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author:("kala, Mart")
1.  Age- and Sex-Specific Causal Effects of Adiposity on Cardiovascular Risk Factors 
Fall, Tove | Hägg, Sara | Ploner, Alexander | Mägi, Reedik | Fischer, Krista | Draisma, Harmen H.M. | Sarin, Antti-Pekka | Benyamin, Beben | Ladenvall, Claes | Åkerlund, Mikael | Kals, Mart | Esko, Tõnu | Nelson, Christopher P. | Kaakinen, Marika | Huikari, Ville | Mangino, Massimo | Meirhaeghe, Aline | Kristiansson, Kati | Nuotio, Marja-Liisa | Kobl, Michael | Grallert, Harald | Dehghan, Abbas | Kuningas, Maris | de Vries, Paul S. | de Bruijn, Renée F.A.G. | Willems, Sara M. | Heikkilä, Kauko | Silventoinen, Karri | Pietiläinen, Kirsi H. | Legry, Vanessa | Giedraitis, Vilmantas | Goumidi, Louisa | Syvänen, Ann-Christine | Strauch, Konstantin | Koenig, Wolfgang | Lichtner, Peter | Herder, Christian | Palotie, Aarno | Menni, Cristina | Uitterlinden, André G. | Kuulasmaa, Kari | Havulinna, Aki S. | Moreno, Luis A. | Gonzalez-Gross, Marcela | Evans, Alun | Tregouet, David-Alexandre | Yarnell, John W.G. | Virtamo, Jarmo | Ferrières, Jean | Veronesi, Giovanni | Perola, Markus | Arveiler, Dominique | Brambilla, Paolo | Lind, Lars | Kaprio, Jaakko | Hofman, Albert | Stricker, Bruno H. | van Duijn, Cornelia M. | Ikram, M. Arfan | Franco, Oscar H. | Cottel, Dominique | Dallongeville, Jean | Hall, Alistair S. | Jula, Antti | Tobin, Martin D. | Penninx, Brenda W. | Peters, Annette | Gieger, Christian | Samani, Nilesh J. | Montgomery, Grant W. | Whitfield, John B. | Martin, Nicholas G. | Groop, Leif | Spector, Tim D. | Magnusson, Patrik K. | Amouyel, Philippe | Boomsma, Dorret I. | Nilsson, Peter M. | Järvelin, Marjo-Riitta | Lyssenko, Valeriya | Metspalu, Andres | Strachan, David P. | Salomaa, Veikko | Ripatti, Samuli | Pedersen, Nancy L. | Prokopenko, Inga | McCarthy, Mark I. | Ingelsson, Erik
Diabetes  2015;64(5):1841-1852.
Observational studies have reported different effects of adiposity on cardiovascular risk factors across age and sex. Since cardiovascular risk factors are enriched in obese individuals, it has not been easy to dissect the effects of adiposity from those of other risk factors. We used a Mendelian randomization approach, applying a set of 32 genetic markers to estimate the causal effect of adiposity on blood pressure, glycemic indices, circulating lipid levels, and markers of inflammation and liver disease in up to 67,553 individuals. All analyses were stratified by age (cutoff 55 years of age) and sex. The genetic score was associated with BMI in both nonstratified analysis (P = 2.8 × 10−107) and stratified analyses (all P < 3.3 × 10−30). We found evidence of a causal effect of adiposity on blood pressure, fasting levels of insulin, C-reactive protein, interleukin-6, HDL cholesterol, and triglycerides in a nonstratified analysis and in the <55-year stratum. Further, we found evidence of a smaller causal effect on total cholesterol (P for difference = 0.015) in the ≥55-year stratum than in the <55-year stratum, a finding that could be explained by biology, survival bias, or differential medication. In conclusion, this study extends previous knowledge of the effects of adiposity by providing sex- and age-specific causal estimates on cardiovascular risk factors.
doi:10.2337/db14-0988
PMCID: PMC4407863  PMID: 25712996
2.  Single base resolution analysis of 5-hydroxymethylcytosine in 188 human genes: implications for hepatic gene expression 
Nucleic Acids Research  2016;44(14):6756-6769.
To improve the epigenomic analysis of tissues rich in 5-hydroxymethylcytosine (hmC), we developed a novel protocol called TAB-Methyl-SEQ, which allows for single base resolution profiling of both hmC and 5-methylcytosine by targeted next-generation sequencing. TAB-Methyl-SEQ data were extensively validated by a set of five methodologically different protocols. Importantly, these extensive cross-comparisons revealed that protocols based on Tet1-assisted bisulfite conversion provided more precise hmC values than TrueMethyl-based methods. A total of 109 454 CpG sites were analyzed by TAB-Methyl-SEQ for mC and hmC in 188 genes from 20 different adult human livers. We describe three types of variability of hepatic hmC profiles: (i) sample-specific variability at 40.8% of CpG sites analyzed, where the local hmC values correlate to the global hmC content of livers (measured by LC-MS), (ii) gene-specific variability, where hmC levels in the coding regions positively correlate to expression of the respective gene and (iii) site-specific variability, where prominent hmC peaks span only 1 to 3 neighboring CpG sites. Our data suggest that both the gene- and site-specific components of hmC variability might contribute to the epigenetic control of hepatic genes. The protocol described here should be useful for targeted DNA analysis in a variety of applications.
doi:10.1093/nar/gkw316
PMCID: PMC5001587  PMID: 27131363
3.  Adiposity as a cause of cardiovascular disease: a Mendelian randomization study 
Background: Adiposity, as indicated by body mass index (BMI), has been associated with risk of cardiovascular diseases in epidemiological studies. We aimed to investigate if these associations are causal, using Mendelian randomization (MR) methods.
