TWIST1 and thanatophoric dysplasia: However, unexpectedly, the relative fold change in TGFβ-induced mRNA expression of major EMT-regulatory factors (ZEB1, ZEB2, TWIST, SNAIL and SLUG), whose expression is positively regulated in a Smad-dependent manner [12], was markedly lower in TD cells than in control cells, despite the higher basal expression levels of these genes (except for TWIST) in TD cells (Figure 2A).