Lack of association between peroxisome proliferator-activated receptors alpha and gamma2 polymorphisms and progressive liver damage in patients with non-alcoholic fatty liver disease: a case control study

Associations of peroxisome proliferator-activated receptor-γ Pro12Ala polymorphism with non-alcoholic fatty liver disease: A meta-analysis

BACKGROUND

Polymorphisms in peroxisome proliferator-activated receptor-γ pro12Ala (PPAR-γ Pro12Ala) have been associated with Non-alcoholic Fatty Liver Disease (NAFLD) in several studies. However, the results of these studies are not entirely consistent. Thus, we performed a meta-analysis to investigate the association between the PPAR-γ Pro12Ala polymorphisms and NAFLD.

METHODS

Studies were identified by searching PubMed database and manual assessment of the cited references in the retrieved articles. Study-specific relative risks (RRs) and 95 % confidence intervals (CIs) were estimated using a random-effect model. Study quality was assessed using the Newcastle-Ottawa scale.

RESULTS

Relevant medical researches show that 11 studies have been conducted on the analysis of NAFLD for meta-analysis, with a total of 2404 cases and 3959 participating controls. Meta-analysis results show that PPAR-γ Pro12Ala polymorphism and NALAD Ala alleles[no association between dominance model (OR = 0.968, 95%CI: 0.734-1.276, P = 0.815); Pro/Ala vs. Pro/Pro (OR = 0.930, 95 % CI: 0.701-1.233, P = 0.612); Ala/Ala vs. Pro/Pro (OR = 1.220, 95 % CI: 0.668-2.230, P = 0.518); recessive model (OR = 0.907, 95 % CI: 0.516-1.596, P = 0.736)]. Moreover, stratification by ethnicity also revealed that no matter it is in Caucasian populations or in Asian populations, NAFLD has no association with the PPAR-γ Pro12Ala polymorphism.

CONCLUSIONS

According to the meta-analysis, both in Asians and Caucasian populations, the PPAR-γ Pro12Ala polymorphism can't be demonstrated to have any link with susceptibility to NAFLD.

G Allele of the rs1801282 Polymorphism in PPARγ Gene Confers an Increased Risk of Obesity and Hypercholesterolemia, While T Allele of the rs3856806 Polymorphism Displays a Protective Role Against Dyslipidemia: A Systematic Review and Meta-Analysis

BACKGROUND

The relationships between the rs1801282 and rs3856806 polymorphisms in nuclear receptor peroxisome proliferator-activated receptor gamma (PPARγ) gene and obesity indexes as well as serum lipid levels have been extensively investigated in various studies, but the results were inconsistent and even contradictory.

METHODS

PubMed, Google Scholar, Embase, Cochrane Library, Web of Science, Wanfang, CNKI and VIP databases were searched for eligible studies. The random-effTPDEects model was used, and standardized mean difference (SMD) with 95% confidence interval (CI) was calculated to estimate the differences in obesity indexes and serum lipid levels between the subjects with different genotypes in a dominant model. Heterogeneity among studies was assessed by Cochran's x²-based Q-statistic test. Publication bias was identified by using Begg's test.

RESULTS

One hundred and twenty studies (70,317 subjects) and 33 studies (18,353 subjects) were identified in the analyses for the rs1801282 and rs3856806 polymorphisms, respectively. The G allele carriers of the rs1801282 polymorphism had higher levels of body mass index (SMD = 0.08 kg/m², 95% CI = 0.04 to 0.12 kg/m², p < 0.001), waist circumference (SMD = 0.12 cm, 95% CI = 0.06 to 0.18 cm, p < 0.001) and total cholesterol (SMD = 0.07 mmol/L, 95% CI = 0.02 to 0.11 mmol/L, p < 0.01) than the CC homozygotes. The T allele carriers of the rs3856806 polymorphism had lower levels of low-density lipoprotein cholesterol (SMD = -0.09 mmol/L, 95% CI = -0.15 to -0.03 mmol/L, p < 0.01) and higher levels of high-density lipoprotein cholesterol (SMD = 0.06 mmol/L, 95% CI = 0.02 to 0.10 mmol/L, p < 0.01) than the CC homozygotes.

CONCLUSIONS

The meta-analysis suggests that the G allele of the rs1801282 polymorphism confers an increased risk of obesity and hypercholesterolemia, while the T allele of the rs3856806 polymorphism displays a protective role against dyslipidemia, which can partly explain the associations between these polymorphisms and cardiovascular disease.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/prospero/, identifier [CRD42022319347].

Computational Analysis of Gly482Ser Single-Nucleotide Polymorphism in PPARGC1A Gene Associated with CAD, NAFLD, T2DM, Obesity, Hypertension, and Metabolic Diseases

Peroxisome proliferator-activated receptor-gamma coactivator 1-alpha (PPARGC1A) regulates the expression of energy metabolism's genes and mitochondrial biogenesis. The essential roles of PPARGC1A encouraged the researchers to assess the relation between metabolism-related diseases and its variants. To study Gly482Ser (+1564G/A) single-nucleotide polymorphism (SNP) after PPARGC1A modeling, we substitute Gly482 for Ser482. Stability prediction tools showed that this substitution decreases the stability of PPARGC1A or has a destabilizing effect on this protein. We then utilized molecular dynamics simulation of both the Gly482Ser variant and wild type of the PPARGC1A protein to analyze the structural changes and to reveal the conformational flexibility of the PPARGC1A protein. We observed loss flexibility in the RMSD plot of the Gly482Ser variant, which was further supported by a decrease in the SASA value in the Gly482Ser variant structure of PPARGC1A and an increase of H-bond with the increase of β-sheet and coil and decrease of turn in the DSSP plot of the Gly482Ser variant. Such alterations may significantly impact the structural conformation of the PPARGC1A protein, and it might also affect its function. It showed that the Gly482Ser variant affects the PPARGC1A structure and makes the backbone less flexible to move. In general, molecular dynamics simulation (MDS) showed more flexibility in the native PPARGC1A structure. Essential dynamics (ED) also revealed that the range of eigenvectors in the conformational space has lower extension of motion in the Gly482Ser variant compared with WT. The Gly482Ser variant also disrupts PPARGC1A interaction. Due to this single-nucleotide polymorphism in PPARGC1A, it became more rigid and might disarray the structural conformation and catalytic function of the protein and might also induce type 2 diabetes mellitus (T2DM), coronary artery disease (CAD), and nonalcoholic fatty liver disease (NAFLD). The results obtained from this study will assist wet lab research in expanding potent treatment on T2DM.

PPARγ gene Pro12Ala variants reduce the risk of obese individuals to non-alcoholic fatty liver: A study in Uygur Chinese population residing in Northwestern China

OBJECTIVE

To investigate the association of polymorphisms of Pro12Ala of peroxisome proliferator-activated receptor gamma (PPARγ) gene with clinical and biochemical parameters in Uygur Chinese population with non-alcoholic fatty liver (NAFLD) METHODS: In this case-control study, we recruited 467 NAFLD cases and 524 controls. Examination of abdominal ultrasound, clinical and biochemical profiles, as well as polymerase chain reaction-restriction fragment length polymorphisms of Pro12Ala of PPARγ gene were performed. The association of PPARγ gene Pro12Ala variants with clinical and biochemical parameters was analyzed.

