HDAC4 and post-traumatic stress disorder: The same study found an association between PTSD diagnosis and methylation of CpG sites on a gene encoding histone deacetylase 4 (HDAC4). Validation of this observation was suggested by finding, in mice, that increased Hdac4 transcription was associated with low estrogen levels after fear conditioning in naturally cycling females (Maddox et al., 2018).