Methods: The associations of BMI with cardiovascular outcomes [coronary heart disease (CHD), heart failure and ischaemic stroke], and associations of a genetic score (32 BMI single nucleotide polymorphisms) with BMI and cardiovascular outcomes were examined in up to 22 193 individuals with 3062 incident cardiovascular events from nine prospective follow-up studies within the ENGAGE consortium. We used random-effects meta-analysis in an MR framework to provide causal estimates of the effect of adiposity on cardiovascular outcomes.
Results: There was a strong association between BMI and incident CHD (HR = 1.20 per SD-increase of BMI, 95% CI, 1.12–1.28, P = 1.9·10−7), heart failure (HR = 1.47, 95% CI, 1.35–1.60, P = 9·10−19) and ischaemic stroke (HR = 1.15, 95% CI, 1.06–1.24, P = 0.0008) in observational analyses. The genetic score was robustly associated with BMI (β = 0.030 SD-increase of BMI per additional allele, 95% CI, 0.028–0.033, P = 3·10−107). Analyses indicated a causal effect of adiposity on development of heart failure (HR = 1.93 per SD-increase of BMI, 95% CI, 1.12–3.30, P = 0.017) and ischaemic stroke (HR = 1.83, 95% CI, 1.05–3.20, P = 0.034). Additional cross-sectional analyses using both ENGAGE and CARDIoGRAMplusC4D data showed a causal effect of adiposity on CHD.
Conclusions: Using MR methods, we provide support for the hypothesis that adiposity causes CHD, heart failure and, previously not demonstrated, ischaemic stroke.
doi:10.1093/ije/dyv094
PMCID: PMC4553708  PMID: 26016847
Cardiovascular disease; epidemiology; body mass index; Mendelian randomization
4.  Structured education can improve primary-care management of headache: the first empirical evidence, from a controlled interventional study 
Background
Headache disorders are under-recognized and under-diagnosed. A principal factor in their suboptimal management is lack of headache-related training among health-care providers, especially in primary care. In Estonia, general practitioners (GPs) refer many headache patients to neurological specialist services, mostly unnecessarily. GPs request “diagnostic” investigations, which are usually unhelpful and therefore wasteful. GP-made headache diagnoses are often arcane and non-specific, and treatments based on these are inappropriate.
The aim of this study was to develop, implement and test an educational model intended to improve headache-related primary health care in Estonia.
Methods
This was a controlled study consisting of baseline observation, intervention and follow-up observation using the same measures of effect. It involved six GPs in Põlva and the surrounding region in Southern Estonia, together with their future patients presenting consecutively with headache as their main complaint, all with their consent. The primary outcome measure was referral rate (RR) to neurological specialist services. Secondary measures included number of GP-requested investigations, GP-made headache diagnoses and how these conformed to standard terminology (ICD-10), and GP-recommended or initiated treatments.
Results
RR at baseline (n = 490) was 39.5 %, falling to 34.7 % in the post-intervention group (n = 295) (overall reduction 4.8 %; p = 0.21). In the large subgroup of patients (88 %) for whom GPs made clearly headache-related ICD-10 diagnoses, RR fell by one fifth (from 40 to 32 %; p = 0.08), but the only diagnosis-related RR that showed a statistically significant reduction was (pericranial) myalgia (19 to 3 %; p = 0.03). There was a significant increase towards use of more specific diagnoses. Use of investigations in diagnosing headache reduced from 26 to 4 % (p < 0.0001). Initiation of treatment by GPs increased from 58 to 81 % (p < 0.0001).
Conclusions
These were modest changes in GPs’ entrenched behaviour. Nevertheless they were empirical evidence that GPs’ practice in the field of headache could be improved by structured education. Furthermore, the changes were likely to be cost-saving. To our knowledge this study is the first to produce such evidence.
doi:10.1186/s10194-016-0613-1
PMCID: PMC4788653  PMID: 26969188
Education; Effect measurement; Headache disorders; Management; Primary care; Global Campaign against Headache
5.  Coffin–Siris Syndrome with obesity, macrocephaly, hepatomegaly and hyperinsulinism caused by a mutation in the ARID1B gene 
European Journal of Human Genetics  2014;22(11):1327-1329.
Coffin–Siris Syndrome (CSS, MIM 135900) is a rare genetic disorder, and mutations in ARID1B were recently shown to cause CSS. In this study, we report a novel ARID1B mutation identified by whole-exome sequencing in a patient with clinical features of CSS. We identified a novel heterozygous frameshift mutation c.1584delG in exon 2 of ARID1B (NM_020732.3) predicting a premature stop codon p.(Leu528Phefs*65). Sanger sequencing confirmed the c.1584delG mutation as a de novo in the proband and that it was not present either in her parents, half-sister or half-brother. Clinically, the patient presented with extreme obesity, macrocephaly, hepatomegaly, hyperinsulinism and polycystic ovarian syndrome (PCOS), which have previously not been described in CSS patients. We suggest that obesity, macrocephaly, hepatomegaly and/or PCOS may be added to the list of clinical features of ARID1B mutations, but further clinical reports are required to make a definite conclusion.
doi:10.1038/ejhg.2014.25
PMCID: PMC4200437  PMID: 24569609
6.  Whole-exome sequencing identifies de novo mutation in the COL1A1 gene to underlie the severe osteogenesis imperfecta 
Human Genomics  2015;9(1):6.
