Association of Incident Cardiovascular Disease With Time Course and Cumulative Exposure to Multiple Risk Factors.

BACKGROUND: The quantitative relationship of incident cardiovascular disease (CVD) to lifetime cumulative risk factor exposure is not well understood. OBJECTIVES: Using CARDIA (Coronary Artery Risk Development in Young Adults) study data, we examined the quantitative associations of cumulative exposure over time to multiple, simultaneously operating risk factors with CVD incidence and the incidence of its components. METHODS: Regression models were developed quantifying the influence of the time course and severity of multiple CVD risk factors, operating simultaneously, on risk of incident CVD. The outcomes were incident CVD and the incidence of its components: coronary heart disease, stroke, and congestive heart failure. RESULTS: Our study included 4,958 asymptomatic adults enrolled in CARDIA from 1985 to 1986 (ages 18 to 30 years) who were followed for 30 years. Risk of incident CVD depends on the time course and severity of a series of independent risk factors, the impact of which is mediated by their effects on individual CVD components after age 40 years. Cumulative exposure (AUC vs time) to low-density lipoprotein cholesterol and triglycerides was independently associated with risk of incident CVD. Of the blood pressure variables, areas under the mean arterial pressure vs time curve and the pulse pressure vs time curve were strongly and independently associated with incident CVD risk. CONCLUSIONS: The quantitative description of the link between risk factors and CVD informs the construction of individualized CVD mitigation strategies, design of primary prevention trials, and assessment of public health impact of risk factor-based interventions.

Reproductive and Hormonal Factors in Relation to Lung Cancer Among Nepali Women.

Background: Of the 1.8 million global incident lung cancer cases estimated in 2012, approximately 60% occurred in less developed regions. Prior studies suggest sex differences in lung cancer risk and a potential role for reproductive and hormonal factors in lung cancer among women. However, the majority of these studies were conducted in developed regions. No prior study has assessed these relationships among Nepali women. Methods: Using data from a hospital-based case-control study conducted in B. P. Koirala Memorial Cancer Hospital (Nepal, 2009-2012), relationships between reproductive and hormonal factors and lung cancer were examined among women aged 23-85 years. Lung cancer cases (n = 268) were frequency-matched to controls (n = 226) based on age (±5 years), ethnicity and residential area. The main exposures in this analysis included menopausal status, age at menarche, age at menopause, menstrual duration, gravidity, and age at first live-birth. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated using multivariable logistic regression. Results: Among postmenopausal women, those with a younger age at menopause (<45 years; 45-49 years) had an increased odds of lung cancer compared to those with an older (≥50 years) age at menopause [OR (95%CI): 2.14 (1.09, 4.17); OR (95% CI): 1.93 (1.07, 3.51)], after adjusting for age and cumulative active smoking years. No statistically significant associations were observed with the other reproductive and hormonal factors examined. Conclusion: These results suggest that Nepali women with prolonged exposure to endogenous ovarian hormones, via later age at menopause, may have a lower odds of lung cancer.

Isoflavone pharmacokinetics and metabolism after consumption of a standardized soy and soy-almond bread in men with asymptomatic prostate cancer.

Epidemiologic associations suggest that populations consuming substantial amounts of dietary soy exhibit a lower risk of prostate cancer. A 20-week randomized, phase II, crossover trial was conducted in 32 men with asymptomatic prostate cancer. The crossover involved 8 weeks each of soy bread (SB) and soy-almond bread (SAB). The primary objective was to investigate isoflavone bioavailability and metabolite profile. Secondary objectives include safety, compliance, and assessment of biomarkers linked to prostate carcinogenesis. Two distinct SBs were formulated to deliver approximately 60 mg aglycone equivalents of isoflavones per day. The isoflavones were present as aglycones (∼78% as aglycones) in the SAB whereas in the standard SB predominantly as glucosides (18% total isoflavones as aglycones). Compliance to SB (97% ± 4%) and SAB (92% ± 18%) was excellent; toxicity was rare and limited to grade 1 gastrointestinal complaints. Pharmacokinetic studies between SB and SAB showed modest differences. Peak serum concentration time (Tmax) was significantly faster with SAB meal compared with SB in some isoflavonoids, and AUC0 to 24 h of dihydrodaidzein and O-desmethylangolensin was significantly greater after an SB meal. An exploratory cluster analysis was used to identify four isoflavone-metabolizing phenotypes. Insulin-like growth factor-binding protein increased significantly by 41% (P = 0.024) with soy intervention. Findings from this study provide the necessary framework to study isoflavone-metabolizing phenotypes as a strategy for identification of individuals that might benefit or show resistance to cancer preventive strategies using dietary soy. A standardized SB used for future large-scale randomized clinical trials to affect human prostate carcinogenesis is feasible.

