Thyroid function, pernicious anemia and erythropoiesis: a two-sample Mendelian randomization study.

Autoimmune thyroid disease (AITD) and pernicious anemia (PA) often coexist, but the directionality is unknown. In a two-sample Mendelian randomization (MR) analysis, using summary statistics from large genome-wide association studies (GWASs) in Europeans (N = 49 269-755 406), we examined the genetic associations between thyroid function, PA and markers of erythropoiesis. We performed inverse variance weighted random-effects MR, several sensitivity MR analyses, and bidirectional MR and MR Steiger for directionality. AITD and PA were associated bidirectionally (P ≤ 8 × 10-6). Neither euthyroid thyroid stimulating hormone (TSH) nor free thyroxine (FT4) were causally associated with PA. One standard deviation (SD) increase in euthyroid FT4 regulated by genetic variants in deiodinases 1 and 2 genes (DIO1/DIO2), corresponding to low-normal free triiodothyronine (FT3) levels, was causally associated with a pernicious/macrocytic anemia pattern, i.e. decreased erythrocyte counts (rank-based inverse normal transformed ß = -0,064 [95% confidence interval: -0,085, -0,044], P = 8 × 10-10) and hemoglobin (-0.028 [-0.051, -0.005], P = 0.02) and increased mean corpuscular hemoglobin (0.058 [0.025, 0.091], P = 5 × 10-4) and mean corpuscular volume levels (0.075 [0.052, 0.098], P = 1 × 10-8). Meanwhile, subclinical hyperthyroidism mirrored that pattern. AITD was causally associated with increased erythrocyte distribution width (P = 0.007) and decreased reticulocyte counts (P ≤ 0.02), whereas high-normal FT4 regulated by DIO1/DIO2 variants was causally associated with decreased bilirubin (-0.039 (-0.064, -0.013), P = 0.003). In conclusion, the bidirectional association between AITD and PA suggests a shared heritability for these two autoimmune diseases. AITD was causally associated with impaired erythropoiesis and not autoimmune hemolysis. Additionally, in euthyroid individuals, local regulation of thyroid hormones by deiodinases likely plays a role in erythropoiesis.

Allometric body shape indices, type 2 diabetes and kidney function: A two-sample Mendelian randomization study.

AIM: To examine the association between body mass index (BMI)-independent allometric body shape indices and kidney function. MATERIALS AND METHODS: We performed a two-sample Mendelian randomization (MR) analysis, using summary statistics from UK Biobank, CKDGen and DIAGRAM. BMI-independent allometric body shape indices were: A Body Shape Index (ABSI), Waist-Hip Index (WHI) and Hip Index (HI). Kidney function outcomes were: urinary albumin-to-creatinine ratio (UACR), estimated glomerular filtration rate and blood urea nitrogen. Furthermore, we investigated type 2 diabetes (T2D) as a potential mediator on the pathway to albuminuria. The main analysis was inverse variance-weighted random-effects MR in participants of European ancestry. We also performed several sensitivity MR analyses. RESULTS: A 1-standard deviation (SD) increase in genetically predicted ABSI and WHI levels was associated with higher UACR (ß = 0.039 [95% confidence interval: 0.016, 0.063] log [UACR], P = 0.001 for ABSI, and ß = 0.028 [0.012, 0.044] log [UACR], P = 6 x 10-4 for WHI) in women, but not in men. Meanwhile, a 1-SD increase in genetically predicted HI was associated with lower UACR in women (ß = -0.021 [-0.041, 0.000] log [UACR], P = 0.05) and in men (ß = -0.026 [-0.058, 0.005] log [UACR], P = 0.10). Corresponding estimates in individuals with diabetes were substantially augmented. Risk of T2D increased for genetically high ABSI and WHI in women (P < 6 x 10-19 ) only, but decreased for genetically high HI in both sexes (P < 9 x 10-3 ). No other associations were observed. CONCLUSIONS: Genetically high HI was associated with decreased risk of albuminuria, mediated through decreased T2D risk in both sexes. Opposite associations applied to genetically high ABSI and WHI in women only.

Obesity and Kidney Function: A Two-Sample Mendelian Randomization Study.

