Another is DNA damage by reactive oxygen species, highly destructive molecules usually formed as a byproduct of cellular respiration. Researchers from the University of Texas have discovered how these two pieces of the neuro-degenerative disease puzzle fit together, the Journal of Alzheimer’s Disease reports. “Reactive oxygen species cause the majority of the brain cell DNA damage that we see in Alzheimer’s and Parkinson’s disease, as well as most other neuro-degenerative disorders,” said researcher Muralidhar Hegde.