In acid sphingomyelinase-deficient NPD (ASM-deficient NPD), underlying defects are due to SMPD1 gene mutations (type A, B, and intermediate forms), whereas in NP type C (NPC), which is currently described as a cholesterol trafficking defect, is due to NPC1 or NPC2 gene mutations [28,29]. This evidence concerns the gene SMPD1 and nasopharyngeal carcinoma.