BACKGROUND: Obesity and type 2 diabetes (T2D) are correlated risk factors for chronic kidney disease (CKD). METHODS: Using summary data from GIANT (Genetic Investigation of Anthropometric Traits), DIAGRAM (DIAbetes Genetics Replication And Meta-analysis), and CKDGen (CKD Genetics), we examined causality and directionality of the association between obesity and kidney function. Bidirectional 2-sample Mendelian randomization (MR) estimated the total causal effects of body mass index (BMI) and waist-to-hip ratio (WHR) on kidney function, and vice versa. Effects of adverse obesity and T2D were examined by stratifying BMI variants by their association with WHR and T2D. Multivariable MR estimated the direct causal effects of BMI and WHR on kidney function. The inverse variance weighted random-effects MR for Europeans was the main analysis, accompanied by several sensitivity MR analyses. RESULTS: One standard deviation (SD ≈ 4.8 kg/m2) genetically higher BMI was associated with decreased estimated glomerular filtration rate (eGFR) [ß=-0.032 (95% confidence intervals: -0.036, -0.027) log[eGFR], P = 1 × 10-43], increased blood urea nitrogen (BUN) [ß = 0.010 (0.005, 0.015) log[BUN], P = 3 × 10-6], increased urinary albumin-to-creatinine ratio [ß = 0.199 (0.067, 0.332) log[urinary albumin-to-creatinine ratio (UACR)], P = 0.003] in individuals with diabetes, and increased risk of microalbuminuria [odds ratios (OR) = 1.15 [1.04-1.28], P = 0.009] and CKD [1.13 (1.07-1.19), P = 3 × 10-6]. Corresponding estimates for WHR and for trans-ethnic populations were overall similar. The associations were driven by adverse obesity, and for microalbuminuria additionally by T2D. While genetically high BMI, unlike WHR, was directly associated with eGFR, BUN, and CKD, the pathway to albuminuria was likely through T2D. Genetically predicted kidney function was not associated with BMI or WHR. CONCLUSIONS: Genetically high BMI is associated with impaired kidney function, driven by adverse obesity, and for albuminuria additionally by T2D.

Kidney function and risk of dementia: Observational study, meta-analysis, and two-sample mendelian randomization study.

Whether impaired kidney function is associated with increased risk of developing dementia is unclear. We investigated the association between estimated glomerular filtration rate (eGFR) and dementia. Using a triangulation approach, we performed (1) a prospective study in 90,369 Danes from the Copenhagen General Population Study (CGPS), (2) a meta-analysis in 468,699 Scandinavians (including CGPS) and (3) a two-sample Mendelian randomization study in 218,792-1,004,040 Europeans using summary data from largest publicly available genome wide association studies (GWASs). During up to 15 years of follow-up (CGPS), 2,468 individuals developed dementia. Age and sex standardized percentile of eGFR below versus above the median conferred a multifactorially adjusted hazard ratio of 1.09 (95% confidence interval: 1.01-1.18). In meta-analysis, random-effects risk of dementia was 1.14 (1.06-1.22) for mildly decreased eGFR (60-90 mL/min/1.73 m2), 1.31 (0.92-1.87) for moderately decreased eGFR (30-59 mL/min/1.73 m2) and 1.91 (1.21-3.01) for severely decreased eGFR (< 30 mL/min/1.73 m2), compared to reference eGFR (> 90 mL/min/1.73 m2). Using directly comparable eGFR measures (log[eGFR] scaled to one standard deviation, as well as eGFR below versus above 60 mL/min/1.73 m2), we found no association with risk of dementia in observational CGPS or in Mendelian randomization analyses. In conclusion, impaired kidney function was associated with modestly increased risk of developing dementia. This was not supported by causal, genetic analyses using a Mendelian randomization approach. However, future stronger genetic instruments for kidney function and larger GWASs with more dementia cases, particularly for the vascular dementia subtype, warrant a re-evaluation of the causal hypothesis.

Thyroid function, sex hormones and sexual function: a Mendelian randomization study.

Hypothyroidism and hyperthyroidism are observationally associated with sex hormone concentrations and sexual dysfunction, but causality is unclear. We investigated whether TSH, fT4, hypo- and hyperthyroidism are causally associated with sex hormones and sexual function. We used publicly available summary statistics from genome-wide association studies on TSH and fT4 and hypo- and hyperthyroidism from the ThyroidOmics Consortium (N ≤ 54,288). Outcomes from UK Biobank (women ≤ 194,174/men ≤ 167,020) and ReproGen (women ≤ 252,514) were sex hormones (sex hormone binding globulin [SHBG], testosterone, estradiol, free androgen index [FAI]) and sexual function (ovulatory function in women: duration of menstrual period, age at menarche and menopause, reproductive lifespan, and erectile dysfunction in men). We performed two-sample Mendelian randomization (MR) analyses on summary level, and unweighted genetic risk score (GRS) analysis on individual level data. One SD increase in TSH was associated with a 1.332 nmol/L lower (95% CI: - 0.717,- 1.946; p = 2 × 10-5) SHBG and a 0.103 nmol/l lower (- 0.051,V0.154; p = 9 × 10-5) testosterone in two-sample MR, supported by the GRS approach. Genetic predisposition to hypothyroidism was associated with decreased and genetic predisposition to hyperthyroidism with increased SHBG and testosterone in both approaches. The GRS for fT4 was associated with increased testosterone and estradiol in women only. The GRS for TSH and hypothyroidism were associated with increased and the GRS for hyperthyroidism with decreased FAI in men only. While genetically predicted thyroid function was associated with sex hormones, we found no association with sexual function.