RESULTS

There was no statistically significant difference between NAFLD and control groups in the frequencies of genotypic and allele distribution (P>0.05), while significantly difference of genotypic (P=0.032) and allele (P=0.015) distribution was found between NAFLD and control groups in the obese. Using logistics multivariate regression analysis by adjusting age, sex, body mass index, diabetes, hyperuricemia and dyslipidemia, both Pro12Ala and Ala12Ala polymorphisms were not associated with the presence of NAFLD. However, above two polymorphisms were found to be related to NAFLD in obesity group (odds ratio=0.442, P=0.031 and odds ratio=0.039, P=0.010, respectively) CONCLUSION: In Uygur Chinese population, PPARr gene Ala variants reduce the risk of NAFLD in obese individuals.

Impact of PPAR-Alpha Polymorphisms-The Case of Metabolic Disorders and Atherosclerosis

Peroxisome proliferator activated receptor α (PPARα) has the most relevant biological functions among PPARs. Activation by drugs and dietary components lead to major metabolic changes, from reduced triglyceridemia to improvement in the metabolic syndrome. Polymorphisms of PPARα are of interest in order to improve our understanding of metabolic disorders associated with a raised or reduced risk of diseases. PPARα polymorphisms are mainly characterized by two sequence changes, L162V and V227A, with the latter occurring only in Eastern nations, and by numerous SNPs (Single nucleotide polymorphisms) with a less clear biological role. The minor allele of L162V associates with raised total cholesterol, LDL-C (low-density lipoprotein cholesterol), and triglycerides, reduced HDL-C (high-density lipoprotein metabolism), and elevated lipoprotein (a). An increased cardiovascular risk is not clear, whereas a raised risk of diabetes or of liver steatosis are not well supported. The minor allele of the V227A polymorphism is instead linked to a reduction of steatosis and raised γ-glutamyltranspeptidase levels in non-drinking Orientals, the latter being reduced in drinkers. Lastly, the minor allele of rs4353747 is associated with a raised high-altitude appetite loss. These and other associations indicate the predictive potential of PPARα polymorphisms for an improved understanding of human disease, which also explain variability in the clinical response to specific drug treatments or dietary approaches.

Association between PPARGC1A single nucleotide polymorphisms and increased risk of nonalcoholic fatty liver disease among Iranian patients with type 2 diabetes mellitus

Background/aim

Environmental and genetic factors may play a major role in the development of nonalcoholic fatty liver disease (NAFLD) among people with obesity and type 2 diabetes mellitus. Based on the fact that PGC-1α, as the protein encoded by the PPARGC1A gene, plays a key role in energy metabolism pathways, it has been hypothesized that polymorphisms within the PPARGC1A gene may be associated with increased risks of NAFLD. Thus, this study was designed to evaluate the Gly482Ser polymorphism (rs8192678) within the PPARGC1A gene and its association with the increased risk of NAFLD in Iranian patients with type 2 diabetes.

Materials and methods

A total of 145 NAFLD patients with a history of type 2 diabetes and 145 healthy control subjects were included in the study. Gly482Ser polymorphism genotyping was done using the amplification refractory mutation system-polymerase chain reaction (ARMS-PCR) technique.

Results

The results showed a significant difference between the PPARGC1A Gly482Ser polymorphism in NAFLD patients and the healthy controls. Accordingly, the AA genotype and A allele were increased in the NAFLD patients when compared to the healthy controls. However, no significant correlation was observed between the Gly482Ser polymorphism and the physiological and biochemical parameters.

Conclusion

Based on the results, the AA genotype, which is associated with the insertion of Ser, can be considered as a risk factor for the development of NAFLD in Iranian patients with diabetes type 2.

The Pro12Ala polymorphism in the PPAR-γ2 gene is not associated with an increased risk of NAFLD in Iranian patients with type 2 diabetes mellitus

BACKGROUND

The peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that belong to the nuclear hormone receptor superfamily. Several studies have demonstrated a significant association between Pro12Ala polymorphism of the PPAR-γ2 gene and metabolic disorders. Therefore, this study aimed to evaluate the association of Pro12Ala polymorphism with increased risk of NAFLD in Iranian patients with type 2 diabetes mellitus.

METHODS

This cross-sectional study was performed on 145 healthy control subjects and 145 NAFLD patients with a history of type 2 diabetes. Pro12Ala polymorphism genotyping was performed using PCR-restriction fragment length polymorphism (RFLP) technique with the Bs1I restriction enzyme.

RESULTS

Our results demonstrated that CC and GG genotypes of Pro12Ala were found in the participants, but there was no statistically significant difference between NAFLD patients and healthy controls (P = 0.64 and χ2 = 0.21).

CONCLUSION

This study suggests that Pro12Ala polymorphism of the PPAR-γ2 gene cannot be considered as a risk factor for NAFLD in the Iranian population.

Association between PPARs Gene Functional Polymorphisms and Ischemic Stroke in Chinese Uyghur Population

PPARγ and PPARα belong to a receptor family of ligand-activated transcription factors involved in the regulation of inflammation, cellular glucose uptake, protection against atherosclerosis and endothelial cell function. Through these effects, they might be involved with the ischemic stroke (IS). We recruited 100 IS patients diagnosed by CTs or/and magnetic resonance imaging (MRI) and 100 normal healthy controls from Chinese Uyghur Population to assess the nature of the functional polymorphisms of PPARs and any links with IS in this unique population which has 60% European ancestry and 40% East Asian ancestry. We found that the Ala allele of the PPARγ Pro12Ala polymorphism was more common in controls than IS subjects (P = 0.008, corrected for multiple testing) in the Uyghur Population. Pro/Ala carriage may be associated with a decreased risk of IS in Uyghurs (OR 0.542, 95% CI 0.346-0.850). Additionally, the 162Val allele frequency at the DNA-binding region of PPARα was extremely rare in Chinese Uguhur IS patients and controls. Our population and ethnic-based study demonstrates that the 162Val allele frequency was extremely low in the Chinese Uyghur Population different from Some European and African populations and the PPARγ 12 Pro/Ala resulting in an amino acid exchange in N-terminal sequence may be an independent protective factor for IS in the Chinese Uyghur Population.

Genetics and epigenetics of NAFLD and NASH: Clinical impact

Non-alcoholic fatty liver disease (NAFLD) is now recognised as the most common liver disease worldwide. It encompasses a broad spectrum of conditions, from simple steatosis, through non-alcoholic steatohepatitis, to fibrosis and ultimately cirrhosis and hepatocellular carcinoma. A hallmark of NAFLD is the substantial inter-patient variation in disease progression. NAFLD is considered a complex disease trait such that interactions between the environment and a susceptible polygenic host background determine disease phenotype and influence progression. Recent years have witnessed multiple genome-wide association and large candidate gene studies, which have enriched our understanding of the genetic basis of NAFLD. Notably, the I148M PNPLA3 variant has been identified as the major common genetic determinant of NAFLD. Variants with moderate effect size in TM6SF2, MBOAT7 and GCKR have also been shown to have a significant contribution. The premise for this review is to discuss the status of research into important genetic and epigenetic modifiers of NAFLD progression. The potential to translate the accumulating wealth of genetic data into the design of novel therapeutics and the clinical implementation of diagnostic/prognostic biomarkers will be explored. Finally, personalised medicine and the opportunities for future research and challenges in the immediate post genetics era will be illustrated and discussed.

