TET2 and Alzheimer disease: However, 5‐hmC is enriched in intragenic regions in AD brains [158] and TET1 overexpression impairs hippocampus‐dependent long‐term memory [159] and TET2 loss shows a neuroprotective effect in Parkinson's disease (PD) [160], indicating that tight regulation of 5‐hmC is required for normal neuronal functions and survival.