Smoking, blood cells and myeloproliferative neoplasms: meta-analysis and Mendelian randomization of 2·3 million people.

Meta-analyses and Mendelian randomization (MR) may clarify the associations of smoking, blood cells and myeloproliferative neoplasms (MPN). We investigated the association of smoking with blood cells in the Danish General Suburban Population Study (GESUS, n = 11 083), by meta-analyses (including GESUS) of 92 studies (n = 531 741) and MR of smoking variant CHRNA3 (rs1051730[A]) in UK Biobank, and with MPN in a meta-analysis of six studies (n (total/cases):1 425 529/2187), totalling 2 307 745 participants. In the meta-analysis the random-effects standardized mean difference (SMD) in current smokers versus non-smokers was 0·82 (0·75-0·89, P = 2·0 * 10-108 ) for leukocytes, 0·09 (-0·02 to 0·21, P = 0·12) for erythrocytes, 0·53 (0·42-0·64, P = 8·0 * 10-22 ) for haematocrit, 0·42 (0·34-0·51, P = 7·1 * 10-21 ) for haemoglobin, 0·19 (0·08-0·31, P = 1·2 * 10-3 ) for mean corpuscular haemoglobin (MCH), 0·29 (0·19-0·39, P = 1·6 * 10-8 ) for mean corpuscular volume (MCV), and 0·04 (-0·04 to 0·13, P = 0·34) for platelets with trends for ever/ex-/current smokers, light/heavy smokers and female/male smokers. Analyses presented high heterogeneity but low publication bias. Per allele in CHRNA3, cigarettes per day in current smokers was associated with increased blood cell counts (leukocytes, neutrophils), MCH, red cell distribution width (RDW) and MCV. The pooled fixed-effects odds ratio for MPN was 1·44 [95% confidence interval (CI): 1·33-1·56; P = 1·8 * 10-19 ; I2  = 0%] in current smokers, 1·29 (1·15-1·44; P = 8·0 * 10-6 ; I2  = 0%) in ex-smokers, 1·49 (1·26-1·77; P = 4·4 * 10-6 ; I2  = 0%) in light smokers and 2·04 (1·74-2·39, P = 2·3 * 10-18 ; I2  = 51%) in heavy smokers compared with non-smokers. Smoking is observationally and genetically associated with increased leukocyte counts and red blood cell indices (MCH, MCV, RDW) and observationally with risk of MPN in current and ex-smokers versus non/never-smokers.

Observationally and Genetically High YKL-40 and Risk of Venous Thromboembolism in the General Population: Cohort and Mendelian Randomization Studies.

OBJECTIVE: High baseline YKL-40 is associated with later development of ischemic stroke, but not with myocardial infarction. Whether high YKL-40 levels are associated with increased risk of venous thromboembolism is presently unknown. We tested the hypothesis that observationally and genetically high YKL-40 is associated with increased risk of venous thromboembolism in the general population. APPROACH AND RESULTS: Cohort and Mendelian randomization studies in 96 110 individuals from the Danish general population, with measured plasma levels of YKL-40 (N=21 647) and CHI3L1 rs4950928 genotype (N=94 579). From 1977 to 2013, 1489 individuals developed pulmonary embolism, 2647 developed deep vein thrombosis, and 3750 developed venous thromboembolism (pulmonary embolism and deep vein thrombosis). For the 91% to 100% versus 0% to 33% YKL-40 percentile category, the multifactorially adjusted hazard ratio was 2.38 (95% confidence interval, 1.25-4.55) for pulmonary embolism, 1.98 (1.09-3.59) for deep vein thrombosis, and 2.13 (1.35-3.35) for venous thromboembolism. Compared with rs4950928 GG homozygosity, presence of C-allele was associated with a doubling (CG) or tripling (CC) in YKL-40 levels, but not with risk of venous thromboembolism. A doubling in YKL-40 was associated with a multifactorially adjusted observational hazard ratio for pulmonary embolism of 1.17 (1.00-1.38) and a genetic odds ratio of 0.97 (0.76-1.23). Corresponding risk estimates were 1.28 (1.12-1.47) observationally and 1.11 (0.91-1.35) genetically for deep vein thrombosis and 1.23 (1.10-1.38) observationally and 1.08 (0.92-1.27) genetically for venous thromboembolism. CONCLUSIONS: High YKL-40 levels were associated with a 2-fold increased risk of venous thromboembolism, but the association was not causal.