The Association between Pediatric NAFLD and Common Genetic Variants

Non-alcoholic fatty liver disease (NAFLD) is one of the most common complications of obesity. Several studies have shown that genetic predisposition probably plays an important role in its pathogenesis. In fact, in the last few years a large number of genetic studies have provided compelling evidence that some gene variants, especially those in genes encoding proteins regulating lipid metabolism, are associated with intra-hepatic fat accumulation. Here we provide a comprehensive review of the gene variants that have affected the natural history of the disease.

Development of gene polymorphisms in meditators of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most prevalent liver disease worldwide, the morbidity of which closely correlates with diversity of ethnicity, minority, family and location. Its histology spans from simple steatosis, to nonalcoholic steatohepatitis, which ultimately results in fibrosis, cirrhosis and hepatocellular carcinoma. The accelerating prevalence of NAFLD is due to an incremental incidence of metabolic syndrome that is distinguished by dyslipidemia, glucose impairment, obesity, excessive oxidative stress and adipocytokine impairment. Additionally, the pathogenesis of NAFLD is thought to be a multifactorial and complicated disease associated with lifestyle habits, nutritional factors and genetics. However, the pathogenesis and underlying mechanism in the development of NAFLD caused by genetics remains unclear. People have been increasingly emphasizing on the relationship between NAFLD and gene polymorphisms in recent years, with the aim of having a comprehensive elucidation of associated gene polymorphisms influencing the pathogenesis of the disease. In the current article, the authors attempted to critically summarize the most recently identified gene polymorphisms from the facets of glucose metabolism, fatty acid metabolism, oxidative stress and related cytokines in NAFLD that contribute to promoting the progression of the disease.

The association of nonalcoholic fatty liver disease with genetic polymorphisms: a multicenter study

INTRODUCTION

Growing evidence suggests that multiple factors, such as insulin resistance, nutritional factors, gut microbiota, and hormones released from the adipose tissue, act together on genetically predisposed individuals. We aimed to investigate whether various single-nucleotide polymorphisms (SNPs) play a role in the development of nonalcoholic fatty liver disease (NAFLD) and severity of liver damage in the Anatolian population.

METHODS

Two hundred and sixteen patients with biopsy-proven NAFLD and 150 control participants, aged 18-70 years, were consecutively enrolled in this multicenter study. Blood samples were genotyped for the PNPLA3 (rs738409), IL28B (rs12979860, rs12980275, rs8099917), PPAR-α 227 ALA, PPAR-γ pro 12 ALA, SOD2 C47T, and LOX-1 IVS4-14 polymorphisms using the custom-made LightSNiP assays on a LightCycler 480 II instrument.

RESULTS

Genotypic distributions of PNPLA3 rs738409 SNPs were different between NAFLD and control participants, but not for other SNPs. The PNPLA3 rs738409 GG polymorphism was associated with a 27-fold increased risk of development of NAFLD (odds ratio=27.8, 95% confidence interval: 3.5-218.4; P=0.002). Patients with the PNPLA3 GG genotype had higher nonalcoholic fatty liver disease activity score levels compared with patients with the PNPLA3 CC genotype (P<0.005). NAFLD patients without fibrosis had a higher frequency of IL28B rs12979860 TT and rs12980275 GG genotypes compared with NAFLD patients with fibrosis (P<0.005).

CONCLUSION

The present study proposes that polymorphisms in the PNPLA3 gene have highly predictive value in the development of NAFLD and are independently associated with the severity of liver histology in patients with NAFLD. The results of this study suggest that IL28B rs12979860 TT or rs12980275 GG may play an important protective role against the development of advanced fibrosis and even cirrhosis.

Significance of genetic polymorphisms in patients with nonalcoholic fatty liver disease

Because of recent advances in genetic research such as genome-wide association studies, the underlying genetic mechanisms of nonalcoholic fatty liver disease (NAFLD) pathophysiology have been elucidated. Here, we present a review of the current literature on the impact of genetic polymorphisms in patients with NAFLD. These genetic polymorphisms, which regulate lipid metabolism, glucose metabolism, and the renin-angiotensin system, are involved in NAFLD onset, steatosis, inflammation, fibrosis, and hepatocellular carcinoma (HCC). Among these genetic polymorphisms, many studies and meta-analyses have demonstrated that position 148 (rs738409 C/G) of the patatin-like phospholipase domain-containing protein (PNPLA3) is a genetic factor associated with NAFLD pathophysiological features, such as hepatic fat level, hepatic inflammation, fibrosis, and HCC. However, the impact of genetic polymorphisms on NAFLD pathophysiology appears to differ among ethnic groups. Therefore, further studies with larger sample sizes are needed for each ethnic group.

Genetic factors that affect nonalcoholic fatty liver disease: A systematic clinical review

AIM: To investigate roles of genetic polymorphisms in non-alcoholic fatty liver disease (NAFLD) onset, severity, and outcome through systematic literature review.

METHODS: The authors conducted both systematic and specific searches of PubMed through December 2015 with special emphasis on more recent data (from 2012 onward) while still drawing from more historical data for background. We identified several specific genetic polymorphisms that have been most researched and, at this time, appear to have the greatest clinical significance on NAFLD and similar hepatic diseases. These were further investigated to assess their specific effects on disease onset and progression and the mechanisms by which these effects occur.

RESULTS: We focus particularly on genetic polymorphisms of the following genes: PNPLA3, particularly the p. I148M variant, TM6SF2, particularly the p. E167K variant, and on variants in FTO, LIPA, IFNλ4, and iron metabolism, specifically focusing on HFE, and HMOX-1. We discuss the effect of these genetic variations and their resultant protein variants on the onset of fatty liver disease and its severity, including the effect on likelihood of progression to cirrhosis and hepatocellular carcinoma. While our principal focus is on NAFLD, we also discuss briefly effects of some of the variants on development and severity of other hepatic diseases, including hepatitis C and alcoholic liver disease. These results are briefly discussed in terms of clinical application and future potential for personalized medicine.

CONCLUSION: Polymorphisms and genetic factors of several genes contribute to NAFLD and its end results. These genes hold keys to future improvements in diagnosis and management.

Genetics of nonalcoholic fatty liver disease

Epidemiological, familial, and twin studies indicate that non-alcoholic fatty liver disease, now the leading cause of liver damage in developed countries, has a strong heritability. The common I148M variant of PNPLA3 impairing hepatocellular lipid droplets remodeling is the major genetic determinant of hepatic fat content. The I148M variant has a strong impact on the full spectrum of liver damage related to fatty liver, encompassing non-alcoholic steatohepatitis, advanced fibrosis, and hepatocellular carcinoma, and influences the response to therapeutic approaches. Common variants in GCKR enhance de novo hepatic lipogenesis in response to glucose and liver inflammation. Furthermore, the low-frequency E167K variant of TM6SF2 and rare mutations in APOB, which impair very low-density lipoproteins secretion, predispose to progressive fatty liver.

