NPC1 and Tangier disease: NPC1 is characterised in part by reduced acidic store Ca2+ levels, which was previously measured using calcium release assays and calcium sensors within LE/Lys.1 As the Tangier patient derived fibroblasts shared many of the downstream defects and lipid storage phenotypes observed in NPC, we also measured acidic store Ca2+ release in response to GPN (glycyl‐l‐phenylalanine 2‐naphthylamide) in Tangier disease cells.