Genetic risk accentuates dietary effects on hepatic steatosis, inflammation and fibrosis in a population-based cohort.

BACKGROUND & AIMS: Steatotic liver disease (SLD), characterized by elevated liver fat content (LFC), is influenced by genetics and diet. However, whether diet has a differential effect based on genetic risk is not well-characterized. We aimed to determine how genetic factors interact with diet to affect SLD in a large national biobank. METHODS: We included UK Biobank participants with dietary intake measured by 24-hour recall and genotyping. The primary predictors were dietary pattern, PNPLA3-rs738409-G, TM6SF2-rs58542926-T, a 16-variant hepatic steatosis polygenic risk score (PRS), and gene-environment interactions. The primary outcome was LFC, and secondary outcomes were iron-controlled T1 time (cT1, a measure of liver inflammation and fibrosis) and liver-related events/mortality. RESULTS: A total of 21,619 participants met inclusion criteria. In non-interaction models, Mediterranean diet and intake of fruit/vegetables/legumes and fish associated with lower LFC, while higher red/processed meat intake and all genetic predictors associated with higher LFC. In interaction models, all genetic predictors interacted with Mediterranean diet and fruit/vegetable/legume intake, while the steatosis PRS interacted with fish intake and the TM6SF2 genotype interacted with red/processed meat intake, to affect LFC. Dietary effects on LFC were up to 3.8-fold higher in PNPLA3-rs738409-GG vs. -CC individuals, and 1.4-3.0-fold higher in the top vs. bottom quartile of the steatosis PRS. Gene-diet interactions were stronger in participants with vs. without overweight. The steatosis PRS interacted with Mediterranean diet and fruit/vegetable/legume intake to affect cT1 and most dietary and genetic predictors associated with risk of liver-related events or mortality by age 70. CONCLUSIONS: Effects of diet on LFC and cT1 were markedly accentuated in patients at increased genetic risk for SLD, implying dietary interventions may be more impactful in these populations. IMPACT AND IMPLICATIONS: Genetic variants and diet both influence risk of hepatic steatosis, inflammation/fibrosis, and hepatic decompensation; however, how gene-diet interactions influence these outcomes has previously not been comprehensively characterized. We investigated this topic in the community-based UK Biobank and found that genetic risk and dietary quality interacted to influence hepatic steatosis and inflammation/fibrosis on liver MRI, so that the effects of diet were greater in people at elevated genetic risk. These results are relevant for patients and medical providers because they show that genetic risk is not fixed (i.e. modifiable factors can mitigate or exacerbate this risk) and realistic dietary changes may result in meaningful improvement in liver steatosis and inflammation/fibrosis. As genotyping becomes more routinely used in clinical practice, patients identified to be at high baseline genetic risk may benefit even more from intensive dietary counseling than those at lower risk, though future prospective studies are required.

PNPLA3 Genotype and Diabetes Identify Patients With Nonalcoholic Fatty Liver Disease at High Risk of Incident Cirrhosis.

BACKGROUND & AIMS: Non-alcoholic fatty liver disease (NAFLD) can progress to cirrhosis and hepatic decompensation, but whether genetic variants influence the rate of progression to cirrhosis or are useful in risk stratification among patients with NAFLD is uncertain. METHODS: We included participants from 2 independent cohorts, they Michigan Genomics Initiative (MGI) and UK Biobank (UKBB), who had NAFLD defined by elevated alanine aminotransferase (ALT) levels in the absence of alternative chronic liver disease. The primary predictors were genetic variants and metabolic comorbidities associated with cirrhosis. We conducted time-to-event analyses using Fine-Gray competing risk models. RESULTS: We included 7893 and 46,880 participants from MGI and UKBB, respectively. In univariable analysis, PNPLA3-rs738409-GG genotype, diabetes, obesity, and ALT of ≥2× upper limit of normal were associated with higher incidence rate of cirrhosis in both MGI and UKBB. PNPLA3-rs738409-GG had additive effects with clinical risk factors including diabetes, obesity, and ALT elevations. Among patients with indeterminate fibrosis-4 (FIB4) scores (1.3-2.67), those with diabetes and PNPLA3-rs738409-GG genotype had an incidence rate of cirrhosis comparable to that of patients with high-risk FIB4 scores (>2.67) and 2.9-4.8 times that of patients with diabetes but CC/CG genotypes. In contrast, FIB4 <1.3 was associated with an incidence rate of cirrhosis significantly lower than that of FIB4 of >2.67, even in the presence of clinical risk factors and high-risk PNPLA3 genotype. CONCLUSIONS: PNPLA3-rs738409 genotype and diabetes identified patients with NAFLD currently considered indeterminate risk (FIB4 1.3-2.67) who had a similar risk of cirrhosis as those considered high-risk (FIB4 >2.67). PNPLA3 genotyping may improve prognostication and allow for prioritization of intensive intervention.