Elevated plasma YKL-40, lipids and lipoproteins, and ischemic vascular disease in the general population.

BACKGROUND AND PURPOSE: We tested the hypothesis that observationally and genetically elevated YKL-40 is associated with elevated lipids and lipoproteins and with increased risk of ischemic vascular disease. METHODS: We conducted cohort and Mendelian randomization studies in 96 110 individuals from the Danish general population, with measured plasma levels of YKL-40 (n=21 647), plasma lipids and lipoproteins (n=94 461), and CHI3L1 rs4950928 genotype (n=94 579). RESULTS: From 1977 to 2013, 3256 individuals developed ischemic stroke, 5629 ischemic cerebrovascular disease, 4183 myocardial infarction, and 10 271 developed ischemic heart disease. The 91% to 100% versus 0% to 33% YKL-40 percentile category was associated with a 34% increase in triglycerides, but only with minor changes in other lipids and lipoproteins. For these categories, the multifactorially adjusted hazard ratio was 1.99 (95% confidence interval, 1.49-2.67) for ischemic stroke, 1.85 (1.44-2.37) for ischemic cerebrovascular disease, 1.28 (0.95-1.73) for myocardial infarction, and 1.23 (1.01-1.51) for ischemic heart disease. When compared with rs4950928 CC homozygosity, the presence of G-allele was associated with a doubling (GC) or tripling (GG) in YKL-40 levels, but not with triglyceride levels or with risk of ischemic vascular disease. A doubling in YKL-40 was associated with a multifactorially adjusted observational hazard ratio for ischemic stroke of 1.18 (1.11-1.27), and a genetic odds ratio of 1.04 (0.95-1.15). Corresponding risk estimates were 1.15 (1.09-1.22) observationally and 1.06 (0.99-1.14) genetically for ischemic cerebrovascular disease, 1.08 (1.00-1.15) observationally and 1.04 (0.96-1.13) genetically for myocardial infarction, and 1.07 (1.02-1.12) observationally and 1.01 (0.96-1.07) genetically for ischemic heart disease. CONCLUSIONS: Elevated YKL-40 was associated with a 34% increase in triglyceride levels and with a 2-fold increased risk of ischemic stroke, whereas genetically elevated YKL-40 were not.

Observational and genetic plasma YKL-40 and cancer in 96,099 individuals from the general population.

Plasma YKL-40 is high in patients with cancer and in individuals who later develop cancer. Whether YKL-40 is only a marker or indeed a cause of cancer is presently unknown. We tested the hypothesis that observationally and genetically, high plasma YKL-40 is associated with high risk of cancer. For this purpose, we performed cohort and Mendelian randomization studies in 96,099 individuals from the Danish general population. Plasma levels of YKL-40 were measured in 21,643 and CHI3L1 rs4950928 was genotyped in 94,568 individuals. From 1943 through 2011, 2,291 individuals developed gastrointestinal cancer, 913 developed lung cancer, 2,863 women developed breast cancer, 1,557 men developed prostate cancer and 5,146 individuals developed other cancer. Follow-up was 100% complete. Multifactorially and CRP adjusted hazard ratio (HR) for gastrointestinal cancer was 1.82 (95%CI, 1.16-2.86) for 96-100% versus 0-33% YKL-40 percentile category. Corresponding HR were 1.71 (0.95-3.07) for lung cancer, but insignificant for breast cancer, prostate cancer and other cancers. CHI3L1 rs4950928 genotype was associated with plasmaYKL-40 levels, but not with risk of any cancer category. For gastrointestinal cancer, a doubling in YKL-40 was associated with a multifactorially and CRP adjusted observational HR of 1.14(1.05-1.23) for gastrointestinal cancer, but a corresponding genetic odds ratio of 1.06(0.94-1.18). For lung cancer, corresponding risk estimates were 1.11(1.00-1.22) observationally and 1.01(0.84-1.20) genetically. For other cancer categories, observational and genetic findings were insignificant. This study shows that high plasma YKL-40 levels were associated with high risk of gastrointestinal and likely of lung cancer, but genetic high levels were not.

YKL-40 and alcoholic liver and pancreas damage and disease in 86,258 individuals from the general population: cohort and mendelian randomization studies.

