The Genetics of Nonalcoholic Fatty Liver Disease: Spotlight on PNPLA3 and TM6SF2

Nonalcoholic fatty liver disease (NAFLD) encompasses a spectrum that spans simple steatosis, through nonalcoholic steatohepatitis (NASH) to fibrosis and ultimately cirrhosis. Nonalcoholic fatty liver disease is characterized by substantial interpatient variation in rate of progression and disease outcome: Although up to 25% of the general population are at risk of progressive disease, only aminority experience associated liver-related morbidity. Nonalcoholic fatty liver disease is considered a complex disease trait that occurs when environmental exposures act upon a susceptible polygenic background composed of multiple independent modifiers. Recent advances include the identification of PNPLA3 as a modifier of disease outcome across the full spectrum of NAFLD from steatosis to advanced fibrosis and hepatocellular carcinoma; and the discovery of TM6SF2 as a potential "master regulator" of metabolic syndrome outcome, determining not only risk of advanced liver disease, but also cardiovascular disease outcomes. In this article, the authors will review the field, discussing in detail the current status of research into these important genetic modifiers of NAFLD progression.