X-linked dyskeratosis congenita (X-linked DC) is associated with mutations in the DKC1 gene encoding dyskerin.281 Dyskerin is an enzyme that catalyzes the pseudouridylation of specific uridine residues in newly synthesized rRNAs.264 Pseudouridines regulate ribosome and rRNA biogenesis when associated with small nucleolar RNAs (snoRNA). The gene discussed is DKC1; the disease is dyskeratosis congenita.