Genetic factors contribute to variation in serum alanine aminotransferase activity independent of obesity and alcohol: a study in monozygotic and dizygotic twins

The 148M allele of the PNPLA3 gene is associated with indices of liver damage early in life

BACKGROUND & AIMS

Childhood obesity is a growing problem worldwide. Non-alcoholic fatty liver disease (NAFLD) is frequently associated with obesity in children. Recently, the PNPLA3 gene I148M (rs738409) variant was demonstrated to be strongly associated with hepatic steatosis in obese adults. In this study we add further insight into the role of PNPLA3 by exploring whether this association begins early in life in obese children or becomes manifest only in adulthood.

METHODS

Four hundred and seventy-five obese/overweight children and adolescents were genotyped for the I148M allele. Clinical and biochemical parameters were collected for all participants, including indices of hepatic injury, glucose tolerance and insulin resistance. Ultrasound imaging of the liver was obtained to assess the degree of steatosis in a subset of children.

RESULTS

Carriers of two 148M alleles had a 52% increase in circulating ALT levels compared to carriers of two 148I alleles, with individuals with one 148M allele showing a 9.5% increase (p=0.001). AST concentration was also significantly higher in carriers of two and one M alleles (17.4% and 4%, respectively, p=0.022). A total of 36% of carries of two 148M alleles showed elevated ALT, defined as >30U/L, compared to only 10% of carriers of two 148I alleles (p<0.001). Liver steatosis was more prevalent in carriers of two 148M alleles. Glucose tolerance and insulin sensitivity were similar across all three genotypes.

CONCLUSIONS

Our data show that the PNPLA3 gene I148M variant is associated with increased levels of ALT/AST in obese children and adolescents, suggesting that it confers genetic susceptibility to liver damage from a young age.

New direct-acting antivirals in the development for hepatitis C virus infection

A large number of new therapies are in development for chronic hepatitis C including direct-acting antiviral drugs (DAA), which target specific hepatitis C virus enzymes. Two of these compounds have already advanced into phase 3 development in the USA and EU, and many more are in phase 2 trials and likely to advance. In this review, the results of recent studies on ribavirin analogues, nonstructural (NS) 3/4 serine protease inhibitors, NS5B polymerase inhibitors, cyclophilin inhibitors, silimarin components, and thiazolides have been updated. Each compound includes a brief summary of its proposed mechanism of action, results of early clinical trials, and more advanced trial data where available. These compounds are likely to be the first approved in the USA and EU and will initially be used in combination with the current standard of care. It is possible that future treatment paradigms with these agents will offer the potential of interferon-free regimens. It is most likely that patients for these new therapies will be selected carefully by identifying and treating first those who have excellent sustained virologic response rates with 24 weeks of pegylated interferon and ribavirin, the current standard of care. It is also likely that there will be a need to identify those patients who are not likely to have a sustained virologic response with the addition of a protease inhibitor to the current standard of care and delaying their therapy until combination viral suppression therapy becomes an option. The cost and side effects of the DAA will be important considerations for treating physicians. This review is current through 2009; however, data are rapidly changing.

From the metabolic syndrome to NAFLD or vice versa?

The metabolic syndrome encompasses metabolic and cardiovascular risk factors which predict diabetes and cardiovascular disease (CVD) better than any of its individual components. Nonalcoholic fatty liver disease (NAFLD) comprises a disease spectrum which includes variable degrees of simple steatosis (nonalcoholic fatty liver, NAFL), nonalcoholic steatohepatitis (NASH) and cirrhosis. NAFLD is the hepatic manifestation of the metabolic syndrome, with insulin resistance as the main pathogenetic mechanism. Recent data indicate that hyperinsulinemia is probably the consequence rather than cause of NAFLD and NAFLD can be considered an independent predictor of cardiovascular disease. Serum free fatty acids derived from lipolysis of visceral adipose tissue are the main source of hepatic triglycerides in NAFLD, although hepatic de novo lipogenesis and dietary fat supply contribute to the pathogenesis of NAFLD. Approximately 10-25% NAFLD patients develop NASH, the evolutive form of hepatic steatosis. Presumably in a genetically predisposed environment, this increased lipid overload overwhelms the oxidative capacity and reactive oxygen species are generated, leading to lipid peroxidation, cytokine induction, chemoattraction of inflammatory cells, hepatic stellate cell activation and finally fibrogenesis with extracellular matrix deposition. No currently available therapies for NAFLD and NASH exist. Recently nuclear receptors have emerged as key regulators of lipid and carbohydrate metabolism for which specific pharmacological ligands are available, making them attractive therapeutic targets for NAFLD and NASH.

Prediction of non-alcoholic fatty liver disease and liver fat using metabolic and genetic factors

BACKGROUND & AIMS

Our aims were to develop a method to accurately predict non-alcoholic fatty liver disease (NAFLD) and liver fat content based on routinely available clinical and laboratory data and to test whether knowledge of the recently discovered genetic variant in the PNPLA3 gene (rs738409) increases accuracy of the prediction.

METHODS

Liver fat content was measured using proton magnetic resonance spectroscopy in 470 subjects, who were randomly divided into estimation (two thirds of the subjects, n = 313) and validation (one third of the subjects, n = 157) groups. Multivariate logistic and linear regression analyses were used to create an NAFLD liver fat score to diagnose NAFLD and liver fat equation to estimate liver fat percentage in each individual.

RESULTS

The presence of the metabolic syndrome and type 2 diabetes, fasting serum (fS) insulin, fS-aspartate aminotransferase (AST), and the AST/alanine aminotransferase ratio were independent predictors of NAFLD. The score had an area under the receiver operating characteristic curve of 0.87 in the estimation and 0.86 in the validation group. The optimal cut-off point of -0.640 predicted increased liver fat content with sensitivity of 86% and specificity of 71%. Addition of the genetic information to the score improved the accuracy of the prediction by only <1%. Using the same variables, we developed a liver fat equation from which liver fat percentage of each individual could be estimated.

CONCLUSIONS

The NAFLD liver fat score and liver fat equation provide simple and noninvasive tools to predict NAFLD and liver fat content.