leg muscle mass (−0.29 ± 0.03 vs. −0.23 ± 0.01 kg, P < 0.05) and strength (−16.5 ± 1.2 vs. −12.4 ± 0.5 Nm, P = 0.001) compared with older adults without diabetes. Leg muscle quality, expressed as maximal strength per unit of muscle mass (Newton meters per kilogram), also declined more rapidly in older adults with diabetes (−1.6 ± 0.2 vs. −1.2 ± 0.1 Nm/kg, P < 0.05). Changes in arm muscle strength and quality were not different between those with and without diabetes. Rapid declines in leg muscle strength and quality were attenuated but remained significant after controlling for demographics, body composition, physical activity, combined chronic diseases, interleukin-6, and tumor necrosis factor-α. CONCLUSIONS—In older adults, type 2 diabetes is associated with accelerated loss of leg muscle strength and quality.

Meta‐Analysis of Genome‐Wide Scans Provides Evidence for Sex‐ and Site‐Specific Regulation of Bone Mass

Several genome‐wide scans have been performed to detect loci that regulate BMD, but these have yielded inconsistent results, with limited replication of linkage peaks in different studies. In an effort to improve statistical power for detection of these loci, we performed a meta‐analysis of genome‐wide scans in which spine or hip BMD were studied. Evidence was gained to suggest that several chromosomal loci regulate BMD in a site‐specific and sex‐specific manner.

Association between the Severity of Angiographic Coronary Artery Disease and Paraoxonase Gene Polymorphisms in the National Heart, Lung, and Blood Institute–Sponsored Women’s Ischemia Syndrome Evaluation (WISE) Study

Paraoxonase (PON), a high-density lipoprotein-associated enzyme, is believed to protect against low-density lipoprotein oxidation and thus affects the risk of coronary artery disease (CAD). Three polymorphisms in the PON1 (Leu55Met and Gln192Arg) and PON2 (Ser311Cys) genes have been shown to be associated with the risk of CAD in several European or European-derived populations. In the present study, we examined the associations between these three markers and the severity of CAD as determined by the number of diseased coronary artery vessels in 711 subjects (589 whites and 122 blacks) from the Womens Ischemia Syndrome Evaluation (WISE) study. WISE is a National Heart, Lung, and Blood Institute-sponsored multicenter study designed to address issues related to ischemic-heart-disease recognition and diagnosis in women. Subjects were classified as having normal/minimal CAD (<20% stenosis), mild CAD (20%-49% stenosis), and significant CAD (>/=50% stenosis). The women who had >/=50% stenosis were further classified into groups with one-, two-, or three-vessel disease if any of the three coronary arteries had diameter stenosis >/=50%. No significant association was found between the PON polymorphisms and stenosis severity in either white or black women. However, among white women, when data were stratified by the number of diseased vessels, the frequency of the PON1 codon 192 Arg/Arg genotype was significantly higher in the group with three-vessel disease than in the other groups (those with one-vessel and two-vessel disease) combined (17.02% vs. 4.58%; P=.0066). Similarly, the frequency of the PON2 codon 311 Cys/Cys genotype was significantly higher in the group with three-vessel disease than in the other groups combined (15.22% vs. 4.61%; P=.018). The adjusted odds ratios for the development of three-vessel disease were 2.80 (95% confidence interval 1.06-7.37; P=.038) for PON1 codon 192 Arg/Arg and 3.68 (95% confidence interval 1.26-10.68; P=.017) for PON2 codon 311 Cys/Cys. Our data indicate that the severity of CAD, in terms of the number of diseased vessels, may be affected by common genetic variation in the PON gene cluster, on chromosome 7.

