Hoyeraal-Hreidarsson syndrome is an X-linked recessive disorder considered to be a severe variant of dyskeratosis congenita. It is a multisystem disorder characterized by intrauterine growth retardation, microcephaly, cerebellar hypoplasia, bone marrow failure associated with immunodeficiency. A missense mutation in the DKC1 gene and premature short telomeres were found in the disease.