BACKGROUND: We tested the hypothesis that observationally and genetically increased YKL-40 concentrations are associated with alcoholic liver and pancreas damage and disease. METHODS: We performed cohort and mendelian randomization in 86,258 individuals from the Danish general population, with measured concentrations of plasma YKL-40 (n = 21 646) and CHI3L1 rs4950928 genotype (n = 84 738). RESULTS: Increased YKL-40 was associated with increased alanine aminotransferase, bilirubin, alkaline phosphatase, γ-glutamyl transferase, erythrocyte mean corpuscular volume, C-reactive protein, and fibrinogen and with decreased albumin; coagulation factors II, VII, and X; and pancreatic amylase. The multifactorially adjusted hazard ratio for alcoholic liver cirrhosis comparing the 96%-100% vs 0%-33% YKL-40 percentile categories was 41 (95% CI 14-118). Corresponding ratios were 7.9 (5.1-12) for any alcoholic liver disease, 4.1 (1.7-10) for alcoholic pancreatitis, and 3.4 (1.9-6.1) for any pancreatitis. CHI3L1 rs4950928 genotype explained 14% of the variation in plasma YKL-40 concentrations but was not associated with alcoholic liver and pancreas damage or disease. A doubling in YKL-40 concentrations was associated with a multifactorially adjusted observational hazard ratio of 2.8 (2.4-3.3) for alcoholic liver cirrhosis and a corresponding genetic odds ratio of 1.1 (0.7-1.5). Corresponding risk estimates were 2.0 (1.8-2.2) observationally and 1.0 (0.8-1.1) genetically for any alcoholic liver disease, 1.4 (1.1-1.9) observationally and 1.1 (0.8-1.5) genetically for alcoholic pancreatitis, and 1.3 (1.1-1.6) observationally and 1.0 (0.8-1.3) genetically for any pancreatitis. Excessive alcohol consumption combined with YKL-40 concentrations in the top 5% was associated with 10-year risk of alcoholic liver cirrhosis of up to 7% in ever-smokers and 2% in never-smokers. CONCLUSIONS: YKL-40 concentration within the top 5% was a marker for alcoholic liver cirrhosis, with no evidence to support a causal relationship.

Genetic variants in CHI3L1 influencing YKL-40 levels: resequencing 900 individuals and genotyping 9000 individuals from the general population.

BACKGROUND: Despite its important role in many serious diseases, the genetic background for plasma YKL-40 has still not been systematically catalogued. Therefore, we aimed at identifying genetic variants in CHI3L1 influencing plasma YKL-40 levels in the general population. METHODS: We resequenced the promoter, all 10 exons and exon-flanking intron segments of CHI3L1 in 904 individuals from the Danish general population (n=8899) with extreme plasma YKL-40 levels, adjusted for age. To potentially identify clinically important genetic variants with elevated plasma YKL-40 levels, we included twice as many individuals with the highest plasma YKL-40 levels (n=603) compared with the lowest plasma YKL-40 levels (n=301). Next, we mapped linkage disequilibrium for all variants with a minor allele frequency (MAF)>0.005. Finally, all participants were genotyped for eight variants that had divergent MAFs in the two extreme plasma YKL-40 groups. RESULTS: We identified 59 genetic variants in CHI3L1. Fifteen of the genetic variants were associated with plasma YKL-40 levels. Three promoter SNPs, 1 non-synonymous SNP, and four intronic SNPs in CHI3L1 were associated with plasma YKL-40 levels at or below genome-wide association significance levels (unadjusted p for trend: from 4 × 10(-8) to 6 × 10(-243); age adjusted percentiles p for trend: from 3 × 10(-12) to 2 × 10(-304)). CONCLUSIONS: In a systematic search to identify genetic variants influencing plasma YKL-40 levels, we identified eight SNPs associated with plasma YKL-40 levels in the general population.

Cardiorespiratory fitness, body composition, diabetes, and longevity: a two-sample Mendelian randomization study.

CONTEXT: Cardiorespiratory fitness, commonly assessed as maximal volume of oxygen consumption (VO2max), has emerged as an important predictor of morbidity and mortality. OBJECTIVE: We investigated the causality and directionality of the associations of VO2max with body composition, physical activity, diabetes, performance enhancers, and longevity. METHODS: Using publicly available summary statistics from the largest genome-wide association studies publicly available, we conducted a bidirectional two-sample Mendelian randomization (MR) study. Bidirectional MR tested directionality, and estimated the total causal effects, whereas multivariable MR (MVMR) estimated independent causal effects. Cardiorespiratory fitness (VO2max) was estimated from a submaximal cycle ramp test (N≈90,000) and scaled to total body weight, and in additional analyses to fat-free mass (mL/min/kg). RESULTS: Genetically predicted higher (per one standard deviation increase) body fat percentage was associated with lower VO2max (ß=-0.36 [95% CI: -0.40, -0.32], p=6E-77). Meanwhile, genetically predicted higher appendicular lean mass (0.10 [0.08,0.13] p=3E-16), physical activity (0.29 [0.07,0.52]), and performance enhancers (fasting insulin, hematocrit, and free testosterone in men) were all positively associated with VO2max (p<0.01). Genetic predisposition to diabetes had no effect on VO2max. MVMR showed independent causal effects of body fat percentage, appendicular lean mass, physical activity, and hematocrit on VO2max, as well as of body fat percentage and type 2 diabetes (T2D) on longevity. Genetically predicted VO2max showed no associations. CONCLUSION: Cardiorespiratory fitness can be improved by favorable body composition, physical activity, and performance enhancers. Despite being a strong predictor of mortality, VO2max is not causally associated with T2D or longevity.

