The effect of survival bias on case-control genetic association studies of highly lethal diseases

Screening embryos for polygenic disease risk: a review of epidemiological, clinical, and ethical considerations

BACKGROUND

The genetic composition of embryos generated by in vitro fertilization (IVF) can be examined with preimplantation genetic testing (PGT). Until recently, PGT was limited to detecting single-gene, high-risk pathogenic variants, large structural variants, and aneuploidy. Recent advances have made genome-wide genotyping of IVF embryos feasible and affordable, raising the possibility of screening embryos for their risk of polygenic diseases such as breast cancer, hypertension, diabetes, or schizophrenia. Despite a heated debate around this new technology, called polygenic embryo screening (PES; also PGT-P), it is already available to IVF patients in some countries. Several articles have studied epidemiological, clinical, and ethical perspectives on PES; however, a comprehensive, principled review of this emerging field is missing.

OBJECTIVE AND RATIONALE

This review has four main goals. First, given the interdisciplinary nature of PES studies, we aim to provide a self-contained educational background about PES to reproductive specialists interested in the subject. Second, we provide a comprehensive and critical review of arguments for and against the introduction of PES, crystallizing and prioritizing the key issues. We also cover the attitudes of IVF patients, clinicians, and the public towards PES. Third, we distinguish between possible future groups of PES patients, highlighting the benefits and harms pertaining to each group. Finally, our review, which is supported by ESHRE, is intended to aid healthcare professionals and policymakers in decision-making regarding whether to introduce PES in the clinic, and if so, how, and to whom.

SEARCH METHODS

We searched for PubMed-indexed articles published between 1/1/2003 and 1/3/2024 using the terms 'polygenic embryo screening', 'polygenic preimplantation', and 'PGT-P'. We limited the review to primary research papers in English whose main focus was PES for medical conditions. We also included papers that did not appear in the search but were deemed relevant.

OUTCOMES

The main theoretical benefit of PES is a reduction in lifetime polygenic disease risk for children born after screening. The magnitude of the risk reduction has been predicted based on statistical modelling, simulations, and sibling pair analyses. Results based on all methods suggest that under the best-case scenario, large relative risk reductions are possible for one or more diseases. However, as these models abstract several practical limitations, the realized benefits may be smaller, particularly due to a limited number of embryos and unclear future accuracy of the risk estimates. PES may negatively impact patients and their future children, as well as society. The main personal harms are an unindicated IVF treatment, a possible reduction in IVF success rates, and patient confusion, incomplete counselling, and choice overload. The main possible societal harms include discarded embryos, an increasing demand for 'designer babies', overemphasis of the genetic determinants of disease, unequal access, and lower utility in people of non-European ancestries. Benefits and harms will vary across the main potential patient groups, comprising patients already requiring IVF, fertile people with a history of a severe polygenic disease, and fertile healthy people. In the United States, the attitudes of IVF patients and the public towards PES seem positive, while healthcare professionals are cautious, sceptical about clinical utility, and concerned about patient counselling.

WIDER IMPLICATIONS

The theoretical potential of PES to reduce risk across multiple polygenic diseases requires further research into its benefits and harms. Given the large number of practical limitations and possible harms, particularly unnecessary IVF treatments and discarded viable embryos, PES should be offered only within a research context before further clarity is achieved regarding its balance of benefits and harms. The gap in attitudes between healthcare professionals and the public needs to be narrowed by expanding public and patient education and providing resources for informative and unbiased genetic counselling.

Polygenic scores for estimated glomerular filtration rate in a population of general adults and elderly - comparative results from the KORA and AugUR study

BACKGROUND

Polygenic scores (PGSs) combining genetic variants found to be associated with creatinine-based estimated glomerular filtration rate (eGFR_crea) have been applied in various study populations with different age ranges. This has shown that PGS explain less eGFR_crea variance in the elderly. Our aim was to understand how differences in eGFR variance and the percentage explained by PGS varies between population of general adults and elderly.

RESULTS

We derived a PGS for cystatin-based eGFR (eGFR_cys) from published genome-wide association studies. We used the 634 variants known for eGFR_crea and the 204 variants identified for eGFR_cys to calculate the PGS in two comparable studies capturing a general adult and an elderly population, KORA S4 (n = 2,900; age 24-69 years) and AugUR (n = 2,272, age ≥ 70 years). To identify potential factors determining age-dependent differences on the PGS-explained variance, we evaluated the PGS variance, the eGFR variance, and the beta estimates of PGS association on eGFR. Specifically, we compared frequencies of eGFR-lowering alleles between general adult and elderly individuals and analyzed the influence of comorbidities and medication intake. The PGS for eGFR_crea explained almost twice as much (R² = 9.6%) of age-/sex adjusted eGFR variance in the general adults compared to the elderly (4.6%). This difference was less pronounced for the PGS for eGFR_cys (4.7% or 3.6%, respectively). The beta-estimate of the PGS on eGFR_crea was higher in the general adults compared to the elderly, but similar for the PGS on eGFR_cys. The eGFR variance in the elderly was reduced by accounting for comorbidities and medication intake, but this did not explain the difference in R²-values. Allele frequencies between general adult and elderly individuals showed no significant differences except for one variant near APOE (rs429358). We found no enrichment of eGFR-protective alleles in the elderly compared to general adults.

CONCLUSIONS

We concluded that the difference in explained variance by PGS was due to the higher age- and sex-adjusted eGFR variance in the elderly and, for eGFR_crea, also by a lower PGS association beta-estimate. Our results provide little evidence for survival or selection bias.

Analysis of CF patient survival confirms STAT3 as a CF-modifying gene with changing impact over time

INTRODUCTION AND AIM

The signal transducer and activator of transcription 3 (STAT3) has been identified as one of the cystic fibrosis (CF) modifying genes. In this study, we aimed to assess the association between STAT3 genotype and CF patient survival over several decades and to investigate the effect of STAT3 inhibition on epithelial CFTR expression.

METHODS

We analyzed the informative genetic marker STAT3Sat for its association with survival in 174 p.Phe508del-CFTR homozygous CF patients treated at the CF center in Hannover spanning birth cohorts from >3 decades (1959-1994). Furthermore, we treated two epithelial cell lines with STAT3 inhibitors and monitored changes of CFTR protein expression by western blot.

RESULTS

Only for p.Phe508del-CFTR homozygous patients born prior to 1975, survival was significantly influenced by STAT3sat genotype (P = 0.023). The expression levels of STAT3 and CFTR positively correlated in epithelial cell lines (P = 0.01).

CONCLUSIONS

Our results in different birth cohorts identified a time-dependent impact of STAT3 genotype on CF patients' survival and found that improved symptomatic treatment of later-born CF patients obviates STAT3's modifying influence. Consistent with our previous results, STAT3-specific inhibition resulted in increased CFTR expression in the epithelial cell line 16HBE14o-. Thus, care should be taken when CF-modifying genes are studied in cross-sectional cohorts as the impact of modifying genes might not be invariant in the light of changing therapeutic regimens.

Adjusting for collider bias in genetic association studies using instrumental variable methods

Genome‐wide association studies have provided many genetic markers that can be used as instrumental variables to adjust for confounding in epidemiological studies. Recently, the principle has been applied to other forms of bias in observational studies, especially collider bias that arises when conditioning or stratifying on a variable that is associated with the outcome of interest. An important case is in studies of disease progression and survival. Here, we clarify the links between the genetic instrumental variable methods proposed for this problem and the established methods of Mendelian randomisation developed to account for confounding. We highlight the critical importance of weak instrument bias in this context and describe a corrected weighted least‐squares procedure as a simple approach to reduce this bias. We illustrate the range of available methods on two data examples. The first, waist–hip ratio adjusted for body‐mass index, entails statistical adjustment for a quantitative trait. The second, smoking cessation, is a stratified analysis conditional on having initiated smoking. In both cases, we find little effect of collider bias on the primary association results, but this may propagate into more substantial effects on further analyses such as polygenic risk scoring and Mendelian randomisation.

