NPC1 and REM sleep behavior disorder: Recently, various subclinical abnormalities in asymptomatic heterozygote NPC1-mutation carriers have been described including hepatosplenomegaly, increased cholestantriol, and plasma chitotriosidase and features of early neurodegenerative disease, e.g., impaired cognitive function, hyposmia, features suggestive of REM sleep behavior disorder, and decreased glucose metabolic rates on PET imaging [26].