CONCLUSIONS

These and other recent findings reviewed here indicate that impaired lipid handling by hepatocytes has a major role in the pathogenesis of non-alcoholic fatty liver disease by triggering inflammation, fibrogenesis, and carcinogenesis. These discoveries have provided potential novel biomarkers for clinical use and have revealed intriguing therapeutic targets.

Genetic Factors That Affect Risk of Alcoholic and Nonalcoholic Fatty Liver Disease

Genome-wide association studies and candidate gene studies have informed our understanding of factors contributing to the well-recognized interindividual variation in the progression and outcomes of alcoholic liver disease and nonalcoholic fatty liver disease. We discuss the mounting evidence for shared modifiers and common pathophysiological processes that contribute to development of both diseases. We discuss the functions of proteins encoded by risk variants of genes including patatin-like phospholipase domain-containing 3 and transmembrane 6 superfamily member 2, as well as epigenetic factors that contribute to the pathogenesis of alcoholic liver disease and nonalcoholic fatty liver disease. We also discuss important areas of future genetic research and their potential to affect clinical management of patients.

The Role of Nuclear Receptors in the Pathophysiology, Natural Course, and Drug Treatment of NAFLD in Humans

Nonalcoholic fatty liver disease (NAFLD) describes steatosis, nonalcoholic steatohepatitis with or without fibrosis, and hepatocellular carcinoma, namely the entire alcohol-like spectrum of liver disease though observed in the nonalcoholic, dysmetabolic, individual free of competing causes of liver disease. NAFLD, which is a major public health issue, exhibits intrahepatic triglyceride storage giving rise to lipotoxicity. Nuclear receptors (NRs) are transcriptional factors which, activated by ligands, are master regulators of metabolism and also have intricate connections with circadian control accounting for cyclical patterns in the metabolic fate of nutrients. Several transcription factors, such as peroxisome proliferator-activated receptors, liver X receptors, farnesoid X receptors, and their molecular cascades, finely regulate energetic fluxes and metabolic pathways. Dysregulation of such pathways is heavily implicated in those metabolic derangements characterizing insulin resistance and metabolic syndrome and in the histogenesis of progressive NAFLD forms. We review the role of selected NRs in NAFLD pathogenesis. Secondly, we analyze the role of NRs in the natural history of human NAFLD. Next, we discuss the results observed in humans following administration of drug agonists or antagonists of the NRs pathogenically involved in NAFLD. Finally, general principles of treatment and lines of research in human NAFLD are briefly examined.

Genetic and epigenetic mechanisms of NASH

Along with the obesity epidemic, the prevalence of nonalcoholic fatty liver disease (NAFLD) has increased exponentially. The histological disease spectrum of NAFLD ranges from bland fatty liver (hepatic steatosis), to the concomitant presence of inflammation and ballooning which defines nonalcoholic steatohepatitis (NASH). The latter can progress in a subset to fibrosis, leading ultimately to cirrhosis and hepatocellular carcinoma. The past decade has seen tremendous advances in our understanding of the genetic and epigenetic bases of NAFLD, mainly through the application of high end technology platforms including genome-wide association studies (GWAS). These have helped to define common gene variants (minor allele frequency >5 %) that contribute to the NAFLD phenotype. Looking to the future, these discoveries are expected to lead to improved diagnostics, the personalization of medicine, and a better understanding of the pathophysiological underpinnings that drive the transition from NAFLD to steatohepatitis and fibrosis, leading to the identification of novel therapeutic targets. In this review, we summarize data on the current state of knowledge with regard to the genetic and epigenetic mechanisms for the development of NASH.

Genetic background in nonalcoholic fatty liver disease: A comprehensive review

In the Western world, nonalcoholic fatty liver disease (NAFLD) is considered as one of the most significant liver diseases of the twenty-first century. Its development is certainly driven by environmental factors, but it is also regulated by genetic background. The role of heritability has been widely demonstrated by several epidemiological, familial, and twin studies and case series, and likely reflects the wide inter-individual and inter-ethnic genetic variability in systemic metabolism and wound healing response processes. Consistent with this idea, genome-wide association studies have clearly identified Patatin-like phosholipase domain-containing 3 gene variant I148M as a major player in the development and progression of NAFLD. More recently, the transmembrane 6 superfamily member 2 E167K variant emerged as a relevant contributor in both NAFLD pathogenesis and cardiovascular outcomes. Furthermore, numerous case-control studies have been performed to elucidate the potential role of candidate genes in the pathogenesis and progression of fatty liver, although findings are sometimes contradictory. Accordingly, we performed a comprehensive literature search and review on the role of genetics in NAFLD. We emphasize the strengths and weaknesses of the available literature and outline the putative role of each genetic variant in influencing susceptibility and/or progression of the disease.

Donor PPARα Gene Polymorphisms Influence the Susceptibility to Glucose and Lipid Disorders in Liver Transplant Recipients: A Strobe-Compliant Observational Study

Peroxisome proliferator-activated receptor α (PPARα) is an important regulator of glucose and lipid metabolism, and is predominantly expressed in the liver. We aimed to evaluate the effect of donor hepatic PPARα gene polymorphisms on the development of metabolic disorders following liver transplantation (LT).A total of 176 patients undergoing primary LT were included in this Review Board-approved study. Genomic DNA was extracted from fresh frozen donor liver tissues (biopsy specimens for pathological testing at surgery). Eight single nucleotide polymorphisms in the PPARα gene were chosen from either the HapMap CHB database or previous reports.The distribution of metabolic disorders differed significantly between the wild-type and variant genotypes of both the rs5767743 and rs5767700 loci (P < 0.05 for all). After an adjustment for other factors (body mass index and tacrolimus blood concentration), the rs5767743 genetic variant was found to be an independent protective factor (P = 0.005, odds ratio = 0.416 per C allele, 95% confidence interval  = 0.225-0.768). When compared with the wild-type genotype, the variant genotypes rs5767743 and rs5767700 correlated with significantly increased PPARα and CYP3A4 mRNA expression and lower tacrolimus trough concentration/dose ratios (P < 0.05 for all).Donor PPARα gene polymorphisms influence the susceptibility to metabolic disorders following LT and may also be associated with a fasten tacrolimus metabolism because of elevated CYP3A4 expression.

Genetic Factors in the Pathogenesis of Nonalcoholic Fatty Liver and Steatohepatitis

Liver fat accumulation generally related to systemic insulin resistance characterizes nonalcoholic fatty liver disease (NAFLD), which in the presence of nonalcoholic steatohepatitis (NASH) can progress towards cirrhosis and hepatocellular carcinoma. Due to the epidemic of obesity, NAFLD is now the most frequent liver disease in Western countries. Epidemiological, familial, and twin studies provide evidence for a strong genetic component of NAFLD susceptibility. Recently, genome-wide association studies led to the identification of the major inherited determinants of hepatic fat accumulation: patatin-like phospholipase domain-containing 3 (PNPLA3) I148M gene and transmembrane 6 superfamily member 2 (TM6SF2) E167K gene variants, involved in lipid droplets remodelling and very low-density lipoproteins secretion, are the major determinants of interindividual differences in liver steatosis, and susceptibility to progressive NASH. In this review, we aimed to provide an overview of recent insights into the genetics of hepatic fat accumulation and steatohepatitis.

Systematic review of genetic association studies involving histologically confirmed non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease has an increasing prevalence in Western countries, affecting up to 20% of the population.

