In Reply:

Dr. Kopp raises an important point that Dr. Planel and I should have mentioned in our editorial.¹  There is no question that mitochondria, reactive oxygen species, and various neurodegeneration pathways, including tauopathy, are linked in some way. And there is also no question that we often treat patients (and animals and cells in our studies) with oxygen as if it is inert. It is most certainly not. However, there is a dearth of literature on the effect of inhaled oxygen on any of the neurodegenerative diseases, so it is not yet clear whether the hypothetical concern raised by Dr. Kopp is real and if so, of what magnitude? Until such data become available, it is important to take Dr. Kopp’s advice and adequately control our studies with respect to oxygen.