Thus, the increased inhibition of Smo due to elevated Ptch1 levels in DS, subsequently leading to repressed SHH activity, may contribute to the observed downregulation of a whole cluster of genes associated with OPC differentiation and myelination [11] and the delayed differentiation of OPCs, subsequently leading to hypomyelination in DS brains [18]. The gene discussed is SHH; the disease is Dravet syndrome.