The critical role of the H/ACA complex in cellular homeostasis is evident from the observation that inherited mutations in the genes encoding dyskerin [i.e., Dyskeratosis Congenita 1 (DKC1)], NHP2 and NOP10, cause the telomere disorder known as dyskeratosis congenita and its more severe form, referred to as Hoyeraal-Hreidarsson syndrome, associated with various developmental defects, shorter telomeres, and an increased risk for cancer (30–36). Here, DKC1 is linked to Hoyeraal-Hreidarsson syndrome.