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Hepatocarcinogenesis: a polygenic model of inherited predisposition to cancer.

The murine inbred strain C3H provides an experimental model of inherited predisposition to hepatocellular cancer. Hepatocellular neoplastic lesions induced by chemical carcinogens reach a volume 10-100-fold greater in C3H mice than in genetically resistant strains. However, the huge strain differences in tumor size are explained by relatively small differences (10%-30%) in tumor cell kinetics. Genetic linkage experiments in different crosses demonstrated that six unlinked hepatocarcinogen sensitivity (Hcs) and two hepatocarcinogen resistance (Hcr) loci determined quantitative variations in susceptibility to hepatocarcinogenesis. Such results provide the genetic basis for the strain variations in susceptibility to hepatocarcinogenesis and demonstrate a new model of polygenic inheritance of predisposition to cancer.

Animals↗

Type I insulin-dependent diabetes mellitus: a model for autoimmune polygenic disorders.

Insulin-dependent diabetes mellitus (IDD) affects between one in 250 and one in 500 Americans. The inheritance of IDD is non-Mendelian and polygenic. Genetic susceptibility predominantly results from specific alleles in the HLA complex and insulin gene region. Autoimmune destruction of pancreatic beta cells leads to profound insulinopenia (Atkinson and Maclaren, 1990). Without insulin treatment, fatal diabetic ketoacidosis results. Even with insulin treatment, after 10 to 20 years of IDD, devastating micro- and macrovascular complications lead to significant morbidity and premature mortality (Rosenbloom, 1983). In order to prevent this catastrophic disease and its consequences, we must understand the pathogenesis and immunogenetics of insulitis (the histologic lesion characteristic of IDD), whose ultimate expression is beta cell necrosis (Cudworth, 1978; Cahill and McDevitt, 1981; Eisenbarth, 1986). Current advances include recognition of new IDD-autoantigens (e.g., glutamic acid decarboxylase), susceptibility genes (e.g., HLA-DQB1*0201 and 0302), and the development of trials to prevent IDD through tolerization to IDD-autoantigens (e.g., insulin) (Maclaren, 1993; Winter et al., 1993). Unlocking the genetic mechanisms responsible for IDD can also reveal more general mechanisms involved in other organ-specific autoimmune diseases.

Alleles↗

The E670G SNP in the PCSK9 gene is associated with polygenic hypercholesterolemia in men but not in women.

BACKGROUND: Common genetic variants in the PCSK9 gene have been reported to be associated with both elevated and exceptionally low LDL levels. The association of a common haplotype, encompassing the E670G single nucleotide polymorphism, with LDL levels reported by Chen et al (J Am Coll Cardiol 2005; 45: 1644) was not confirmed by Kotowski et al (Am J Hum Genet 2006; 78:410-422). METHODS: The incidence of the E670G SNP was determined in 506 patients attending the lipid clinic, University Hospital, Hamburg. RESULTS: The frequency in men with polygenic hypercholesterolemia, 0.11 was significantly higher than in men with LDL<50th percentile, 0.03, p = 0.01. In women there was no difference in the allele frequencies between the two groups. CONCLUSION: In a European population the E670G SNP in the PCSK9 gene is associated with increased LDL in men but not in women.

Adult↗

Cross-Ancestry and Phenome-Wide Associations of Cancer-Specific Polygenic Risk Scores.

