Alzheimer´s Disease (AD) may be considered as the most important neurodegenerative disease both for its incidence and its destructive nature, and is nowadays a major public health problem. It is the main cause of dementia in old age. Historically, Alois Alzheimer described this disease in 1907 based on the clinical and histopathological data of a woman who died at 55 after suffering from progressive dementia; this is how this disease was first defined for cases starting before the age of 50 (therefore, AD was synonymous with presenile dementia). However, the increase in life expectancy made these manifestations appear in older population (senile dementia). A neurodegenerative disease is an alteration in the structure and function of the CNS. It has an insidious onset and is relentlessly progressive (much slower than metabolic inherited diseases, so much that neither the patient nor his/her family can remember the exact starting point).