Background
Osteogenesis imperfecta (OI) comprises a clinically and genetically heterogeneous group of connective tissue disorders, characterized by low bone mass, increased bone fragility, and blue-gray eye sclera. OI often results from missense mutations in one of the conserved glycine residues present in the Gly-X-Y sequence repeats of the triple helical region of the collagen type I α chain, which is encoded by the COL1A1 gene. The aim of the present study is to describe the phenotype of OI II patient and a novel mutation, causing current phenotype.
Results
We report an undescribed de novo COL1A1 mutation in a patient affected by severe OI. After performing the whole-exome sequencing in a case parent–child trio, we identified a novel heterozygous c.2317G > T missense mutation in the COL1A1 gene, which leads to p.Gly773Cys transversion in the triple helical domain of the collagen type I α chain. The presence of the missense mutation was confirmed with the Sanger sequencing.
Conclusions
Hereby, we report a novel mutation in the COL1A1 gene causing severe, life threatening OI and indicate the role of de novo mutation in the pathogenesis of rare familial diseases. Our study underlines the importance of exome sequencing in disease gene discovery for families where conventional genetic testing does not give conclusive evidence.
doi:10.1186/s40246-015-0028-0
PMCID: PMC4429824  PMID: 25958000
Osteogenesis imperfecta; Type I collagen; OI genotype–phenotype; COL1A1; De novo mutation
7.  CDH13 promoter SNPs with pleiotropic effect on cardiometabolic parameters represent methylation QTLs 
Human Genetics  2014;134:291-303.
CDH13 encodes T-cadherin, a receptor for high molecular weight (HMW) adiponectin and low-density lipoprotein, promoting proliferation and migration of endothelial cells. Genome-wide association studies have mapped multiple variants in CDH13 associated with cardiometabolic traits (CMT) with variable effects across studies. We hypothesized that this heterogeneity might reflect interplay with DNA methylation within the region. Resequencing and EpiTYPER™ assay were applied for the HYPertension in ESTonia/Coronary Artery Disease in Czech (HYPEST/CADCZ; n = 358) samples to identify CDH13 promoter SNPs acting as methylation Quantitative Trait Loci (meQTLs) and to investigate their associations with CMT. In silico data were extracted from genome-wide DNA methylation and genotype datasets of the population-based sample Estonian Genome Center of the University of Tartu (EGCUT; n = 165). HYPEST–CADCZ meta-analysis identified a rare variant rs113460564 as highly significant meQTL for a 134-bp distant CpG site (P = 5.90 × 10−6; β = 3.19 %). Four common SNPs (rs12443878, rs12444338, rs62040565, rs8060301) exhibited effect on methylation level of up to 3 neighboring CpG sites in both datasets. The strongest association was detected in EGCUT between rs8060301 and cg09415485 (false discovery rate corrected P value = 1.89 × 10−30). Simultaneously, rs8060301 showed association with diastolic blood pressure, serum high-density lipoprotein and HMW adiponectin (P < 0.005). Novel strong associations were identified between rare CDH13 promoter meQTLs (minor allele frequency <5 %) and HMW adiponectin: rs2239857 (P = 5.50 × 10−5, β = −1,841.9 ng/mL) and rs77068073 (P = 2.67 × 10−4, β = −2,484.4 ng/mL). Our study shows conclusively that CDH13 promoter harbors meQTLs associated with CMTs. It paves the way to deeper understanding of the interplay between DNA variation and methylation in susceptibility to common diseases.
Electronic supplementary material
The online version of this article (doi:10.1007/s00439-014-1521-6) contains supplementary material, which is available to authorized users.
doi:10.1007/s00439-014-1521-6
PMCID: PMC4318987  PMID: 25543204
8.  Genetic and epigenetic regulation of gene expression in fetal and adult human livers 
BMC Genomics  2014;15(1):860.
Background
The liver plays a central role in the maintenance of homeostasis and health in general. However, there is substantial inter-individual variation in hepatic gene expression, and although numerous genetic factors have been identified, less is known about the epigenetic factors.
Results
By analyzing the methylomes and transcriptomes of 14 fetal and 181 adult livers, we identified 657 differentially methylated genes with adult-specific expression, these genes were enriched for transcription factor binding sites of HNF1A and HNF4A. We also identified 1,000 genes specific to fetal liver, which were enriched for GATA1, STAT5A, STAT5B and YY1 binding sites. We saw strong liver-specific effects of single nucleotide polymorphisms on both methylation levels (28,447 unique CpG sites (meQTL)) and gene expression levels (526 unique genes (eQTL)), at a false discovery rate (FDR) < 0.05. Of the 526 unique eQTL associated genes, 293 correlated significantly not only with genetic variation but also with methylation levels. The tissue-specificities of these associations were analyzed in muscle, subcutaneous adipose tissue and visceral adipose tissue. We observed that meQTL were more stable between tissues than eQTL and a very strong tissue-specificity for the identified associations between CpG methylation and gene expression.
Conclusions
Our analyses generated a comprehensive resource of factors involved in the regulation of hepatic gene expression, and allowed us to estimate the proportion of variation in gene expression that could be attributed to genetic and epigenetic variation, both crucial to understanding differences in drug response and the etiology of liver diseases.
