Hereditary fructose intolerance is an inherited disorder caused by the lack of an enzyme called aldolase B. This enzyme is required for digestion of ingested fructose, a simple sugar found primarily in fruits. Affected individuals develop symptoms when fructose or sucrose is introduced into the diet in infancy. Ingestion of fructose- or sucrose-containing food causes abdominal pain, vomiting, and diarrhea. Persistent fructose intake can lead to severe low blood sugar, progressive liver damage and kidney failure, coma, and eventually death. People can be mildly or severely affected by this disease. By carefully removing fructose and sucrose in the diet, people may be symptom free. Intellectual disability is possible if the condition is left untreated. A careful diet may not prevent liver disease in some people who have a severe form of the disease. Hereditary fructose intolerance disease is caused by pathogenic variants in the ALDOB gene.