In the last decade a large body of literature data from epidemiological studies, animal experiments and clinical trials showed the link between vitamin D deficiency and/or VDR gene polymorphisms and several central or peripheral neurodegenerative diseases, particularly multiple sclerosis (MS), amyotrophic lateral sclerosis, Parkinson’s disease (PD) and Alzheimer’s disease (AD), and neuropsychiatric disorders, i.e., depression, autism and schizophrenia [52]. The gene discussed is VDR; the disease is Alzheimer disease.