Evaluation of antigen-detecting and antibody-detecting diagnostic test combinations for diagnosing melioidosis

Background

Melioidosis, an infectious disease caused by Burkholderia pseudomallei, is endemic in many tropical developing countries and has a high mortality. Here we evaluated combinations of a lateral flow immunoassay (LFI) detecting B. pseudomallei capsular polysaccharide (CPS) and enzyme-linked immunosorbent assays (ELISA) detecting antibodies against hemolysin co-regulated protein (Hcp1) or O-polysaccharide (OPS) for diagnosing melioidosis.

Methodology/Principal findings

We conducted a cohort-based case-control study. Both cases and controls were derived from a prospective observational study of patients presenting with community-acquired infections and sepsis in northeast Thailand (Ubon-sepsis). Cases included 192 patients with a clinical specimen culture positive for B. pseudomallei. Controls included 502 patients who were blood culture positive for Staphylococcus aureus, Escherichia coli or Klebsiella pneumoniae or were polymerase chain reaction assay positive for malaria or dengue. Serum samples collected within 24 hours of admission were stored and tested using a CPS-LFI, Hcp1-ELISA and OPS-ELISA. When assessing diagnostic tests in combination, results were considered positive if either test was positive. We selected ELISA cut-offs corresponding to a specificity of 95%. Using a positive cut-off OD of 2.912 for Hcp1-ELISA, the combination of the CPS-LFI and Hcp1-ELISA had a sensitivity of 67.7% (130/192 case patients) and a specificity of 95.0% (477/502 control patients). The sensitivity of the combination (67.7%) was higher than that of the CPS-LFI alone (31.3%, p<0.001) and that of Hcp1-ELISA alone (53.6%, p<0.001). A similar phenomenon was also observed for the combination of CPS-LFI and OPS-ELISA. In case patients, positivity of the CPS-LFI was associated with a short duration of symptoms, high modified Sequential (sepsis-related) Organ Failure Assessment (SOFA) score, bacteraemia and mortality outcome, while positivity of Hcp1-ELISA was associated with a longer duration of symptoms, low modified SOFA score, non-bacteraemia and survival outcome.

Conclusions/Significance

A combination of antigen-antibody diagnostic tests increased the sensitivity of melioidosis diagnosis over individual tests while preserving high specificity. Point-of-care tests for melioidosis based on the use of combination assays should be further developed and evaluated.

Melioidosis is an infection caused by the Gram-negative bacterium Burkholderia pseudomallei. There are currently no commercially available and reliable point-of-care diagnostic tests for melioidosis. We previously demonstrated that a prototype lateral flow immunoassay (LFI) developed to detect B. pseudomallei capsular polysaccharide (CPS) had limited sensitivity (31.3%) but high specificity (98.8%) for diagnosing melioidosis among patients presenting with community-acquired infection or sepsis in northeast Thailand. Here, we evaluated combinations of the CPS-LFI and enzyme-linked immunosorbent assays (ELISA) that detect antibodies against hemolysin co-regulated protein (Hcp1) or O-polysaccharide (OPS). When used in combination, results were considered positive if either test was positive. We selected ELISA cut-offs corresponding to a specificity of 95%. Our results demonstrated that a combination of antigen-detection (CPS-LFI) and antibody-detection (Hcp1-ELISA or OPS-ELISA) tests increased the sensitivity for diagnosis of melioidosis (68% or 63%, respectively) over any single test, while maintaining high specificity (95%). In case patients, positivity of the CPS-LFI was associated with a short duration of symptoms, severe infections (as measured by an organ failure assessment score), bacteraemia and mortality outcome, while positivity of Hcp1-ELISA was associated with a long duration of symptoms, non-bacteraemia and survival outcome. Based on our findings, we propose that point-of-care melioidosis diagnostic tests using combinations of antigen- and antibody-detection should be further developed and evaluated.

Clinical Conditions and Their Impact on Utility of Genetic Scores for Prediction of Acute Coronary Syndrome

BACKGROUND

Acute coronary syndrome (ACS) is a clinically significant presentation of coronary heart disease. Genetic information has been proposed to improve prediction beyond well-established clinical risk factors. While polygenic scores (PS) can capture an individual's genetic risk for ACS, its prediction performance may vary in the context of diverse correlated clinical conditions. Here, we aimed to test whether clinical conditions impact the association between PS and ACS.

METHODS

We explored the association between 405 clinical conditions diagnosed before baseline and 9080 incident cases of ACS in 387 832 individuals from the UK Biobank. Results were replicated in 6430 incident cases of ACS in 177 876 individuals from FinnGen.

RESULTS

We identified 80 conventional (eg, stable angina pectoris and type 2 diabetes) and unconventional (eg, diaphragmatic hernia and inguinal hernia) associations with ACS. The association between PS and ACS was consistent in individuals with and without most clinical conditions. However, a diagnosis of stable angina pectoris yielded a differential association between PS and ACS. PS was associated with a significantly reduced (interaction P=2.87×10^-8) risk for ACS in individuals with stable angina pectoris (hazard ratio, 1.163 [95% CI, 1.082-1.251]) compared with individuals without stable angina pectoris (hazard ratio, 1.531 [95% CI, 1.497-1.565]). These findings were replicated in FinnGen (interaction P=1.38×10^-6).

CONCLUSIONS

In summary, while most clinical conditions did not impact utility of PS for prediction of ACS, we found that PS was substantially less predictive of ACS in individuals with prevalent stable coronary heart disease. PS may be more appropriate for prediction of ACS in asymptomatic individuals than symptomatic individuals with clinical suspicion for coronary heart disease.

Comparison of genetic risk prediction models to improve prediction of coronary heart disease in two large cohorts of the MONICA/KORA study

It is still unclear how genetic information, provided as single-nucleotide polymorphisms (SNPs), can be most effectively integrated into risk prediction models for coronary heart disease (CHD) to add significant predictive value beyond clinical risk models. For the present study, a population-based case-cohort was used as a trainingset (451 incident cases, 1488 noncases) and an independent cohort as testset (160 incident cases, 2749 noncases). The following strategies to quantify genetic information were compared: A weighted genetic risk score including Metabochip SNPs associated with CHD in the literature (GRS_Metabo ); selection of the most predictive SNPs among these literature-confirmed variants using priority-Lasso (PL_Metabo ); validation of two comprehensive polygenic risk scores: GRS_Gola based on Metabochip data, and GRS_Khera (available in the testset only) based on cross-validated genome-wide genotyping data. We used Cox regression to assess associations with incident CHD. C-index, category-free net reclassification index (cfNRI) and relative integrated discrimination improvement (IDI_rel ) were used to quantify the predictive performance of genetic information beyond Framingham risk score variables. In contrast to GRS_Metabo and PL_Metabo , GRS_Gola significantly improved the prediction (delta C-index [95% confidence interval]: 0.0087 [0.0044, 0.0130]; IDI_rel : 0.0509 [0.0131, 0.0894]; cfNRI improved only in cases: 0.1761 [0.0253, 0.3219]). GRS_Khera yielded slightly worse prediction results than GRS_Gola .

Genome-Wide Variants Associated With Longitudinal Survival Outcomes Among Individuals With Coronary Artery Disease

Objective

Coronary artery disease (CAD) is an age-associated condition that greatly increases the risk of mortality. The purpose of this study was to identify gene variants associated with all-cause mortality among individuals with clinically phenotyped CAD using a genome-wide screening approach.

Approach and Results

We performed discovery (n = 684), replication (n = 1,088), and meta-analyses (N = 1,503) for association of genomic variants with survival outcome using secondary data from White participants with CAD from two GWAS sub-studies of the Duke Catheterization Genetics Biorepository. We modeled time from catheterization to death or last follow-up (median 7.1 years, max 12 years) using Cox multivariable regression analysis. Target statistical screening thresholds were p × 10^–8 for the discovery phase and Bonferroni-calculated p-values for the replication (p < 5.3 × 10^–4) and meta-analysis (p < 1.6 × 10^–3) phases. Genome-wide analysis of 785,945 autosomal SNPs revealed two SNPs (rs13007553 and rs587936) that had the same direction of effect across all three phases of the analysis, with suggestive p-value association in discovery and replication and significant meta-analysis association in models adjusted for clinical covariates. The rs13007553 SNP variant, LINC01250, which resides between MYTIL and EIPR1, conferred increased risk for all-cause mortality even after controlling for clinical covariates [HR 1.47, 95% CI 1.17–1.86, p(adj) = 1.07 × 10^–3 (discovery), p(adj) = 0.03 (replication), p(adj) = 9.53 × 10^–5 (meta-analysis)]. MYT1L is involved in neuronal differentiation. TSSC1 is involved in endosomal recycling and is implicated in breast cancer. The rs587936 variant annotated to DAB2IP was associated with increased survival time [HR 0.65, 95% CI 0.51–0.83, p(adj) = 4.79 × 10^–4 (discovery), p(adj) = 0.02 (replication), p(adj) = 2.25 × 10^–5 (meta-analysis)]. DAB2IP is a ras/GAP tumor suppressor gene which is highly expressed in vascular tissue. DAB2IP has multiple lines of evidence for protection against atherosclerosis.

