Lysosomal pH is of key relevance to both the etiology and treatment of an extensive range of human disorders: lysosomal acidification defects are found in lysosomal storage disorders (LSDs) such as PPT1/CLN1 mutation [62] and nearly all neuronal ceroid lipofuscinoses [63], mitochondrial disorders [64] as well as dementias such as frontotemporal dementia, Parkinson disease [65,66] and Alzheimer disease [67]. The gene discussed is PPT1; the disease is dementia.