The role of thyroid function in borderline personality disorder and schizophrenia: a Mendelian Randomisation study.

BACKGROUND: Genome-wide association studies have reported a genetic overlap between borderline personality disorder (BPD) and schizophrenia (SCZ). Epidemiologically, the direction and causality of the association between thyroid function and risk of BPD and SCZ are unclear. We aim to test whether genetically predicted variations in TSH and FT4 levels or hypothyroidism are associated with the risk of BPD and SCZ. METHODS: We employed Mendelian Randomisation (MR) analyses using genetic instruments associated with TSH and FT4 levels as well as hypothyroidism to examine the effects of genetically predicted thyroid function on BPD and SCZ risk. Bidirectional MR analyses were employed to investigate a potential reverse causal association. RESULTS: Genetically predicted higher FT4 was not associated with the risk of BPD (OR: 1.18; P = 0.60, IVW) or the risk of SCZ (OR: 0.93; P = 0.19, IVW). Genetically predicted higher TSH was not associated with the risk of BPD (OR: 1.11; P = 0.51, IVW) or SCZ (OR: 0.98, P = 0.55, IVW). Genetically predicted hypothyroidism was not associated with BPD or SCZ. We found no evidence for a reverse causal effect between BPD or SCZ on thyroid function. CONCLUSIONS: We report evidence for a null association between genetically predicted FT4, TSH or hypothyroidism with BPD or SCZ risk. There was no evidence for reverse causality.

A Review of Major Danish Biobanks: Advantages and Possibilities of Health Research in Denmark.

Biobank research may lead to an improved understanding of disease etiology and advance personalized medicine. Denmark (population ~5.9 million) provides a unique setting for population-based health research. The country is a rich source of biobanks and the universal, tax-funded healthcare system delivers routinely collected data to numerous registries and databases. By virtue of the civil registration number (assigned uniquely to all Danish citizens), biological specimens stored in biobanks can be combined with clinical and demographic data from these population-based health registries and databases. In this review, we aim to provide an understanding of advantages and possibilities of biobank research in Denmark. As knowledge about the Danish setting is needed to grasp the full potential, we first introduce the Danish healthcare system, the Civil Registration System, the population-based registries, and the interface with biobanks. We then describe the biobank infrastructures, comprising the Danish National Biobank Initiative, the Bio- and Genome Bank Denmark, and the Danish National Genome Center. Further, we briefly provide an overview of fourteen selected biobanks, including: The Danish Newborn Screening Biobank; The Danish National Birth Cohort; The Danish Twin Registry Biobank; Diet, Cancer and Health; Diet, Cancer and Health - Next generations; Danish Centre for Strategic Research in Type 2 Diabetes; Vejle Diabetes Biobank; The Copenhagen Hospital Biobank; The Copenhagen City Heart Study; The Copenhagen General Population Study; The Danish Cancer Biobank; The Danish Rheumatological Biobank; The Danish Blood Donor Study; and The Danish Pathology Databank. Last, we inform on practical aspects, such as data access, and discuss future implications.

Homocysteine and female fertility, pregnancy loss and offspring birthweight: a two-sample Mendelian randomization study.

BACKGROUND/OBJECTIVES: Observational studies link elevated homocysteine concentrations (Hcy) with female fertility, pregnancy loss, and low offspring birthweight. Maternal rs1801133, a functional variant in MTHFR strongly associated with lifelong elevated Hcy, is associated with recurrent pregnancy loss and offspring birthweight in Asian women. We investigated if genetically elevated Hcy is associated with fertility, pregnancy loss, and offspring birthweight in European women. SUBJECTS/METHODS: We performed a two-sample Mendelian randomization (MR) study using publicly available data. We obtained 18 genetic variants (five involved in Hcy metabolism) explaining up to 5.9% of the variance in Hcy from a genome-wide association meta-analysis of 44,147 European individuals (82% women). We investigated fertility (including age at menopause), pregnancy loss, and offspring birthweight in the UK Biobank (N = 194,174), EGG (N = 190,406), and ReproGen (N = 69,360-252,514) consortia using summary statistics. We calculated inverse-variance weighted, and several sensitivity MR regression statistics. RESULTS: rs1801133 was associated with a 7.45 months (95% CI: 4.09, 10.80) increase in age at menopause and 29.69 (12.87, 46.51) g decrease in offspring birthweight per SD increase in Hcy in the UK biobank, and confirmed in EGG and ReproGen. MR for Hcy metabolism alone (five variants in MTHFR, MTR, CBS) showed similar results for offspring birthweight across consortia. However, using all 18 variants resulted in no association for any of the outcomes across consortia. CONCLUSION: Hcy and suggestively vitamin B variants are most likely the drug targets for folate supplementation in pregnant women on the offspring birthweight, while Hcy variants related to renal function or diabetes are not involved.

