Niemann-Pick disease, type C1 (NPC1) is a disease of a membrane protein that mediates intracellular cholesterol trafficking in mammals. In humans the protein is encoded by the NPC1 gene (chromosome location 18q11). NPC1 was identified as the gene that when mutated, results in Niemann-Pick disease, type C. Niemann-Pick disease, type C is a rare neurovisceral lipid storage disorder resulting from autosomal recessively inherited loss-of-function mutations in either NPC1 or NPC2. This disrupts intracellular lipid transport, leading to the accumulation of lipid products in the late endosomes and lysosomes. Approximately 95% of NPC patients are found to have mutations in the NPC1 gene. NPC1 encodes a putative integral membrane protein containing sequence motifs consistent with a role in intracellular transport of cholesterol to post-lysosomal destinations.