NPC1 and nasopharyngeal carcinoma: The trafficking behaviour of NPC1 in fibroblasts taken from NPC patients was examined by testing the sensitivity of NPC1 protein to Endo H. Endo H distinguishes between the mannose-rich immature form of proteins that are located in the ER or in the early secretory pathway and their complex glycosylated mature counterparts that have been processed in the Golgi apparatus.