Allele-specific variation at APOE increases nonalcoholic fatty liver disease and obesity but decreases risk of Alzheimer's disease and myocardial infarction.

Nonalcoholic fatty liver disease (NAFLD) is a leading cause of chronic liver disease and is highly correlated with metabolic disease. NAFLD results from environmental exposures acting on a susceptible polygenic background. This study performed the largest multiethnic investigation of exonic variation associated with NAFLD and correlated metabolic traits and diseases. An exome array meta-analysis was carried out among eight multiethnic population-based cohorts (n = 16 492) with computed tomography (CT) measured hepatic steatosis. A fixed effects meta-analysis identified five exome-wide significant loci (P < 5.30 × 10-7); including a novel signal near TOMM40/APOE. Joint analysis of TOMM40/APOE variants revealed the TOMM40 signal was attributed to APOE rs429358-T; APOE rs7412 was not associated with liver attenuation. Moreover, rs429358-T was associated with higher serum alanine aminotransferase, liver steatosis, cirrhosis, triglycerides and obesity; as well as, lower cholesterol and decreased risk of myocardial infarction and Alzheimer's disease (AD) in phenome-wide association analyses in the Michigan Genomics Initiative, United Kingdom Biobank and/or public datasets. These results implicate APOE in imaging-based identification of NAFLD. This association may or may not translate to nonalcoholic steatohepatitis; however, these results indicate a significant association with advanced liver disease and hepatic cirrhosis. These findings highlight allelic heterogeneity at the APOE locus and demonstrate an inverse link between NAFLD and AD at the exome level in the largest analysis to date.

A common variant that alters SUN1 degradation associates with hepatic steatosis and metabolic traits in multiple cohorts.

BACKGROUND & AIMS: Non-alcoholic fatty liver disease (NAFLD), and its progressive form steatohepatitis (NASH), represent a genetically and phenotypically diverse entity for which there is no approved therapy, making it imperative to define the spectrum of pathways contributing to its pathogenesis. Rare variants in genes encoding nuclear envelope proteins cause lipodystrophy with early-onset NAFLD/NASH; we hypothesized that common variants in nuclear envelope-related genes might also contribute to hepatic steatosis and NAFLD. METHODS: Using hepatic steatosis as the outcome of interest, we performed an association meta-analysis of nuclear envelope-related coding variants in three large discovery cohorts (N >120,000 participants), followed by phenotype association studies in large validation cohorts (N >600,000) and functional testing of the top steatosis-associated variant in cell culture. RESULTS: A common protein-coding variant, rs6461378 (SUN1 H118Y), was the top steatosis-associated variant in our association meta-analysis (p <0.001). In ancestrally distinct validation cohorts, rs6461378 associated with histologic NAFLD and with NAFLD-related metabolic traits including increased serum fatty acids, type 2 diabetes, hypertension, cardiovascular disease, and decreased HDL. SUN1 H118Y was subject to increased proteasomal degradation relative to wild-type SUN1 in cells, and SUN1 H118Y-expressing cells exhibited insulin resistance and increased lipid accumulation. CONCLUSIONS: Collectively, these data support a potential causal role for the common SUN1 variant rs6461378 in NAFLD and metabolic disease. IMPACT AND IMPLICATIONS: Non-alcoholic fatty liver disease (NAFLD), with an estimated global prevalence of nearly 30%, is a growing cause of morbidity and mortality for which there is no approved pharmacologic therapy. Our data provide a rationale for broadening current concepts of NAFLD genetics and pathophysiology to include the nuclear envelope, and particularly Sad1 and UNC84 domain containing 1 (SUN1), as novel contributors to this common liver disease. Furthermore, if future studies confirm causality of the common SUN1 H118Y variant, it has the potential to become a broadly relevant therapeutic target in NAFLD and metabolic disease.

