However, miR-27a-3p was found to be significantly reduced in several brain diseases characterized by loss of claudin-5 and increased barrier permeability, including multiple sclerosis [7, 23, 24], intracerebral hemorrhage [29], Alzheimer’s diseases [30], Huntington’s disease [59] and traumatic brain injury [60], while miR-27a-3p elevation was shown to exert neuroprotective effects. Here, CLDN5 is linked to Alzheimer disease.