Conclusion

Replicated findings identified two candidate genes for further study regarding association with survival in high-risk CAD patients: novel loci LINC01250 (rs13007553) and biologically relevant candidate DAB2IP (rs587936). These candidates did not overlap with validated longevity candidate genes. Future research could further define the role of common variants in survival outcomes for people with CAD and, ultimately, improve longitudinal outcomes for these patients.

Genetic loci associated with prevalent and incident myocardial infarction and coronary heart disease in the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) Consortium

BACKGROUND

Genome-wide association studies have identified multiple genomic loci associated with coronary artery disease, but most are common variants in non-coding regions that provide limited information on causal genes and etiology of the disease. To overcome the limited scope that common variants provide, we focused our investigation on low-frequency and rare sequence variations primarily residing in coding regions of the genome.

METHODS AND RESULTS

Using samples of individuals of European ancestry from ten cohorts within the Cohorts for Heart and Aging Research in Genomic Epidemiology (CHARGE) consortium, both cross-sectional and prospective analyses were conducted to examine associations between genetic variants and myocardial infarction (MI), coronary heart disease (CHD), and all-cause mortality following these events. For prevalent events, a total of 27,349 participants of European ancestry, including 1831 prevalent MI cases and 2518 prevalent CHD cases were used. For incident cases, a total of 55,736 participants of European ancestry were included (3,031 incident MI cases and 5,425 incident CHD cases). There were 1,860 all-cause deaths among the 3,751 MI and CHD cases from six cohorts that contributed to the analysis of all-cause mortality. Single variant and gene-based analyses were performed separately in each cohort and then meta-analyzed for each outcome. A low-frequency intronic variant (rs988583) in PLCL1 was significantly associated with prevalent MI (OR = 1.80, 95% confidence interval: 1.43, 2.27; P = 7.12 × 10-7). We conducted gene-based burden tests for genes with a cumulative minor allele count (cMAC) ≥ 5 and variants with minor allele frequency (MAF) < 5%. TMPRSS5 and LDLRAD1 were significantly associated with prevalent MI and CHD, respectively, and RC3H2 and ANGPTL4 were significantly associated with incident MI and CHD, respectively. No loci were significantly associated with all-cause mortality following a MI or CHD event.

CONCLUSION

This study identified one known locus (ANGPTL4) and four new loci (PLCL1, RC3H2, TMPRSS5, and LDLRAD1) associated with cardiovascular disease risk that warrant further investigation.

Survival Bias in Mendelian Randomization Studies: A Threat to Causal Inference

It has been argued that survival bias may distort results in Mendelian randomization studies in older populations. Through simulations of a simple causal structure we investigate the degree to which instrumental variable (IV)-estimators may become biased in the context of exposures that affect survival. We observed that selecting on survival decreased instrument strength and, for exposures with directionally concordant effects on survival (and outcome), introduced downward bias of the IV-estimator when the exposures reduced the probability of survival till study inclusion. Higher ages at study inclusion generally increased this bias, particularly when the true causal effect was not equal to null. Moreover, the bias in the estimated exposure-outcome relation depended on whether the estimation was conducted in the one- or two-sample setting. Finally, we briefly discuss which statistical approaches might help to alleviate this and other types of selection bias. See video abstract at, http://links.lww.com/EDE/B589.

Cerebellar-cortical function and connectivity during sensorimotor behavior in aging FMR1 gene premutation carriers

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FMR1 premutation carriers show increased variability in motor control.

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Premutation carriers show reduced extrastriate activation during motor behavior.

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Premutation carriers show reduced extrastriate-cerebellar functional connectivity.

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Reduced extrastriate-cerebellar functional connectivity is related to motor issues.

Introduction

Premutation carriers of the FMR1 gene are at risk of developing fragile X-associated tremor/ataxia syndrome (FXTAS), a neurodegenerative disease characterized by motor, cognitive, and psychiatric decline as well as cerebellar and cerebral white matter pathology. Several studies have documented preclinical sensorimotor issues in aging premutation carriers, but the extent to which sensorimotor brain systems are affected and may represent early indicators of atypical neurodegeneration has not been determined.

Materials and methods

Eighteen healthy controls and 16 FMR1 premutation carriers (including five with possible, probable, or definite FXTAS) group-matched on age, sex, and handedness completed a visually guided precision gripping task with their right hand during fMRI. During the test, they used a modified pinch grip to press at 60% of their maximum force against a custom fiber-optic transducer. Participants viewed a horizontal white force bar that moved upward with increased force and downward with decreased force and a static target bar that was red during rest and turned green to cue the participant to begin pressing at the beginning of each trial. Participants were instructed to press so that the white force bar stayed as steady as possible at the level of the green target bar. Trials were 2-sec in duration and alternated with 2-sec rest periods. Five 24-sec blocks consisting of six trials were presented. Participants’ reaction time, the accuracy of their force relative to the target force, and the variability of their force accuracy across trials were examined. BOLD signal change and task-based functional connectivity (FC) were examined during force vs. rest.

Results

Relative to healthy controls, premutation carriers showed increased trial-to-trial variability of force output, though this was specific to younger premutation carriers in our sample. Relative to healthy controls, premutation carriers also showed reduced extrastriate activation during force relative to rest. FC between ipsilateral cerebellar Crus I and extrastriate cortex was reduced in premutation carriers compared to controls. Reduced Crus I-extrastriate FC was related to increased force accuracy variability in premutation carriers. Increased reaction time was associated with more severe clinically rated neurological abnormalities.

Conclusions

Findings of reduced activation in extrastriate cortex and reduced Crus I-extrastriate FC implicate deficient visual feedback processing and reduced cerebellar modulation of corrective motor commands. Our results are consistent with documented cerebellar pathology and visual-spatial processing in FXTAS and pre-symptomatic premutation carriers, and suggest FC alterations of cerebellar-cortical networks during sensorimotor behavior may represent a “prodromal” feature associated with FXTAS degeneration.

Effects of blood lead on coronary artery disease and its risk factors: a Mendelian Randomization study

Lead is pervasive, although lead exposure has fallen in response to public health efforts. Observationally, lead is positively associated with cardiovascular disease and hypertension. We used separate-sample instrumental variable analysis with genetic instruments (Mendelian randomization) based on 13 single nucleotide polymorphisms (SNP), from a genome wide association study, strongly (p-value < 5 × 10^-6) and independently associated with blood lead. These SNPs were applied to a large extensively genotyped coronary artery disease (CAD) study (cases = <76014, controls = <264785) largely based on CARDIoGRAPMplusC4D 1000 Genomes and the UK Biobank SOFT CAD, to the UK Biobank (n = 361,194) for blood pressure and to the DIAGRAM 1000 genomes diabetes case (n = 26,676)-control (n = 132,532) study. SNP-specific Wald estimates were combined using inverse variance weighting, MR-Egger and MR-PRESSO. Genetically instrumented blood lead was not associated with CAD (odds ratio (OR) 1.01 per effect size of log transformed blood lead, 95% confidence interval (CI) 0.97, 1.05), blood pressure (systolic -0.18 mmHg, 95% CI -0.44 to 0.08 and diastolic -0.03 mmHg, 95% CI -0.09 to 0.15) or diabetes (OR 0.98, 95% CI 0.92 to 1.03) using MR-PRESSO estimates corrected for an outlier SNP (rs550057) from the highly pleiotropic gene ABO. Exogenous lead may have different effects from endogenous lead; nevertheless, this study raises questions about the role of blood lead in CAD.