Association of the variants in the PPARG gene and serum lipid levels: a meta-analysis of 74 studies

Considerable studies have been carried out to investigate the relationship between the polymorphisms of PPARG (Pro12Ala, C161T and C1431T) and serum lipid levels, but the results were inconclusive. Hence, we conducted a meta-analysis to clarify the association. MEDLINE, EMBASE and the Cochrane Library databases were searched systematically. The subgroup analysis was performed based on ethnicity. Seventy-four studies with 54,953 subjects were included in this meta-analysis. In Pro12Ala, the group with the ‘PP’ (C/C genotype) genotype group had lower levels of total cholesterol (TC) (mean difference, MD: −0.02, P < 0.00001; I² = 28%), low-density lipoprotein cholesterol (LDL-C) (MD: −0.02, P < 0.00001; I² = 30%) and higher levels of triglyceride (TG) (MD: 0.06, P < 0.00001; I² = 30%) than the combined ‘PA+AA’ (PA = C/G genotype, AA = G/G genotype) genotype group in Asian population, and the group with the ‘PP’ genotype had higher levels of TG (MD: 0.07, P < 0.02; I² = 67%) than the combined ‘PA+AA’ genotype group in non-Asian population. No statistically significant differences in the levels of TC, TG, high-density lipoprotein cholesterol, LDL-C were detected between different genotypes in C161T(Asian or non-Asian) and C1431T(Asian) polymorphisms. This meta-analysis was a renewed and confirmed study to assess the association between PPARG polymorphisms and serum lipid levels in Asian and non-Asian populations. There is a prominent association between Pro12Ala polymorphism and the levels of TC, LDL-C and TG in Asian population. No statistically significant differences in serum lipid levels were detected between different genotypes in C161T and C1431T polymorphisms.

Gene-Gene Interactions among Pparα/δ/γ Polymorphisms for Apolipoprotein (Apo) A-I/Apob Ratio in Chinese Han Population

BACKGROUND

The peroxisome proliferator-activated receptors (PPARs) -α, -δ/β and -γ are the ligand-activated transcription factors involved in the regulation of fatty acid and lipoprotein metabolism, energy balance, cell proliferation and differentiation and atherosclerosis, etc. We investigated the associations of 10 single-nucleotide polymorphisms (SNPs) in PPARs with apolipoprotein (apo) A-I/apoB ratio in Chinese Han population.

METHODS

Overall, 630 subjects (212 males, 418 females) were randomly selected from the Prevention of Metabolic Syndrome and Multiple Metabolic Disorders in Jiangsu Province of China Study Cohort. Population analyzed was as the general population which involved healthy people and individuals with disorders of apoA-I or apoB. 10 SNPs (rs1800206, rs135539, rs4253778, rs2016520, rs9794, rs10865710, rs1805192, rs709158, rs3856806 and rs4684847) were genotyped. Mean difference (Difference) and 95% confident interval (95%CI) were calculated.

RESULTS

After covariates adjustment, rs1800206-V allele (LV+VV) and rs3856806-T allele (CT+TT) were significantly associated with a decreased apoA-I/apoB ratio than those wild type carriers, Difference (95%CI) were -1.29 (-1.96-0.62) and -0.8 (-1.42~-0.17), respectively. Rs4253778-C allele was significantly associated with an increased apoA-I/apoB ratio compared to the wild type carriers (GG), Difference (95%CI) was 0.76 (0.04-1.48). Generalized multifactor dimensionality reduction analysis showed that three-to-eight-locus models were significant with apoA-I/apoB ratio (P<0.05). We chose the seven-locus model (P=0.0010) as the best GMDR model (cross-validation consistency was 7/10 and testing accuracy was 62.97%).

CONCLUSION

Our data provided the evidence that PPARs polymorphisms might be involved in regulation of apoA-I/apoB ratio in independently and/or in an interactive manner.

The Wide and Complex Field of NAFLD Biomarker Research: Trends

Background. Nonalcoholic fatty liver disease is now acknowledged as a complex public health issue linked to sedentary lifestyle, obesity, and related disorders like type 2 diabetes and metabolic syndrome. Aims. We aimed to retrieve its trends out of the huge amount of published data. Therefore, we conducted an extensive literature search to identify possible biomarker and/or biomarker combinations by retrospectively assessing and evaluating common and novel biomarkers to predict progression and prognosis of obesity related liver diseases. Methodology. We analyzed finally 62 articles accounting for 157 cohorts and 45,288 subjects. Results. Despite the various approaches, most cohorts were considerably small and rarely comparable. Also, we found that the same standard parameters were measured rather than novel biomarkers. Diagnostics approaches appeared incomparable. Conclusions. Further collaborative investigations on harmonizing ways of data acquisition and identifying such biomarkers for clinical use are necessary to yield sufficient significant results of potential biomarkers.

Meta-analysis of associations between the peroxisome proliferator-activated receptor-γ Pro12Ala polymorphism and susceptibility to nonalcoholic fatty liver disease, rheumatoid arthritis, and psoriatic arthritis

INTRODUCTION

The purpose of this study was to examine whether a Proline (Pro)-to-Alanine (Ala) exchange at codon 12 (Pro12Ala) polymorphism of the peroxisome proliferator-activated receptor-gamma (PPARγ) is associated with susceptibility to nonalcoholic fatty liver disease (NAFLD), rheumatoid arthritis (RA), and psoriatic arthritis (PsA).

METHODS

A meta-analysis was conducted on the association between the PPARγ Pro12Ala polymorphism and NAFLD, RA, and PsA.

RESULTS

Nine studies, including five on NAFLD, two on RA, and two on PsA, were available for the meta-analysis consisting of 8082 cases and 3790 controls. The meta-analysis revealed no association between the Ala allele of the PPARγ Pro12Ala polymorphism and NAFLD (odds ratios [OR]=0.936, 95% confidence interval [CI]=0.672-1.302, p=0.693). However, stratification by ethnicity indicated an association between the Ala allele and NAFLD in East Asians (OR=0.700, 95% CI=0.496-0.987, p=0.042), but not in Europeans (OR=1.128, 95% CI=0.863-1.475, p=0.378). Analysis using the dominant model showed the same Ala allele pattern in East Asians and Europeans (OR=0.688, 95% CI=0.484-0.978, p=0.037; OR=1.051, 95% CI=0.782-1.413, p=0.742), demonstrating a significant association between the Ala allele and NAFLD in East Asians. The meta-analysis revealed no association between the Ala allele and RA in East Asians (OR=0.467, 95% CI=0.188-1.161, p=0.101), and no association was found between the Ala allele and PsA in Europeans (OR=0.869, 95% CI=0.465-1.627, p=0.662).

CONCLUSIONS

Our meta-analysis demonstrates that the PPARγ Pro12Ala polymorphism is associated with susceptibility to NAFLD in East Asians, but not in European populations.