Elevated plasma YKL-40 levels and ischemic stroke in the general population.

OBJECTIVE: We hypothesized that elevated plasma YKL-40 levels are associated with increased risk of ischemic cardiovascular disease in the general population. In contrast to C-reactive protein (CRP) produced in the liver in response to inflammation, YKL-40 is produced by lipid-laden macrophages inside the vessel wall. METHODS: We measured plasma YKL-40 in 8,899 21- to 93-year-old participants of the Copenhagen City Heart Study 1991-1994 examination, and followed them for up to 18 years. Endpoints were ischemic stroke, ischemic cerebrovascular disease, myocardial infarction, and ischemic heart disease. Hazard ratios were calculated for plasma YKL-40 levels in 10-year age percentile categories of 34 to 66%, 67 to 90%, and 91 to 100% versus 0 to 33%. RESULTS: Multifactorially and CRP-adjusted hazard ratios for ischemic stroke were 1.2 (95% confidence interval, 0.9-1.6) for 33 to 66%, 1.8 (1.3-2.4) for 67 to 90%, and 2.3 (1.5-3.3) for 91 to 100% versus the 0 to 33% percentile category (p-trend < 0.001). Corresponding hazard ratios for ischemic cerebrovascular disease were 1.2 (0.9-1.5), 1.6 (1.2-2.0), and 2.2 (1.6-3.2) (p-trend < 0.001). Hazard ratios for myocardial infarction were not significant, whereas corresponding hazard ratios for ischemic heart disease were 1.0 (0.8-1.2), 1.2 (1.0-1.5), and 1.3 (1.0-1.6) (p-trend = 0.01). Stratifying for CRP or other risk factors gave similar results. A doubling in plasma YKL-40 was associated with multifactorially and CRP-adjusted increased risk of 20% (95% confidence interval, 11%-30%) for ischemic stroke, 16% (8%-24%) for ischemic cerebrovascular disease, 3% (-5%-11%) for myocardial infarction, and 7% (1%-12%) for ischemic heart disease. INTERPRETATION: In the general population, elevated plasma YKL-40 levels are associated with increased risk of ischemic stroke and ischemic cerebrovascular disease, independent of plasma CRP levels.

Kidney disease and risk of dementia: a Danish nationwide cohort study.

OBJECTIVES: It is unclear whether kidney disease is a risk factor for developing dementia. We examined the association between kidney disease and risk of future dementia. DESIGN AND SETTING: Nationwide historical registry-based cohort study in Denmark based on data from 1 January 1995 until 31 December 2016. PARTICIPANTS: All patients diagnosed with kidney disease and matched general population cohort without kidney disease (matched 1:5 on age, sex and year of kidney disease diagnosis). PRIMARY AND SECONDARY OUTCOME MEASURES: All-cause dementia and its subtypes: Alzheimer's disease, vascular dementia and other specified or unspecified dementia. We computed 5-year cumulative incidences (risk) and hazard ratios (HRs) for outcomes using Cox regression analyses. RESULTS: The study cohort comprised 82 690 patients with kidney disease and 413 405 individuals from the general population. Five-year and ten-year mortality rates were twice as high in patients with kidney disease compared with the general population. The 5-year risk for all-cause dementia was 2.90% (95% confidence interval: 2.78% to 3.08%) in patients with kidney disease and 2.98% (2.92% to 3.04%) in the general population. Compared with the general population, the adjusted HRs for all-cause dementia in patients with kidney disease were 1.06 (1.00 to 1.12) for the 5-year follow-up and 1.08 (1.03 to 1.12) for the entire study period. Risk estimates for dementia subtypes differed substantially and were lower for Alzheimer's disease and higher for vascular dementia. CONCLUSIONS: Patients diagnosed with kidney disease have a modestly increased rate of dementia, mainly driven by vascular dementia. Moreover, patients with kidney disease may be underdiagnosed with dementia due to high mortality and other comorbidities of higher priority.

Genetic Variants in the Protein S ( PROS1 ) Gene and Protein S Deficiency in a Danish Population.