Lean mass, grip strength and risk of type 2 diabetes: a bi-directional Mendelian randomisation study

AIMS/HYPOTHESIS

Muscle mass and strength may protect against type 2 diabetes as a sink for glucose disposal. In randomised controlled trials, resistance training improves glucose metabolism in people with the metabolic syndrome. Whether increasing muscle mass and strength protects against diabetes in the general population is unknown. We assessed the effect of markers of muscle mass and strength on diabetes and glycaemic traits using bi-directional Mendelian randomisation.

METHODS

Inverse variance weighting estimates were obtained by applying genetic variants that predict male lean mass, female lean mass and grip strength, obtained from the UK Biobank GWAS, to the largest available case-control study of diabetes (DIAbetes Genetics Replication And Meta-analysis [DIAGRAM]; n = 74,124 cases and 824,006 controls) and to a study of glycaemic traits (Meta-Analyses of Glucose and Insulin-related traits Consortium [MAGIC]). Conversely, we also applied genetic variants that predict diabetes, HbA_1c, fasting glucose, fasting insulin and HOMA-B to UK Biobank summary statistics for genetic association with lean mass and grip strength. As sensitivity analyses we used weighted median, Mendelian randomisation (MR)-Egger and Mendelian Randomization Pleiotropy RESidual Sum and Outlier (MR-PRESSO) and removed pleiotropic SNPs.

RESULTS

Grip strength was not significantly associated with diabetes using inverse variance weighting (OR 0.72 per SD increase in grip strength, 95% CI 0.51, 1.01, p = 0.06) and including pleiotropic SNPs but was significantly associated with diabetes using MR-PRESSO (OR 0.77, 95% CI 0.62, 0.95, p = 0.02) after removing pleiotropic SNPs. Female lean mass was significantly associated with diabetes (OR 0.91, 95% CI 0.84, 0.99, p = 0.02) while male lean mass was not significant but directionally similar (OR 0.94, 95% CI 0.88, 1.01, p = 0.09). Conversely, diabetes was inversely and significantly associated with male lean mass (β -0.02 SD change in lean mass, 95% CI -0.04, -0.00, p = 0.04) and grip strength (β -0.01, 95% CI -0.02, -0.00, p = 0.01).

CONCLUSIONS/INTERPRETATION

Increased muscle mass and strength may be related to lower diabetes risk. Diabetes may also be associated with grip strength and lean mass. Muscle strength could warrant further investigation as a possible target of intervention for diabetes prevention.

Association of Apolipoprotein E With Intracerebral Hemorrhage Risk by Race/Ethnicity: A Meta-analysis

Importance

Genetic studies of intracerebral hemorrhage (ICH) have focused mainly on white participants, but genetic risk may vary or could be concealed by differing nongenetic coexposures in nonwhite populations. Transethnic analysis of risk may clarify the role of genetics in ICH risk across populations.

Objective

To evaluate associations between established differences in ICH risk by race/ethnicity and the variability in the risks of apolipoprotein E (APOE) ε4 alleles, the most potent genetic risk factor for ICH.

Design, Setting, and Participants

This case-control study of primary ICH meta-analyzed the association of APOE allele status on ICH risk, applying a 2-stage clustering approach based on race/ethnicity and stratified by a contributing study. A propensity score analysis was used to model the association of APOE with the burden of hypertension across race/ethnic groups. Primary ICH cases and controls were collected from 3 hospital- and population-based studies in the United States and 8 in European sites in the International Stroke Genetic Consortium. Participants were enrolled from January 1, 1999, to December 31, 2017. Participants with secondary causes of ICH were excluded from enrollment. Controls were regionally matched within each participating study.

Main Outcomes and Measures

Clinical variables were systematically obtained from structured interviews within each site. APOE genotype was centrally determined for all studies.

Results

In total, 13 124 participants (7153 [54.5%] male with a median [interquartile range] age of 66 [56-76] years) were included. In white participants, APOE ε2 (odds ratio [OR], 1.49; 95% CI, 1.24-1.80; P < .001) and APOE ε4 (OR, 1.51; 95% CI, 1.23-1.85; P < .001) were associated with lobar ICH risk; however, within self-identified Hispanic and black participants, no associations were found. After propensity score matching for hypertension burden, APOE ε4 was associated with lobar ICH risk among Hispanic (OR, 1.14; 95% CI, 1.03-1.28; P = .01) but not in black (OR, 1.02; 95% CI, 0.98-1.07; P = .25) participants. APOE ε2 and ε4 did not show an association with nonlobar ICH risk in any race/ethnicity.

Conclusions and Relevance

APOE ε4 and ε2 alleles appear to affect lobar ICH risk variably by race/ethnicity, associations that are confirmed in white individuals but can be shown in Hispanic individuals only when the excess burden of hypertension is propensity score-matched; further studies are needed to explore the interactions between APOE alleles and environmental exposures that vary by race/ethnicity in representative populations at risk for ICH.

Association of Chromosome 9p21 With Subsequent Coronary Heart Disease Events

Supplemental Digital Content is available in the text.

Background:

Genetic variation at chromosome 9p21 is a recognized risk factor for coronary heart disease (CHD). However, its effect on disease progression and subsequent events is unclear, raising questions about its value for stratification of residual risk.

Methods:

A variant at chromosome 9p21 (rs1333049) was tested for association with subsequent events during follow-up in 103 357 Europeans with established CHD at baseline from the GENIUS-CHD (Genetics of Subsequent Coronary Heart Disease) Consortium (73.1% male, mean age 62.9 years). The primary outcome, subsequent CHD death or myocardial infarction (CHD death/myocardial infarction), occurred in 13 040 of the 93 115 participants with available outcome data. Effect estimates were compared with case/control risk obtained from the CARDIoGRAMplusC4D consortium (Coronary Artery Disease Genome-wide Replication and Meta-analysis [CARDIoGRAM] plus The Coronary Artery Disease [C4D] Genetics) including 47 222 CHD cases and 122 264 controls free of CHD.

Results:

Meta-analyses revealed no significant association between chromosome 9p21 and the primary outcome of CHD death/myocardial infarction among those with established CHD at baseline (GENIUS-CHD odds ratio, 1.02; 95% CI, 0.99–1.05). This contrasted with a strong association in CARDIoGRAMPlusC4D odds ratio 1.20; 95% CI, 1.18–1.22; P for interaction <0.001 compared with the GENIUS-CHD estimate. Similarly, no clear associations were identified for additional subsequent outcomes, including all-cause death, although we found a modest positive association between chromosome 9p21 and subsequent revascularization (odds ratio, 1.07; 95% CI, 1.04–1.09).

Conclusions:

In contrast to studies comparing individuals with CHD to disease-free controls, we found no clear association between genetic variation at chromosome 9p21 and risk of subsequent acute CHD events when all individuals had CHD at baseline. However, the association with subsequent revascularization may support the postulated mechanism of chromosome 9p21 for promoting atheroma development.

ADAMTS-13 activity and ischemic heart disease: a Mendelian randomization study

Essentials Cardiovascular disease remains the leading cause of global mortality despite progress in control. We assessed the role of ADAMTS-13 in ischemic heart disease using Mendelian randomization. Genetically instrumented ADAMTS-13 activity reduced ischemic heart disease. Therapeutics targeting ADAMTS-13 activity could perhaps be repurposed in ischemic heart disease.

BACKGROUND

Despite great progress in the prevention and control of cardiovascular disease, it remains the leading cause of global mortality and morbidity, with new unexpected risk factors emerging and few effective new pharmaceutical treatments. ADAMTS-13 is involved in a clotting disorder, thrombotic thrombocytopenic purpura, for which new treatments are being developed. Observationally, ADAMTS-13 activity is inversely associated with ischemic heart disease (IHD) but positively associated with diabetes.

OBJECTIVES

To obtain unconfounded estimates of the effect of ADAMTS-13 on IHD, diabetes and lipids.

