From NAFLD in clinical practice to answers from guidelines.

This review of the literature consists of three sections. First, papers concerning non-alcoholic fatty liver disease (NAFLD) awareness among the general population, general practitioners, and liver and non-liver specialists were retrieved and analyzed to highlight the perception of disease, verify knowledge of current recommendations, and identify the main difficulties experienced in clinical practice. Next, position papers and clinical practice guidelines issued by International and National Hepatological Scientific Societies were identified and critically assessed in order to pinpoint the areas of convergence/difference. Finally, practical suggestions on NAFLD diagnosis and management in daily practice are provided and the open questions highlighted.

Clinical spectrum and therapy of non-alcoholic steatohepatitis.

Non-alcoholic fatty liver disease is increasingly being diagnosed worldwide and considered to be the commonest liver disorder in Western countries. It comprises a disease spectrum ranging from simple steatosis (fatty liver) through non-alcoholic steatohepatitis (NASH) to fat with fibrosis and, ultimately, cirrhosis. Simple steatosis is largely benign and non-progressive, whereas NASH can lead to cirrhosis, liver failure and hepatocellular carcinoma. Therapeutic strategies can be divided into those directed at components of the metabolic syndrome with potential beneficial liver effects and those directed specifically at the liver. Recent data suggest that diet and exercise improve NASH, particular in those achieving >7% weight loss. Obesity surgery has been shown to improve steatosis in all studies and inflammation and fibrosis in some. With respect to anti-diabetic drugs, results for metformin have not been convincing and concerns over the safety of glitazones have reduced the initial enthusiasm for their use. ACE inhibitors and angiotensin II receptor blockers hold the most promise as anti-hypertensive agents for patients with NASH and hypertension. With respect to more specific liver-directed therapies, there have been promising studies of antioxidants, including betaine and probucol, and vitamin E may improve NASH in adults and children. The TNF-α-lowering agent pentoxifylline may have beneficial effects on NASH. Liver transplantation is successful, but the disease recurrence rate is high in the absence of treatment of the underlying metabolic syndrome.

Genetic and environmental susceptibility to non-alcoholic fatty liver disease.

While the majority of those with non-alcoholic fatty liver disease (NAFLD) will have simple hepatic steatosis, a minority will develop progressive steatohepatitis. Family studies and inter-ethnic variations in susceptibility suggest that genetic factors may be important in determining disease risk. Although no genetic associations with advanced NAFLD have been replicated in large studies, preliminary data suggest that polymorphisms in genes controlling lipid metabolism, pro-inflammatory cytokines, fibrotic mediators and oxidative stress may be associated with steatohepatitis and/or fibrosis. Recent whole genome-wide scans have identified genes contributing to inherited susceptibility to steatosis and it seems likely that similar approaches will identify genes associated with disease progression in the near future.

Current and future therapeutic strategies in NAFLD.

Non alcoholic fatty liver disease (NAFLD) is increasingly diagnosed worldwide and considered to be the commonest liver disorder in Western countries. It comprises a disease spectrum ranging from simple steatosis (fatty liver), through non-alcoholic steatohepatitis (NASH) to fat with fibrosis and ultimately cirrhosis. Simple steatosis is largely benign and non-progressive, whereas NASH, characterized by hepatocyte injury, inflammation and fibrosis can lead to cirrhosis, liver failure and hepatocellular carcinoma (HCC). NAFLD is strongly associated with obesity, insulin resistance, hypertension and dyslipidaemia and is now regarded as the liver manifestation of the metabolic syndrome. Rapid spread of the obesity 'pandemic' in adults and children, coupled with the realisation that the outcomes of obesity-related liver disease are not entirely benign, has led to rapid growth in clinical and basic studies in NAFLD over the past decade. These studies are now beginning to inform management strategies for patients with NAFLD.

Genes and nonalcoholic fatty liver disease.

Whereas most individuals with nonalcoholic fatty liver disease (NAFLD) will have steatosis, only a minority will ever develop progressive disease. Family studies and interethnic variations in susceptibility suggest that genetic factors may be important in determining disease risk. Although no genetic associations with advanced NAFLD have been replicated in large studies, preliminary data suggest that polymorphisms in the genes encoding microsomal triglyceride transfer protein, superoxide dismutase 2, the CD14 endotoxin receptor, tumor necrosis factor-alpha, transforming growth factor-beta, and angiotensinogen may be associated with steatohepatitis and/or fibrosis. With the advent of high-throughput gene analyses and the reduced cost of whole genome-wide scans, it seems likely that genes contributing to inherited susceptibility to this common disease will be identified in the near future.