Genome-wide meta-analysis points to CTC1 and ZNF676 as genes regulating telomere homeostasis in humans

Leukocyte telomere length (LTL) is associated with a number of common age-related diseases and is a heritable trait. Previous genome-wide association studies (GWASs) identified two loci on chromosomes 3q26.2 (TERC) and 10q24.33 (OBFC1) that are associated with the inter-individual LTL variation. We performed a meta-analysis of 9190 individuals from six independent GWAS and validated our findings in 2226 individuals from four additional studies. We confirmed previously reported associations with OBFC1 (rs9419958 P = 9.1 × 10−11) and with the telomerase RNA component TERC (rs1317082, P = 1.1 × 10−8). We also identified two novel genomic regions associated with LTL variation that map near a conserved telomere maintenance complex component 1 (CTC1; rs3027234, P = 3.6 × 10−8) on chromosome17p13.1 and zinc finger protein 676 (ZNF676; rs412658, P = 3.3 × 10−8) on 19p12. The minor allele of rs3027234 was associated with both shorter LTL and lower expression of CTC1. Our findings are consistent with the recent observations that point mutations in CTC1 cause short telomeres in both Arabidopsis and humans affected by a rare Mendelian syndrome. Overall, our results provide novel insights into the genetic architecture of inter-individual LTL variation in the general population.

Quantitative Trait Loci on Chromosomes 2p, 4p, and 13q Influence Bone Mineral Density of the Forearm and Hip in Mexican Americans

We performed a genome scan using BMD data of the forearm and hip on 664 individuals in 29 Mexican‐American families. We obtained evidence for QTL on chromosome 4p, affecting forearm BMD overall, and on chromosomes 2p and 13q, affecting hip BMD in men.

Association of a Common Interferon Regulatory Factor 5 (IRF5) Variant with Increased Risk of Systemic Lupus Erythematosus (SLE)

Interferon regulatory factor 5 (IRF5) belongs to a family of transcription factors that control the transactivation of type I interferon system‐related genes, as well as the expression of several other genes involved in immune response, cell signalling, cell cycle control and apoptosis. Two recent studies reported a significant association between the IRF5/rs2004640 T allele and systemic lupus erythematosus (SLE). The purpose of this study was to determine whether the reported rs2004640 T allele association could be replicated in our independent SLE case‐control sample. We genotyped DNA samples from 370 white SLE‐affected female subjects and 462 white healthy female controls using the TaqMan Assay‐on‐Demand for rs2004640, and performed a case‐control genetic association analysis. Frequency of the rs2004640 T allele was significantly higher in cases than in controls (56.5% vs. 50%; P= 0.008). The odds ratio for T allele carriers was 1.68 (95% CI: 1.20 – 2.34; P= 0.003). Our results in an independent case‐control sample confirm the robust association of the IRF5/rs2004640 T allele with SLE risk, and further support the relevance of the type I interferon system in the pathogenesis of SLE and autoimmunity.

Genetic Variation in Lectin-Like Oxidized Low-Density Lipoprotein Receptor 1 (LOX1) Gene and the Risk of Coronary Artery Disease

Background—We examined the association of 3 polymorphisms in the lectin-like oxidized LDL receptor-1 (LOX1 or OLR1) gene with coronary artery disease in the Women’s Ischemia Syndrome Evaluation (WISE) study population. Methods and Results—The WISE sample comprised 589 white and 122 black women who underwent angiography for suspected ischemia. The sample was divided into 3 groups: <20% stenosis (38.7%), 20% to 49% stenosis (24.9%), and ≥50% stenosis (35.3%). The three LOX1 polymorphisms (intron 4/G→A, intron 5/T→G, and 3′ UTR/T→C) were in linkage disequilibrium and thus behaved as a single polymorphism. The frequency of the 3′UTR/T allele was significantly higher in whites than blacks (49% versus 19%; P <0.0001). Among white women, the frequency of the 3′UTR/T allele carriers (TC+TT genotypes) increased gradually from 67.9% to 75.0% and 79.2% in the <20%, 20% to 49%, and ≥50% stenosis groups, respectively (&khgr;2 trend=6.23; P =0.013). Logistic regression analyses indicated that APOE (odds ratio, 1.90; P =0.007) and LOX1 (odds ratio, 1.67; P =0.025) genotypes were independently associated with the risk of disease and that there was no interaction between the two genes. The 3′UTR/T allele carriers also had significantly higher IgG anti-oxLDL levels than individuals carrying the CC genotype (0.94±0.20 versus 0.86±0.16; P =0.032). Furthermore, our electrophoretic mobility shift assay data show that the 3′UTR polymorphic sequence affects the binding of a putative transcription factor in an allele-specific manner. Conclusions—Our data suggest that common genetic variation in the LOX1 gene may be associated with the risk of coronary artery disease in white women.