PURPOSE: Genome-wide association studies have identified many common variants associated at low effect sizes with various cancers. Summing the effects of these variants into polygenic risk scores (PRS) can improve cancer risk prediction. However, cross-cancer and cross-phenotype pleiotropic associations of cancer-specific PRS are limited. METHODS: Using logistic regression models, we tested the association of 13 cancer-specific PRS with curated phenotypes representing the same 13 cancers and 340 cancer and cardiometabolic phecodes in 560,287 individuals (114,255 African ancestry [AFR] and 446,032 European ancestry [EUR]) from the Million Veteran Program. Models were stratified by ancestry and used age, principal components, and cancer-specific PRS per standard deviation as independent variables, and correction was applied for multiple comparisons. RESULTS: All 13 cancer-specific PRS were significantly associated with their respective cancers among EUR individuals with odds ratios per standard deviation of PRS (odds ratio [OR]) 1.05-1.70. Among AFR individuals, the effect sizes of the cancer PRS were lower, with OR 1.01-1.48, and cancer-specific PRS were significantly associated with their respective cancers for five of 13 cancers (bladder, breast in female patients, colorectal, prostate, and thyroid). In cancer-cancer pleiotropy studies, only the renal cancer-specific PRS was significantly associated with skin cancer (OR = 1.04, P = 4.5 &#xd7; 10-06) among EUR individuals. PheWAS demonstrated five positive pleotropic associations with cardiometabolic conditions (thyroid cancer PRS with thyroid goiter, oral cancer PRS with diabetes phenotypes, and hypothyroidism) and two negative associations (oral and lung cancer PRS separately with coronary artery disease). CONCLUSION: Cancer PRS have stronger associations per cancer among EUR versus AFR individuals. In contrast to PRS of other chronic diseases, the majority of cancer-related PRS are highly specific and pleiotropic associations with other cancers and cardiometabolic traits are uncommon.

Female↗

Association of Vitamin D Polygenic Risk Scores and Disease Outcome in People With Multiple Sclerosis.

BACKGROUND AND OBJECTIVES: Observational studies suggest low levels of 25-hydroxyvitamin D (25[OH]D) may be associated with increased disease activity in people with multiple sclerosis (PwMS). Large-scale genome-wide association studies (GWAS) suggest 25(OH)D levels are partly genetically determined. The resultant polygenic scores (PGSs) could serve as a proxy for 25(OH)D levels, minimizing potential confounding and reverse causation in analyses with outcomes. Herein, we assess the association of genetically determined 25(OH)D and disease outcomes in MS. METHODS: We generated 25(OH)D PGS for 1,924 PwMS with available genotyping data pooled from 3 studies: the CombiRx trial (n = 575), Johns Hopkins MS Center (n = 1,152), and Immune-Mediated Inflammatory Diseases study (n = 197). 25(OH)D-PGS were derived using summary statistics (p < 5 &#xd7; 10-8) from a large GWAS including 485,762 individuals with circulating 25(OH)D levels measured. We included clinical and imaging outcomes: Expanded disability status scale (EDSS), timed 25-foot walk (T25FW), nine-hole peg test (9HPT), radiologic activity, and optical coherence tomography-derived ganglion cell inner plexiform layer (GCIPL) thickness. A subset (n = 935) had measured circulating 25(OH)D levels. We fitted multivariable models based on the outcome of interest and pooled results across studies using random effects meta-analysis. Sensitivity analyses included a modified p value threshold for inclusion in the PGS (5 &#xd7; 10-5) and applying Mendelian randomization (MR) rather than using PGS. RESULTS: Initial analyses demonstrated a positive association between generated 25(OH)D-PGS and circulating 25(OH)D levels (per 1SD increase in 25[OH]D PGS: 3.08%, 95% CI: 1.77%, 4.42%; p = 4.33e-06; R2 = 2.24%). In analyses with outcomes, we did not observe an association between 25(OH)D-PGS and relapse rate (per 1SD increase in 25[OH]D-PGS: 0.98; 95% CI: 0.87-1.10), EDSS worsening (per 1SD: 1.05; 95% CI: 0.87-1.28), change in T25FW (per 1SD: 0.07%; 95% CI: -0.34 to 0.49), or change in 9HPT (per 1SD: 0.09%; 95% CI: -0.15 to 0.33). 25(OH)D-PGS was not associated with new lesion accrual, lesion volume or other imaging-based outcomes (whole brain, gray, white matter volume loss or GCIPL thinning). The results were similarly null in analyses using other p value thresholds or those applying MR. DISCUSSION: Genetically determined lower 25(OH)D levels were not associated with worse disease outcomes in PwMS and raises questions about the plausibility of a treatment effect of vitamin D in established MS.

Humans↗

Evaluating a Genome-Wide Polygenic Score for Handgrip Strength and Its Interplay with Leisure-Time Physical Activity Across the IGEMS Twin Cohorts.

