NPC1 and Niemann-Pick disease type C: Niemann‐Pick disease type C (NPC) is a rare inborn error of metabolism caused by mutations in either NPC1 or NPC2. Cellular hallmarks of NPC include sphingolipid storage and mis‐trafficking, an expanded late endosomal/lysosomal compartment and reduced levels of lysosomal Ca2+ leading to impaired Ca2+ signalling that effects late endosome/lysosome fusion.1 The relationship between NPC1 and NPC2 remains incompletely understood.