METHODS

We applied genetic variants strongly, (P < 5 × 10-8 ), solely and independently associated with ADAMTS-13 to the largest available extensively genotyped case-control studies of IHD and diabetes and to a large study of lipids to obtain Mendelian randomization inverse variance weighted (IVW) estimates. Sensitivity was evaluated through weighted median and MR-Egger estimates.

RESULTS

Genetically predicted ADAMTS-13 activity, based on three genetic variants, was consistently inversely associated with IHD (IVW odds ratio [OR] 0.91 per effect size; 95% confidence interval [CI] 0.86-0.97) but not with diabetes (OR 0.94, 95% CI 0.88-1.01) or high or low-density lipoprotein cholesterol (0.01, 95% CI -0.02 to 0.04; -0.01, 95% CI -0.04 to 0.02, respectively). ADAMTS-13 antigen, based on four genetic variants, was not associated with any outcome.

CONCLUSIONS

This genetic validation of ADAMTS-13 activity as a target of intervention in IHD raises the possibility of new ways of prevention and treatment being developed by repurposing therapeutics that raise ADAMTS-13 activity, or by other environmental or dietary interventions that raise ADAMTS-13 activity.

Re-thinking Alzheimer's disease therapeutic targets using gene-based tests

Background

Alzheimer's disease (AD) is a devastating condition with no known effective drug treatments. Existing drugs only alleviate symptoms. Given repeated expensive drug failures, we assessed systematically whether approved and investigational AD drugs are targeting products of genes strongly associated with AD and whether these genes are targeted by existing drugs for other indications which could be re-purposed.

Methods

We identified genes strongly associated with late-onset AD from the loci of genetic variants associated with AD at genome-wide-significance and from a gene-based test applied to the most extensively genotyped late-onset AD case (n = 17,008)-control (n = 37,154) study, the International Genomics of Alzheimer's Project. We used three gene-to-drug cross-references, Kyoto Encyclopedia of Genes and Genomes, Drugbank and Drug Repurposing Hub, to identify genetically validated targets of AD drugs and any existing drugs or nutraceuticals targeting products of the genes strongly associated with late-onset AD.

Findings

A total of 67 autosomal genes (forming 9 gene clusters) were identified as strongly associated with late-onset AD, 28 from the loci of single genetic variants, 51 from the gene-based test and 12 by both methods. Existing approved or investigational AD drugs did not target products of any of these 67 genes. Drugs for other indications targeted 11 of these genes, including immunosuppressive disease-modifying anti-rheumatic drugs targeting PTK2B gene products.

Interpretation

Approved and investigational AD drugs are not targeting products of genes strongly associated with late-onset AD. However, other drugs targeting products of these genes exist and could perhaps be re-purposing to combat late-onset AD after further scrutiny.

Bias in Mendelian randomization due to assortative mating

Mendelian randomization (MR) has been increasingly used to strengthen causal inference in observational epidemiology. Methodological developments in the field allow detecting and/or adjusting for different potential sources of bias, mainly bias due to horizontal pleiotropy (or "off-target" genetic effects). Another potential source of bias is nonrandom matching between spouses (i.e., assortative mating). In this study, we performed simulations to investigate the bias caused in MR by assortative mating. We found that bias can arise due to either cross-trait assortative mating (i.e., assortment on two phenotypes, such as highly educated women selecting taller men) or single-trait assortative mating (i.e., assortment on a single phenotype), even if the exposure and outcome phenotypes are not the phenotypes under assortment. The simulations also indicate that bias due to assortative mating accumulates over generations and that MR methods robust to horizontal pleiotropy are also affected by this bias. Finally, we show that genetic data from mother-father-offspring trios can be used to detect and correct for this bias.

Hypothesis Tests for Neyman's Bias in Case-Control Studies

Survival bias is a long-recognized problem in case-control studies, and many varieties of bias can come under this umbrella term. We focus on one of them, termed Neyman's bias or "prevalence-incidence bias." It occurs in case-control studies when exposure affects both disease and disease-induced mortality, and we give a formula for the observed, biased odds ratio under such conditions. We compare our result with previous investigations into this phenomenon and consider models under which this bias may or may not be important. Finally, we propose three hypothesis tests to identify when Neyman's bias may be present in case-control studies. We apply these tests to three data sets, one of stroke mortality, another of brain tumors, and the last of atrial fibrillation, and find some evidence of Neyman's bias in the former two cases, but not the last case.

Impact of Selection Bias on Estimation of Subsequent Event Risk

BACKGROUND

Studies of recurrent or subsequent disease events may be susceptible to bias caused by selection of subjects who both experience and survive the primary indexing event. Currently, the magnitude of any selection bias, particularly for subsequent time-to-event analysis in genetic association studies, is unknown.

METHODS AND RESULTS

We used empirically inspired simulation studies to explore the impact of selection bias on the marginal hazard ratio for risk of subsequent events among those with established coronary heart disease. The extent of selection bias was determined by the magnitudes of genetic and nongenetic effects on the indexing (first) coronary heart disease event. Unless the genetic hazard ratio was unrealistically large (>1.6 per allele) and assuming the sum of all nongenetic hazard ratios was <10, bias was usually <10% (downward toward the null). Despite the low bias, the probability that a confidence interval included the true effect decreased (undercoverage) with increasing sample size because of increasing precision. Importantly, false-positive rates were not affected by selection bias.

CONCLUSIONS

In most empirical settings, selection bias is expected to have a limited impact on genetic effect estimates of subsequent event risk. Nevertheless, because of undercoverage increasing with sample size, most confidence intervals will be over precise (not wide enough). When there is no effect modification by history of coronary heart disease, the false-positive rates of association tests will be close to nominal.

Joint Effects of GWAS SNPs in Coagulation System Confer Risk to Hypertensive Intracerebral Hemorrhage

Recent genome-wide association studies (GWAS) have identified numerous single nucleotide polymorphisms (SNPs) associated with coagulation system, including hemostatic factors and hematological phenotypes. However, few articles described the relationships between these SNPs and the risk of hemorrhagic stroke. The aim of our study was to evaluate the roles of these SNPs as risk factors and survival predictors for hemorrhagic stroke. Thirteen SNPs from GWAS in coagulation system were genotyped in a Chinese Han population including 1000 patients with hemorrhagic stroke (intracerebral hemorrhage, ICH = 743; subarachnoid hemorrhage, SAH = 257) and 1044 population-based controls. The associations between the genetics risk score (GRS) and risk of hemorrhagic stroke as well as post-stroke adverse outcomes were determined. No individual SNP was associated with the risk of hemorrhagic stroke. The GRS was calculated by summing the number of risk alleles of each SNP, and a total of 13 SNPs were included. Meanwhile, the GRS cutoffs values were defined to be close to quartiles or tertiles in control subjects. For quartiles, individuals with GRS about 8-9, 10-11, ≥12 had 1.28 (OR 1.28, 95% CI 0.98-1.68, p = 0.067)-, 1.36 (OR 1.36, 95% CI 1.04-1.79, p = 0.026)-, 1.53 (OR 1.53, 95% CI 1.13-2.07, p = 0.006)-fold increase in ICH risk compared to those with GRS ≤7, respectively; for tertiles, individuals with GRS about GRS 9-10, ≥11 had 0.98 (OR 0.98, 95% CI 0.78-1.23, p = 0.067)- and 1.26 (OR 1.26, 95% CI 1.00-1.59, p = 0.048)-fold increase in ICH risk compared to those with GRS ≤8, respectively. Further stratification analyses indicated that this association was only found in hypertensive ICH subjects. However, no statistical difference was found in the volume of hematoma, activities of daily living scale as well as hospital death in the ICH patients based on GRS values. Joint effects of SNPs associated with low coagulation factor levels might confer risk to ICH patients with hypertension. However, the clinical value on risk stratification and survival prediction was limited.

