Niemann-Pick disease is an inherited condition involving lipid metabolism (the breakdown and use of fats and cholesterol in the body) in which harmful amounts of lipids accumulate in the spleen, liver, lungs, bone marrow, and brain. This disorder is divided into four main types based on the genetic cause and the signs and symptoms exhibited by the patient. Type A Niemann-Pick disease begins during infancy and is characterized by an enlarged liver and spleen (hepatosplenomegaly), failure to thrive, and progressive deterioration of the nervous system. Children affected by this condition generally do not survive past early childhood. Type B disease may include signs of hepatosplenomegaly, growth retardation, and problems with lung function including frequent lung infections. Other signs include blood abnormalities such as abnormal cholesterol and lipid levels, and low numbers of blood cells involved in clotting (platelets). People affected by this type of Niemann-Pick disease usually survive into adulthood. Niemann-Pick disease, type C is further subdivided into types C1 and C2, each caused by a different gene mutation. Both types C1 and C2 Niemann-Pick disease are most commonly characterized by onset in childhood, although infant and adult onsets are possible. Other signs include severe liver disease, breathing difficulties, developmental delay, seizures, increased muscle tone (dystonia), lack of coordination, problems with feeding, and an inability to move the eyes vertically. People with this disorder can survive into adulthood.