PURPOSE: Polygenic scores (PGSs) may help assess genetic predisposition to multifactorial traits. We examined whether age, sex, and leisure-time physical activity (LTPA) modify the association between a PGS for handgrip strength (HGS) and measured HGS in older adults. METHODS: PGS for HGS (PGS hgs) , based on Pan-UK Biobank genome-wide association study data, was calculated for 5103 participants (aged 40-96; 44% women) from eight twin cohorts in Denmark, Sweden, Australia, the United States, and Finland within the IGEMS consortium. Sex-standardized HGS and self-reported LTPA were assessed cross-sectionally. Linear mixed models estimated associations between PGS hgs and HGS, including interactions with age, country, and LTPA, as well as an association between PGS hgs and LTPA. Fixed-effect within-pair models were conducted to assess environmental contributions. RESULTS: Higher PGS hgs was associated with greater HGS (&#x3b2; = 2.14, SE = 0.15, P < 0.001), explaining 4.6% of HGS variance overall, with modest variation across countries. In sex-stratified models, PGS hgs explained 5.2% of the variance in females and 4.3% in males. No statistically significant interaction with age was found. A significant PGS hgs &#xd7; LTPA interaction (&#x3b2; = -0.034, P = 0.013) indicated that the association between LTPA and HGS was more pronounced among individuals with lower PGS hgs . The within-pair models offered limited support for the independent environmental impact of LTPA. CONCLUSIONS: The PGS hgs was associated with measured HGS in the meta-analysis, highlighting the potential of PGSs to capture individual differences in strength-related traits across populations. The association of PGS hgs with HGS was moderated by LTPA, such that the beneficial impact of LTPA on HGS was greater among individuals with a lower genetic propensity for HGS.

Humans↗

Disease taxonomy--polygenic.

The practice of medicine depends on the recognition and classification of disease. Correct diagnosis is the cornerstone of correct treatment. The past century has seen the classification of disease move from a reliance on symptoms and signs to the use of more and more sophisticated measurements of human structure and function. However, although most diseases have now have names and schemes of classification, these names still may hide a fundamental lack of understanding of the causes of the disease. The extraordinary progress in molecular genetics in the last 20 years now means that a complete understanding of the constitutional predisposition to disease is possible. All disease results from the interaction between adverse environmental events and constitutional (genetic) resistance or susceptibility. Genetic resistance is modified by ageing. The study of genetics is the process of linking polymorphism in the genetic material to polymorphism or variation in the function or appearance of an organism. The extent to which this becomes clinically useful will be determined by the strength of the genetic effects influencing the disease. Oligogenic disorders, in which just a few genes are impacting on the disease, are more likely to be classifiable by genetic polymorphism than true polygenic disorders, in which a multiplicity of small effects give incremental risks of developing disease. Nevertheless, an improved understanding of the aetiology of disease will in all probability identify previously unrecognised yet distinct subsets of disease.

Alzheimer Disease↗

Methods for&#xa0;modeling gene-environment interplay using polygenic risk scores.

Polygenic risk scores (PRS) are increasingly recognized as pivotal tools for quantifying disease risk through the aggregation of multiple genetic variants. As sample sizes in genome-wide association studies (GWAS) continue to expand and PRS become more powerful, they are set to play a key role in translational research and personalized medicine. Understanding the interplay of PRS with environmental factors is critical for interpreting and applying PRS in diverse contexts. This interplay manifests in two forms: PRS-by-environment interaction (PRS&#xa0;&#xd7;&#xa0;E) and gene-environment correlation (rGE). However, despite the growing application and importance of PRS, there are limited guidelines for performing PRS&#xa0;&#xd7;&#xa0;E interaction analyses while controlling for rGE, which can lead to inconsistencies across studies and misinterpretation of results. Here we provide a review of different methods for performing PRSxE interaction in various epidemiological study designs, propose recommendations for best-practice, and discuss future challenges.

Gene-Environment Interaction↗

Polygenic mutation in Drosophila melanogaster: Mapping spontaneous mutations affecting sensory bristle number.