Assessing discrimination of risk prediction rules in a clustered data setting.

The AUC (area under ROC curve) is a commonly used metric to assess discrimination of risk prediction rules; however, standard errors of AUC are usually based on the Mann-Whitney U test that assumes independence of sampling units. For ophthalmologic applications, it is desirable to assess risk prediction rules based on eye-specific outcome variables which are generally highly, but not perfectly correlated in fellow eyes [e.g. progression of individual eyes to age-related macular degeneration (AMD)]. In this article, we use the extended Mann-Whitney U test (Rosner and Glynn, Biometrics 65:188-197, 2009) for the case where subunits within a cluster may have different progression status and assess discrimination of different prediction rules in this setting. Both data analyses based on progression of AMD and simulation studies show reasonable accuracy of this extended Mann-Whitney U test to assess discrimination of eye-specific risk prediction rules.

Microarray analysis of genes associated with cell surface NIS protein levels in breast cancer.

BACKGROUND: Na+/I- symporter (NIS)-mediated iodide uptake allows radioiodine therapy for thyroid cancer. NIS is also expressed in breast tumors, raising potential for radionuclide therapy of breast cancer. However, NIS expression in most breast cancers is low and may not be sufficient for radionuclide therapy. We aimed to identify biomarkers associated with NIS expression such that mechanisms underlying NIS modulation in human breast tumors may be elucidated. METHODS: Published oligonucleotide microarray data within the National Center for Biotechnology Information Gene Expression Omnibus database were analyzed to identify gene expression tightly correlated with NIS mRNA level among human breast tumors. NIS immunostaining was performed in a tissue microarray composed of 28 human breast tumors which had corresponding oligonucleotide microarray data available for each tumor such that gene expression associated with cell surface NIS protein level could be identified. RESULTS AND DISCUSSION: NIS mRNA levels do not vary among breast tumors or when compared to normal breast tissues when detected by Affymetrix oligonucleotide microarray platforms. Cell surface NIS protein levels are much more variable than their corresponding NIS mRNA levels. Despite a limited number of breast tumors examined, our analysis identified cysteinyl-tRNA synthetase as a biomarker that is highly associated with cell surface NIS protein levels in the ER-positive breast cancer subtype. CONCLUSIONS: Further investigation on genes associated with cell surface NIS protein levels within each breast cancer molecular subtype may lead to novel targets for selectively increasing NIS expression/function in a subset of breast cancers patients.

Joint analysis of current status and marker data: an extension of a bivariate threshold model.

This paper considers joint analysis of current status and marker data using a threshold model based on first hitting times. A failure time is defined as the time at which a subject's latent health status process first decreases to zero. We extend the bivariate Wiener process model in Whitmore et al. (1998) to the case when only current status data are available. We develop maximum likelihood estimation procedures and provide simulation studies. We apply our methods to a motivating example involving liver tumors in mice.

Polymorphisms in human dopamine D2 receptor gene affect gene expression, splicing, and neuronal activity during working memory.

Subcortical dopamine D2 receptor (DRD2) signaling is implicated in cognitive processes and brain disorders, but the effect of DRD2 variants remains ambiguous. We measured allelic mRNA expression in postmortem human striatum and prefrontal cortex and then performed single nucleotide polymorphism (SNP) scans of the DRD2 locus. A previously uncharacterized promoter SNP (rs12364283) located in a conserved suppressor region was associated with enhanced DRD2 expression, whereas previously studied DRD2 variants failed to affect expression. Moreover, two frequent intronic SNPs (rs2283265 and rs1076560) decreased expression of DRD2 short splice variant (expressed mainly presynaptically) relative to DRD2 long (postsynaptic), a finding reproduced in vitro by using minigene constructs. Being in strong linkage disequilibrium with each other, both intronic SNPs (but not rs12364283) were also associated with greater activity of striatum and prefrontal cortex measured with fMRI during working memory and with reduced performance in working memory and attentional control tasks in healthy humans. Our results identify regulatory DRD2 polymorphisms that modify mRNA expression and splicing and working memory pathways.

