The phenotype of Down syndrome, trisomy of chromosome 21, is hypothesized to be produced by the increased expression due to gene dosage of normal chromosome 21 genes, which affects the regulation and function of several proteins (ELK, CREB, ER, GR) and BDNF, which are involved in certain facets of learning, memory and behavior that are abnormal in DS or mouse models [7]. The gene discussed is BDNF; the disease is Down syndrome.