NPC1 and nasopharyngeal carcinoma: Collectively, these results suggest that Npc1 deficiency can alter the expression of selected genes, which may be involved either directly or indirectly in NPC pathogenesis, whereas expression of mutant human APP in Npc1-null background appears to influence disease pathology by regulating the changes that are already altered by Npc1-deficiency rather instigating expression of additional genes.