Genetic predisposition in NAFLD and NASH: impact on severity of liver disease and response to treatment

Liver fat deposition related to systemic insulin resistance defines non-alcoholic fatty liver disease (NAFLD) which, when associated with oxidative hepatocellular damage, inflammation, and activation of fibrogenesis, i.e. non-alcoholic steatohepatitis (NASH), can progress towards cirrhosis and hepatocellular carcinoma. Due to the epidemic of obesity, NAFLD is now the most frequent liver disease and the leading cause of altered liver enzymes in Western countries. Epidemiological, familial, and twin studies provide evidence for an element of heritability of NAFLD. Genetic modifiers of disease severity and progression have been identified through genome-wide association studies. These include the Patatin-like phosholipase domain-containing 3 (PNPLA3) gene variant I148M as a major determinant of inter-individual and ethnicity-related differences in hepatic fat content independent of insulin resistance and serum lipid concentration. Association studies confirm that the I148M polymorphism is also a strong modifier of NASH and progressive hepatic injury. Furthermore, a few large multicentre case-control studies have demonstrated a role for genetic variants implicated in insulin signalling, oxidative stress, and fibrogenesis in the progression of NAFLD towards fibrosing NASH, and confirm that hepatocellular fat accumulation and insulin resistance are key operative mechanisms closely involved in the progression of liver damage. It is now important to explore the molecular mechanisms underlying these associations between gene variants and progressive liver disease, and to evaluate their impact on the response to available therapies. It is hoped that this knowledge will offer further insights into pathogenesis, suggest novel therapeutic targets, and could help guide physicians towards individualised therapy that improves clinical outcome.

Host genetic variants in obesity-related nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a complex disease. The considerable variability in the natural history of the disease suggests an important role for genetic variants in the disease development and progression. There is evidence based on genome-wide association studies and/or candidate gene studies that genetic polymorphisms underlying insulin signaling, lipid metabolism, oxidative stress, fibrogenesis, and inflammation can predispose individuals to NAFLD. This review highlights some of the genetic variants in NAFLD.

Peroxisome proliferator-activated receptors alpha and gamma2 polymorphisms in nonalcoholic fatty liver disease: a study in Brazilian patients

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) refers to the accumulation of hepatic steatosis in the absence of excess alcohol consumption. The pathogenesis of fatty liver disease and steatohepatitis (NASH) is not fully elucidated, but the common association with visceral obesity, hyperlipidemia, hypertension and type 2 diabetes mellitus (T2DM) suggests that it is the hepatic manifestation of metabolic syndrome. Peroxisome proliferator-activated receptor PPARα and PPARγ are members of a family of nuclear receptors involved in the metabolism of lipids and carbohydrates, adipogenesis and sensitivity to insulin. The objective of this study was to analyze the polymorphisms Leu162Val of PPARα and Pro12Ala of PPARγ as genetic risk factors for the development and progression of NAFLD.

METHODS

One hundred and three NAFLD patients (89 NASH, 14 pure steatosis) and 103 healthy volunteers were included. Single nucleotide polymorphisms (SNPs) Leu162Val and Pro12Ala were analyzed by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP).

RESULTS

NASH patients presented higher BMI, AST and prevalence of T2DM than patients with pure steatosis. A higher prevalence of 12Ala allele was observed in the NASH Subgroup when compared to Control Group. When we grouped NASH and Steatosis Subgroups (NAFLD), we found lower serum glucose and more advanced fibrosis in the Leu162Val SNP. On the other hand, there was no statistical difference in clinical, laboratorial and histological parameters according to the Pro12Ala SNP.

CONCLUSIONS

We documented a lower prevalence of 12Ala allele of gene PPARγ in the NASH Subgroup when compared to Control Group. In NAFLD patients, there were no associations among the occurrence of Pro12Ala SNP with clinical, laboratorial and histological parameters. We also documented more advanced fibrosis in the Leu162Val SNP. The obtained data suggest that Pro12Ala SNP may result in protection against liver injury and that Leu162Val SNP may be involved in the progression of NAFLD.

Association between the Pro12Ala polymorphism of PPAR-γ gene and the non-alcoholic fatty liver disease: a meta-analysis

Several studies have been conducted to examine the association between PPAR-γ2 Pro12Ala polymorphism and non-alcoholic fatty liver disease (NAFLD), but the results remain inconsistent. In this study, a meta-analysis was performed to assess the association of PPAR-γ Pro12Ala polymorphism with NAFLD risk. A total of 8 case-control studies, including 1697 cases and 2427 controls, were selected. Pooled odds ratio (OR) with 95% confidence interval (CI) was calculated using fixed- or random-effects model. Overall, no evidence has indicated that the Pro12Ala polymorphism was associated with the susceptibility to NAFLD. Besides, stratified analysis with ethnicity also indicated that no significant association between PPAR-γ Pro12Ala and the risk of NAFLD under all for genetic model in both Asian and Caucasian populations was observed. This meta-analysis indicated that the Pro12Ala polymorphism is not associated with NAFLD risk. Large and well-designed studies are warranted to validate our findings.

The C-681G polymorphism of the PPAR-γ gene is associated with susceptibility to non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is defined as excessive accumulation of fatty acid in the liver, a common disease in the world. The research of single nucleotide polymorphisms (SNPs) provides a new approach for managing NAFLD. SNPs may increase or decrease the functions of the target genes and their encoding proteins. Peroxisome proliferator-activated receptor (PPAR) plays a key role in modulating metabolism of hepatic triglycerides and consequently magnitude of NAFLD. In this study, we investigated the effect of three SNPs in the PPAR-γ gene i.e. rs10865710 (C-681G), rs7649970 (C-689T) and rs1801282 (C34G, also termed Pro12Ala) on susceptibility to NAFLD. The participants were selected from our epidemiological survey. Totally 169 participants were enrolled in NAFLD group, and 699 healthy subjects were included as controls. PCR-RFLP was applied to detect the SNPs. The G allele frequency of rs10865710 in NAFLD group (41.1%) was significantly higher than that (34.8%) in controls (p = 0.03). Differences in other two loci (rs7649970 and rs1801282) were not statistically significant between the two groups (p > 0.05). This result was confirmed by haplotype analysis. The GCC haplotype (a set of 3 adjacent SNPs in linkage disequilibrium, corresponding to the three alleles of above polymorphisms in order) was a risk factor for the susceptibility to NAFLD (p = 0.03). This study has revealed that the G allele of rs10865710 in the PPAR-γ gene is associated with the increased susceptibility to NAFLD. Our findings may provide novel diagnostic biomarkers and therapeutic targets for NAFLD.

Does PPARγ2 gene Pro12Ala polymorphism affect nonalcoholic fatty liver disease risk? Evidence from a meta-analysis

Genetic factors can substantially contribute to the pathogenesis of nonalcoholic fatty liver disease (NAFLD). A missense Pro12Ala substitution in the PPARγ2 gene (rs1801282) has been studied in relation with NAFLD risk in different ethnic groups, but findings have been inconclusive. The aim of this was to evaluate the association between rs1801282 and NAFLD through meta-analysis of all relevant published evidence. A systematic search to find eligible studies was performed in Medline, HuGE Navigator, and SCOPUS databases. The strength of association was evaluated using odds ratios with 95% confidence intervals obtained from a random effect approach and under additive, dominant, co-dominant, recessive, and allelic contrast models. Seven studies comprising 1474 cases and 2259 controls met the eligibility criteria and included in the meta-analysis. Combined results did not indicate any predisposing or protective effect for rs1801282 under any of the assessed modes of inheritance. The rate of heterogeneity was generally high due to the inter-study variations in terms of age, gender, and ethnicity. Evidence from the current meta-analysis indicated that rs1801282 variants are not associated with NAFLD risk. Future large-scale studies are required to substantiate the present findings.

