They also modulate the activity and the expression of the key Hsa21 genes involved in DS pathogenesis, such as dual specificity tyrosine-phosphorylation-regulated kinase 1A (DYRK1A), regulator of calcineurin 1 (RCAN1), amyloid precursor protein (APP) and some miRNAs, such as the miR-155, as well as no-Hsa21-encoded key regulatory proteins for brain development, such as the tropomyosin-related kinase B (TrkB) and the brain-derived neurotrophic factor (BDNF) [29]. Here, BDNF is linked to Dravet syndrome.