The association of PNPLA3 variants with liver enzymes in childhood obesity is driven by the interaction with abdominal fat

Genetic variation and elevated liver enzymes during childhood, adolescence and early adulthood

BACKGROUND

Genetic factors influence the risk of fatty liver disease (FLD) in adults. The aim of this study was to test if, and when, genetic risk factors known to affect FLD in adults begin to exert their deleterious effects during childhood, adolescence and early adulthood.

METHODS

We included up to 4018 British children and adolescents from the Avon Longitudinal Study of Parents and Children (ALSPAC) cohort. Three genetic variants known to associate robustly with FLD in adults (PNPLA3 rs738409, TM6SF2 rs58542926 and HSD17B13 rs72613567) were tested for association with plasma levels of alanine transaminase (ALT) and aspartate transaminase (AST) during childhood (mean age: 9.9 years), early adolescence (15.5 years), late adolescence (17.8 years), and early adulthood (24.5 years). We also tested the associations of a 17-variant score and whole-genome polygenic risk scores (PRS) derived from associations in adults with plasma ALT and AST at the same four time points. Associations with elastography-derived liver steatosis and fibrosis were tested in early adulthood.

RESULTS

Genetic risk factors for FLD (individually, combined into a 3-variant score, a 17-variant score and as a genome-wide PRS), were associated with higher liver enzymes, beginning in childhood and throughout adolescence and early adulthood. The ALT-increasing effects of the genetic risk variants became larger with increasing age. The ALT-PRS was associated with liver steatosis in early adulthood. No genetic associations with fibrosis were observed.

CONCLUSIONS

Genetic factors that promote FLD in adults associate with elevated liver enzymes already during childhood, and their effects get amplified with increasing age.

A Varying Coefficient Model to Jointly Test Genetic and Gene-Environment Interaction Effects

Most human traits are influenced by the interplay between genetic and environmental factors. Many statistical methods have been proposed to screen for gene-environment interaction (GxE) in the post genome-wide association study era. However, most of the existing methods assume a linear interaction between genetic and environmental factors toward phenotypic variations, which diminishes statistical power in the case of nonlinear GxE. In this paper, we present a flexible statistical procedure to detect GxE regardless of whether the underlying relationship is linear or not. By modeling the joint genetic and GxE effects as a varying-coefficient function of the environmental factor, the proposed model is able to capture dynamic trajectories of GxE. We employ a likelihood ratio test with a fast Monte Carlo algorithm for hypothesis testing. Simulations were conducted to evaluate validity and power of the proposed model in various settings. Real data analysis was performed to illustrate its power, in particular, in the case of nonlinear GxE.

Overweight/Obesity Increases the Risk of Overt Hepatic Encephalopathy after Transjugular Intrahepatic Portosystemic Shunt in Cirrhotic Patients

The purpose of this study was to investigate the effect of body mass index (BMI) on the prevalence of overt hepatic encephalopathy (OHE) after the transjugular intrahepatic portosystemic shunt (TIPS) procedure in decompensated cirrhotic patients. A retrospective observational cohort study of 145 cirrhotic patients receiving TIPS was carried out in our department from 2017 to 2020. The relationships between BMI and clinical outcomes including OHE, as well as risk factors of developing post-TIPS OHE, were analyzed. BMI was categorized as normal weight (18.5 ≤ BMI < 23.0 kg/m²), underweight (BMI < 18.5 kg/m²), and overweight/obese (BMI ≥ 23.0 kg/m²). Among the 145 patients, 52 (35.9%) were overweight/obese and 50 (34%) had post-TIPS OHE. Overweight/obese patients more frequently had OHE compared with normal weight patients (OR: 2.754, 95% CI: 1.236-6.140; p = 0.013). Overweight/obesity (p = 0.013) and older age (p = 0.030) were independent risk factors for post-TIPS OHE according to the logistic regression analysis. Kaplan-Meier curve analysis suggested that overweight/obese patients had the highest cumulative incidence of OHE (log-rank p = 0.0118). In conclusion, overweight/obesity and older age may raise the risk of post-TIPS OHE in cirrhotic patients.

The genetic interactions between non-alcoholic fatty liver disease and cardiovascular diseases

The ongoing debate on whether non-alcoholic fatty liver disease (NAFLD) is an active contributor or an innocent bystander in the development of cardiovascular disease (CVD) has sparked interests in understanding the common mediators between the two biologically distinct entities. This comprehensive review identifies and curates genetic studies of NAFLD overlapping with CVD, and describes the colinear as well as opposing correlations between genetic associations for the two diseases. Here, CVD described in relation to NAFLD are coronary artery disease, cardiomyopathy and atrial fibrillation. Unique findings of this review included certain NAFLD susceptibility genes that possessed cardioprotective properties. Moreover, the complex interactions of genetic and environmental risk factors shed light on the disparity in genetic influence on NAFLD and its incident CVD. This serves to unravel NAFLD-mediated pathways in order to reduce CVD events, and helps identify targeted treatment strategies, develop polygenic risk scores to improve risk prediction and personalise disease prevention.

Advances in pediatric non-alcoholic fatty liver disease: From genetics to lipidomics

As a result of the obesity epidemic, non-alcoholic fatty liver disease (NAFLD) represents a global medical concern in childhood with a closely related increased cardiometabolic risk. Knowledge on NAFLD pathophysiology has been largely expanded over the last decades. Besides the well-known key NAFLD genes (including the I148M variant of the PNPLA3 gene, the E167K allele of the TM6SF2, the GCKR gene, the MBOAT7-TMC4 rs641738 variant, and the rs72613567:TA variant in the HSD17B13 gene), an intriguing pathogenic role has also been demonstrated for the gut microbiota. More interestingly, evidence has added new factors involved in the “multiple hits” theory. In particular, omics determinants have been highlighted as potential innovative markers for NAFLD diagnosis and treatment. In fact, different branches of omics including metabolomics, lipidomics (in particular sphingolipids and ceramides), transcriptomics (including micro RNAs), epigenomics (such as DNA methylation), proteomics, and glycomics represent the most attractive pathogenic elements in NAFLD development, by providing insightful perspectives in this field. In this perspective, we aimed to provide a comprehensive overview of NAFLD pathophysiology in children, from the oldest pathogenic elements (including genetics) to the newest intriguing perspectives (such as omics branches).

Effects of PNPLA3, TM6SF2 and SAMM50 on the development and severity of non-alcoholic fatty liver disease in children

BACKGROUND

Although genetic variants of PNPLA3, TM6SF2 and SAMM50 have been reported to increase the risk of non-alcoholic fatty liver disease (NAFLD), no pediatric studies have evaluated the association between SAMM50 and NAFLD.

OBJECTIVE

This study aimed to investigate the risk factors, including genetic variants, of pediatric NAFLD.

METHODS

NAFLD was defined as the presence of hepatic steatosis on ultrasound. We included 228 patients with NAFLD (body mass index-Z [BMI-Z] = 2.51 ± 1.01) and 225 controls (BMI-Z = 0.22 ± 1.48). We genotyped four variants of PNPLA3 (rs738409), TM6SF2 (rs58542926) and SAMM50 (rs2073080 and rs3761472) by TaqMan allelic discrimination. The pediatric NAFLD fibrosis score, aspartate transaminase (AST)/platelet ratio index and fibrosis-4 score were used to evaluate the degree of fibrosis. We calculated the genetic risk score for additive effects according to the sum of risk alleles.

RESULTS

The mean age was 12.6 ± 3.5 years. The four genetic variants, male sex and BMI-Z, independently increased susceptibility to NAFLD. These four variants, in addition to fasting insulin and triglycerides, remained significant risk factors with higher odds ratios in children with overweight. These variants increased the alanine aminotransferase (ALT) level and three fibrosis scores independently. As the genetic risk score increased, AST, ALT and the fibrosis scores increased independently.