Peroxisome proliferator-activated receptor genetic polymorphisms and nonalcoholic Fatty liver disease: any role in disease susceptibility?

Nonalcoholic fatty liver disease (NAFLD) defines a wide spectrum of liver diseases that extend from simple steatosis, that is, increased hepatic lipid content, to nonalcoholic steatohepatitis (NASH), a condition that may progress to cirrhosis with its associated complications. Nuclear hormone receptors act as intracellular lipid sensors that coordinate genetic networks regulating lipid metabolism and energy utilization. This family of transcription factors, in particular peroxisome proliferator-activated receptors (PPARs), represents attractive drug targets for the management of NAFLD and NASH, as well as related conditions such as type 2 diabetes and the metabolic syndrome. The impact on the regulation of lipid metabolism observed for PPARs has led to the hypothesis that genetic variants within the human PPARs genes may be associated with human disease such as NAFLD, the metabolic syndrome, and/or coronary heart disease. Here we review the available evidence on the association between PPARs genetic polymorphism and the susceptibility to NAFLD and NASH, and we provide a meta-analysis of the available evidence. The impact of PPAR variants on the susceptibility to NASH in specific subgroup of patients, and in particular on the response to therapies, especially those targeting PPARs, represents promising new areas of investigation.

Misregulation of PPAR Functioning and Its Pathogenic Consequences Associated with Nonalcoholic Fatty Liver Disease in Human Obesity

Nonalcoholic fatty liver disease in human obesity is characterized by the multifactorial nature of the underlying pathogenic mechanisms, which include misregulation of PPARs signaling. Liver PPAR-α downregulation with parallel PPAR-γ and SREBP-1c up-regulation may trigger major metabolic disturbances between de novo lipogenesis and fatty acid oxidation favouring the former, in association with the onset of steatosis in obesity-induced oxidative stress and related long-chain polyunsaturated fatty acid n-3 (LCPUFA n-3) depletion, insulin resistance, hypoadiponectinemia, and endoplasmic reticulum stress. Considering that antisteatotic strategies targeting PPAR-α revealed that fibrates have poor effectiveness, thiazolidinediones have weight gain limitations, and dual PPAR-α/γ agonists have safety concerns, supplementation with LCPUFA n-3 appears as a promising alternative, which achieves both significant reduction in liver steatosis scores and a positive anti-inflammatory outcome. This latter aspect is of importance as PPAR-α downregulation associated with LCPUFA n-3 depletion may play a role in increasing the DNA binding capacity of proinflammatory factors, NF-κB and AP-1, thus constituting one of the major mechanisms for the progression of steatosis to steatohepatitis.

Association of peroxisome proliferator activated receptor-γ gene with non-alcoholic fatty liver disease in Asian Indians residing in north India

BACKGROUND

Genetics of non-alcoholic fatty liver (NAFLD) in Asian Indians has been inadequately studied. We investigated the association of polymorphisms C161T and Pro12Ala of peroxisome proliferator-activated receptor gamma (PPARγ) with clinical and biochemical parameters in Asian Indians with NAFLD.

METHODS

In this case-control study, 162 NAFLD cases and 173 controls were recruited. Abdominal ultrasound, clinical and biochemical profiles, fasting insulin levels and value of homeostasis model assessment of insulin resistance were determined. Polymerase chain reaction-restriction fragment length polymorphisms of two polymorphisms were performed. The association of these polymorphisms with clinical and biochemical parameters was analysed.

RESULTS

Higher frequency of Ala and T alleles of PPARγ was obtained in cases. Ala/Ala genotype of PPARγ (Pro12Ala) was associated with significantly higher serum triglycerides (TG), alkaline phosphatase (ALK) and waist-hip ratio in cases as compared to controls. In C161T polymorphism, TT genotype was significantly increased TG (p=0.04), total cholesterol (p=0.01), ALK (p=0.04) and gamma-glutamyl transpeptidase (p=0.007) in cases. The linkage disequilibrium for these two single-nucleotide polymorphisms of PPARγ was differed in cases (D1=0.1; p=0.006) and controls (D1=0.07; p=0.1). Using a multivariate analysis after adjusting for age, sex and body mass index, the presence of NAFLD was linked to these two polymorphisms (odds ratio 1.64 (95% CI: 1.09-2.45, p=0.05)].

CONCLUSION

Asian Indians in north India carrying the alleles Ala and T of PPARγ (Pro12Ala and C161T) polymorphisms are predisposed to develop NAFLD.

Update on pparγ and nonalcoholic Fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common initial presentation of obesity and insulin resistance. Uninterrupted progression of hepatic lipid accumulation often leads to fatty liver disease and eventually cirrhosis. Insulin resistance is one of the characteristics of type 2 diabetes. Several types of treatment have been employed against type 2 diabetes some of which ameliorate NAFLD. The frequent line of treatment to improve insulin sensitivity is the use of thiazolidinediones (TZD) which activate the nuclear receptor, peroxisome proliferator activated receptor gamma (Pparγ). Although TZDs are proven to be very effective in promoting insulin sensitivity, its actions on Pparγ have been complicated, specifically on NAFLD. According to studies in different models, Pparγ manifests both beneficial and undesirable effects on NAFLD. This paper will focus on the current knowledge of Pparγ and its effect on NAFLD.

LPIN1 rs13412852 polymorphism in pediatric nonalcoholic fatty liver disease

OBJECTIVES

The aim of the present study was to evaluate whether the lipin1 rs13412852 C>T polymorphism is associated with nonalcoholic steatohepatitis and fibrosis in pediatric Italian patients with nonalcoholic fatty liver disease (NAFLD).

METHODS

A total of 142 untreated, consecutive children and 115 adults with biopsy-proven NAFLD and 337 healthy controls without steatosis were studied. Liver histology was assessed by the NAFLD activity score and the rs13412852 polymorphism by a 5' nuclease Taqman assay.

RESULTS

Homozygosity for the rs13412852 T allele was underrepresented in pediatric, but not adult, patients with NAFLD compared with healthy controls (7% vs 14%; odds ratio [OR] 0.58, 95% confidence interval [CI] 0.35-0.91), and it was associated with lower triglycerides both in pediatric patients and healthy controls (P ≤ 0.01). Affected children carrying the rs13412852 TT genotype had a trend for a lower prevalence of nonalcoholic steatohepatitis, and significantly less severe liver damage, as indicated by NAFLD activity score severity (P = 0.026) and a lower prevalence of liver fibrosis (P = 0.012). The negative association between rs13412852 TT genotype and fibrosis was independent of Patatin-like phospholipase domain-containing-3 genotype and other clinical risk factors, including age, waist circumference, the presence of hyperglycemia, and alanine transaminase levels (OR 0.29; 95% CI 0.11-0.66), and it was confirmed at multivariate analysis in adults (OR 0.15; 95% CI 0.02-0.67).

CONCLUSIONS

Lipin1 rs13412852 single nucleotide polymorphism is associated with the severity of liver damage and fibrosis progression in pediatric patients with histological NAFLD.

