PSEN1 and Alzheimer disease: Additional studies have specifically investigated the hippocampus, one of the brain regions strongly affected by AD and found increased levels of 5-mC [155] and DNMT3a [63] in the hippocampus of aging mice, but reduced 5-mC levels in APP/PS1 transgenic mice (Chouliaras et al., submitted, 2014) and in the hippocampus, entorhinal cortex and cerebellum of AD patients [156,157].