Aging is the major known risk factor for Alzheimer's disease (AD) and Parkinson's disease (PD), but genetic deffects have been associated with familial cases. Huntington's disease (HD) is a purely genetic neurodegenerative disorder, where mutations in the IT15 gene, encoding for the protein huntingtin, determine the development of the disease. The Prion diseases differ from these other disorders because they can also have infections origin.