Polygenic Risk Prediction in Diverticulitis.

OBJECTIVE: To derive and validate a polygenic risk score (PRS) to predict the occurrence and severity of diverticulitis and to understand the potential for incorporation of a PRS in current decision-making. BACKGROUND: PRS quantifies genetic variation into a continuous measure of risk. There is a need for improved risk stratification to guide surgical decision-making that could be fulfilled by PRS. It is unknown how surgeons might integrate PRS in decision-making. METHODS: We derived a PRS with 44 single-nucleotide polymorphisms associated with diverticular disease in the UK Biobank and validated this score in the Michigan Genomics Initiative (MGI). We performed a discrete choice experiment of practicing colorectal surgeons. Surgeons rated the influence of clinical factors and a hypothetical polygenic risk prediction tool. RESULTS: Among 2812 MGI participants with diverticular disease, 1964 were asymptomatic, 574 had mild disease, and 274 had severe disease. PRS was associated with occurrence and severity. Patients in the highest PRS decile were more likely to have diverticulitis [odds ratio (OR)=1.84; 95% confidence interval (CI), 1.42-2.38)] and more likely to have severe diverticulitis (OR=1.61; 95% CI, 1.04-2.51) than the bottom 50%. Among 213 surveyed surgeons, extreme disease-specific factors had the largest utility (3 episodes in the last year, +74.4; percutaneous drain, + 69.4). Factors with strongest influence against surgery included 1 lifetime episode (-63.3), outpatient management (-54.9), and patient preference (-39.6). PRS was predicted to have high utility (+71). CONCLUSIONS: A PRS derived from a large national biobank was externally validated, and found to be associated with the incidence and severity of diverticulitis. Surgeons have clear guidance at clinical extremes, but demonstrate equipoise in intermediate scenarios. Surgeons are receptive to PRS, which may be most useful in marginal clinical situations. Given the current lack of accurate prognostication in recurrent diverticulitis, PRS may provide a novel approach for improving patient counseling and decision-making.

An Assessment of Comparative Medication Durability in Inflammatory Bowel Disease Patients With and Without Co-morbid Psoriasis, Rheumatoid Arthritis, and/or Enteropathic Arthritis.

BACKGROUND: Patients with inflammatory bowel disease (IBD) are at increased risk for many co-morbid diseases. However, little is known about durability of IBD medications in patients with co-morbid diseases. AIMS: Determine medication durability in IBD patients with and without psoriasis, rheumatoid arthritis, and/or enteropathic arthropathy. METHODS: All patients with at least three ICD-9 or 10 diagnoses for IBD were included in the cohort. The risk factors of interest were a co-morbid diagnosis of psoriasis (IBD-Ps), rheumatoid arthritis (IBD-RA), and/or enteropathic arthritis (IBD-EA). Medication durability was defined as days of medication use, calculated using order start and stop dates from the electronic medical record. Significant differences were tested using the Wilcoxon rank sum test for continuous variables and Fisher's exact test or Pearson's Chi-squared test, as appropriate, for categorical variables. Boxplots were constructed for graphical interpretation of results. RESULTS: In the psoriasis group, there were 481 patients with 831 medication exposures [131 IBS-Ps (16%), 700 IBD only (84%)]. The median days of medication use were numerically higher in the IBD-Ps group for all therapies [anti-TNF: 1109 vs 861 (p = 0.17); anti-IL-12/23: 984 vs 834 (p = 0.33); JAKi: 682 vs 230 (p = 0.13)], anti-TNF/IM: 370 vs 202 (p = 0.57), except anti-integrin therapy [214 vs 470 (p = 0.08)]. When restricting to UC only, patients with co-morbid again Ps had a significantly shorter duration on anti-integrin therapy (84 vs 456 days, p = 0.02). While not reaching statistical significance, there was a distinctly longer medication duration on JAKi therapy (910 vs 317, p = 0.10). When restricting to patients with CD only, no results reached statistical significance though there was a trend towards longer anti-TNF durability in CD-Ps (1340 vs 1000 days, p = 0.098). There were no differences in medication durability in IBD-RA or IBD-EA patients. DISCUSSION: Larger studies investigating medication durability of JAKi and anti-integrin therapy in IBD patients with psoriasis would be beneficial given noteworthy trends towards increased and decreased durability, respectively.