Our ability to predict long-term responses to artificial and natural selection, and understand the mechanisms by which naturally occurring variation for quantitative traits is maintained, depends on detailed knowledge of the properties of spontaneous polygenic mutations, including the quantitative trait loci (QTL) at which mutations occur, mutation rates, and mutational effects. These parameters can be estimated by mapping QTL that cause divergence between mutation-accumulation lines that have been established from an inbred base population and selected for high and low trait values. Here, we have utilized quantitative complementation to deficiencies to map QTL at which spontaneous mutations affecting Drosophila abdominal and sternopleural bristle number have occurred in 11 replicate lines during 206 generations of divergent selection. Estimates of the numbers of mutations were consistent with diploid per-character mutation rates for bristle traits of 0.03. The ratio of the per-character mutation rate to total mutation rate (0.023) implies that >2% of the genome could affect just one bristle trait and that there must be extensive pleiotropy for quantitative phenotypes. The estimated mutational effects were not, however, additive and exhibited dependency on genetic background consistent with diminishing epistasis. However, these inferences must be tempered by the potential for epistatic interactions between spontaneous mutations and QTL affecting bristle number on the deficiency-bearing chromosomes, which could lead to overestimates in numbers of QTL and inaccurate inference of gene action.

Animals↗

Phenotypic characterization of polygenic type 2 diabetes in TALLYHO/JngJ mice.

The TALLYHO/JngJ (TH) strain is a newly established, polygenic mouse model for type 2 diabetes (T2D) and obesity, and we have previously reported some key physiological features of this model after the overt onset of diabetes. In the present work, we conducted a comprehensive phenotypic characterization of TH in order to completely characterize this new and relevant model for human T2D and obesity. We monitored the development of obesity and diabetes starting at 4 weeks of age by measuring body weight, glucose tolerance, and plasma levels of insulin, glucose, and triglyceride. Additionally, histological alterations in the pancreas and glucose uptake and glucose transporter 4 (GLUT4) content in soleus muscle were also examined. Compared with age- and sex-matched C57BL/6J (B6) mice, both male and female TH mice were significantly heavier, hyperleptinemic, and hyperinsulinemic at 4 weeks of age, without glucose intolerance or hyperglycemia. TH mice maintained higher body weights throughout the study period of 16 weeks. The hyperinsulinemia in TH mice worsened with age, but to a lesser degree in females than in males. Both the male and the female TH mice had enlarged pancreatic islets. Male TH mice showed impaired glucose tolerance at 8 weeks that became more prominent at 16 weeks. Plasma glucose levels continuously increased with age in male TH mice resulting in frank diabetes, while female TH mice remained normoglycemic throughout the study. Impaired glucose tolerance and hyperglycemia in male TH mice were accompanied by impaired 2-deoxyglucose uptake in the soleus muscle at basal and insulin-stimulated states, but without any reduction in GLUT4 content. Interestingly, male TH mice exhibited a drastic elevation in plasma triglyceride levels in the pre-diabetic stage that was maintained throughout the study. These findings suggest that obesity and insulin resistance are an inherent part of the TH phenotype and glucose intolerance is evident preceding progression to overt diabetes in male TH mice.

Animals↗

Techniques of SNP genotyping and remote sensing applied for elucidation of the contribution of polygene and environmental factors to inter-individual variation in skin pigmentation phenotype.

We present a conceptual framework for applying techniques of SNP genotyping as a molecular biological approach and remote sensing as an ecological approach to elucidation of the contribution of polygene and environmental factors to inter-individual variation in skin pigmentation phenotype. Additionally, we discuss the obstacles that frustrate our efforts to identify how the human genome encodes the complex phenotype and suggest the use of computational methods designed for knowledge discovery within hereditary database.

Atmosphere↗

Partitioned blood pressure polygenic risk reveals differential genetic effects of tissue-specific enhancers and their interactions on cardiovascular disease.