CONCLUSION

PNPLA3, TM6SF2 and SAMM50 are associated with the development and severity of pediatric NAFLD. The impact of genetic variants is greater in children with overweight. The four genetic variants have synergetic effects on the severity of pediatric NAFLD.

Genome-wide association analysis of serum alanine and aspartate aminotransferase, and the modifying effects of BMI in 388k European individuals

Serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are biomarkers for liver health. Here we report the largest genome-wide association analysis to date of serum ALT and AST levels in over 388k people of European ancestry from UK biobank and DiscovEHR. Eleven million imputed markers with a minor allele frequency (MAF) ≥ 0.5% were analyzed. Overall, 300 ALT and 336 AST independent genome-wide significant associations were identified. Among them, 81 ALT and 61 AST associations are reported for the first time. Genome-wide interaction study identified 9 ALT and 12 AST independent associations significantly modified by body mass index (BMI), including several previously reported potential liver disease therapeutic targets, for example, PNPLA3, HSD17B13, and MARC1. While further work is necessary to understand the effect of ALT and AST-associated variants on liver disease, the weighted burden of significant BMI-modified signals is significantly associated with liver disease outcomes. In summary, this study identifies genetic associations which offer an important step forward in understanding the genetic architecture of serum ALT and AST levels. Significant interactions between BMI and genetic loci not only highlight the important role of adiposity in liver damage but also shed light on the genetic etiology of liver disease in obese individuals.

Pediatric obesity-related non-alcoholic fatty liver disease: waist-to-height ratio best anthropometrical predictor

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disorder in pediatric obesity. Our study aims to identify a predictive anthropometrical measure for NAFLD in obese children.

METHODS

We retrospectively enrolled children and adolescents with obesity. Physical, biochemical, and ultrasound assessments were available. ROC curve tests were performed to identify the best predictor of NAFLD among waist-to-height ratio (WHR), BMI z-score, and triponderal mass index (TMI, an anthropometric index recently associated with increased adiposity in children). Subsequently, a cut-off value was identified.

RESULTS

In total, 1900 children and adolescents (1011 with NAFLD) were included. WHR (AUC 0.62, 95% CI 0.59-0.64) was the best predictor of NAFLD compared to BMI z-score (AUC 0.58, 95% CI 0.55-0.60) and TMI (AUC 0.58, 95% CI 0.55-0.61). WHR ≥ 0.53 in boys and 0.63 in girls displayed the best sensitivity and specificity for NAFLD presence. In addition, children with high WHR showed a significantly higher risk of NAFLD (boys: OR 2.43, 95% CI 1.61-3.68, p < 0.0001; girls: OR 1.92, 95% CI 1.58-2.34, p < 0.0001) and elevated ALT (OR 5.71, 95% CI 2.09-15.56, p = 0.0007; girls: OR 2.16, 95% CI 1.70-2.74, p < 0.0001) independent of covariates.

CONCLUSIONS

WHR might represent a good anthropometric tool to candidate children and adolescents to NAFLD screening. WHR cut-off differs according to sex, being lower in boys than girls.

IMPACT

Waist-to-height ratio is a better predictor of non-alcoholic fatty liver disease risk compared to other anthropometric measures in obese children and adolescents. The predictive cut-off of waist-to-height ratio differs between boys and girls, being lower in boys than girls. The use of waist-to-height ratio measurement and its cut-off in clinical practice might help clinician in identifying obese children and adolescents at risk of non-alcoholic fatty liver disease.

Association of Genetic Variation With Cirrhosis: A Multi-Trait Genome-Wide Association and Gene-Environment Interaction Study

BACKGROUND & AIMS

In contrast to most other common diseases, few genetic variants have been identified that impact risk of cirrhosis. We aimed to identify new genetic variants that predispose to cirrhosis, to test whether such variants, aggregated into a polygenic score, enable genomic risk stratification, and to test whether alcohol intake or body mass index interacts with polygenic predisposition.

METHODS

We conducted a multi-trait genome-wide association study combining cirrhosis and alanine aminotransferase levels performed in 5 discovery studies (UK Biobank, Vanderbilt BioVU, Atherosclerosis Risk in Communities study, and 2 case-control studies including 4829 individuals with cirrhosis and 72,705 controls and 362,539 individuals with alanine aminotransferase levels). Identified variants were replicated in 3 studies (Partners HealthCare Biobank, FinnGen, and Biobank Japan including 3554 individuals with cirrhosis and 343,826 controls). A polygenic score was tested in Partners HealthCare Biobank.

RESULTS

Five previously reported and 7 newly identified genetic variants were associated with cirrhosis in both the discovery studies multi-trait genome-wide association study (P < 5 × 10-8) and the replication studies (P < .05), including a missense variant in the APOE gene and a noncoding variant near EFN1A. These 12 variants were used to generate a polygenic score. Among Partners HealthCare Biobank individuals, high polygenic score-defined as the top quintile of the distribution-was associated with significantly increased risk of cirrhosis (odds ratio, 2.26; P < .001) and related comorbidities compared with the lowest quintile. Risk was even more pronounced among those with extreme polygenic risk (top 1% of the distribution, odds ratio, 3.16; P < .001). The impact of extreme polygenic risk was substantially more pronounced in those with elevated alcohol consumption or body mass index. Modeled as risk by age 75 years, probability of cirrhosis with extreme polygenic risk was 13.7%, 20.1%, and 48.2% among individuals with no or modest, moderate, and increased alcohol consumption, respectively (Pinteraction < .001). Similarly, probability among those with extreme polygenic risk was 6.5%, 10.3%, and 19.5% among individuals with normal weight, overweight, and obesity, respectively (Pinteraction < .001).

CONCLUSIONS

Twelve independent genetic variants, 7 of which are newly identified in this study, conferred risk for cirrhosis. Aggregated into a polygenic score, these variants identified a subset of the population at substantially increased risk who are most susceptible to the hepatotoxic effects of excess alcohol consumption or obesity.

Effect of the patatin-like phospholipase domain containing 3 gene (PNPLA3) I148M polymorphism on the risk and severity of nonalcoholic fatty liver disease and metabolic syndromes: A meta-analysis of paediatric and adolescent individuals

BACKGROUND

The effect of the patatin-like phospholipase domain containing 3 gene (PNPLA3) I148M polymorphism on the risk and severity of paediatric and adolescent nonalcoholic fatty liver disease (NAFLD) remains inconclusive.

OBJECTIVES

We aimed to estimate the effect of this polymorphism not only on early-onset NAFLD risk and severity but also on metabolic syndromes susceptibility.

METHODS

A systematic literature search was performed to identify relevant datasets. The odds ratio of the dichotomic variables and the standardized mean difference of quantitative variables with corresponding 95% confidence intervals were calculated to assess the strength of the associations.

RESULTS

Twenty-seven studies comprising 10 070 subjects were eligible. The summary effect showed that this polymorphism increased susceptibility to NAFLD development. Furthermore, it also indicated that nonalcoholic steatohepatitis (NASH) was more frequently observed in G allele carriers among paediatric and adolescent NAFLD patients. Moreover, the meta-analysis suggested that the variant was significantly associated with elevated liver damage indexes, including serum alanine transaminase, aspartate transaminase, gamma-glutamyltransferase concentrations, and liver fat content. However, the summary estimates for insulin resistance, lipid metabolism, and adiposity showed no significant associations.

CONCLUSIONS

The PNPLA3 I148M polymorphism is associated with elevated early-onset NAFLD risk, severity, and liver damage but not with related metabolic syndromes.

