POLR1D and Treacher-Collins syndrome: Mutations in genes encoding the two RNA Pol I subunits, POLR1C and POLR1D, and in the nucleolar protein Treacher Collins-Franceschetti syndrome 1 (TCOF1, also known as treacle) cause the craniofacial disorder, Treacher Collins syndrome (OMIM 248390, OMIM 613717 and OMIM 154500).