Case-Only Survival Analysis Reveals Unique Effects of Genotype, Sex, and Coronary Disease Severity on Survivorship

Survival bias may unduly impact genetic association with complex diseases; gene-specific survival effects may further complicate such investigations. Coronary artery disease (CAD) is a complex phenotype for which little is understood about gene-specific survival effects; yet, such information can offer insight into refining genetic associations, improving replications, and can provide candidate genes for both mortality risk and improved survivorship in CAD. Building on our previous work, the purpose of this current study was to: evaluate LSAMP SNP-specific hazards for all-cause mortality post-catheterization in a larger cohort of our CAD cases; and, perform additional replication in an independent dataset. We examined two LSAMP SNPs—rs1462845 and rs6788787—using CAD case-only Cox proportional hazards regression for additive genetic effects, censored on time-to-all-cause mortality or last follow-up among Caucasian subjects from the Catheterization Genetics Study (CATHGEN; n = 2,224) and the Intermountain Heart Collaborative Study (IMHC; n = 3,008). Only after controlling for age, sex, body mass index, histories of smoking, type 2 diabetes, hyperlipidemia and hypertension (HR = 1.11, 95%CI = 1.01–1.22, p = 0.032), rs1462845 conferred significantly increased hazards of all-cause mortality among CAD cases. Even after controlling for multiple covariates, but in only the primary cohort, rs6788787 conferred significantly improved survival (HR = 0.80, 95% CI = 0.69–0.92, p = 0.002). Post-hoc analyses further stratifying by sex and disease severity revealed replicated effects for rs1462845: even after adjusting for aforementioned covariates and coronary interventional procedures, males with severe burden of CAD had significantly amplified hazards of death with the minor variant of rs1462845 in both cohorts (HR = 1.29, 95% CI = 1.08–1.55, p = 0.00456; replication HR = 1.25, 95% CI = 1.05–1.49, p = 0.013). Kaplan-Meier curves revealed unique cohort-specific genotype effects on survival. Additional analyses demonstrated that the homozygous risk genotype (‘A/A’) fully explained the increased hazard in both cohorts. None of the post-hoc analyses in control subjects were significant for any model. This suggests that genetic effects of rs1462845 on survival are unique to CAD presence. This represents formal, replicated evidence of genetic contribution of rs1462845 to increased risk for all-cause mortality; the contribution is unique to CAD case status and specific to males with severe burden of CAD.

Using family members to augment genetic case-control studies of a life-threatening disease

Survival bias is difficult to detect and adjust for in case-control genetic association studies but can invalidate findings when only surviving cases are studied and survival is associated with the genetic variants under study. Here, we propose a design where one genotypes genetically informative family members (such as offspring, parents, and spouses) of deceased cases and incorporates that surrogate genetic information into a retrospective maximum likelihood analysis. We show that inclusion of genotype data from first-degree relatives permits unbiased estimation of genotype association parameters. We derive closed-form maximum likelihood estimates for association parameters under the widely used log-additive and dominant association models. Our proposed design not only permits a valid analysis but also enhances statistical power by augmenting the sample with indirectly studied individuals. Gene variants associated with poor prognosis can also be identified under this design. We provide simulation results to assess performance of the methods. Copyright © 2016 John Wiley & Sons, Ltd.

Genetic variants at chromosome 9p21 and risk of first versus subsequent coronary heart disease events: a systematic review and meta-analysis

Objectives

The purpose of this analysis was to compare the association between variants at the chromosome 9p21 locus (Ch9p21) and risk of first versus subsequent coronary heart disease (CHD) events through systematic review and meta-analysis.

Background

Ch9p21 is a recognized risk factor for a first CHD event. However, its association with risk of subsequent events in patients with established CHD is less clear.

Methods

We searched PubMed and EMBASE for prospective studies reporting association of Ch9p21 with incident CHD events and extracted information on cohort type (individuals without prior CHD or individuals with established CHD) and effect estimates for risk of events.

Results

We identified 31 cohorts reporting on 193,372 individuals. Among the 16 cohorts of individuals without prior CHD (n = 168,209), there were 15,664 first CHD events. Ch9p21 was associated with a pooled hazard ratio (HR) of a first event of 1.19 (95% confidence interval: 1.17 to 1.22) per risk allele. In individuals with established CHD (n = 25,163), there were 4,436 subsequent events providing >99% and 91% power to detect a per-allele HR of 1.19 or 1.10, respectively. The pooled HR for subsequent events was 1.01 (95% confidence interval: 0.97 to 1.06) per risk allele. There was strong evidence of heterogeneity between the effect estimates for first and subsequent events (p value for heterogeneity = 5.6 × 10⁻¹¹). We found no evidence for biases to account for these findings.

Conclusions

Ch9p21 shows differential association with risk of first versus subsequent CHD events. This has implications for genetic risk prediction in patients with established CHD and for mechanistic understanding of how Ch9p21 influences risk of CHD.

Hyaluronan synthase 3 variant and anthracycline-related cardiomyopathy: a report from the children's oncology group

PURPOSE

The strong dose-dependent association between anthracyclines and cardiomyopathy is further exacerbated by the co-occurrence of cardiovascular risk factors (diabetes and hypertension). The high morbidity associated with cardiomyopathy necessitates an understanding of the underlying pathogenesis so that targeted interventions can be developed.

PATIENTS AND METHODS

By using a two-stage design, we investigated host susceptibility to anthracycline-related cardiomyopathy by using the ITMAT/Broad CARe cardiovascular single nucleotide polymorphism (SNP) array to profile common SNPs in 2,100 genes considered relevant to de novo cardiovascular disease.

RESULTS

By using a matched case-control design (93 cases, 194 controls), we identified a common SNP, rs2232228, in the hyaluronan synthase 3 (HAS3) gene that exerts a modifying effect on anthracycline dose-dependent cardiomyopathy risk (P = 5.3 × 10(-7)). Among individuals with rs2232228 GG genotype, cardiomyopathy was infrequent and not dose related. However, in individuals exposed to high-dose (> 250 mg/m(2)) anthracyclines, the rs2232228 AA genotype conferred an 8.9-fold (95% CI, 2.1- to 37.5-fold; P = .003) increased cardiomyopathy risk compared with the GG genotype. This gene-environment interaction was successfully replicated in an independent set of 76 patients with anthracycline-related cardiomyopathy. Relative HAS3 mRNA levels measured in healthy hearts tended to be lower among individuals with AA compared with GA genotypes (P = .09).

CONCLUSION

Hyaluronan (HA) produced by HAS3 is a ubiquitous component of the extracellular matrix and plays an active role in tissue remodeling. In addition, HA is known to reduce reactive oxygen species (ROS) -induced cardiac injury. The high cardiomyopathy risk associated with AA genotype could be due to inadequate remodeling and/or inadequate protection of the heart from ROS-mediated injury on high anthracycline exposure.

The genetic basis for survivorship in coronary artery disease

Survivorship is a trait characterized by endurance and virility in the face of hardship. It is largely considered a psychosocial attribute developed during fatal conditions, rather than a biological trait for robustness in the context of complex, age-dependent diseases like coronary artery disease (CAD). The purpose of this paper is to present the novel phenotype, survivorship in CAD as an observed survival advantage concurrent with clinically significant CAD. We present a model for characterizing survivorship in CAD and its relationships with overlapping time- and clinically-related phenotypes. We offer an optimal measurement interval for investigating survivorship in CAD. We hypothesize genetic contributions to this construct and review the literature for evidence of genetic contribution to overlapping phenotypes in support of our hypothesis. We also present preliminary evidence of genetic effects on survival in people with clinically significant CAD from a primary case-control study of symptomatic coronary disease. Identifying gene variants that confer improved survival in the context of clinically appreciable CAD may improve our understanding of cardioprotective mechanisms acting at the gene level and potentially impact patients clinically in the future. Further, characterizing other survival-variant genetic effects may improve signal-to-noise ratio in detecting gene associations for CAD.

Tamoxifen-induced venothromboembolic events: exploring validation of putative genetic association

OBJECTIVE

A pilot study to examine accrual rates, efficiency of data capture approaches, study design and genotyping capacity for a future genetic validation study was undertaken.

DESIGN

The process pilot evaluated feasibility of applying a matched case-control design to validate association of two candidate estrogen receptor (ER) single nucleotide polymorphisms (SNPs) with incidence of venothromboembolic events (VTE) in breast cancer patients treated with tamoxifen where criteria included frequency matching by age, number of years diagnosed with breast cancer within 4-year intervals, and geographic residency.

SETTING

The study was conducted at Marshfield Clinic, in central Wisconsin.