Protein S (PS) deficiency is a risk factor for venous thromboembolism (VTE) and can be caused by variants of the gene encoding PS ( PROS1 ). This study aimed to evaluate the clinical value of molecular analysis of the PROS1 gene in PS-deficient participants. We performed Sanger sequencing of the coding region of the PROS1 gene and multiplex ligation-dependent probe amplification to exclude large structural rearrangements. Free PS was measured by a particle-enhanced immunoassay, while PS activity was assessed by a clotting method. A total of 87 PS-deficient participants and family members were included. In 22 index participants, we identified 13 PROS1 coding variants. Five variants were novel. In 21 index participants, no coding sequence variants or structural rearrangements were identified. The free PS level was lower in index participants carrying a PROS1 variant compared with index participants with no variant (0.51 [0.32-0.61] vs. 0.62 [0.57-0.73] × 10 3 IU/L; p < 0.05). The p.(Thr78Met) variant was associated with only slightly decreased free PS levels (0.59 [0.53-0.66] × 10 3 IU/L) compared with the p.(Glu390Lys) variant (0.27 [0.24-0.37] × 10 3 IU/L, p < 0.01). The frequency of VTE in participants with a coding PROS1 variant was 43 and 17% in the group with normal PROS1 gene ( p = 0.05). In conclusion, we report 13 PROS1 coding variants including five novel variants. PS levels differ by PROS1 variant and the frequency of VTE was higher when a coding PROS1 variant was present. Hence, molecular analysis of the PROS1 gene may add clinical value in the diagnostic work-up of PS deficiency.

Inflammatory Biomarker Score Identifies Patients with Six-Fold Increased Risk of One-Year Mortality after Pancreatic Cancer.

We examined whether elevated plasma C-reactive protein (CRP), carbohydrate antigen (CA) 19-9, interleukin-6 (IL-6) and YKL-40, individually or combined, can identify poor survivors among patients with pancreatic ductal adenocarcinoma (PDAC). We measured CRP, CA 19-9, IL-6 and YKL-40 in 993 patients at the time of PDAC diagnosis. The biomarker score was the sum of biomarker categories, coded 0, 1 and 2 for low, intermediate and high plasma concentrations, respectively. High vs. low levels of CRP, CA 19-9 and IL-6 were each independently associated with a two-fold increased risk of one-year mortality. CRP performed best in patients with advanced and CA 19-9 in patients with low cancer stages. YKL-40 was not associated with mortality and, therefore, was not included in the biomarker score. Compared to the biomarker score = 0, the multifactorially adjusted hazard ratios for one-year mortality were 1.56 (95% confidence interval: 0.99-2.44) for score = 1, 2.22 (1.41-3.49) for score = 2, 3.44 (2.20-5.38) for score = 3, 5.13 (3.21-8.17) for score = 4 and 6.32 (3.84-10.41) for score = 5-6 (p-value for trend = 3 × 10-31). This score performed better than any single biomarker or combination of biomarkers when examined in similarly sized or other categories. In conclusion, a combination score of elevated CRP, CA 19-9 and IL-6 identified patients with six-fold higher one-year mortality.

Thyroid Function and the Risk of Alzheimer's Disease: A Mendelian Randomization Study.

Background: Observational studies suggest an association between thyroid function and risk of dementia, but the causality and direction of these effects are unclear. We aim to test whether genetically predicted variation within the normal range of thyroid function and hypothyroidism is causally associated with the risk of Alzheimer's disease (AD). Methods: Mendelian randomization (MR) analyses using genetic instruments are associated with normal range thyrotropin (TSH) and free thyroxine (fT4) levels. Secondary analyses included investigation of the role of hypothyroidism. Bidirectional MR was conducted to address the presence of a potential reverse causal association. Summary statistics were obtained from the ThyroidOmics Consortium involving up to 119,715 individuals and the latest AD genome-wide association study data including up to 71,880 cases. Results: MR analyses show an association between increased genetically predicted normal range TSH levels and a decreased risk of AD (p = 0.02). One standard deviation increased normal range TSH levels were associated with a decreased risk of AD in individuals younger than 50 years old (p = 0.04). There was no evidence for a causal association between fT4 (p = 0.54) and AD. We did not identify any effect of the genetically predicted full range TSH levels (p = 0.06) or hypothyroidism (p = 0.23) with AD. Bidirectional MR did not show any effect of genetic predisposition to AD on TSH or fT4 levels. Conclusions: This MR study shows that increased levels of genetically predicted TSH within the normal range and in younger individuals are associated with a decreased risk of AD. We observed a marginal association between genetically predicted full range TSH and AD risk. There was no evidence for an effect between genetically predicted fT4 or hypothyroidism on AD. Future studies should clarify the underlying pathophysiological mechanisms.