Niemann-Pick disease is a lipid metabolism disorder categorized into three sub-types. Types A and B (NPA and NPB) are caused by acid sphingomyelinase (ASM) deficiency, due to mutations in the SMPD1 gene, leading to sphingomyelin accumulation in multiple organs, and resulting in cell death and the malfunction of major organ. Type C (NPC) patients fail to metabolize cholesterol, due to mutations in the NPC1 or NPC2 gene, leading to cholesterol accumulation within the liver and spleen and accumulation of other lipids in the brain. Abnormal lipid accumulation occurs in the spleen, liver, lungs, bone marrow and brain.