However, it is also possible that TSPO expression is independent of mitochondrial mass,45 and other cell types can also be affected, such as oligodendrocytes,46 or endothelium and smooth muscle cells of the cerebral vasculature.2,36 More extensive postmortem studies of mitochondrial mass and its relation to TSPO expression in the brain of patients with mitochondrial disease are required to fully support TSPO PET imaging as a novel noninvasive in vivo measure of mitochondrial density in the brain. The gene discussed is TSPO; the disease is inborn mitochondrial metabolism disorder.