A nonparametric test for observational non-normally distributed ophthalmic data with eye-specific exposures and outcomes.

PURPOSE: To extend the Wilcoxon rank sum test to the analysis of clustered observational data with a binary exposure variable where not all cluster members (or subunits) have the same exposure status, as in ophthalmologic data where fellow eyes may differ in exposure status. METHODS: The Wilcoxon rank sum test statistic (Wc) is defined as the sum of ranks of all exposed subunits over all clusters. The large sample distribution of Wc is derived based on a two-stage permutation distribution approach which maintains the clustering structure of the exposure distribution in the original data. The procedure is applied to data from the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR) for assessing differences in retinopathy grade between eyes with high vs. low intraocular pressure (IOP). RESULTS: Data analyses based on the WESDR data indicate significant positive associations between IOP and retinopathy grade as assessed by the clustered Wilcoxon test (p = 0.019), but non-significant effects with mixed model procedures based on raw scores (p = 0.30). CONCLUSIONS: The clustered Wilcoxon procedure is an effective approach for analyzing clustered non-normal outcome data with a binary eye-specific exposure which may vary in 2 eyes of an individual.

Extension of the rank sum test for clustered data: two-group comparisons with group membership defined at the subunit level.

The Wilcoxon rank sum test is widely used for two-group comparisons for nonnormal data. An assumption of this test is independence of sampling units both between and within groups. In ophthalmology, data are often collected on two eyes of an individual, which are highly correlated. In ophthalmological clinical trials, randomization is usually performed at the subject level, but the unit of analysis is the eye. If the eye is used as the unit of analysis, then a modification to the usual Wilcoxon rank sum variance formula must be made to account for the within-cluster dependence. For some clustered data designs, where the unit of analysis is the subunit, group membership may be defined at the subunit level. For example, in some randomized ophthalmologic clinical trials, different treatments may be applied to fellow eyes of some patients, while the same treatment may be applied to fellow eyes of other patients. In general, binary eye-specific covariates may be present (scored as exposed or unexposed) and one wishes to compare nonnormally distributed outcomes between exposed and unexposed eyes using the Wilcoxon rank sum test while accounting for the clustering. In this article, we present a corrected variance formula for the Wilcoxon rank sum statistic in the setting of eye (subunit)-specific covariates. We apply it to compare ocular itching scores in ocular allergy patients between eyes treated with active versus placebo eye drops, where some patients receive the same eye drop in both eyes, while other patients receive different eye drops in fellow eyes. We also present comparisons between the clustered Wilcoxon test and each of the signed rank tests and mixed model approaches and show dramatic differences in power in favor of the clustered Wilcoxon test for some designs.

The Wilcoxon signed rank test for paired comparisons of clustered data.

The Wilcoxon signed rank test is a frequently used nonparametric test for paired data (e.g., consisting of pre- and posttreatment measurements) based on independent units of analysis. This test cannot be used for paired comparisons arising from clustered data (e.g., if paired comparisons are available for each of two eyes of an individual). To incorporate clustering, a generalization of the randomization test formulation for the signed rank test is proposed, where the unit of randomization is at the cluster level (e.g., person), while the individual paired units of analysis are at the subunit within cluster level (e.g., eye within person). An adjusted variance estimate of the signed rank test statistic is then derived, which can be used for either balanced (same number of subunits per cluster) or unbalanced (different number of subunits per cluster) data, with an exchangeable correlation structure, with or without tied values. The resulting test statistic is shown to be asymptotically normal as the number of clusters becomes large, if the cluster size is bounded. Simulation studies are performed based on simulating correlated ranked data from a signed log-normal distribution. These studies indicate appropriate type I error for data sets with > or =20 clusters and a superior power profile compared with either the ordinary signed rank test based on the average cluster difference score or the multivariate signed rank test of Puri and Sen. Finally, the methods are illustrated with two data sets, (i) an ophthalmologic data set involving a comparison of electroretinogram (ERG) data in retinitis pigmentosa (RP) patients before and after undergoing an experimental surgical procedure, and (ii) a nutritional data set based on a randomized prospective study of nutritional supplements in RP patients where vitamin E intake outside of study capsules is compared before and after randomization to monitor compliance with nutritional protocols.

