Niemann-Pick disease type C is an autosomal recessive lysosomal lipid storage disorder caused by a defect of NPC1 or NPC2 involved in cholesterol trafficking. The disease is characterized by neurodegeneration starting from early life. While NPC1 is a lysosomal transmembrane protein involved in shuttling of substrates to the Golgi and possibly elsewhere in cells, NPC2 is a soluble lysosomal protein known to bind cholesterol.
Niemann-Pick disease, type D is now thought to be a variant of type C. TypeD has only been found in the French Canadian population of Yarmouth County, Nova Scotia.