POLR1C and Treacher-Collins syndrome: Yet another class of genes can present with distinct disorders due to allelic heterogeneity, e.g. POLR1C associated with recessive hypomyelinating leukodystrophy 11 (MIM 616494) and recessive Treacher Collins syndrome 3 (MIM 248390) [76] and illustrate allelic affinity wherein different clinical disease phenotypes are due to different alleles at the same locus [98].