Ethnic variation in bone turnover in pre- and early perimenopausal women: effects of anthropometric and lifestyle factors.

Bone mineral density (BMD) and fracture rates vary among women of differing ethnicities. Little is known, however, about ethnic variation in bone turnover. We measured serum osteocalcin (OC) and urinary N-telopeptide of type I collagen (NTX) levels in 2313 pre- or early perimenopausal women who were Caucasian (n = 1140), African-American (n = 651), Chinese (n = 247), or Japanese (n = 275) and were participating in the Study of Women's Health Across the Nation. Serum OC and urinary NTX levels were compared before and after adjustment for a series of lifestyle and anthropometric variables that can affect bone turnover. Unadjusted serum OC levels were highest in Caucasian women (P < 0.001 vs. all other groups), higher in African-American than Chinese women (P = 0.006), and similar in Chinese and Japanese women (P = 0.203) and African-American and Japanese women (P = 0.187). Unadjusted serum OC levels were 11-24% higher in Caucasians than in the other groups. Adjustment for covariates did not alter the ethnic pattern of serum OC levels. Unadjusted urinary NTX levels were statistically significantly higher in Caucasian and African-American women than in Chinese women (P < 0.001) for both comparisons). Unadjusted urinary NTX levels were higher in Caucasian than in Japanese women (P = 0.071) and higher in Japanese than in Chinese women (P = 0.055), but these differences were of borderline statistical significance. Unadjusted urinary NTX levels were 9-18% higher in African-Americans and Caucasians than in the other groups. Among Caucasians, there were significant geographic regional variations in both serum OC and urinary NTX levels, with higher levels in women from the Northeast and the Midwest than in women from California. These data demonstrate significant ethnic differences in bone turnover in pre- and early perimenopausal women. Although these differences in adult bone turnover may explain some of the known ethnic variation in BMD, ethnic patterns of adult bone turnover do not parallel patterns of BMD. Other factors, such as differences in bone accretion, are likely responsible for much of the ethnic variation in adult BMD.

Ethnic variation in bone density in premenopausal and early perimenopausal women: effects of anthropometric and lifestyle factors.

Bone mineral density (BMD) and fracture rates vary among women of differing ethnicities. Most reports suggest that BMD is highest in African-Americans, lowest in Asians, and intermediate in Caucasians, yet Asians have lower fracture rates than Caucasians. To assess the contributions of anthropometric and lifestyle characteristics to ethnic differences in BMD, we assessed lumbar spine and femoral neck BMD by dual-energy x-ray absorptiometry in 2277 (for the lumbar spine) and 2330 (for the femoral neck) premenopausal or early perimenopausal women (mean age, 46.2 yr) participating in the Study of Women's Health Across the Nation. Forty-nine percent of the women were Caucasian, 28% were African-American, 12% were Japanese, and 11% were Chinese. BMDs were compared among ethnic groups before and after adjustment for covariates. Before adjustment, lumbar spine and femoral neck BMDs were highest in African-American women, next highest in Caucasian women, and lowest in Chinese and Japanese women. Unadjusted lumbar spine and femoral neck BMDs were 7-12% and 14-24% higher, respectively, in African-American women than in Caucasians, Japanese, or Chinese women. After adjustment, lumbar spine and femoral neck BMD remained highest in African-American women, and there were no significant differences between the remaining groups. When BMD was assessed in a subset of women weighing less than 70 kg and then adjusted for covariates, lumbar spine BMD became similar in African-American, Chinese, and Japanese women and was lowest in Caucasian women. Adjustment for bone size increased values for Chinese women to levels equal to or above those of Caucasian and Japanese women. Among women of comparable weights, there are no differences in lumbar spine BMD among African-American, Chinese, and Japanese women, all of whom have higher BMDs than Caucasians. Femoral neck BMD is highest in African-Americans and similar in Chinese, Japanese, and Caucasians. These findings may explain why Caucasian women have higher fracture rates than African-Americans and Asians.