Polygenic risk scores (PRS) compress genome-wide associations into a single predictor, but this aggregation obscures the distinct biological mechanisms through which genetic variation shapes complex traits. Here we introduce a framework that additively decomposes a trait's PRS, without loss of SNP heritability, into independent components defined by the tissue-specific and tissue-agnostic cis-regulatory elements (CREs) in which its variants act. Applied to blood pressure (BP) using ~0.5 million CREs across four BP-relevant tissues (adrenal gland, artery, heart, kidney), the framework reveals that regulatory effects are globally additive across tissues yet locally non-additive, and that the resulting partitioned scores carry pronounced, reproducible heterogeneity in their effects on BP and cardiovascular outcomes. We show this heterogeneity reflects gene-environment interactions, and trace one example to its mechanism: a kidney-CRE-partitioned score is protective against coronary artery disease and myocardial infarction through an interaction between ATP2B1 and antihypertensive medication. Explicitly modeling these interactions improves prediction and transferability, and tissue-focused partitioning increases power to resolve causal genes and reveals genes such as ADAMTS8 with antagonistic effects across BP components. Validated in an independent All of Us cohort, these findings recast the PRS from a blunt aggregate predictor into a mechanistic probe of context-dependent genetic architecture.

Journal Article↗

Rethinking target discovery in polygenic diseases.

Despite an extraordinary investment in R&D the yield of successful new drugs has been disproportionately low in recent years, suggesting that the whole process of drug development requires rethinking and reform. Most analyses on this issue focus on molecular target discovery considerations. Target identification is characterized by a surplus of potential targets, but there is a translational bottleneck primarily due to limitations of currently employed target validation platforms. Meanwhile, the clinical entities, to which treatments are directed, are also highly complex in terms of pathophysiologic mechanisms and manifestations. In the present study we discuss the limitations of current molecular target discovery approaches mainly in regard to selectivity and efficacy. We also describe the constraints imposed on drug development by the current diagnostic constructs and the tendency towards dissecting the complex clinical phenotypes to component intermediate phenotypes. Finally, we describe how the reconsideration of molecular and clinical targets in polygenic diseases may lead to new strategies of pharmacological intervention directed against component dysfunctions, rather than the whole complex phenotype. Such strategies involve the combination of single ligands that act selectively on multiple molecules involved in a particular disease, or the employment of "multi-targeted" drugs, i.e. single drug molecules that hit selectively multiple receptors sharing common binding sites.

Animals↗

A polygenic model of the metabolic syndrome with reduced circulating and intra-adipose glucocorticoid action.

Despite major advances in understanding monogenic causes of morbid obesity, the complex genetic and environmental etiology of idiopathic metabolic syndrome remains poorly understood. One hypothesis suggests that similarities between the metabolic disease of plasma glucocorticoid excess (Cushing's syndrome) and idiopathic metabolic syndrome results from increased glucocorticoid reamplification within adipose tissue by 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD-1). Indeed, 11beta-HSD-1 is now a major therapeutic target. Because much supporting evidence for a role of adipose 11beta-HSD-1 comes from transgenic or obese rodents with single-gene mutations, we investigated whether the predicted traits of metabolic syndrome and glucocorticoid metabolism were coassociated in a unique polygenic model of obesity developed by long-term selection for divergent fat mass (Fat and Lean mice with 23 vs. 4% fat as body weight, respectively). Fat mice exhibited an insulin-resistant metabolic syndrome including fatty liver and hypertension. Unexpectedly, Fat mice had a marked intra-adipose (11beta-HSD-1) and plasma glucocorticoid deficiency but higher liver glucocorticoid action. Furthermore, metabolic disease was exacerbated only in Fat mice when challenged with exogenous glucocorticoids or a high-fat diet. Our data suggest that idiopathic metabolic syndrome might associate with such a novel pattern of glucocorticoid action and sensitivity in humans, with implications for tissue-specific therapeutic targeting of 11beta-HSD-1.

Adipose Tissue↗

Effects of feeding pattern and dietary regimen on growth and adipose tissue cellularity in polygenic obese mice.

