The fact that NCC specification and differentiation are similarly affected by mutations in nucleolar proteins – TCOF1/Treacle and a common subunit of RNA polymerases I and III in Treacher-Collins Syndrome [54], [55], and Wdr43 in fan mutants - leads to the intriguing question of why NCCs may be more sensitive to ribosome biogenesis defects as compared with other tissues. Here, TCOF1 is linked to Treacher-Collins syndrome.