NPC1 and Niemann-Pick disease type C: Niemann–Pick type C disease (NPC) is a lysosomal storage disorder caused by mutations in the genes NPC1 or NPC2. The resulting dysfunction in proteins involved in intracellular cholesterol transport and homeostasis leads to intracellular accumulation of cholesterol and sphingolipids in late endosomes and lysosomes [18,36,37].