POLR1D and Treacher-Collins syndrome: The identification of causative mutations in the TCOF1 gene (85% of the cases (Vincent et al., 2016)), but also in the RNA polymerase I (Pol I) subunits POLR1C, POLR1D and recently, POLR1B (Dauwerse et al., 2011; Sanchez et al., 2020) strongly suggests that perturbation of ribosome biogenesis is the underlying cause of Treacher Collins Syndrome.