They also suggest that, in AD, ATM activity in neurons is low, as indicated by three indirect measurements of ATM signalling including (i) the nuclear translocation of histone deacetylase 4 (HDAC4); (ii) the trimethylation of histone H3; and (iii) the appearance of cell cycle proteins, specifically cyclin A2 [152]. Here, HDAC4 is linked to Alzheimer disease.