Review article: the emerging role of genetics in precision medicine for patients with non-alcoholic steatohepatitis

BACKGROUND

Non-alcoholic steatohepatitis (NASH) is a severe form of non-alcoholic fatty liver disease (NAFLD) characterised by liver fat accumulation, inflammation and progressive fibrosis. Emerging data indicate that genetic susceptibility increases risks of NAFLD, NASH and NASH-related cirrhosis.

AIMS

To review NASH genetics and discuss the potential for precision medicine approaches to treatment.

METHOD

PubMed search and inclusion of relevant literature.

RESULTS

Single-nucleotide polymorphisms in PNPLA3, TM6SF2, GCKR, MBOAT7 and HSD17B13 are clearly associated with NASH development or progression. These genetic variants are common and have moderate-to-large effect sizes for development of NAFLD, NASH and hepatocellular carcinoma (HCC). The genes play roles in lipid remodelling in lipid droplets, hepatic very low-density lipoprotein (VLDL) secretion and de novo lipogenesis. The PNPLA3 I148M variant (rs738409) has large effects, with approximately twofold increased odds of NAFLD and threefold increased odds of NASH and HCC per allele. Obesity interacts with PNPLA3 I148M to elevate liver fat content and increase rates of NASH. Although the isoleucine-to-methionine substitution at amino acid position 148 of the PNPLA3 enzyme inactivates its lipid remodelling activity, the effect of PNPLA3 I148M results from trans-repression of another lipase (ATGL/PNPLA2) by sequestration of a shared cofactor (CGI-58/ABHD5), leading to decreased hepatic lipolysis and VLDL secretion. In homozygous Pnpla3 I148M knock-in rodent models of NAFLD, targeted PNPLA3 mRNA knockdown reduces hepatic steatosis, inflammation and fibrosis.

CONCLUSION

The emerging genetic and molecular understanding of NASH paves the way for novel interventions, including precision medicines that can modulate the activity of specific genes associated with NASH.

Genetic Risk Factors and Disease Modifiers of Nonalcoholic Steatohepatitis

Nonalcoholic fatty liver disease is strongly associated with obesity and the metabolic syndrome, but genetic factors also contribute to disease susceptibility. Human genetic studies have identified several common genetic variants contributing to nonalcoholic fatty liver disease initiation and progression. These findings have provided new insights into the pathogenesis of nonalcoholic fatty liver disease and opened up new avenues for the development of therapeutic interventions. In this review, we summarize the current state of knowledge about the genetic determinants of nonalcoholic fatty liver disease, focusing on the most robustly validated genetic risk factors and on recently discovered modifiers of disease progression.

The rs72613567: TA Variant in the Hydroxysteroid 17-beta Dehydrogenase 13 Gene Reduces Liver Damage in Obese Children

We first investigated in obese children the protective role of the hydroxysteroid 17-beta dehydrogenase 13 (HSD17B13) rs72613567:TA variant in liver damage. Six hundred eighty-five obese children were genotyped for HSD17B13, patatin-like phospholipase domain containing 3 (PNPLA3), transmembrane 6 superfamily member 2 (TM6SF2), and membrane bound O-acyltransferase domain containing 7 (MBOAT7) polymorphisms and underwent anthropometrical, ultrasonographic, and biochemical evaluation. Indirect measurement of liver fibrosis (Pediatric NAFLD Fibrosis Index [PNFI]) was calculated. The population was clustered in 2 genetic risk groups based on the numbers of steatogenic alleles (low: carriers up to 3 risk alleles, high: 4-6 risk alleles). Carriers of the HSD17B13 rare A allele showed lower percentage of hepatic steatosis and both lower serum transaminase and PNFI levels than noncarriers, even after adjustments for confounders. These findings were also confirmed in both risk groups. We demonstrated the protective effect of the rs72613567:TA HSD17B13 variant in reducing liver damage in obese children regardless of genetic predisposition.

High Risk of Fatty Liver Disease Amplifies the Alanine Transaminase-Lowering Effect of a HSD17B13 Variant

A common loss-of-function variant in HSD17B13 (rs72613567:TA) was recently found to protect from chronic liver disease. Whether the variant confers protection from specific risk factors for liver disease is unclear. We tested the association of rs72613567 with plasma levels of alanine transaminase (ALT) and clinical liver disease and mortality in 111,612 individuals from the Danish general population, including 497 with cirrhosis and 113 with hepatocellular carcinoma. HSD17B13 rs72613567:TA was associated with stepwise lower levels of plasma ALT of up to 1.3 U/L in TA/TA homozygotes versus T/T homozygotes. For each TA-allele, the risk of cirrhosis and hepatocellular carcinoma was reduced by 15% and 28%, respectively. In prospective analyses, the TA-allele was associated with up to 33% lower rates of liver-related mortality in the general population, and with up to 49% reduced liver-related mortality in patients with cirrhosis. The ALT-lowering effect of rs72613567:TA was amplified by increasing adiposity, alcohol consumption, and genetic risk of fatty liver disease. The TA-allele was associated with only marginally lower ALT in lean nondrinkers with low genetic risk of hepatic steatosis. In contrast, compared with T/T homozygotes, TA/TA homozygotes had 12% to 18% lower plasma ALT among the most obese, in heavy drinkers, and in individuals carrying three or four steatogenic alleles in patatin-like phospholipase domain-containing protein 3 (PNPLA3) and transmembrane 6 superfamily 2 (TM6SF2). Conclusion: High risk of fatty liver disease amplifies the ALT-lowering effect of HSD17B13 rs72613567:TA in the Danish general population.

The relationship among GNB3 rs5443, PNPLA3 rs738409, GCKR rs780094 gene polymorphisms, type of maternal gestational weight gain and neonatal outcomes (STROBE-compliant article)

The gestational weight gain is determined by food habits, environmental and genetic factors.The aims of this paper were to establish relationships between maternal gene polymorphisms (patatin-like phospholipase domain-containing protein 3 rs738409 [PNPLA3 rs738409], glucokinase regulatory protein rs780094 [GCKR rs780094], and guanine nucleotide-binding protein rs5443 [GNB3 rs5443]) and mothers' gestational weight gain, but also neonatal outcomes (birth weight, length, and ponderal index [PI]).We performed a cross-sectional study in a sample of 158 mothers and their product of conception' in an Obstetrics-Gynecology Clinic from Romania. We divided the pregnant women according to the Institute of Medicine recommendations into 3 subgroups: (1) insufficient gestational weight gain; (2) normal gestational weight gain; and (3) excessive gestational weight gain.The gestational weight gain among pregnant women included in this study was classified as insufficient (10.1%), normal (31%), and excessive (58.9%). We found a tendency towards statistical significance for mothers that were overweight or obese before pregnancy to present an excessive gestational weight gain as compared to the normal weight ones. Similarly, we identified a tendency for statistical significance regarding the association between the variant genotype of GNB3 rs5443 and excessive gestational weight gain. We noticed differences that tended to be statistical significant concerning aspartate aminotransferase values between the 3 subgroups, mothers with excessive gestational weight gain having higher values than mothers with normal gestational weight gain (median, IQR: 22.89[17.53; 31.59] for mothers with excessive gestational weight gain versus 22.71[18.58; 27.37] for mothers with normal gestational weight gain). In mothers with excessive gestational weight gain, we found a significant association between the variant genotype of PNPLA3 rs738409 polymorphism and neonatal PI noticing a decrease of this index in case of newborns from mothers carrying the variant genotype.Excessive gestational weight gain was noticed in pregnant women that were obese and overweight before pregnancy. We found a positive association between the variant genotype of GNB3 rs5443 polymorphism and excessive gestational weight gain. Similarly, the presence of variant genotype of PNPLA3 rs738409 in mothers was associated with a lower PI in their newborns. Our study pointed out the most important factors that influence gestational weight gain and related birth outcomes.

