Additionally, although healthy BBB impedes PCSK9 entry into the brain [72], it cannot be excluded that several physio-pathological states, such as ageing, infections, cancer, diabetes, atherosclerosis, stroke, and post-traumatic and environmental pollutant-associated injuries [200,201,202,203,204,205], could allow PCSK9 loading into the brain by destabilizing the BBB. This evidence concerns the gene PCSK9 and diabetes mellitus.