Evidence for Linkage of Postchallenge Insulin Levels With Intestinal Fatty Acid-Binding Protein (FABP2) in Mexican-Americans

Single genes with large effects may contribute to insulin resistance or influence susceptibility to non-insulin-dependent diabetes mellitus (NIDDM). In the Pima Indians, results from sib-pair analysis have suggested that a gene on chromosome 4q influences both fasting insulin levels and maximal insulin action. We conducted sib-pair and logarithm of odds (LOD)-score linkage analysis to seek evidence for linkage between genes influencing insulin levels and chromosome 4q loci. Analyses were conducted on nondiabetic individuals from 28 different families participating in the San Antonio Family Diabetes Study. All subjects received a 2-h oral glucose tolerance test. Fasting insulin levels were measured in 382 nondiabetic individuals, and 2-h insulin levels were measured in 366 individuals. Initial sib-pair linkage analysis revealed a possible association between 2-h post–glucose challenge insulin levels and the intestinal fatty acid–binding protein (FABP2) locus located in the region of chromosome 4q28–31 (P = 0.006). Subsequent sib-pair linkage analysis of 11 additional chromosome 4q markers supported this hypothesis. We next conducted segregation analyses to estimate allele frequencies and other model parameters for the putative locus influencing 2-h insulin levels. Results of LOD-score linkage analysis indicated possible linkage between the major gene described by the segregation model and FABP2. Using combined segregation and linkage analysis, we obtained a LOD-score of 2.80 at recombination frequency of 0.0 between FABP2 and the putative locus influencing 2-h insulin levels. The maximum likelihood estimate of the allele associated with low insulin levels was 0.21. Individuals having one or two copies of this allele had a mean ln(2-h insulin level) equal to 3.484 (back-transformed mean = 298.4 pmol/1), compared with 4.480 (back-transformed mean = 807.8 pmol/1) for individuals in whom this allele was absent. Approximately 32% of the total phenotypic variance in ln(2-h insulin levels) could be attributed to this locus. These results are consistent with the hypothesis that FABP2, or a tightly linked gene, influences 2-h insulin levels. This gene may be associated with insulin resistance.

META-ANALYSIS OF GENOME-WIDE STUDIES IDENTIFIES WNT16 AND ESR1 SNPS ASSOCIATED WITH BONE MINERAL DENSITY IN PREMENOPAUSAL WOMEN **

Previous genome‐wide association studies (GWAS) have identified common variants in genes associated with variation in bone mineral density (BMD), although most have been carried out in combined samples of older women and men. Meta‐analyses of these results have identified numerous single‐nucleotide polymorphisms (SNPs) of modest effect at genome‐wide significance levels in genes involved in both bone formation and resorption, as well as other pathways. We performed a meta‐analysis restricted to premenopausal white women from four cohorts (n = 4061 women, aged 20 to 45 years) to identify genes influencing peak bone mass at the lumbar spine and femoral neck. After imputation, age‐ and weight‐adjusted bone‐mineral density (BMD) values were tested for association with each SNP. Association of an SNP in the WNT16 gene (rs3801387; p = 1.7 × 10−9) and multiple SNPs in the ESR1/C6orf97 region (rs4870044; p = 1.3 × 10−8) achieved genome‐wide significance levels for lumbar spine BMD. These SNPs, along with others demonstrating suggestive evidence of association, were then tested for association in seven replication cohorts that included premenopausal women of European, Hispanic‐American, and African‐American descent (combined n = 5597 for femoral neck; n = 4744 for lumbar spine). When the data from the discovery and replication cohorts were analyzed jointly, the evidence was more significant (WNT16 joint p = 1.3 × 10−11; ESR1/C6orf97 joint p = 1.4 × 10−10). Multiple independent association signals were observed with spine BMD at the ESR1 region after conditioning on the primary signal. Analyses of femoral neck BMD also supported association with SNPs in WNT16 and ESR1/C6orf97 (p < 1 × 10−5). Our results confirm that several of the genes contributing to BMD variation across a broad age range in both sexes have effects of similar magnitude on BMD of the spine in premenopausal women. These data support the hypothesis that variants in these genes of known skeletal function also affect BMD during the premenopausal period.