Pathogenesis of non-alcoholic fatty liver disease in children and adolescence: From “two hit theory” to “multiple hit model”

Nonalcoholic fatty liver disease (NAFLD) has become the dominant form of chronic liver disease in children and adolescents with the increasing prevalence of obesity worldwide. NAFLD represents a wide spectrum of conditions, ranging from fatty liver - which generally follows a benign, non-progressive clinical course - to non-alcoholic steatohepatitis, a subset of NAFLD that may progress to cirrhosis and end-stage liver disease or liver carcinoma. The underlying pathophysiological mechanism of “pediatric” NAFLD remains unclear, although it is strongly associated with obesity and insulin resistance. In this review we provide a general overview on the current understanding of NAFLD in children and adolescents, which underpins practice, enabling early diagnosis and appropriate therapeutic intervention for this life-threatening liver disease.

The Membrane-bound O-Acyltransferase7 rs641738 Variant in Pediatric Nonalcoholic Fatty Liver Disease

BACKGROUND

The rs641738 polymorphism in the membrane-bound O-acyltransferase domain containing protein 7 (MBOAT7) gene has been associated with increased risk of nonalcoholic fatty liver disease (NAFLD).

OBJECTIVES

To investigate the association between the MBOAT7 rs641738 polymorphism and both hepatic steatosis and biochemical markers of liver damage and to evaluate the potential additive effect of this variant and the I148M patatin-like phospholipase domain-containing 3 (PNPLA3) and the rs58542926 transmembrane 6 superfamily member 2 (TM6SF2) polymorphisms.

METHODS

One thousand and 2 obese children were genotyped for MBOAT7, PNPLA3, and TM6SF2 polymorphisms and underwent anthropometrical, ultrasonographic, and biochemical evaluation. Indirect measurement of liver fibrosis (Pediatric NAFLD Fibrosis Index [PNFI]) and a genetic risk score from these polymorphisms were calculated.

RESULTS

Carriers of the MBOAT7 T allele showed both higher alanine transaminase (ALT) (P = 0.004) and PNFI values (P = 0.04) than noncarriers. These findings were confirmed also for the carriers of the MBOAT7 T allele polymorphism with hepatic steatosis compared with noncarriers. A higher genetic risk score was associated with higher ALT (P = 0.011) and with an odds ratio (OR) to show elevated ALT of 3.4 (95% CI 1.3-5.5, P = 0.003). Patients belonging to genetic risk score 3 group had an OR to present steatosis of 2.6 (95% CI 1.43-4.83, P = 0.0018) compared with those belonging to lower genetic risk score group.

CONCLUSIONS

We first demonstrated in childhood obesity the role of the MBOAT7 rs641738 variant on serum ALT and the combined effect of the MBOAT7, PNPLA3, and TM6SF2 variants on NAFLD risk. We also provided the first pediatric association of the MBOAT7 polymorphism with indirect markers of liver fibrosis.

Patatin-like phospholipase domain–containing protein 3 promotes transfer of essential fatty acids from triglycerides to phospholipids in hepatic lipid droplets

Fatty liver disease (FLD) is a burgeoning health problem. A missense variant (I148M) in patatin-like phospholipase domain-containing protein 3 (PNPLA3) confers susceptibility to FLD, although the mechanism is not known. To glean first insights into the physiological function of PNPLA3, we performed detailed lipidomic profiling of liver lysates and lipid droplets (LDs) from WT and Pnpla3^-/- (KO) mice and from knock-in (ki) mice expressing either the 148M variant (IM-ki mice) or a variant (S47A) that renders the protein catalytically inactive (SA-ki mice). The four strains differed in composition of very-long-chain polyunsaturated fatty acids (vLCPUFA) in hepatic LDs. In the LDs of IM-ki mice, vLCPUFAs were depleted from triglycerides and enriched in phospholipids. Conversely, vLCPUFAs were enriched in triglycerides and depleted from phospholipids in SA-ki and Pnpla3^-/- mice. Release of vLCPUFAs from hepatic LDs incubated ex vivo was increased in droplets from IM-ki mice and decreased from droplets isolated from Pnpla3^-/- and SA-ki mice relative to those of WT mice. Thus, the physiological role of PNPLA3 appears to be to remodel triglycerides and phospholipids in LDs, perhaps to accommodate changes in LD size in response to feeding. Because SA-ki and IM-ki both cause FLD and yet have opposite effects on the lipidomic profile of LDs, we conclude that the FLD associated with genetic variation in PNPLA3 is not related to the enzyme's role in remodeling LD lipids.

The rs626283 Variant in the MBOAT7 Gene is Associated with Insulin Resistance and Fatty Liver in Caucasian Obese Youth

OBJECTIVES

Non alcoholic fatty liver disease (NAFLD) is a leading cause of liver damage in childhood, its occurrence is influenced by genetic and environmental factors. Recently, the rs626283 polymorphism in the MBOAT7 gene has been found to be associated with alcoholic liver disease and NAFLD in adults.

METHODS

In a multiethnic cohort of obese children and adolescents we genotyped the rs626283 polymorphism in the MBOAT7 gene, evaluated insulin sensitivity by an oral glucose tolerance test, and measured the intra-hepatic fat content (HFF%) by magnetic resonance imaging.

RESULTS

In Caucasian youth, the minor allele (C) was associated with HFF% in (P=0.003), fasting insulin (P=0.03), area under the curve of glucose (P=0.03), and lower degree of whole-body insulin sensitivity (P=0.01) independent of age, gender, and body mass index z-score. A partial correlation showed that the association between the rs626283 variant and insulin resistance was driven by the presence of hepatic steatosis (P=0.009). However, there was no association between the rs626283 and hepatic steatosis among Hispanic and African American children and youth. The association between the rs626283 in the MBOAT7 gene among Caucasians was independent of the PNPLA3 rs738409, GCKR 1260326, and TM6SF2 rs58542926 (P=0.01). The four polymorphisms combined explained~19% of the HFF% in Caucasian obese children and adolescents.

CONCLUSIONS

The rs626283 variant in the MBOAT7 gene is associated with NAFLD and may affect glucose metabolism by modulating intra-hepatic fat content in Caucasian obese children and adolescents.

The Genetics of Pediatric Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is the leading cause of chronic liver disease in children. Severe fibrosis and cirrhosis are potential consequences of pediatric NAFLD and can occur within a few years of diagnosis. Observations suggest that genetics may be a strong modifying factor in the presentation, severity, and natural history of the disease. There is increasing interest in determining at-risk populations based on genetics in the hope of finding genotypes that correlate to NAFLD phenotype. Ultimately, the hope is to be able to tailor therapeutics to genetic predispositions and decrease disease morbidity in children with NAFLD.

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.

Adiposity amplifies the genetic risk of fatty liver disease conferred by multiple loci

Complex traits arise from the interplay between genetic and environmental factors. The actions of these factors usually appear to be additive, and few compelling examples of gene-environment synergy have been documented. Here we show that adiposity significantly amplifies the effect of three sequence variants (PNPLA3-I148M, TM6SF2-E167K and GCKR-P446L) associated with nonalcoholic fatty liver disease (NAFLD). Synergy between adiposity and genotype promoted the full spectrum of NAFLD, from steatosis to hepatic inflammation to cirrhosis. We found no evidence of strong interactions between adiposity and sequence variants influencing other adiposity-associated traits. These results indicate that adiposity may augment genetic risk of NAFLD at multiple loci through at least three different metabolic mechanisms.

