There are several options to diagnose NPC: skin and liver biopsy for filipin staining of cultured fibroblasts; electron microscopic analysis of vacuolation or hepatocytes containing “myelin figures” (Figure 2) [27,28,29]; molecular genetic analysis with direct sequencing of NPC1 and NPC2 gene mutations [28]; bone marrow aspiration for the detection of foamy histiocytes [30,31]; and use of cholesterol esterification assays and oxysterol assay-based screening to measure the increase of cholestane-3β,5α,6β-triol (cholesterol oxidation product, “triol”) [32,33,34,35]. Here, NPC1 is linked to nasopharyngeal carcinoma.