The effect of varying feed intake and feeding pattern during the early postweaning period on growth, body composition and adipose tissue cellularity was studied in polygenic obese and control normal mice. Male mice were assigned to the following dietary treatments at 4.5 wk of age: stock diet fed ad libitum(AL), four palatable foods cafeteria-fed(CF), stock diet fed every 2 h by automatic feeders adjusted for maximum intake(MI), fed same procedure as MI but restricted to produce 70% of the gain of mice fed ad libitum(RE), and stock diet fed one meal/d the same amount fed RE mice(PM). Mice were killed after 5 wk on treatment. Cafeteria-fed control mice were heavier (P less than .05) than RE control mice, but they were not different (P greater than .05) from AL, MI and PM control mice, while CF obese mice were heavier and RE obese mice were smaller than AL, MI and PM obese mice (P less than .05). Cafeteria-fed mice were fatter than mice from all other treatments in both the obese and control lines. Maximum intake, PM and RE mice were fatter than AL mice but this effect was only significant in the obese line. Alterations in feeding pattern can affect body composition even though body weight may not show a correlated response. Cafeteria-fed obese mice had larger fat pads and more small (less than 40 micron) and large (greater than 110 micron) adipocytes than other obese mice. Results indicate that the difference in the development of obesity on cafeteria diet was due primarily to genetic effects while the increase in percentage fat after restriction on MI, PM and RE treatments was due mainly to the acute change of feeding pattern.

Adipose Tissue↗

Evaluation of population-specific polygenic risk scores for blood lipids: insights from Taiwanese cohorts and multiancestry meta-analysis.

BACKGROUND: Blood lipids are heritable risk factors for cardiovascular disease (CVD), a leading cause of mortality worldwide. However, the genetic architecture of lipid traits and the performance of polygenic risk scores (PRSs) remain underexplored in East Asian (EAS) populations, including Taiwanese Han individuals. METHODS: We conducted genome-wide association studies and PRS analyses for five lipid traits: total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, triglycerides, and the ratio of low-density lipoprotein cholesterol to total cholesterol. Lipid profile data were obtained from the China Medical University Hospital cohort. PRSs were evaluated on the basis of their correlations with measured lipid levels. To evaluate trans-ancestry PRS transferability, localized models were systematically compared against models derived from discovery-stage GWAS meta-analyses incorporating five ancestry groups from the Global Lipids Genetics Consortium. The performance of the PRS models in predicting lipid-related diseases was evaluated through receiver operating characteristic curve analyses. RESULTS: The population-specific PRS models explained 11%-40% of the variance in lipid levels within the target cohort. Models leveraging global multiancestry GWAS meta-analysis weights revealed limited predictive performance (r 2 = 0.04-0.19), whereas analyses incorporating EAS-specific data yielded higher correlations (r 2 = 0.13-0.30), although these correlations did not exceed those derived from the hospital-based cohort alone. When combined with age and sex, the PRS models demonstrated strong predictive performance for coronary artery disease, atherosclerosis, and ischemic stroke, with area under the curve values of 0.910, 0.926, and 0.854, respectively. CONCLUSION: Population-specific PRS models derived from a Taiwanese population outperformed meta-analysis-derived frameworks in predicting lipid levels and demonstrated substantial potential for predicting CVD risk, indicating the importance of ancestry-matched genetic studies in precision medicine.

LDL-C/TC ratio↗

Characterizing the Uncertainty, Misclassification and Inconsistency of Polygenic Prediction.

Polygenic risk scores (PRSs) hold promise for precision medicine, yet their clinical translation is hindered by substantial uncertainty in individual risk estimates and often limited agreement in risk stratification across multiple PRSs for the same disease. We develop a unified inferential framework to calibrate PRS point estimates and uncertainties for both quantitative traits and binary phenotypes, and to characterize how PRS accuracy, uncertainty, pairwise correlation jointly determine misclassification and classification inconsistency. We show, both theoretically and empirically, that individual- and population-level misclassification and inconsistency rates are highly predictable in independent datasets. We further evaluate PRS integration and uncertainty-aware probabilistic thresholding strategies that reduce misclassification and improve concordance in risk stratification. Together, these results demonstrate that instability in PRS-based classification is a predictable statistical consequence of uncertainty and establish a principled foundation for incorporating uncertainty into PRS-based risk interpretation, communication, and clinical decision-making.

Journal Article↗