Physical activity and sedentary behavior can modulate the effect of the PNPLA3 variant on childhood NAFLD: a case-control study in a Chinese population

Background

The patatin like phospholipase containing domain 3 gene (PNPLA3) rs738409 C > G polymorphism, one of the most important gene polymorphisms involved in hepatic steatosis, has been reported to interact with different nutrients and dietary patterns on Non-Alcoholic Fatty Liver Disease (NAFLD), but no studies have focused on its interaction with physical activity or sedentary behavior. Therefore, this study aims at determining whether physical activity or sedentary behavior could modulate the effect of the PNPLA3 variant on childhood NAFLD.

Methods

A case-control study was conducted including 1027 Chinese children aged 7–18 years old (162 children with NAFLD and 865 children without). The anthropometric measurements, liver ultrasound examination, questionnaires and genotyping of the PNPLA3 rs738409 polymorphism were performed.

Results

Stratified analyses showed that the proportions of NAFLD increased with the G-allele number only in children who did not have enough physical activity (physical activity < 1 h/d) (OR 3.05, 95% CI 1.82–5.12, P < 0.001), and in children with a sedentary lifestyle (sedentary behavior ≥ 2 h/d) (OR 3.41, 95% CI 1.88–6.18, P < 0.001). Significant interactions on childhood NAFLD were found between the G-allele number in the PNPLA3 rs738409 polymorphism and behaviors, including physical activity (P = 0.001), sedentary behavior (P = 0.010) and the combination of physical activity and sedentary behavior (P < 0.001).

Conclusion

This is the first study to report the interaction between the PNPLA3 rs738409 polymorphism and physical activity or sedentary behavior on NAFLD, providing new clues on the function of the PNPLA3 gene, which will also be useful for future risk assessment and personalized treatment of NAFLD.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-016-0352-9) contains supplementary material, which is available to authorized users.

Metabolic syndrome in children (Review)

Metabolic syndrome (MetS) is a cluster of cardiometabolic risk factors, including central obesity, insulin resistance, glucose intolerance, dyslipidemia and increased blood pressure. The prevalence of MetS is on the increase worldwide owing to the epidemic of overweight and obesity. The risk of prevalence of MetS greatly increases during adulthood for those children exposed to cardiometabolic risk factors in their early lives. MetS has also been associated with liver fat accumulation in children. Elevated levels of plasma alanine aminotransferase and γ-glutamyl transferase have been associated with liver fat accumulation. The present review aimed to expand knowledge on the clustering of cardiometabolic risk factors responsible for the widespread occurrence of metabolic disease in children.

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.

TM6SF2 Glu167Lys polymorphism is associated with low levels of LDL-cholesterol and increased liver injury in obese children

BACKGROUND

The Glu167Lys (E167K) transmembrane 6 superfamily member 2 (TM6SF2) variant has been associated with liver steatosis, high alanine transaminase (ALT) levels and reduced plasma levels of liver-derived triglyceride-rich lipoproteins.

OBJECTIVES

The objectives of this study were to investigate in a group of obese children the association among the 167K allele of TM6SF2 gene and ALT, cholesterol and triglycerides levels, and hepatic steatosis, and to evaluate the potential interaction between this variant and the I148M patatin like phospholipase 3 gene (PNPLA3) polymorphism on liver enzymes.

METHODS

We genotyped 1010 obese children for TM6SF2 E167K and PNPLA3 I148M polymorphisms. Anthropometrical and biochemical data were collected. Ultrasound imaging of the liver was performed.

RESULTS

The 167K allele showed an association with steatosis (P < 0.0001), higher ALT levels (P < 0.001) and lower total cholesterol (P < 0.00001), low-density lipoprotein cholesterol (P < 0.0001), triglycerides (P = 0.02) and non-high-density lipoprotein cholesterol levels (P < 0.000001). The subjects homozygous for the PNPLA3 148M allele carrying the rare variant of TM6SF2 showed an odds ratio of 12.2 (confidence interval 3.8-39.6, P = 0.000001) to present hypertransaminasaemia compared with the remaining patients.

CONCLUSION

Although the TMS6SF2 E167K variant predisposes the obese children to non-alcoholic fatty liver disease, there is an association between this variant and lower levels of cardiovascular risk factors. Overall, the data suggest differential effects of TMS6SF2 E167K variant on liver and heart health.

A "systems medicine" approach to the study of non-alcoholic fatty liver disease

The prevalence of fatty liver (steatosis) in the general population is rapidly increasing worldwide. The progress of knowledge in the physiopathology of fatty liver is based on the systems biology approach to studying the complex interactions among different physiological systems. Similarly, translational and clinical research should address the complex interplay between these systems impacting on fatty liver. The clinical needs drive the applications of systems medicine to re-define clinical phenotypes, assessing the multiple nature of disease susceptibility and progression (e.g. the definition of risk, prognosis, diagnosis criteria, and new endpoints of clinical trials). Based on this premise and in light of recent findings, the complex mechanisms involved in the pathology of fatty liver and their impact on the short- and long-term clinical outcomes of cardiovascular, metabolic liver diseases associated with steatosis are presented in this review using a new "systems medicine" approach. A new data set is proposed for studying the impairments of different physiological systems that have an impact on fatty liver in different subsets of subjects and patients.

PNPLA3 148M Carriers with Inflammatory Bowel Diseases Have Higher Susceptibility to Hepatic Steatosis and Higher Liver Enzymes

BACKGROUND

Inflammatory bowel diseases (IBD) are characterized by chronic relapsing inflammation of the gastrointestinal tract and encompass Crohn's disease and ulcerative colitis. IBD are often associated with extraintestinal manifestations affecting multiple organs including the liver. Increased levels of serum aminotransferases, possibly related to nonalcoholic fatty liver disease, constitute one of the most frequently described IBD-related liver diseases. The PNPLA3 I148M substitution is a major common genetic determinant of hepatic fat content and progression to chronic liver disease. The aim of this study was to investigate whether carriers of PNPLA3 148M allele with IBD have higher risk of liver steatosis and increase in transaminases levels.

METHODS

The PNPLA3 I148M (rs738409) genotype was performed by Taqman assays in 158 individuals from Southern Italy (namely, Catanzaro cohort) and in 207 individuals from Northern Italy (namely, Milan cohort) with a definite diagnosis of IBD. Demographic and clinical data and also alanine transaminase levels were collected for both cohorts. The Catanzaro cohort underwent liver evaluation by sonography and liver stiffness and controlled attenuation parameter measurements by transient elastography.

RESULTS

Here, we show for the first time that carriers of the PNPLA3 148M allele with IBD have a greater risk of hepatic steatosis (odds ratio, 2.9, and confidence interval, 1.1-7.8), higher controlled attenuation parameter values (P = 0.029), and increased circulating alanine transaminase (P = 0.035) in the Catanzaro cohort. We further confirm the higher alanine transaminase levels in the Milan cohort (P < 0.001).

CONCLUSIONS

Our results show that PNPLA3 148M carriers with IBD have higher susceptibility to hepatic steatosis and liver damage.

Insights from Genome-Wide Association Analyses of Nonalcoholic Fatty Liver Disease

Nonalcoholic fatty liver disease (NAFLD) is caused by hepatic steatosis, which can progress to nonalcoholic steatohepatitis, fibrosis/cirrhosis, and hepatocellular carcinoma in the absence of excessive alcohol consumption. Nonalcoholic fatty liver disease will become the number one cause of liver disease worldwide by 2020. Nonalcoholic fatty liver disease is correlated albeit imperfectly with obesity and other metabolic diseases such as diabetes, hyperlipidemia, and cardiovascular disease, but exactly how having one of these diseases contributes to the development of other metabolic diseases is only now being elucidated. Development of NAFLD and related metabolic diseases is genetically influenced in the population, and recent genome-wide association studies (GWASs) have discovered genetic variants that associate with these diseases. These GWAS-associated variants cannot only help us to identify individuals at high risk of developing NAFLD, but also to better understand its pathophysiology so that we can develop more effective treatments for this disease and related metabolic diseases in the future.