Loci identified by a genome-wide association study of carotid artery stenosis in the eMERGE network.

Carotid artery atherosclerotic disease (CAAD) is a risk factor for stroke. We used a genome-wide association (GWAS) approach to discover genetic variants associated with CAAD in participants in the electronic Medical Records and Genomics (eMERGE) Network. We identified adult CAAD cases with unilateral or bilateral carotid artery stenosis and controls without evidence of stenosis from electronic health records at eight eMERGE sites. We performed GWAS with a model adjusting for age, sex, study site, and genetic principal components of ancestry. In eMERGE we found 1793 CAAD cases and 17,958 controls. Two loci reached genome-wide significance, on chr6 in LPA (rs10455872, odds ratio [OR] (95% confidence interval [CI]) = 1.50 (1.30-1.73), p = 2.1 × 10-8 ) and on chr7, an intergenic single nucleotide variant (SNV; rs6952610, OR (95% CI) = 1.25 (1.16-1.36), p = 4.3 × 10-8 ). The chr7 association remained significant in the presence of the LPA SNV as a covariate. The LPA SNV was also associated with coronary heart disease (CHD; 4199 cases and 11,679 controls) in this study (OR (95% CI) = 1.27 (1.13-1.43), p = 5 × 10-5 ) but the chr7 SNV was not (OR (95% CI) = 1.03 (0.97-1.09), p = .37). Both variants replicated in UK Biobank. Elevated lipoprotein(a) concentrations ([Lp(a)]) and LPA variants associated with elevated [Lp(a)] have previously been associated with CAAD and CHD, including rs10455872. With electronic health record phenotypes in eMERGE and UKB, we replicated a previously known association and identified a novel locus associated with CAAD.

Perturbation of TM6SF2 Expression Alters Lipid Metabolism in a Human Liver Cell Line.

Non-alcoholic fatty liver disease (NAFLD) is caused by excess lipid accumulation in hepatocytes. Genome-wide association studies have identified a strong association of NAFLD with non-synonymous E167K amino acid mutation in the transmembrane 6 superfamily member 2 (TM6SF2) protein. The E167K mutation reduces TM6SF2 stability, and its carriers display increased hepatic lipids and lower serum triglycerides. However, the effects of TM6SF2 on hepatic lipid metabolism are not completely understood. We overexpressed wild-type or E167K variant of TM6SF2 or knocked down TM6SF2 expression in lipid-treated Huh-7 cells and used untargeted lipidomic analysis, RNAseq transcriptome analysis, and fluorescent imaging to determine changes in hepatic lipid metabolism. Both TM6SF2 knockdown and E167K overexpression increased hepatic lipid accumulation, while wild-type overexpression decreased acylglyceride levels. We also observed lipid chain remodeling for acylglycerides by TM6SF2 knockdown, leading to a relative increase in species with shorter, more saturated side chains. RNA-sequencing revealed differential expression of several lipid metabolizing genes, including genes belonging to AKR1 family and lipases, primarily in cells with TM6SF2 knockdown. Taken together, our data show that overexpression of TM6SF2 gene or its loss-of-function changes hepatic lipid species composition and expression of lipid metabolizing genes. Additionally, our data further confirms a loss-of-function effect for the E167K variant.

Identification of seven novel loci associated with amino acid levels using single-variant and gene-based tests in 8545 Finnish men from the METSIM study.

