Monarch Disease Ontology entry MONDO_0007027 (metabolic dysfunction-associated steatohepatitis) (MASH, formerly known as nonalcoholic steatohepatitis or NASH) is a type of fatty liver disease. It often develops due to a metabolic disorder, such as obesity or diabetes, resulting in a toxic buildup of fat in the liver. It is the most severe form of metabolic dysfunction-associated steatotic liver disease (MASLD, formerly known as nonalcoholic fatty liver disease or NAFLD). Also known as: MASH, NASH, NASH - nonalcoholic steatohepatitis, non-alcoholic steatohepatitis, nonalcoholic steatohepatitis.