NPC2 and Niemann-Pick disease type C: If changes in cholesterol and lipid metabolism were responsible for the mtDNA phenotypes displayed by ATAD3-deficient cells (Fig. 4), then mtDNA abnormalities should be evident in genetic disorders of cholesterol metabolism such as Niemann-Pick disease type C, caused by mutations in the intracellular cholesterol transporters NPC1 (MIM 257220) or NPC2 (MIM 607625) (Roff et al., 1991).