Omega-3 fatty acids: Mechanisms of benefit and therapeutic effects in pediatric and adult NAFLD

Non-alcoholic fatty liver disease (NAFLD) is currently considered the most common liver disease in industrialized countries, and it is estimated that it will become the most frequent indication for liver transplantation in the next decade. NAFLD may be associated with moderate (i.e. steatosis) to severe (i.e. steatohepatitis and fibrosis) liver damage and affects all age groups. Furthermore, subjects with NAFLD may be at a greater risk of other obesity-related complications later in life, and people with obesity and obesity-related complications (e.g. metabolic syndrome, type 2 diabetes and cardiovascular disease) are at increased risk of developing NAFLD. To date, there is no licensed treatment for NAFLD and therapy has been mainly centered on weight loss and increased physical activity. Unfortunately, it is often difficult for patients to adhere to the advised lifestyle changes. Therefore, based on the known pathogenesis of NAFLD, several clinical trials with different nutritional supplementation and prescribed drugs have been undertaken or are currently underway. Experimental evidence has emerged about the health benefits of omega-3 fatty acids, a group of polyunsaturated fatty acids that are important for a number of health-related functions. Omega-3 fatty acids are present in some foods (oils, nuts and seeds) that also contain omega-6 fatty acids, and the best sources of exclusively omega-3 fatty acids are oily fish, krill oil and algae. In this review, we provide a brief overview of the pathogenesis of NAFLD, and we also discuss the molecular and clinical evidence for the benefits of different omega-3 fatty acid preparations in NAFLD.

The Frequent Adiponutrin (PNPLA3) Variant p.Ile148Met Is Associated with Early Liver Injury: Analysis of a German Pediatric Cohort

Introduction. The common adiponutrin (PNPLA3) variant p.Ile148Met is associated with liver injury. Here, we investigate the association of this polymorphism with hepatic and metabolic traits in a pediatric cohort. Patients and Methods. The study cohort comprised 142 German children (age 5-9 years, 98 overweight, 19 children with NAFLD). Results. Overweight children presented with increased serum ALT (P = 0.001) and GGT (P < 0.001) activities. ALT activities differed significantly (P = 0.02) between carriers of different PNPLA3 genotypes in the entire study cohort, in normal weight children (P = 0.02) and in children younger than 7 years (P = 0.02). Carriers of the prosteatotic PNPLA3 genotype p.148Met/Met displayed higher ALT activities as compared to children with the frequent genotype p.148Ile/Ile (P = 0.01). The BMI was however a stronger predictor of ALT activities compared to the PNPLA3 genotype (P < 0.001 and P = 0.06, resp.). The variant was associated with increased serum glucose levels (P = 0.01) and HOMA index (P = 0.02) in carriers of the p.148Ile/Met genotype but did not affect other metabolic traits or the presence of NAFLD. Discussion. The frequent PNPLA3 variant p.Ile148Met is associated with serum ALT activities already at a young age.

PNPLA3 I148M Variant Influences Circulating Retinol in Adults with Nonalcoholic Fatty Liver Disease or Obesity

BACKGROUND

Retinol is a lipid-soluble essential nutrient that is stored as retinyl esters in lipid droplets of hepatic stellate cells. Patatin-like phospholipase domain-containing 3 (PNPLA3), through its retinyl-palmitate lipase activity, releases retinol from lipid droplets in hepatic stellate cells in vitro and ex vivo. We have shown that the genetic variant I148M (rs738409) reduces the PNPLA3 retinyl-palmitate lipase activity.

OBJECTIVE

The aim of the present genetic association study was to test whether overweight/obese carriers of the PNPLA3 148M mutant allele had lower circulating concentrations of retinol than individuals who are homozygous for the 148I allele.

METHODS

PNPLA3 I148M (rs738409) was genotyped by Taqman assay in 76 overweight/obese individuals [BMI (kg/m(2)) ≥25; mean ± SD age: 59.7 ± 11.4 y; male gender: 70%] with a histologic diagnosis of nonalcoholic fatty liver disease (NAFLD; namely the Milan NAFLD cohort) and in 413 obese men (BMI ≥30; mean ± SD age: 57.1 ± 4.9 y) from the α-Tocopherol, β-Carotene Cancer Prevention (ATBC) Study. Serum concentrations of retinol and α-tocopherol were measured by HPLC in both cohorts. β-Carotene concentrations in the ATBC study were measured by using HPLC.

RESULTS

The PNPLA3 148M mutant allele was associated with lower fasting circulating concentrations of retinol (β = -0.289, P = 0.03) in adults with NAFLD (Milan NAFLD cohort). The PNPLA3 148M mutant allele was also associated with lower fasting circulating concentrations of retinol in adults with a BMI ≥30 (ATBC study; β = -0.043, P = 0.04).

CONCLUSION

We showed for the first time, to our knowledge, that carriers of the PNPLA3 148M allele with either fatty liver plus obesity or obesity alone have lower fasting circulating retinol concentrations.

Linked PNPLA3 polymorphisms confer susceptibility to nonalcoholic steatohepatitis and decreased viral load in chronic hepatitis B

AIM: To investigate the association of PNPLA3 polymorphisms with concurrent chronic hepatitis B (CHB) and nonalcoholic fatty liver disease (NAFLD).

METHODS: A cohort of Han patients with biopsy-proven CHB, with or without NAFLD (CHB group, n = 51; CHB + NAFLD group, n = 57), and normal controls (normal group, n = 47) were recruited from Northern (Tianjin), Central (Shanghai), and Southern (Zhangzhou) China. Their PNPLA3 polymorphisms were genotyped by gene sequencing. The association between PNPLA3 polymorphisms and susceptibility to NAFLD, and clinical characteristics of NAFLD were evaluated on the basis of physical indices, liver function tests, glycolipid metabolism, and histopathologic scoring. The association of PNPLA3 polymorphisms and hepatitis B virus (HBV) load was determined by the serum level of HBV DNA.

RESULTS: After adjusting for age, sex, and body mass index, we found that four linked single nucleotide polymorphisms (SNPs) of PNPLA3, including the rs738409 G allele (CHB + NAFLD group vs CHB group: odds ratio [OR] = 2.77, 95% confidence interval [CI]: 1.18-6.54; P = 0.02), rs3747206 T allele (CHB + NAFLD group vs CHB group: OR = 2.77, 95%CI: 1.18-6.54; P = 0.02), rs4823173 A allele (CHB + NAFLD group vs CHB group: OR = 2.73, 95%CI: 1.16-6.44; P = 0.02), and rs2072906 G allele (CHB + NAFLD group vs CHB group: OR = 3.05, 95%CI: 1.28-7.26; P = 0.01), conferred high risk to NAFLD in CHB patients. In patients with both CHB and NAFLD, these genotypes of PNPLA3 polymorphisms were associated with increased susceptibility to nonalcoholic steatohepatitis (NASH) (NAFLD activity score ≥ 3; P = 0.01-0.03) and liver fibrosis (> 1 Metavir grading; P = 0.01-0.04). As compared to those with C/C and C/G at rs738409, C/C and C/T at rs3747206, G/G and G/A at rs4823173, and A/A and A/G at rs2072906, patients in the CHB + NAFLD group with G/G at rs738409, T/T at rs3747206, A/A at rs4823173, and G/G at rs2072906 showed significantly lower serum levels of HBV DNA (P < 0.01-0.05).

