POLR1D and Treacher-Collins syndrome: Specifically, allele variants encoding mutated versions of the Pol III subunits RPC1, RPC2, RPAC1 and RPAC2 subunits have been established as causative mutations of hypomyelinating leukodystrophy (HL)7–10,33–37, Treacher–Collins syndrome (TCS)11,12 and Wiedemann–Rautenstrauch syndrome (WRS)13,14.