NPC1 and Niemann-Pick disease, type C1: Niemann-Pick type C1 disease (NPC1) is a rare autosomal recessive disorder caused by mutations in the Npc1 gene, which encodes a transmembrane protein that mediates the egress of low-density lipoprotein (LDL)–derived cholesterol from the endosomal/lysosomal compartments [1, 2].