H1-0 and Alzheimer disease: Thus, Schutzer et al. [67] demonstrate that the extracellular histones H1, H2A, H2B, H3, and H4 are present at detectable levels in human cerebrospinal fluid (CSF), and Begcevic et al. [68] report 1.6 times higher concentrations of H2A in the CSF of AD patients compared to age-matched controls.