label: Hoyeraal-Hreidarsson syndrome
label_lc: hoyeraal-hreidarsson syndrome
description: Hoyeraal-Hreidarsson syndrome (HHS) is a very rare X-linked recessive disorder considered to be a severe variant of dyskeratosis congenita characterized by intrauterine growth retardation, microcephaly, cerebellar hypoplasia, progressive combined immune deficiency and aplastic anemia.