Genetic variation in the peroxisome proliferator activated receptor-gamma gene is associated with histologically advanced NAFLD

BACKGROUND

The peroxisome proliferator activated receptor-gamma (PPARG) is a nuclear receptor that regulates adipocyte differentiation, insulin sensitivity and lipid metabolism, thus, it represents a good candidate gene for non-alcoholic fatty liver disease (NAFLD).

PURPOSE AND METHOD

We investigated the association of two PPARG variants (Pro12Ala and C1431T) with NAFLD and its histological features. DNA was extracted from 274 archived, formalin-fixed liver biopsy specimens from 212 patients with NAFLD and 62 controls with normal liver histology.

RESULTS

Individual SNPs did not show significant association with NAFLD or its histological features. A haplotype comprised of both minor alleles (GT) was less enriched whereas a haplotype comprised of the two major alleles (CC) was more enriched in subjects with NAFLD compared to controls [9.3% vs. 28.1% for GT (P = 0.001, OR 0.26 (range 0.14-0.48) and 80.4% vs. 64.8% for CC (P = 0.037, OR 2.23 (range 1.30-3.81)]. Both haplotypes were significantly associated with steatosis and fibrosis. The GT haplotype was also associated with lobular inflammation.

CONCLUSIONS

Genetic variation in PPARG is associated with NAFLD, and the GT haplotype is associated with inflammatory and fibrotic changes that denote histologically advanced NAFLD.

Nuclear receptor variants in liver disease

This review aims to provide a snapshot of the actual state of knowledge on genetic variants of nuclear receptors (NR) involved in regulating important aspects of liver metabolism. It recapitulates recent evidence for the application of NR in genetic diagnosis of monogenic ("Mendelian") liver disease and their use in clinical diagnosis. Genetic analysis of multifactorial liver diseases such as viral hepatitis or fatty liver disease identifies key players in disease predisposition and progression. Evidence from these analyses points towards a role of NR polymorphisms in common diseases, linking regulatory networks to complex and variable phenotypes. The new insights into NR variants also offer perspectives and cautionary advice for their use as handles towards diagnosis and treatment.

Nuclear receptor variants in liver disease

This review aims to provide a snapshot of the actual state of knowledge on genetic variants of nuclear receptors (NR) involved in regulating important aspects of liver metabolism. It recapitulates recent evidence for the application of NR in genetic diagnosis of monogenic (“Mendelian”) liver disease and their use in clinical diagnosis. Genetic analysis of multifactorial liver diseases such as viral hepatitis or fatty liver disease identifies key players in disease predisposition and progression. Evidence from these analyses points towards a role of NR polymorphisms in common diseases, linking regulatory networks to complex and variable phenotypes. The new insights into NR variants also offer perspectives and cautionary advice for their use as handles towards diagnosis and treatment.

The APOC3 T-455C and C-482T promoter region polymorphisms are not associated with the severity of liver damage independently of PNPLA3 I148M genotype in patients with nonalcoholic fatty liver

BACKGROUND & AIMS

The T-455C and C-482T APOC3 promoter region polymorphisms (SNPs) have recently been reported to predispose to dyslipidemia, insulin resistance, and nonalcoholic fatty liver disease (NAFLD) in Indian subjects, but the association with liver damage has not been evaluated so far. The aim was to assess the association between APOC3 SNPs and liver damage in Caucasian patients.

METHODS

We considered 437 Italian patients with histological diagnosis of NAFLD (including 137 children, 120 morbid obese) and 316 healthy controls, 71 Italian family trios, and 321 patients from the UK. APOC3 SNPs were determined by sequencing, allele-specific oligonucleotide probes and PCR-restriction fragment length polymorphism analysis, hepatic APOC3 mRNA levels by real-time PCR.

RESULTS

APOC3 SNPs were not associated with NAFLD in Italian subjects, although a borderline significance for the transmission of the -455T allele was observed in the family study. Homozygosity for the APOC3 wild-type genotype (APOC3 WT) was associated with a more favorable lipid profile in control subjects, and consistently with lower hepatic APOC3 mRNA levels in obese patients without diabetes. However, APOC3 SNPs, alone or in combination, were not associated with insulin resistance, altered lipid levels, liver enzymes, and with liver damage (severity of steatosis, nonalcoholic steatohepatitis, and moderate/severe fibrosis) in Italian as well as in UK patients, and in the whole cohort. Stratification for the I148M PNPLA3 mutation, associated with the susceptibility to NASH, did not alter the results.

CONCLUSIONS

APOC3 genotype is not associated with progressive liver damage in Caucasian patients with NAFLD.

Genetic factors associated with the presence and progression of nonalcoholic fatty liver disease: a narrative review

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in the world. Whereas insulin resistance and obesity are considered major risk factors for the development and progression of NAFLD, the genetic underpinnings are unclear. Before 2008, candidate gene studies based on prior knowledge of pathophysiology of fatty liver yielded conflicting results. In 2008, Romeo et al. published the first genome wide association study and reported the strongest genetic signal for the presence of fatty liver (PNPLA3, patatin-like phospholipase domain containing 3; rs738409). Since then, two additional genome wide scans were published and identified 9 additional genetic variants. Whereas these results shed light into the understanding of the genetics of NAFLD, most of associations have not been replicated in independent samples and, therefore, remain undetermined the significance of these findings. This review aims to summarize the understanding of genetic epidemiology of NAFLD and highlights the gaps in knowledge.

Roles of PPARs in NAFLD: potential therapeutic targets

Non-alcoholic fatty liver disease (NAFLD) is a liver pathology with increasing prevalence due to the obesity epidemic. Hence, NAFLD represents a rising threat to public health. Currently, no effective treatments are available to treat NAFLD and its complications such as cirrhosis and liver cancer. Peroxisome proliferator-activated receptors (PPARs) are ligand-activated nuclear receptors which regulate lipid and glucose metabolism as well as inflammation. Here we review recent findings on the pathophysiological role of PPARs in the different stages of NAFLD, from steatosis development to steatohepatitis and fibrosis, as well as the preclinical and clinical evidence for potential therapeutical use of PPAR agonists in the treatment of NAFLD. PPARs play a role in modulating hepatic triglyceride accumulation, a hallmark of the development of NAFLD. Moreover, PPARs may also influence the evolution of reversible steatosis toward irreversible, more advanced lesions. Presently, large controlled trials of long duration are needed to assess the long-term clinical benefits of PPAR agonists in humans. This article is part of a Special Issue entitled Triglyceride Metabolism and Disease.

Genetic variants in candidate genes influencing NAFLD progression

Nonalcoholic fatty liver disease (NAFLD) is a metabolic disorder including simple steatosis and nonalcoholic steatohepatitis (NASH). Advanced stages of NASH result ultimately in fibrosis, cirrhosis, and hepatocarcinoma. A diagnosis of NASH entails an increased risk of both liver-related and cardiovascular mortality as worsening of the metabolic syndrome. Because of its escalation, many investigations have been performed to elucidate the pathophysiologic origins of the disease progression. Human epidemiologic studies describing polymorphisms in a number of genes involved in metabolic dysfunctions have contributed to clarify the causes leading to the disease evolution. In this review, we attempt to outline critically the most recently identified genetic variants in NAFLD patients to identify possible risk factors promoting the progression of the disease. The evaluation of altered genotypes together with other clinical variables may facilitate the clinical management of these patients.