Comprehensive metabolite profiling captures many highly heritable traits, including amino acid levels, which are potentially sensitive biomarkers for disease pathogenesis. To better understand the contribution of genetic variation to amino acid levels, we performed single variant and gene-based tests of association between nine serum amino acids (alanine, glutamine, glycine, histidine, isoleucine, leucine, phenylalanine, tyrosine, and valine) and 16.6 million genotyped and imputed variants in 8545 non-diabetic Finnish men from the METabolic Syndrome In Men (METSIM) study with replication in Northern Finland Birth Cohort (NFBC1966). We identified five novel loci associated with amino acid levels (P = < 5×10-8): LOC157273/PPP1R3B with glycine (rs9987289, P = 2.3×10-26); ZFHX3 (chr16:73326579, minor allele frequency (MAF) = 0.42%, P = 3.6×10-9), LIPC (rs10468017, P = 1.5×10-8), and WWOX (rs9937914, P = 3.8×10-8) with alanine; and TRIB1 with tyrosine (rs28601761, P = 8×10-9). Gene-based tests identified two novel genes harboring missense variants of MAF <1% that show aggregate association with amino acid levels: PYCR1 with glycine (Pgene = 1.5×10-6) and BCAT2 with valine (Pgene = 7.4×10-7); neither gene was implicated by single variant association tests. These findings are among the first applications of gene-based tests to identify new loci for amino acid levels. In addition to the seven novel gene associations, we identified five independent signals at established amino acid loci, including two rare variant signals at GLDC (rs138640017, MAF=0.95%, Pconditional = 5.8×10-40) with glycine levels and HAL (rs141635447, MAF = 0.46%, Pconditional = 9.4×10-11) with histidine levels. Examination of all single variant association results in our data revealed a strong inverse relationship between effect size and MAF (Ptrend<0.001). These novel signals provide further insight into the molecular mechanisms of amino acid metabolism and potentially, their perturbations in disease.

17-Beta Hydroxysteroid Dehydrogenase 13 Is a Hepatic Retinol Dehydrogenase Associated With Histological Features of Nonalcoholic Fatty Liver Disease.

Nonalcoholic fatty liver disease (NAFLD) is a common cause of chronic liver disease. A single-nucleotide polymorphism (SNP), rs6834314, was associated with serum liver enzymes in the general population, presumably reflecting liver fat or injury. We studied rs6834314 and its nearest gene, 17-beta hydroxysteroid dehydrogenase 13 (HSD17B13), to identify associations with histological features of NAFLD and to characterize the functional role of HSD17B13 in NAFLD pathogenesis. The minor allele of rs6834314 was significantly associated with increased steatosis but decreased inflammation, ballooning, Mallory-Denk bodies, and liver enzyme levels in 768 adult Caucasians with biopsy-proven NAFLD and with cirrhosis in the general population. We found two plausible causative variants in the HSD17B13 gene. rs72613567, a splice-site SNP in high linkage with rs6834314 (r2 = 0.94) generates splice variants and shows a similar pattern of association with NAFLD histology. Its minor allele generates simultaneous expression of exon 6-skipping and G-nucleotide insertion variants. Another SNP, rs62305723 (encoding a P260S mutation), is significantly associated with decreased ballooning and inflammation. Hepatic expression of HSD17B13 is 5.9-fold higher (P = 0.003) in patients with NAFLD. HSD17B13 is targeted to lipid droplets, requiring the conserved amino acid 22-28 sequence and amino acid 71-106 region. The protein has retinol dehydrogenase (RDH) activity, with enzymatic activity dependent on lipid droplet targeting and cofactor binding site. The exon 6 deletion, G insertion, and naturally occurring P260S mutation all confer loss of enzymatic activity. Conclusion: We demonstrate the association of variants in HSD17B13 with specific features of NAFLD histology and identify the enzyme as a lipid droplet-associated RDH; our data suggest that HSD17B13 plays a role in NAFLD through its enzymatic activity.

Genetic variants that associate with cirrhosis have pleiotropic effects on human traits.

BACKGROUND AND AIMS: Cirrhosis is characterized by extensive fibrosis of the liver and is a major cause of liver-related mortality. Cirrhosis is partially heritable but genetic contributions to cirrhosis have not been systemically explored. Here, we carry out association analyses with cirrhosis in two large biobanks and determine the effects of cirrhosis associated variants on multiple human disease/traits. METHODS: We carried out a genome-wide association analysis of cirrhosis as a diagnosis in UK BioBank (UKBB; 1088 cases vs. 407 873 controls) and then tested top-associating loci for replication with cirrhosis in a hospital-based cohort from the Michigan Genomics Initiative (MGI; 875 cases of cirrhosis vs. 30 346 controls). For replicating variants or variants previously associated with cirrhosis that also affected cirrhosis in UKBB or MGI, we determined single nucleotide polymorphism effects on all other diagnoses in UKBB (PheWAS), common metabolic traits/diseases and serum/plasma metabolites. RESULTS: Unbiased genome-wide association study identified variants in/near PNPLA3 and HFE, and candidate variant analysis identified variants in/near TM6SF2, MBOAT7, SERPINA1, HSD17B13, STAT4 and IFNL4 that reproducibly affected cirrhosis. Most affected liver enzyme concentrations and/or aspartate transaminase-to-platelet ratio index. PheWAS, metabolic trait and serum/plasma metabolite association analyses revealed effects of these variants on lipid, inflammatory and other processes including new effects on many human diseases and traits. CONCLUSIONS: We identified eight loci that reproducibly associate with population-based cirrhosis and define their diverse effects on human diseases and traits.