Electronic supplementary material
The online version of this article (doi:10.1186/1471-2164-15-860) contains supplementary material, which is available to authorized users.
doi:10.1186/1471-2164-15-860
PMCID: PMC4287518  PMID: 25282492
eQTL; meQTL; eQTM; Gene expression; Methylation; HumanMethylation450; Liver
9.  Preoperative corticosteroid injections are associated with worse long-term outcome of surgical carpal tunnel release 
Acta Orthopaedica  2014;85(1):102-106.
Background and purpose
Failed closed treatment of carpal tunnel syndrome (CTS) is often followed by surgery. We investigated whether preoperative steroid injections could have a negative effect on the long-term outcome of the operation.
Patients and methods
174 hands (164 patients) were operated on by a single surgeon at Tartu University Hospital in 2005. The patients were interviewed by telephone 5–6 years after the operation. Self-reported data were gathered retrospectively concerning the number of steroid injections received before the surgery and the perceived regression of symptoms (on a 100-point numeric rating scale) at the time of interview. The patients were also asked about the presence of specific symptoms of CTS if regression of their symptoms had not been complete.
Results
93 of the 174 hands had complete regression of symptoms. Each additional injection was associated with an increased risk of occurrence of pain (RR = 1.1, 95% CI: 1.02–1-2), paresthesiae (RR = 1.1, CI: 1.1–1.2), and nocturnal awakenings (RR = 1.2, CI: 1.1–1.3). There was a weak association between the number of injections and the score given to regression of symptoms.
Interpretation
This is the first study to indicate that patients who received a greater number of local steroid injections preoperatively were more likely to have postoperative complaints associated with CTS.
doi:10.3109/17453674.2013.867781
PMCID: PMC3940985  PMID: 24286569
10.  RegScan: a GWAS tool for quick estimation of allele effects on continuous traits and their combinations 
Briefings in Bioinformatics  2013;16(1):39-44.
Genome-wide association studies are becoming computationally more demanding with the growing amounts of data. Combinatorial traits can increase the data dimensions beyond the computational capabilities of the current tools. We addressed this issue by creating an application for quick association analysis that is ten to hundreds of times faster than the leading fast methods. Our tool (RegScan) is designed for performing basic linear regression analysis with continuous traits maximally fast on large data sets. RegScan specifically targets association analysis of combinatorial traits in metabolomics. It can both generate and analyze the combinatorial traits efficiently. RegScan is capable of analyzing any number of traits together without the need to specify each trait individually. The main goal of the article is to show that RegScan can be the preferred analytical tool when large amounts of data need to be analyzed quickly using the allele frequency test.
Availability: Precompiled RegScan (all major platforms), source code, user guide and examples are freely available at www.biobank.ee/regscan.
Requirements: Qt 4.4.3 or newer for dynamic compilations.
doi:10.1093/bib/bbt066
PMCID: PMC4293375  PMID: 24008273
GWAS; genome-wide analysis; linear regression; continuous traits; combinatorial traits; metabolomics
11.  Ontogeny, distribution and potential roles of 5-hydroxymethylcytosine in human liver function 
Genome Biology  2013;14(8):R83.
Background
Interindividual differences in liver functions such as protein synthesis, lipid and carbohydrate metabolism and drug metabolism are influenced by epigenetic factors. The role of the epigenetic machinery in such processes has, however, been barely investigated. 5-hydroxymethylcytosine (5hmC) is a recently re-discovered epigenetic DNA modification that plays an important role in the control of gene expression.
Results
In this study, we investigate 5hmC occurrence and genomic distribution in 8 fetal and 7 adult human liver samples in relation to ontogeny and function. LC-MS analysis shows that in the adult liver samples 5hmC comprises up to 1% of the total cytosine content, whereas in all fetal livers it is below 0.125%. Immunohistostaining of liver sections with a polyclonal anti-5hmC antibody shows that 5hmC is detected in most of the hepatocytes. Genome-wide mapping of the distribution of 5hmC in human liver samples by next-generation sequencing shows significant differences between fetal and adult livers. In adult livers, 5hmC occupancy is overrepresented in genes involved in active catabolic and metabolic processes, whereas 5hmC elements which are found in genes exclusively in fetal livers and disappear in the adult state, are more specific to pathways for differentiation and development.
Conclusions
Our findings suggest that 5-hydroxymethylcytosine plays an important role in the development and function of the human liver and might be an important determinant for development of liver diseases as well as of the interindividual differences in drug metabolism and toxicity.
