As suggested in DS, DS-derived iPSCs, and DS mouse models, overexpression of genes DYRK1A, APP, EURL involved in various cell functions and structural aspects of neurogenesis, of OLIG1/2 responsible for myelinating cells and oligodendrocyte differentiation, and of ERG, and RCAN1 affecting the central nervous system, is probably among the most noxious mechanisms in T21 brain etiopathology [23]. This evidence concerns the gene C21orf91 and Dravet syndrome.