CONCLUSION: Four linked SNPs of PNPLA3 (rs738409, rs3747206, rs4823173, and rs2072906) are correlated with susceptibility to NAFLD, NASH, liver fibrosis, and HBV dynamics in CHB patients.

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.

Calcium-independent phospholipases A2 and their roles in biological processes and diseases

Among the family of phospholipases A2 (PLA2s) are the Ca(2+)-independent PLA2s (iPLA2s) and they are designated group VI iPLA2s. In relation to secretory and cytosolic PLA2s, the iPLA2s are more recently described and details of their expression and roles in biological functions are rapidly emerging. The iPLA2s or patatin-like phospholipases (PNPLAs) are intracellular enzymes that do not require Ca(2+) for activity, and contain lipase (GXSXG) and nucleotide-binding (GXGXXG) consensus sequences. Though nine PNPLAs have been recognized, PNPLA8 (membrane-associated iPLA2γ) and PNPLA9 (cytosol-associated iPLA2β) are the most widely studied and understood. The iPLA2s manifest a variety of activities in addition to phospholipase, are ubiquitously expressed, and participate in a multitude of biological processes, including fat catabolism, cell differentiation, maintenance of mitochondrial integrity, phospholipid remodeling, cell proliferation, signal transduction, and cell death. As might be expected, increased or decreased expression of iPLA2s can have profound effects on the metabolic state, CNS function, cardiovascular performance, and cell survival; therefore, dysregulation of iPLA2s can be a critical factor in the development of many diseases. This review is aimed at providing a general framework of the current understanding of the iPLA2s and discussion of the potential mechanisms of action of the iPLA2s and related involved lipid mediators.

Associations of I148M variant in PNPLA3 gene with plasma ALT levels during 2-year follow-up in normal weight and overweight children: the PANIC Study

OBJECTIVES

PNPLA3 I148M polymorphism (rs738409) has been strongly associated with liver fat content and plasma alanine aminotransferase (ALT) levels in obese adults and children, but little is known about these relationships in normal weight individuals. We studied the associations and interactions of overweight and the PNPLA3 I148M polymorphism with plasma ALT levels during 2-year follow-up in children.

METHODS

Subjects were a population sample of 481 Caucasian children aged 6-8 years examined at baseline and 419 children re-examined after 2-year follow-up. Altogether, 58 (12%) of 481 children at baseline and 71 (17%) of 419 children after 2-year follow-up were overweight. We assessed plasma ALT levels and other cardiometabolic risk factors and genotyped the PNPLA3 I148M polymorphism.

RESULTS

Being overweight and carrying PNPLA3 148M allele were associated with increased ALT levels at baseline (P = 0.002; P = 0.033) and after 2-year follow-up (P < 0.001; P = 0.001). Being overweight (P < 0.001) and carrying PNPLA3 148M allele (P = 0.001) were also associated with increase in ALT levels during 2-year follow-up. PNPLA3 148M allele carriers had increased ALT levels at baseline (P = 0.024 for interaction) and after 2-year follow-up (P = 0.002 for interaction) as well as a larger increase in ALT levels during 2-year follow-up (P = 0.002 for interaction) if they were overweight but not if they were normal weight. Further adjustment for clinical puberty, dietary factors, physical activity or sedentary behaviour had little or no effect on these associations.

CONCLUSION

PNPLA3 148M allele carriers had higher plasma ALT levels and larger increase in ALT levels during follow-up than non-carriers only among overweight children.

Meta-analysis reveals a specific association of the PNPLA3 I148M polymorphism with ALT level in adolescents

AIM

To evaluate potential link between the PNPLA3 rs738409 polymorphism and alanine aminotransferase (ALT) levels through an evidence-based study.

MATERIALS & METHODS

Electronic literature databases, including PubMed, Embase and the Institute for Scientific Information, were searched for relevant studies. Pooling standardized mean differences for quantitative variables and summary odds ratios (OR) were respectively calculated using per-allele comparison.

RESULTS

Although a genotype-phenotype association was inconsistent in adults, this genetic effect was stable in adolescents. There was an approximate increase of 23% in ALT value, and 1.99-fold higher ALT elevation per risk allele increase with low heterogeneity.

CONCLUSION

The PNPLA3 rs738409 polymorphism can have a differentiated influence on ALT level. Our meta-analysis provides reference data for the adjustment of diverse susceptibility due to the rs738409 polymorphism when evaluating liver injury in various populations.

Isoleucine-to-methionine substitution at residue 148 variant of PNPLA3 gene and metabolic outcomes in gestational diabetes

BACKGROUND

A single nucleotide polymorphism (SNP) of the patatin-like phospholipase-3 (PNPLA3)/adiponutrin gene (rs738409 C>G) is strongly associated with nonalcoholic fatty liver disease; to our knowledge, no data are available on the impact of this PNPLA3 SNP on liver and metabolic outcomes during pregnancy in patients with gestational diabetes (GD).

OBJECTIVE

We evaluated the impact of the PNPLA3 rs738409 SNP on liver enzymes, metabolic indexes, and maternal and neonatal outcomes in 200 GD patients enrolled in a lifestyle intervention.

DESIGN

In a randomized trial with a 2 × 2 factorial design, exercise significantly improved maternal and neonatal outcomes in GD patients. Effects of the G allele on metabolic and liver indexes and maternal and neonatal outcomes were evaluated in these patients.

RESULTS

At the end of the trial, fasting insulin and homeostasis model assessment of insulin resistance (HOMA-IR) values were significantly lower and liver enzymes significantly higher in PNPLA3 G-allele carriers. In a multiple regression model, the G allele was associated directly with aspartate aminotransferase (β = 2.60; 95% CI: 0.99, 4.20), alanine aminotransferase (β = 3.70; 95% CI: 1.78, 5.62), and γ-glutamyl transferase (β = 3.70; 95% CI: 0.80, 6.60) and inversely with insulin (β = -2.01; 95% CI: -3.24, -0.78) and HOMA-IR (β = -0.39; -0.64, -0.14) values at the end of the trial. In a multiple logistic regression model, the G allele was associated directly with risk of developing liver enzyme elevation during pregnancy (OR: 4.21; 95% CI: 1.78, 9.97) and inversely with the birth of large-for-gestational-age newborns (OR: 0.19; 95% CI: 0.06, 0.62). No diet × genotype or exercise × genotype interaction was shown.

CONCLUSION

The PNPLA3 SNP rs738409 G allele was associated with risk of mildly elevated transaminases in GD independent of a lifestyle intervention and despite a significant reduction in insulin resistance and risk of macrosomic offspring. This trial was registered at clinicaltrials.gov as NCT01506310.