doi:10.1186/gb-2013-14-8-r83
PMCID: PMC4054829  PMID: 23958281
12.  The Role of Adiposity in Cardiometabolic Traits: A Mendelian Randomization Analysis 
Fall, Tove | Hägg, Sara | Mägi, Reedik | Ploner, Alexander | Fischer, Krista | Horikoshi, Momoko | Sarin, Antti-Pekka | Thorleifsson, Gudmar | Ladenvall, Claes | Kals, Mart | Kuningas, Maris | Draisma, Harmen H. M. | Ried, Janina S. | van Zuydam, Natalie R. | Huikari, Ville | Mangino, Massimo | Sonestedt, Emily | Benyamin, Beben | Nelson, Christopher P. | Rivera, Natalia V. | Kristiansson, Kati | Shen, Huei-yi | Havulinna, Aki S. | Dehghan, Abbas | Donnelly, Louise A. | Kaakinen, Marika | Nuotio, Marja-Liisa | Robertson, Neil | de Bruijn, Renée F. A. G. | Ikram, M. Arfan | Amin, Najaf | Balmforth, Anthony J. | Braund, Peter S. | Doney, Alexander S. F. | Döring, Angela | Elliott, Paul | Esko, Tõnu | Franco, Oscar H. | Gretarsdottir, Solveig | Hartikainen, Anna-Liisa | Heikkilä, Kauko | Herzig, Karl-Heinz | Holm, Hilma | Hottenga, Jouke Jan | Hyppönen, Elina | Illig, Thomas | Isaacs, Aaron | Isomaa, Bo | Karssen, Lennart C. | Kettunen, Johannes | Koenig, Wolfgang | Kuulasmaa, Kari | Laatikainen, Tiina | Laitinen, Jaana | Lindgren, Cecilia | Lyssenko, Valeriya | Läärä, Esa | Rayner, Nigel W. | Männistö, Satu | Pouta, Anneli | Rathmann, Wolfgang | Rivadeneira, Fernando | Ruokonen, Aimo | Savolainen, Markku J. | Sijbrands, Eric J. G. | Small, Kerrin S. | Smit, Jan H. | Steinthorsdottir, Valgerdur | Syvänen, Ann-Christine | Taanila, Anja | Tobin, Martin D. | Uitterlinden, Andre G. | Willems, Sara M. | Willemsen, Gonneke | Witteman, Jacqueline | Perola, Markus | Evans, Alun | Ferrières, Jean | Virtamo, Jarmo | Kee, Frank | Tregouet, David-Alexandre | Arveiler, Dominique | Amouyel, Philippe | Ferrario, Marco M. | Brambilla, Paolo | Hall, Alistair S. | Heath, Andrew C. | Madden, Pamela A. F. | Martin, Nicholas G. | Montgomery, Grant W. | Whitfield, John B. | Jula, Antti | Knekt, Paul | Oostra, Ben | van Duijn, Cornelia M. | Penninx, Brenda W. J. H. | Davey Smith, George | Kaprio, Jaakko | Samani, Nilesh J. | Gieger, Christian | Peters, Annette | Wichmann, H.-Erich | Boomsma, Dorret I. | de Geus, Eco J. C. | Tuomi, TiinaMaija | Power, Chris | Hammond, Christopher J. | Spector, Tim D. | Lind, Lars | Orho-Melander, Marju | Palmer, Colin Neil Alexander | Morris, Andrew D. | Groop, Leif | Järvelin, Marjo-Riitta | Salomaa, Veikko | Vartiainen, Erkki | Hofman, Albert | Ripatti, Samuli | Metspalu, Andres | Thorsteinsdottir, Unnur | Stefansson, Kari | Pedersen, Nancy L. | McCarthy, Mark I. | Ingelsson, Erik | Prokopenko, Inga
PLoS Medicine  2013;10(6):e1001474.
In this study, Prokopenko and colleagues provide novel evidence for causal relationship between adiposity and heart failure and increased liver enzymes using a Mendelian randomization study design.
Please see later in the article for the Editors' Summary
Background
The association between adiposity and cardiometabolic traits is well known from epidemiological studies. Whilst the causal relationship is clear for some of these traits, for others it is not. We aimed to determine whether adiposity is causally related to various cardiometabolic traits using the Mendelian randomization approach.
Methods and Findings
We used the adiposity-associated variant rs9939609 at the FTO locus as an instrumental variable (IV) for body mass index (BMI) in a Mendelian randomization design. Thirty-six population-based studies of individuals of European descent contributed to the analyses.
Age- and sex-adjusted regression models were fitted to test for association between (i) rs9939609 and BMI (n = 198,502), (ii) rs9939609 and 24 traits, and (iii) BMI and 24 traits. The causal effect of BMI on the outcome measures was quantified by IV estimators. The estimators were compared to the BMI–trait associations derived from the same individuals. In the IV analysis, we demonstrated novel evidence for a causal relationship between adiposity and incident heart failure (hazard ratio, 1.19 per BMI-unit increase; 95% CI, 1.03–1.39) and replicated earlier reports of a causal association with type 2 diabetes, metabolic syndrome, dyslipidemia, and hypertension (odds ratio for IV estimator, 1.1–1.4; all p<0.05). For quantitative traits, our results provide novel evidence for a causal effect of adiposity on the liver enzymes alanine aminotransferase and gamma-glutamyl transferase and confirm previous reports of a causal effect of adiposity on systolic and diastolic blood pressure, fasting insulin, 2-h post-load glucose from the oral glucose tolerance test, C-reactive protein, triglycerides, and high-density lipoprotein cholesterol levels (all p<0.05). The estimated causal effects were in agreement with traditional observational measures in all instances except for type 2 diabetes, where the causal estimate was larger than the observational estimate (p = 0.001).
Conclusions
We provide novel evidence for a causal relationship between adiposity and heart failure as well as between adiposity and increased liver enzymes.
Please see later in the article for the Editors' Summary
Editors' Summary
Cardiovascular disease (CVD)—disease that affects the heart and/or the blood vessels—is a major cause of illness and death worldwide. In the US, for example, coronary heart disease—a CVD in which narrowing of the heart's blood vessels by fatty deposits slows the blood supply to the heart and may eventually cause a heart attack—is the leading cause of death, and stroke—a CVD in which the brain's blood supply is interrupted—is the fourth leading cause of death. Globally, both the incidence of CVD (the number of new cases in a population every year) and its prevalence (the proportion of the population with CVD) are increasing, particularly in low- and middle-income countries. This increasing burden of CVD is occurring in parallel with a global increase in the incidence and prevalence of obesity—having an unhealthy amount of body fat (adiposity)—and of metabolic diseases—conditions such as diabetes in which metabolism (the processes that the body uses to make energy from food) is disrupted, with resulting high blood sugar and damage to the blood vessels.
