The disease is the more serious form of nonalcoholic fatty liver disease (NAFLD), in which excess fat builds up in the organ. Between 30 percent and 40 percent of adults and about 10 percent of children in the United States have this condition, which has grown along with obesity rates, according to the National Institute of Diabetes and Digestive and Kidney Diseases. About 20 percent of people with that condition will develop NASH, which can lead to cirrhosis and eventually organ failure.