Niemann-Pick disease type C (NPC) is a very rare, inherited neurodegenerative disease that results from an abnormal processing in body tissues of fatty substances (lipids), particularly cholesterol. Fatty substances accumulate in the brain, spleen, liver and lung, causing dementia and other symptoms leading to disability and premature death. NPC is one of many rare hereditary disorders of the metabolism of lipids and other molecules that result in a neurodegenerative disease.