Functional Analysis of the Dengue Virus Genome Using an Insertional Mutagenesis Screen.

In the last few decades, dengue virus, an arbovirus, has spread to over 120 countries. Although a vaccine has been approved in some countries, limitations on its effectiveness and a lack of effective antiviral treatments reinforce the need for additional research. The functions of several viral nonstructural proteins are essentially unknown. To better understand the functions of these proteins and thus dengue virus pathogenesis, we embarked on a genomewide transposon mutagenesis screen with next-generation sequencing to determine sites in the viral genome that tolerate 15-nucleotide insertions. Using this approach, we generated support for several published predicted transmembrane and enzymatic domains. Next, we created 7 mutants containing the 15-nucleotide insertion from the original selection and found 6 of them were capable of replication in both mammalian and mosquito tissue culture cells. Interestingly, one mutation had a significant impairment of viral assembly, and this mutation may lead to a better understanding of viral assembly and release. In addition, we created a fully infectious virus expressing a functionally tagged NS4B protein, which will provide a much-needed tool to elucidate the role of NS4B in viral pathogenesis.IMPORTANCE Dengue virus is a mosquito-borne virus distributed in tropical and subtropical regions globally that can result in hospitalization and even death in some cases. Although a vaccine exists, its limitations and a lack of approved antiviral treatments highlight our limited understanding of dengue virus pathogenesis and host immunity. The functions of many viral proteins are poorly understood. We used a previously published approach using transposon mutagenesis to develop tools to study these proteins' functions by adding insertions randomly throughout the viral genomes. These genomes were transferred into cells, and infectious progeny were recovered to determine sites that tolerated insertions, as only the genomes that tolerated insertions would be able to propagate. Using these results, we created viruses with epitope tags, one in the viral structural protein Capsid and one in the viral nonstructural protein NS4B. Further investigation of these mutants may elucidate the roles of Capsid and NS4B during dengue virus infections.

Independent markers of nonalcoholic fatty liver disease in a gentrifying population-based Chinese cohort.

BACKGROUND: Prevalence of nonalcoholic fatty liver disease (NAFLD) is increasing in developing countries, but its causes are not known. We aimed to ascertain the prevalence and determinants of NAFLD in a new largely unmedicated population-based cohort from the rapidly gentrifying region of Pinggu, China. METHODS: We randomized cluster sampled 4002 Pinggu residents aged 26 to 76 years. Data from 1238 men and 1928 women without significant alcohol drinking or hepatitis virus B or C infection were analysed. NAFLD was defined using a liver-spleen ratio (L/S ratio) ≤1.1 on unenhanced abdominal computed tomography (CT) scanning. RESULTS: Of men and women, 26.5% and 20.1%, respectively, had NAFLD. NAFLD prevalence was highest in younger men and older women. In multivariate logistic regression models, higher body mass index, waist circumference, serum triglyceride, alanine transaminase, and haemoglobin A1c independently increased the odds of NAFLD in both men and women separately. Higher annual household income and systolic blood pressure for men and higher serum uric acid and red meat intake and lower physical activity levels for women also independently associated with higher odds of NAFLD. Individuals with L/S ratio ≤1.1 had linearly increasing rates of obesity, diabetes, and metabolic syndrome that paralleled fatty liver increase. CONCLUSIONS: NAFLD is common in a gentrifying Chinese population particularly in younger men of high socioeconomic status and older women with sedentary behaviour who eat red meat. Demographic factors add independent risk of NAFLD above traditional metabolic risk factors. A CT L/S ratio of ≤1.1 identifies individuals at high risk of metabolic disease.

Recent Advances in Human Genetics and Epigenetics of Adiposity: Pathway to Precision Medicine?