PARTICIPANTS

Study-eligible cases with a breast cancer diagnosis between 1994 and 2006 who experienced a VTE within 5 years of last tamoxifen exposure were matched at a ratio of 1:4 to controls with a breast cancer diagnosed between 1994 and 2006 with no VTE history following tamoxifen exposure for ≥2 years.

METHODS

Feasibility of enrolling, phenotyping, and genotyping 20% of the total number of validated eligible cases and controls was tested in order to project enrollment rates and assess probability of enrolling the projected sample size for the prospective validation study and adequacy of planned data capture. Conditional logistic regression analysis was conducted for the matched case-control study design.

RESULTS

Enrollment accruals included 19 of 24 targeted cases (79%), and 74 of 96 (77%) targeted controls. Electronic data capture for most variables was nearly 100%. No unexpected statistically significant differences were observed between cases and controls. Capacity to conduct in-house screening for rs2234689 (ER1 PvuII), rs9340799 (ER1 XbaI), rs13146272 (CYP4V2), rs2227589 (SERPINC 1) and rs1613662 (GP6) was successfully established. Association of GP6 with VTE was further validated (P=0.0403; OR, 0.19).

CONCLUSION

Accrual rates to the larger prospective study will require a multi-center design to ensure enrollment of adequate numbers of cases and controls for achieving the projected sample size required to validate association of the ER SNPs. To prevent study failure due to poor accrual, the importance of conducting feasibility studies before launching large scale validation studies of genetic association and adverse drug events, is discussed.

Burden of blood pressure-related alleles is associated with larger hematoma volume and worse outcome in intracerebral hemorrhage

BACKGROUND AND PURPOSE

Intracerebral hemorrhage (ICH) is the acute manifestation of a progressive disease of the cerebral small vessels. The severity of this disease seems to influence not only risk of ICH but also the size of the hematoma. As the burden of high blood pressure-related alleles is associated with both hypertension-related end-organ damage and risk of ICH, we sought to determine whether this burden influences ICH baseline hematoma volume.

METHODS

Prospective study in subjects of European descent with supratentorial ICH who underwent genome-wide genotyping. Forty-two single nucleotide polymorphisms associated with high blood pressure were identified from a publicly available database. A genetic risk score was constructed based on these single nucleotide polymorphisms. The score was used as the independent variable in univariate and multivariate regression models for admission ICH volume and poor clinical outcome (modified Rankin Scale, 3-6).

RESULTS

A total of 323 ICH cases were enrolled in the study (135 deep and 188 lobar intracranial hematomas). The blood pressure-based genetic risk score was associated with both baseline hematoma volume and poor clinical outcome specifically in deep ICH. In multivariate regression analyses, each additional SD of the score increased mean deep ICH volume by 28% (or 2.7 mL increase; β=0.28; SE=0.11; P=0.009) and risk of poor clinical outcome by 71% (odds ratio, 1.71; 95% confidence interval, 1.05-2.80; P=0.03).

CONCLUSIONS

Increasing numbers of high blood pressure-related alleles are associated with mean baseline hematoma volume and poor clinical outcome in ICH. These findings suggest that the small vessel vasculopathy responsible for the occurrence of the hemorrhage also influences its volume.

Lack of association between the MTHFR C677T variant and migraine with aura in an older population: could selective survival play a role?

BACKGROUND

Several studies, but not all, of primarily middle-aged or younger adults have suggested that the common MTHFR C677T variant is a genetic risk factor for migraine with aura (MA). Here, we consider whether this variant is associated with MA risk in an older non-clinical population (AGES-Reykjavik cohort).

METHODS

Participants are a sub-sample ( N  = 1976) of subjects from the Reykjavik Study (RS; mean age 50) and its continuation, AGES-RS (mean age 76). We estimated the relative odds of MA in TT versus CC carriers using multinomial logistic regression. As both MA and the TT genotype may be linked with modestly reduced longevity, we performed a simple simulation to illustrate the effect that selective survival may have had on our observed gene-disease association.

RESULTS

TT versus CC carriers were at marginally reduced odds of MA (ORTT 0.55 (0.3-1.0), P  = 0.07), significantly for women (ORTT 0.45 (0.2-0.9), P  = 0.03). Assuming the 'true' (e.g. mid-life) effect of the TT genotype is ORTT 1.26, from a recent meta-analysis, our simulation suggested that if 25-year mortality had been (hypothetically) 13% higher in MA subjects with the TT versus CC genotype, the measured effect of the TT genotype on MA would have been attenuated to non-significance (e.g. ORTT 1.00). Our observed protective effect was consistent with the most extreme selective mortality scenario, in which essentially all of the previously reported increased mortality in MA subjects was (hypothetically) found in CT or TT carriers.

CONCLUSION

The MTHFR 677TT genotype was associated with marginally reduced risk of MA in our older population. Our simulation illustrated how even modest selective survival might obscure the apparent effect of a genetic or other risk factor in older populations. We speculate that some of the heterogeneity previously observed for this particular genetic variant may be due to age range differences in the studied populations.

Cardiovascular events as a function of serum bilirubin levels in a large, statin-treated cohort

BACKGROUND

Serum bilirubin is an endogenous antioxidant that is routinely measured before a statin is prescribed primarily to assess liver function, but the association with cardiovascular disease (CVD) in this population has not been explored.

METHOD AND RESULTS

We identified patients from a United Kingdom primary care database (The Health Improvement Network) with measurements of serum total bilirubin levels recorded 3 months before the first statin treatment between January 1, 2000, and December 31, 2010, and no history of liver disease or CVD. In total, 130 052 patients met the inclusion criteria, and after a median follow-up of 43 months, there were 7850 CVD events. In men, the incidence of CVD in the lowest decile category of bilirubin (1-6 μmol/L [0.06-0.35 mg/dL]) was 215 per 10 000 person-years compared with 163 per 10 000 person-years in the highest decile (19-40 μmol/L [1.1-2.3 mg/dL]). Similar differences were seen for women. After conventional CVD risk factors were accounted for, the associations with bilirubin were nonlinear (L shaped), and the models predicted that, compared with patients with a bilirubin level of 10 μmol/L (0.6 mg/dL), those with a similar CVD risk profile but a bilirubin level of 5 μmol/L (0.3 mg/dL) had an 18% (95% confidence interval, 9-27) higher risk of any CVD event, a 34% (95% confidence interval, 13-56) higher risk of myocardial infarction, and a 33% (95% confidence interval, 21-46) higher risk of death resulting from any cause.

CONCLUSIONS

Serum bilirubin level measured before a statin prescription to assess liver function is an independent risk factor for CVD and death in both men and women.

Burden of risk alleles for hypertension increases risk of intracerebral hemorrhage

BACKGROUND AND PURPOSE

Genetic variation influences risk of intracerebral hemorrhage (ICH). Hypertension (HTN) is a potent risk factor for ICH and several common genetic variants (single nucleotide polymorphisms [SNPs]) associated with blood pressure levels have been identified. We sought to determine whether the cumulative burden of blood pressure-related SNPs is associated with risk of ICH and pre-ICH diagnosis of HTN.

METHODS

We conducted a prospective multicenter case-control study in 2272 subjects of European ancestry (1025 cases and 1247 control subjects). Thirty-nine SNPs reported to be associated with blood pressure levels were identified from the National Human Genome Research Institute genomewide association study catalog. Single-SNP association analyses were performed for the outcomes ICH and pre-ICH HTN. Subsequently, weighted and unweighted genetic risk scores were constructed using these SNPs and entered as the independent variable in logistic regression models with ICH and pre-ICH HTN as the dependent variables.

RESULTS

No single SNP was associated with either ICH or pre-ICH HTN. The blood pressure-based unweighted genetic risk score was associated with risk of ICH (OR, 1.11; 95% CI, 1.02-1.21; P=0.01) and the subset of ICH in deep regions (OR, 1.18; 95% CI, 1.07-1.30; P=0.001), but not with the subset of lobar ICH. The score was associated with a history of HTN among control subjects (OR, 1.17; 95% CI, 1.04-1.31; P=0.009) and ICH cases (OR, 1.15; 95% CI, 1.01-1.31; P=0.04). Similar results were obtained when using a weighted score.

