POLR1C and leukodystrophy: 21 However, to this day, there have been no studies specifically dedicated to exploring the craniofacial features in POLR3-HLD. Here, we further expand the phenotypic description of POLR3-HLD caused by biallelic variants in POLR3A, POLR3B and POLR1C by systematically assessing and characterizing the craniofacial features of 31 identified affected individuals.