Obesity is a heritable trait that contributes to substantial global morbidity and mortality. Here, we summarize findings from the past decade of genetic and epigenetic research focused on unravelling the underpinnings of adiposity. More than 140 genetic regions now are known to influence adiposity traits. The genetics of general adiposity, as measured by body mass index, and that of abdominal obesity, as measured by waist-to-hip ratio, have distinct biological backgrounds. Gene expression associated with general adiposity is enriched in the nervous system. In contrast, genes associated with abdominal adiposity function in adipose tissue. Recent population-based epigenetic analyses have highlighted additional distinct loci. We discuss how associated genetic variants can lead to understanding causal mechanisms, and to disentangling reverse causation in epigenetic analyses. Discoveries emerging from population genomics are identifying new disease markers and potential novel drug targets to better define and combat obesity and related diseases.

Body mass index trajectories in young adulthood predict non-alcoholic fatty liver disease in middle age: The CARDIA cohort study.

BACKGROUND & AIMS: Non-alcoholic fatty liver disease is an epidemic. Identifying modifiable risk factors for non-alcoholic fatty liver disease development is essential to design effective prevention programmes. We tested whether 25-year patterns of body mass index change are associated with midlife non-alcoholic fatty liver disease. METHODS: In all, 4423 participants from Coronary Artery Risk Development in Young Adults, a prospective population-based biracial cohort (age 18-30), underwent body mass index measurement at baseline (1985-1986) and 3 or more times over 25 years. At Year 25, 3115 had liver fat assessed by non-contrast computed tomography. Non-alcoholic fatty liver disease was defined as liver attenuation ≤40 Hounsfield Units after exclusions. Latent mixture modelling identified 25-year trajectories in body mass index per cent change (%Δ) from baseline. RESULTS: We identified four distinct trajectories of BMI%Δ: stable (26.2% of cohort, 25-year BMI %Δ = 3.1%), moderate increase (46.0%, BMI%Δ = 21.7%), high increase (20.9%, BMI%Δ = 41.9%) and extreme increase (6.9%, BMI%Δ = 65.9%). Y25 non-alcoholic fatty liver disease prevalence was higher in groups with greater BMI %Δ: 4.1%, 9.3%, 13.0%, and 17.6%, respectively (P-trend <.0001). In multivariable analyses, participants with increasing BMI%Δ had increasingly greater odds of non-alcoholic fatty liver disease compared to the stable group: OR: 3.35 (95% CI: 2.07-5.42), 7.80 (4.60-13.23) and 12.68 (6.68-24.09) for moderate, high and extreme body mass index increase, respectively. Associations were only moderately attenuated when adjusted for baseline or Y25 body mass index. CONCLUSIONS: Trajectories of weight gain during young adulthood are associated with greater non-alcoholic fatty liver disease prevalence in midlife independent of metabolic covariates and baseline or concurrent body mass index highlighting the importance of weight maintenance throughout adulthood as a target for primary non-alcoholic fatty liver disease prevention.

Twenty-five-year trajectories of insulin resistance and pancreatic ß-cell response and diabetes risk in nonalcoholic fatty liver disease.

BACKGROUND & AIMS: Insulin resistance is a risk marker for non-alcoholic fatty liver disease, and a risk factor for liver disease progression. We assessed temporal trajectories of insulin resistance and ß-cell response to serum glucose concentration throughout adulthood and their association with diabetes risk in non-alcoholic fatty liver disease. METHODS: Three thousand and sixty participants from Coronary Artery Risk Development in Young Adults, a prospective bi-racial cohort of adults age 18-30 years at baseline (1985-1986; Y0) who completed up to 5 exams over 25 years and had fasting insulin and glucose measurement were included. At Y25 (2010-2011), non-alcoholic fatty liver disease was assessed by noncontrast computed tomography after exclusion of other liver fat causes. Latent mixture modelling identified 25-year trajectories in homeostatic model assessment insulin resistance and ß-cell response homeostatic model assessment-ß. RESULTS: Three distinct trajectories were identified, separately, for homeostatic model assessment insulin resistance (low-stable [47%]; moderate-increasing [42%]; and high-increasing [12%]) and homeostatic model assessment-ß (low-decreasing [16%]; moderate-decreasing [63%]; and high-decreasing [21%]). Y25 non-alcoholic fatty liver disease prevalence was 24.5%. Among non-alcoholic fatty liver disease, high-increasing homeostatic model assessment insulin resistance (referent: low-stable) was associated with greater prevalent (OR 95% CI = 8.0, 2.0-31.9) and incident (OR = 10.5, 2.6-32.8) diabetes after multivariable adjustment including Y0 or Y25 homeostatic model assessment insulin resistance. In contrast, non-alcoholic fatty liver disease participants with low-decreasing homeostatic model assessment-ß (referent: high-decreasing) had the highest odds of prevalent (OR = 14.1, 3.9-50.9) and incident (OR = 10.3, 2.7-39.3) diabetes. CONCLUSION: Trajectories of insulin resistance and ß-cell response during young and middle adulthood are robustly associated with diabetes risk in non-alcoholic fatty liver disease. Thus, how persons with non-alcoholic fatty liver disease develop resistance to insulin provides important information about risk of diabetes in midlife above and beyond degree of insulin resistance at the time of non-alcoholic fatty liver disease assessment.