Why Was This Study Done?
Epidemiological studies—investigations that record the patterns and causes of disease in populations—have reported an association between adiposity (indicated by an increased body mass index [BMI], which is calculated by dividing body weight in kilograms by height in meters squared) and cardiometabolic traits such as coronary heart disease, stroke, heart failure (a condition in which the heart is incapable of pumping sufficient amounts of blood around the body), diabetes, high blood pressure (hypertension), and high blood cholesterol (dyslipidemia). However, observational studies cannot prove that adiposity causes any particular cardiometabolic trait because overweight individuals may share other characteristics (confounding factors) that are the real causes of both obesity and the cardiometabolic disease. Moreover, it is possible that having CVD or a metabolic disease causes obesity (reverse causation). For example, individuals with heart failure cannot do much exercise, so heart failure may cause obesity rather than vice versa. Here, the researchers use “Mendelian randomization” to examine whether adiposity is causally related to various cardiometabolic traits. Because gene variants are inherited randomly, they are not prone to confounding and are free from reverse causation. It is known that a genetic variant (rs9939609) within the genome region that encodes the fat-mass- and obesity-associated gene (FTO) is associated with increased BMI. Thus, an investigation of the associations between rs9939609 and cardiometabolic traits can indicate whether obesity is causally related to these traits.
What Did the Researchers Do and Find?
The researchers analyzed the association between rs9939609 (the “instrumental variable,” or IV) and BMI, between rs9939609 and 24 cardiometabolic traits, and between BMI and the same traits using genetic and health data collected in 36 population-based studies of nearly 200,000 individuals of European descent. They then quantified the strength of the causal association between BMI and the cardiometabolic traits by calculating “IV estimators.” Higher BMI showed a causal relationship with heart failure, metabolic syndrome (a combination of medical disorders that increases the risk of developing CVD), type 2 diabetes, dyslipidemia, hypertension, increased blood levels of liver enzymes (an indicator of liver damage; some metabolic disorders involve liver damage), and several other cardiometabolic traits. All the IV estimators were similar to the BMI–cardiovascular trait associations (observational estimates) derived from the same individuals, with the exception of diabetes, where the causal estimate was higher than the observational estimate, probably because the observational estimate is based on a single BMI measurement, whereas the causal estimate considers lifetime changes in BMI.
What Do These Findings Mean?
Like all Mendelian randomization studies, the reliability of the causal associations reported here depends on several assumptions made by the researchers. Nevertheless, these findings provide support for many previously suspected and biologically plausible causal relationships, such as that between adiposity and hypertension. They also provide new insights into the causal effect of obesity on liver enzyme levels and on heart failure. In the latter case, these findings suggest that a one-unit increase in BMI might increase the incidence of heart failure by 17%. In the US, this corresponds to 113,000 additional cases of heart failure for every unit increase in BMI at the population level. Although additional studies are needed to confirm and extend these findings, these results suggest that global efforts to reduce the burden of obesity will likely also reduce the occurrence of CVD and metabolic disorders.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001474.
The American Heart Association provides information on all aspects of cardiovascular disease and tips on keeping the heart healthy, including weight management (in several languages); its website includes personal stories about stroke and heart attacks
The US Centers for Disease Control and Prevention has information on heart disease, stroke, and all aspects of overweight and obesity (in English and Spanish)
The UK National Health Service Choices website provides information about cardiovascular disease and obesity, including a personal story about losing weight
The World Health Organization provides information on obesity (in several languages)
The International Obesity Taskforce provides information about the global obesity epidemic
Wikipedia has a page on Mendelian randomization (note: Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)
MedlinePlus provides links to other sources of information on heart disease, on vascular disease, on obesity, and on metabolic disorders (in English and Spanish)
The International Association for the Study of Obesity provides maps and information about obesity worldwide
The International Diabetes Federation has a web page that describes types, complications, and risk factors of diabetes
doi:10.1371/journal.pmed.1001474
PMCID: PMC3692470  PMID: 23824655
13.  In-solution hybrid capture of bisulfite-converted DNA for targeted bisulfite sequencing of 174 ADME genes 
Nucleic Acids Research  2013;41(6):e72.
DNA methylation is one of the most important epigenetic alterations involved in the control of gene expression. Bisulfite sequencing of genomic DNA is currently the only method to study DNA methylation patterns at single-nucleotide resolution. Hence, next-generation sequencing of bisulfite-converted DNA is the method of choice to investigate DNA methylation profiles at the genome-wide scale. Nevertheless, whole genome sequencing for analysis of human methylomes is expensive, and a method for targeted gene analysis would provide a good alternative in many cases where the primary interest is restricted to a set of genes.
