HDAC9 and Alzheimer disease: However, the development of the selective class I (HDAC isoforms 1, 2, 3) HDAC PET radioligand [11C]Martinostat has enabled antemortem studies of HDAC changes in living people.(37–39) In a recent study of AD, the density of class I HDACs assessed with [11C]Martinostat correlated with regional postmortem levels.(40) Unexpectedly, class I HDAC expression was reduced in posterior cortices.