FTO genotype is associated with phenotypic variability of body mass index.

There is evidence across several species for genetic control of phenotypic variation of complex traits, such that the variance among phenotypes is genotype dependent. Understanding genetic control of variability is important in evolutionary biology, agricultural selection programmes and human medicine, yet for complex traits, no individual genetic variants associated with variance, as opposed to the mean, have been identified. Here we perform a meta-analysis of genome-wide association studies of phenotypic variation using ∼170,000 samples on height and body mass index (BMI) in human populations. We report evidence that the single nucleotide polymorphism (SNP) rs7202116 at the FTO gene locus, which is known to be associated with obesity (as measured by mean BMI for each rs7202116 genotype), is also associated with phenotypic variability. We show that the results are not due to scale effects or other artefacts, and find no other experiment-wise significant evidence for effects on variability, either at loci other than FTO for BMI or at any locus for height. The difference in variance for BMI among individuals with opposite homozygous genotypes at the FTO locus is approximately 7%, corresponding to a difference of ∼0.5 kilograms in the standard deviation of weight. Our results indicate that genetic variants can be discovered that are associated with variability, and that between-person variability in obesity can partly be explained by the genotype at the FTO locus. The results are consistent with reported FTO by environment interactions for BMI, possibly mediated by DNA methylation. Our BMI results for other SNPs and our height results for all SNPs suggest that most genetic variants, including those that influence mean height or mean BMI, are not associated with phenotypic variance, or that their effects on variability are too small to detect even with samples sizes greater than 100,000.

Novel association of TM6SF2 rs58542926 genotype with increased serum tyrosine levels and decreased apoB-100 particles in Finns.

A glutamate-to-lysine variant (rs58542926-T) in transmembrane 6 superfamily member 2 (TM6SF2) is associated with increased fatty liver disease and diabetes in conjunction with decreased cardiovascular disease risk. To identify mediators of the effects of TM6SF2, we tested for associations between rs58542926-T and serum lipoprotein/metabolite measures in cross-sectional data from nondiabetic statin-naïve participants. We identified independent associations between rs58542926-T and apoB-100 particles (ß = -0.057 g/l, P = 1.99 × 10-14) and tyrosine levels (ß = 0.0020 mmol/l, P = 1.10 × 10-8), controlling for potential confounders, in 6,929 Finnish men. The association between rs58542926-T and apoB-100 was confirmed in an independent sample of 2,196 Finnish individuals from the FINRISK study (ßreplication = -0.029, Preplication = 0.029). Secondary analyses demonstrated an rs58542926-T dose-dependent decrease in particle concentration, cholesterol, and triglyceride (TG) content for VLDL and LDL particles (P < 0.001 for all). No significant associations between rs58542926-T and HDL measures were observed. TM6SF2 SNP rs58542926-T and tyrosine levels were associated with increased incident T2D risk in both METSIM and FINRISK. Decreased liver production/secretion of VLDL, decreased cholesterol and TGs in VLDL/LDL particles in serum, and increased tyrosine levels identify possible mechanisms by which rs58542926-T exerts its effects on increasing risk of fatty liver disease, decreasing cardiovascular disease, and increasing diabetes risk, respectively.