Here, we report the successful use of a custom Agilent SureSelect Target Enrichment system for the hybrid capture of bisulfite-converted DNA. We prepared bisulfite-converted next-generation sequencing libraries, which are enriched for the coding and regulatory regions of 174 ADME genes (i.e. genes involved in the metabolism and distribution of drugs). Sequencing of these libraries on Illumina’s HiSeq2000 revealed that the method allows a reliable quantification of methylation levels of CpG sites in the selected genes, and validation of the method using pyrosequencing and the Illumina 450K methylation BeadChips revealed good concordance.
doi:10.1093/nar/gks1467
PMCID: PMC3616706  PMID: 23325842
14.  Assessing non-response to a mailed health survey including self-collection of biological material 
Background: Collection of biological material via mailed health surveys is an emerging trend. This study was conducted to assess non-response bias in a study of sexually transmitted infection utilizing self-collected, home-obtained specimens. Methods: Data from a nationwide administrative database on health care utilization together with data from a research study were used. The research study was an outreach screening programme including home-obtained, participant-collected, mail-delivered testing for Chlamydia trachomatis. A random sample of 1690 persons aged 18–35 years from the population registry was selected. Study materials (specimen collection kit, informed consent, questionnaire) were mailed in three waves. Results: The first mailing yielded a response rate of 18.5% (n = 259), the second 10.1% (n = 141) and the third 11.4% (n = 160). Women were more likely to respond than men, and responders were less likely to have had medical care in the past year and more likely to have had a prior sexually transmitted infection than non-responders. Chlamydia trachomatis infection rates tended to be higher in early responders. Late responders appeared more like non-responders in terms of demographic factors, health care utilization patterns and potential disease status. Conclusion: Non-response in a health survey including biological material self-collection warrants research as it may differ from non-response in general health questionnaires.
doi:10.1093/eurpub/ckq053
PMCID: PMC3139099  PMID: 20457781
Chlamydia; epidemiologic study; participant collected specimen; participation
15.  Evidence of Inbreeding Depression on Human Height 
McQuillan, Ruth | Eklund, Niina | Pirastu, Nicola | Kuningas, Maris | McEvoy, Brian P. | Esko, Tõnu | Corre, Tanguy | Davies, Gail | Kaakinen, Marika | Lyytikäinen, Leo-Pekka | Kristiansson, Kati | Havulinna, Aki S. | Gögele, Martin | Vitart, Veronique | Tenesa, Albert | Aulchenko, Yurii | Hayward, Caroline | Johansson, Åsa | Boban, Mladen | Ulivi, Sheila | Robino, Antonietta | Boraska, Vesna | Igl, Wilmar | Wild, Sarah H. | Zgaga, Lina | Amin, Najaf | Theodoratou, Evropi | Polašek, Ozren | Girotto, Giorgia | Lopez, Lorna M. | Sala, Cinzia | Lahti, Jari | Laatikainen, Tiina | Prokopenko, Inga | Kals, Mart | Viikari, Jorma | Yang, Jian | Pouta, Anneli | Estrada, Karol | Hofman, Albert | Freimer, Nelson | Martin, Nicholas G. | Kähönen, Mika | Milani, Lili | Heliövaara, Markku | Vartiainen, Erkki | Räikkönen, Katri | Masciullo, Corrado | Starr, John M. | Hicks, Andrew A. | Esposito, Laura | Kolčić, Ivana | Farrington, Susan M. | Oostra, Ben | Zemunik, Tatijana | Campbell, Harry | Kirin, Mirna | Pehlic, Marina | Faletra, Flavio | Porteous, David | Pistis, Giorgio | Widén, Elisabeth | Salomaa, Veikko | Koskinen, Seppo | Fischer, Krista | Lehtimäki, Terho | Heath, Andrew | McCarthy, Mark I. | Rivadeneira, Fernando | Montgomery, Grant W. | Tiemeier, Henning | Hartikainen, Anna-Liisa | Madden, Pamela A. F. | d'Adamo, Pio | Hastie, Nicholas D. | Gyllensten, Ulf | Wright, Alan F. | van Duijn, Cornelia M. | Dunlop, Malcolm | Rudan, Igor | Gasparini, Paolo | Pramstaller, Peter P. | Deary, Ian J. | Toniolo, Daniela | Eriksson, Johan G. | Jula, Antti | Raitakari, Olli T. | Metspalu, Andres | Perola, Markus | Järvelin, Marjo-Riitta | Uitterlinden, André | Visscher, Peter M. | Wilson, James F.
PLoS Genetics  2012;8(7):e1002655.
Stature is a classical and highly heritable complex trait, with 80%–90% of variation explained by genetic factors. In recent years, genome-wide association studies (GWAS) have successfully identified many common additive variants influencing human height; however, little attention has been given to the potential role of recessive genetic effects. Here, we investigated genome-wide recessive effects by an analysis of inbreeding depression on adult height in over 35,000 people from 21 different population samples. We found a highly significant inverse association between height and genome-wide homozygosity, equivalent to a height reduction of up to 3 cm in the offspring of first cousins compared with the offspring of unrelated individuals, an effect which remained after controlling for the effects of socio-economic status, an important confounder (χ2 = 83.89, df = 1; p = 5.2×10−20). There was, however, a high degree of heterogeneity among populations: whereas the direction of the effect was consistent across most population samples, the effect size differed significantly among populations. It is likely that this reflects true biological heterogeneity: whether or not an effect can be observed will depend on both the variance in homozygosity in the population and the chance inheritance of individual recessive genotypes. These results predict that multiple, rare, recessive variants influence human height. Although this exploratory work focuses on height alone, the methodology developed is generally applicable to heritable quantitative traits (QT), paving the way for an investigation into inbreeding effects, and therefore genetic architecture, on a range of QT of biomedical importance.