Hepatocellular carcinoma in chronic HBV-HCV co-infection is correlated to fibrosis and disease duration

Hepatocellular carcinoma (HCC) is a development of severe liver disease frequently due to HBV and/or HCV infection. The aim of this retrospective study was to evaluate the development of HCC in patients with HBV-HCV chronic infection compared with patients with single HBV or HCV infection and the viral and host factors correlated to HCC in co-infected patients. We studied 268 patients with histology proven chronic hepatitis: 56 had HBV-HCV co-infection (HBV-HCV group), 46 had HBV infection (HBV group) and 166 had HCV infection (HCV group). Patients were followed up for at least 3 years. Viral and host factors were studied. HCC was more frequent in HBV-HCV group (14%) compared with HBV (2%, p = 0.006) and HCV monoinfected (4%, p = 0.006). The Mantel-Haenszel test used to investigate the relationship between HBV-HCV co-infection and development of HCC indicated an association between development of HCC and HBV-HCV co-infection (p < 0.001). In the HBV-HCV group, patients with HCC were significantly older (p = 0.000), had longer disease duration (p = 0.001), higher blood glucose levels (p = 0.001), lower levels of steatosis (p = 0.02), higher levels of fibrosis (p = 0.000), higher HCV RNA (p = 0.01) than those without HCC. ALT, lipid profile, PNPLA3 variant distribution and HBV viral load did not differ among co-infected patients with or without HCC. In conclusion HCC was more frequent in our patients with HBV-HCV co-infection, than in those with HBV or HCV mono-infection; possible associated risk factors for HCC development seem a long duration of disease, high levels of fibrosis and carbohydrate intolerance.

Metabolic syndrome in pediatrics

The ever growing prevalence of childhood obesity is being accompanied by an increase in the pediatric population of diseases once believed to be exclusive of the adulthood such as the metabolic syndrome (MS). The MS has been defined as the link between insulin resistance, hypertension, dyslipidemia, impaired glucose tolerance, and other metabolic abnormalities associated with an increased risk of atherosclerotic cardiovascular diseases in adults. In this review, we will discuss the peculiar aspects of the pediatric MS and the role of novel molecules and biomarkers in its pathogenesis.

Novel association between a nonsynonymous variant (R270H) of the G-protein-coupled receptor 120 and liver injury in children and adolescents with obesity

The G-protein-coupled receptor 120 (GPR120) is a receptor for polyunsaturated fatty acids with anti-inflammatory activity. The R270H variant of GPR120 enhances inflammation in adipose and hepatic tissues. We investigated whether the R270H variant could play a role in determining liver injury in children and adolescents with obesity. Five hundred eighty-one children with obesity were studied. No homozygotes and 20 heterozygotes for the 270H allele were found. Heterozygotes showed higher alanine transaminase (ALT) levels (P = 0.01) than wild-type subjects, and also showed an odds ratio to have pathologic ALT of 3.2 (95% confidence interval [CI] 1.2-8.0, P < 0.05). Moreover, we genotyped the same patients for the patatin-like phospholipase-containing domain 3 (PNPLA3) I148M polymorphism, which is implicated in the development of liver steatosis. Stratifying the patients with the GPR120 270H variant on the basis of their PNPLA3 polymorphism, we demonstrated a significant interaction effect on ALT levels (P = 0.00001), suggesting a driving effect of the PNPLA3 148M allele on liver injury in children with obesity carrying this variant.

Insulin resistance and steatosis in HBV-HCV co-infected patients: Role of PNPLA3 polymorphisms and impact on liver fibrosis progression

AIM: To evaluate steatosis, insulin resistance (IR) and patatin-like phospholipase domain-containing 3 (PNPLA3) and their relation to disease progression in hepatitis B and C viruses (HCV-HBV) co-infected patients.

METHODS: Three hundred and thirty patients with biopsy proven chronic hepatitis were enrolled: 66 had HBV-HCV, 66 HBV and 198 HCV infection. Prevalence of steatosis, IR and PNPLA3 polymorphisms and their relation to anthropometric, biochemical, virological and histological parameters were evaluated.

RESULTS: Prevalence of steatosis in group HBV-HCV was similar to that in HCV (47.0% vs 49.5%, respectively); group HBV showed the lowest steatosis (33.3%). Group HBV-HCV had a lesser degree of steatosis than HCV (P = 0.016), lower HCV RNA levels (P = 0.025) and lower prevalence and degree of IR (P = 0.01). PNPLA3 polymorphisms were associated with steatosis. Group HBV-HCV showed higher levels of liver fibrosis than group HCV (P = 0.001), but similar to that observed in HBV group. In HBV-HCV group, liver fibrosis was not associated with steatosis, IR or PNPLA3. HBV infection was the independent predictor of advanced liver fibrosis.

CONCLUSION: HBV-HCV co-infected patients have lower degree of hepatic steatosis, IR and HCV RNA than HCV mono-infected; co-infected patients showed a more rapid liver fibrosis progression that seems to be due to the double infection and/or HBV dominance.

Crystal structure of patatin-17 in complex with aged and non-aged organophosphorus compounds

Patatin is a non-specific plant lipase and the eponymous member of a broad class of serine hydrolases termed the patatin-like phospholipase domain containing proteins (PNPLAs). Certain PNPLA family members can be inhibited by organophosphorus (OP) compounds. Currently, no structural data are available on the modes of interaction between the PNPLAs and OP compounds or their native substrates. To this end, we present the crystal structure of patatin-17 (pat17) in its native state as well as following inhibition with methyl arachidonyl fluorophosphonate (MAFP) and inhibition/aging with diisopropylphosphorofluoridate (DFP). The native pat17 structure revealed the existence of two portals (portal1 and portal2) that lead to its active-site chamber. The DFP-inhibited enzyme underwent the aging process with the negatively charged phosphoryl oxygen, resulting from the loss of an isopropyl group, being within hydrogen-binding distance to the oxyanion hole. The MAFP-inhibited pat17 structure showed that MAFP did not age following its interaction with the nucleophilic serine residue (Ser77) of pat17 since its O-methyl group was intact. The MAFP moiety is oriented with its phosphoryl oxygen in close proximity to the oxyanion hole of pat17 and its O-methyl group located farther away from the oxyanion hole of pat17 relative to the DFP-bound state. The orientation of the alkoxy oxygens within the two OP compounds suggests a role for the oxyanion hole in stabilizing the emerging negative charge on the oxygen during the aging reaction. The arachidonic acid side chain of MAFP could be contained within portals 1 or 2. Comparisons of pat17 in the native, inhibited, and aged states showed no significant global conformational changes with respect to their Cα backbones, consistent with observations from other α/β hydrolases such as group VIIA phospholipase A2.

PNPLA3 genotype increases susceptibility of nonalcoholic steatohepatitis among obese patients with nonalcoholic fatty liver disease

BACKGROUND

The patatin-like phospholipase domain-containing protein 3 (PNPLA3) rs738409 variant is associated with histologic disease severity in patients with nonalcoholic fatty liver disease (NAFLD); however, whether the PNPLA3 genotype has an effect on susceptibility of nonalcoholic steatohepatitis (NASH) from NAFLD among severely obese patients remains unclear. The objective of this study was to investigate the role of the PNPLA3 genotype on NASH in severely obese Asian patients with NAFLD.

METHODS

The PNPLA3 rs738409 genotype was determined in 181 severely obese patients who underwent bariatric surgery. The diagnosis of NASH and the NAFLD activity score (NAS) were determined by liver histopathology.

RESULTS

Of the 181 patients, 29 (16.0%), 60 (33.2%), and 92 (50.8%) were in the non-NAFLD, steatosis, and NASH groups, respectively. The PNPLA3 rs738409 GG genotype was associated with higher liver enzymes and a higher risk for NASH (odds ratio [OR], 3.72; 95% CI, 1.25-11.05). The GG genotype was also associated with histologic severity of NAFLD, including higher steatosis grade (OR, 9.94; 95% CI, 2.20-44.83 for patients with grade 3 steatosis) and NAS (OR, 11.49; 95% CI, 2.50-52.83 for patients with a NAS ≥5). Finally, multiple logistic regression also showed that the GG genotype was an independent risk factor for NASH (OR, 3.58; 95% CI, 1.15-11.12) in NAFLD patients.

CONCLUSION

The PNPLA3 rs738409 GG genotype increases susceptibility of NASH in severely obese Asians with NAFLD and correlates to histologic severity of NAFLD.