Nonalcoholic fatty liver disease (NAFLD) is a chronic liver disease which can progress to cirrhosis and hepatocellular cancer in some individuals. The clinical-histologic phenotype of the disease extends from fatty liver (FL) to nonalcoholic steatohepatitis (NASH). NASH is more likely to progress to cirrhosis than FL. It is not known why some subjects develop NASH while others develop FL and why only some subjects progress to cirrhosis. Recent genome-wide association studies (GWAS) have identified individual polymorphisms that are associated with steatosis, NASH and cirrhosis. It is however known that inherited variation in genes in biologic pathways may determine the network’s functional status and thus the disease phenotype. Such information is not available for NASH.