Author Summary
Studies investigating the extent to which genetics influences human characteristics such as height have concentrated mainly on common variants of genes, where having one or two copies of a given variant influences the trait or risk of disease. This study explores whether a different type of genetic variant might also be important. We investigate the role of recessive genetic variants, where two identical copies of a variant are required to have an effect. By measuring genome-wide homozygosity—the phenomenon of inheriting two identical copies at a given point of the genome—in 35,000 individuals from 21 European populations, and by comparing this to individual height, we found that the more homozygous the genome, the shorter the individual. The offspring of first cousins (who have increased homozygosity) were predicted to be up to 3 cm shorter on average than the offspring of unrelated parents. Height is influenced by the combined effect of many recessive variants dispersed across the genome. This may also be true for other human characteristics and diseases, opening up a new way to understand how genetic variation influences our health.
doi:10.1371/journal.pgen.1002655
PMCID: PMC3400549  PMID: 22829771
16.  Expanded syringe exchange programs and reduced HIV infection among new injection drug users in Tallinn, Estonia 
BMC Public Health  2011;11:517.
Background
Estonia has experienced an HIV epidemic among intravenous drug users (IDUs) with the highest per capita HIV prevalence in Eastern Europe. We assessed the effects of expanded syringe exchange programs (SEP) in the capital city, Tallinn, which has an estimated 10,000 IDUs.
Methods
SEP implementation was monitored with data from the Estonian National Institute for Health Development. Respondent driven sampling (RDS) interview surveys with HIV testing were conducted in Tallinn in 2005, 2007 and 2009 (involving 350, 350 and 327 IDUs respectively). HIV incidence among new injectors (those injecting for < = 3 years) was estimated by assuming (1) new injectors were HIV seronegative when they began injecting, and (2) HIV infection occurred at the midpoint between first injection and time of interview.
Results
SEP increased from 230,000 syringes exchanged in 2005 to 440,000 in 2007 and 770,000 in 2009. In all three surveys, IDUs were predominantly male (80%), ethnic Russians (>80%), and young adults (mean ages 24 to 27 years). The proportion of new injectors decreased significantly over the years (from 21% in 2005 to 12% in 2009, p = 0.005). HIV prevalence among all respondents stabilized at slightly over 50% (54% in 2005, 55% in 2007, 51% in 2009), and decreased among new injectors (34% in 2005, 16% in 2009, p = 0.046). Estimated HIV incidence among new injectors decreased significantly from 18/100 person-years in 2005 and 21/100 person-years in 2007 to 9/100 person-years in 2009 (p = 0.026).
Conclusions
In Estonia, a transitional country, a decrease in the HIV prevalence among new injectors and in the numbers of people initiating injection drug use coincided with implementation of large-scale SEPs. Further reductions in HIV transmission among IDUs are still required. Provision of 70 or more syringes per IDU per year may be needed before significant reductions in HIV incidence occur.
doi:10.1186/1471-2458-11-517
PMCID: PMC3146432  PMID: 21718469
17.  High-prevalence and high-estimated incidence of HIV infection among new injecting drug users in Estonia: need for large scale prevention programs 
Objective
To examine HIV risk behavior and HIV infection among new injectors in Tallinn, Estonia.
Design and methods
Data from two cross-sectional surveys of injecting drug users (IDUs) recruited from a syringe exchange program (N = 162, Study 1) or using respondent driven sampling (N = 350, Study 2). Behavioral surveys were administered; serum samples were collected for HIV testing. Subjects were categorized into new injectors (injecting ≤ 3 years) and long-term injectors (injecting > 3 years).
Results
Twenty-eight of 161 (17%, Study 1) and 73/350 (21%, Study 2) of the study subjects were new injectors. HIV infection was substantial among the newer injectors: HIV prevalence was 50% (Study 1) and 34% (Study 2), and estimated HIV incidence 31/100 PY and 21/100 PY, respectively. In Study 2, new injectors were more likely to be female and ethnic Estonian and less likely to be injecting daily compared with long-term injectors. No significant difference was found among two groups on sharing injecting equipment or reported number of sexual partners.
Conclusions
A continuing HIV epidemic among new injectors is of critical public health concern. Interventions to prevent initiation into injecting drug use and scaling up HIV prevention programs for IDUs in Estonia are of utmost importance.
doi:10.1093/pubmed/fdn014
PMCID: PMC2925676  PMID: 18308743
Estonia; HIV; IDU; injection drug use; new injecting drug users
18.  Population-based type-specific prevalence of high-risk human papillomavirus infection in Estonia 
Background
Effective prophylactic vaccines are available against human papillomavirus (HPV) types 6, 11, 16, and 18 which are licensed for routine use among young women. Monitoring is needed to demonstrate protection against cervical cancer, to verify duration of protection, and assess replacement frequency of non-vaccine types among vaccinated cohorts.
Methods
Data from a population-based study were used to assess the type-specific prevalence of HPV in a non-vaccinated population in Estonia: 845 self-administered surveys and self-collected vaginal swabs were distributed, 346 were collected by mail and tested for HPV DNA from female participants 18-35 years of age.
Results
The overall HPV prevalence (weighted estimate to account for the sampling method) in the study population (unvaccinated women aged 18-35) was calculated to be 38% (95% CI 31-45%), with estimated prevalences of high- and low-risk HPV types 21% (95% CI 16-26%), and 10% (95% CI 7-14%), respectively. Of the high-risk HPV types, HPV 16 was detected most frequently (6.4%; 95% CI 4.0-9.8%) followed by HPV 53 (4.3%; 95% CI 2.3-7.2%) and HPV 66 (2.8%; 95% CI 1.3-5.2%).
Conclusions
We observed a high prevalence of total and high-risk type HPV in an Eastern European country. The most common high-risk HPV types detected were HPV 16, 53, and 66.
doi:10.1186/1471-2334-10-63
PMCID: PMC2841185  PMID: 20222944

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