Non-alcoholic fatty liver disease: the mist gradually clears.

Non-alcoholic fatty liver disease (NAFLD) is now the commonest liver disorder in the developed world affecting up to a third of individuals. It is closely associated with features of the metabolic syndrome, particularly obesity and diabetes. It can progress to cirrhosis, hepatocellular carcinoma and liver failure and is an increasing indication for transplantation. Dietary and genetic factors determine susceptibility to NAFLD and its progression. NAFLD may also be involved in the pathogenesis of cardiovascular disease. Most patients present with incidentally found abnormal liver blood tests. Diagnosis is usually one of exclusion. Liver biopsy is required for disease staging, but new imaging modalities and biomarkers are emerging which may eventually fulfil this role. There is, as yet no firm evidence-based treatment for NAFLD. Therapy is currently directed at treating components of the metabolic syndrome which may also be beneficial for the liver. The recent elucidation of the mechanisms leading to progressive disease suggests a variety of novel targets worthy of testing in animal models of NAFLD and subsequently in pilot studies in humans.

Treatment of alcoholic liver disease.

Severe alcoholic steatohepatitis (ASH) is the major complication of advanced alcoholic liver disease (ALD) and has a high mortality even when treated with corticosteroids. Despite the importance of reactive oxygen species in the pathophysiology of ALD and ASH, antioxidants provide no benefit in the treatment of patients with ASH. Proinflammatory cytokines are important in the pathophysiology of ALD and might mediate most of the inflammatory aspects of these disorders. New treatment modalities in ASH might involve antagonism of proinflammatory cytokines such as tumor necrosis factor (TNF) by specific antibodies or other TNF-interfering treatment strategies. Propylthiouracil and S-adenosyl methionine may be beneficial to patients with alcoholic cirrhosis, but both require further randomized, controlled trials before their use can be recommended.Liver transplantation is an effective therapy for patients with advanced alcoholic cirrhosis who have not recovered after a period of abstinence.

Genetics of alcoholic liver disease and nonalcoholic fatty liver disease.

Although the vast majority of heavy drinkers and individuals with obesity, insulin resistance, and the metabolic syndrome have steatosis, only a minority ever develop steatohepatitis, fibrosis, and cirrhosis. Genetic and environmental risk factors for advanced alcoholic liver disease (ALD) and nonalcoholic fatty liver disease (NAFLD) seem likely to include factors that influence the severity of steatosis and oxidative stress, the cytokine milieu, the magnitude of the immune response, and/or the severity of liver fibrosis. For ALD, the dose and pattern of alcohol intake, coffee intake, and dietary and other lifestyle factors leading to obesity are the most important environmental determinants of disease risk. For NAFLD, dietary saturated fat and antioxidant intake, small bowel bacterial overgrowth, and obstructive sleep apnea syndrome may play a role. Family studies and interethnic variations in susceptibility suggest that genetic factors are important in determining disease risk. For ALD, functional polymorphisms in the ADH and ALDH alcohol metabolizing genes play a role in determining susceptibility in Oriental populations. No genetic associations with advanced NAFLD have been replicated in large studies. Preliminary data suggest that polymorphisms in the genes encoding microsomal triglyceride transfer protein, superoxide dismutase 2, the CD14 endotoxin receptor, tumor necrosis factor alpha, transforming growth factor beta, and angiotensinogen may be associated with steatohepatitis or hepatic fibrosis or both.

Genetic studies to identify hepatic fibrosis genes and SNPs in human populations.

Increasing evidence suggests that non-sex-linked genetic factors play a role in determining both susceptibility to, and progression of, liver fibrosis. The elucidation of these factors will have many potential benefits in the management of patients with chronic liver disease. A variety of approaches can be used to look for genetic factors playing a role in liver fibrosis. In the future, genome-wide single nucleotide polymorphism (SNP) scanning of cases and controls may become feasible; however, to date, studies have relied on candidate-gene, case-control, allele-association methodology. This section will focus on the design and interpretation of case-control association studies in liver disease using non-alcoholic fatty liver disease (NAFLD) to illustrate the key issues and potential pitfalls of this approach.