CONCLUSIONS

Increasing numbers of high blood pressure-related alleles are associated with increased risk of deep ICH as well as with clinically identified HTN.

Methods for meta-analyses of genome-wide association studies: critical assessment of empirical evidence

There has been a steep increase in the number of meta-analyses of genome-wide association (GWA) studies aimed at identifying genetic variants with increasingly smaller effects, but pressure to publish findings of new genetic associations has limited the time available for careful consideration of all of their methodological aspects. The authors surveyed the literature (2007-2010) to provide empirical evidence on the methods used in GWA meta-analyses, including their organization, requirements about the uniformity of methods used in primary studies, methods for data pooling, investigation of between-study heterogeneity, and quality of reporting. This review showed that a great variety of methods are being used, but the rationale for their choice is often unclear. It also highlights how important methodological aspects have received insufficient attention, potentially leading to missed opportunities for improving gene discovery and characterization. Evaluation of power to replicate findings was inadequate, and the number of variants selected for replication was not associated with replication sample size. A low proportion of GWA meta-analyses investigated the presence and magnitude of heterogeneity, even when there was little uniformity in methods used in primary studies. More methodological work is required before clear guidance can be offered as to optimal methods or tradeoffs between alternative methods. However, there is a clear need for guidelines for reporting the results of GWA meta-analyses.

Anthracycline-related cardiomyopathy after childhood cancer: role of polymorphisms in carbonyl reductase genes--a report from the Children's Oncology Group

PURPOSE

Carbonyl reductases (CBRs) catalyze reduction of anthracyclines to cardiotoxic alcohol metabolites. Polymorphisms in CBR1 and CBR3 influence synthesis of these metabolites. We examined whether single nucleotide polymorphisms in CBR1 (CBR1 1096G>A) and/or CBR3 (CBR3 V244M) modified the dose-dependent risk of anthracycline-related cardiomyopathy in childhood cancer survivors.

PATIENTS AND METHODS

One hundred seventy survivors with cardiomyopathy (patient cases) were compared with 317 survivors with no cardiomyopathy (controls; matched on cancer diagnosis, year of diagnosis, length of follow-up, and race/ethnicity) using conditional logistic regression techniques.

RESULTS

A dose-dependent association was observed between cumulative anthracycline exposure and cardiomyopathy risk (0 mg/m(2): reference; 1 to 100 mg/m(2): odds ratio [OR], 1.65; 101 to 150 mg/m(2): OR, 3.85; 151 to 200 mg/m(2): OR, 3.69; 201 to 250 mg/m(2): OR, 7.23; 251 to 300 mg/m(2): OR, 23.47; > 300 mg/m(2): OR, 27.59; P(trend) < .001). Among individuals carrying the variant A allele (CBR1:GA/AA and/or CBR3:GA/AA), exposure to low- to moderate-dose anthracyclines (1 to 250 mg/m(2)) did not increase the risk of cardiomyopathy. Among individuals with CBR3 V244M homozygous G genotypes (CBR3:GG), exposure to low- to moderate-dose anthracyclines increased cardiomyopathy risk when compared with individuals with CBR3:GA/AA genotypes unexposed to anthracyclines (OR, 5.48; P = .003), as well as exposed to low- to moderate-dose anthracyclines (OR, 3.30; P = .006). High-dose anthracyclines (> 250 mg/m(2)) were associated with increased cardiomyopathy risk, irrespective of CBR genotype status.

CONCLUSION

This study demonstrates increased anthracycline-related cardiomyopathy risk at doses as low as 101 to 150 mg/m(2). Homozygosis for G allele in CBR3 contributes to increased cardiomyopathy risk associated with low- to moderate-dose anthracyclines, such that there seems to be no safe dose for patients homozygous for the CBR3 V244M G allele. These results suggest a need for targeted intervention for those at increased risk of cardiomyopathy.

Associations between genetic polymorphisms of insulin-like growth factor axis genes and risk for age-related macular degeneration

PURPOSE

To investigate whether insulin-like growth factor (IGF) axis genes, together with a novel dietary risk factor, the dietary glycemic index (dGI), and body mass index (BMI) affect the risk for age-related macular degeneration (AMD).

METHODS

This case-control study involved 962 subjects originally recruited through the Age-Related Eye Disease Study (AREDS) Genetic Repository. After those with missing covariates or invalid calorie intake (n = 23), diabetes (n = 59), and non-Caucasian race (n = 16) were excluded, 864 participants were used, including 209 AREDS category 1 participants (control group), 354 category 2 or 3 participants (drusen group), and 301 category 4 participants (advanced AMD group). A total of 25 single-nucleotide polymorphisms (SNPs) selected from IGF-1 (n = 9), IGF-2 (n = 1), IGF binding protein 1 (IGFBP1; n = 3), IGFBP3 (n = 3), acid-labile subunit of IGFBP (IGFALS; n = 2), IGF1 receptor (IGF1R; n = 4), and IGF2R (n = 3) were genotyped. SNP-AMD associations were measured with genotype, allele χ(2) tests and Armitage's trend test. Odds ratios (OR), 95% confidence intervals (CIs), and SNP-exposure interactions were evaluated by multivariate logistic regression.

RESULTS

One SNP (rs2872060) in IGF1R revealed a significant association with advanced AMD (P-allele = 0.0009, P-trend = 0.0008; the significance level was set at 0.05/25 = 0.002 for multiple comparisons). The risk allele (G) in the heterozygous and homozygous states (OR, 1.67 and 2.93; 95% CI, 1.03-2.71 and 1.60-5.36, respectively) suggests susceptibility and an additive effect on AMD risk. Further stratification analysis remained significant for both neovascularization (OR, 1.49 and 2.61; 95% CI, 0.90-2.48 and 1.39-4.90, respectively) and geographic atrophy (OR, 2.57 and 4.52; 95% CI, 0.99-6.71 and 1.49-13.74, respectively). The G allele interaction analysis with BMI was significant for neovascularization (P = 0.042) but not for geographic atrophy (P = 0.47). No significant interaction was found with dGI.

CONCLUSIONS

These data suggest a role of IGF1R on the risk for advanced AMD in this group of subjects.

Differential impact of race and risk factors on incidence of atrial fibrillation

Despite some common risk factors for atrial fibrillation (AF) being more prevalent among blacks, African Americans are increasingly being reported with lower prevalence and incidence of AF compared with whites. Contemporary studies have not provided a complete explanation for this apparent AF paradox in African Americans. Although many traditional and novel risk factors for AF have been identified, the role of ethnic-specific risk factors has not been examined. Whereas hypertension has been the most common risk factor associated with AF, coronary artery disease also plays an important role in AF pathophysiology in whites. Thereby, elucidating the role of ethnic-specific risk factors for AF may provide important insight into why African Americans are protected from AF or why whites are more prone to develop the arrhythmia. The link between AF susceptibility and genetic processes has only been recently uncovered. Polymorphisms in renin-angiotensin system genes have been characterized as predisposing to AF under certain environmental conditions. Several ion channel genes, signaling molecules, and several genetic loci have been linked with AF. Thereby, studies investigating genetic variants contributing to the differential AF risk in individuals of African American versus European ancestry may also provide important insight into the etiology of the AF paradox in blacks.

Genetic susceptibility to ischemic stroke

Clinicians who treat patients with stroke need to be aware of several single-gene disorders that have ischemic stroke as a major feature, including sickle cell disease, Fabry disease, cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy, and retinal vasculopathy with cerebral leukodystrophy. The reported genome-wide association studies of ischemic stroke and several related phenotypes (for example, ischemic white matter disease) have shown that no single common genetic variant imparts major risk. Larger studies with samples numbering in the thousands are ongoing to identify common variants with smaller effects on risk. Pharmacogenomic studies have uncovered genetic determinants of response to warfarin, statins and clopidogrel. Despite increasing knowledge of stroke genetics, incorporating this new knowledge into clinical practice remains a challenge. The goals of this article are to review common single-gene disorders relevant to ischemic stroke, summarize the status of candidate gene and genome-wide studies aimed at discovering genetic stroke risk factors, and to briefly discuss pharmacogenomics related to stroke treatment.