• bone marrow transplantation;
  • dyskeratosis congenita;
  • dyskerin;
  • Hoyeraal–Hreidarsson syndrome;
  • severe combined immunodeficiency

Summary.  X-linked Hoyeraal–Hreidarsson syndrome (XL-HHS) is the severe infantile variant of X-linked dyskeratosis congenita (XL-DC) and both are due to mutations in the DKC1 gene within Xq28. We report a novel missense mutation in DKC1 exon 3 (T113[RIGHTWARDS ARROW]C, Ile38Thr) in a Sardinian infant with XL-HHS in whom the disease was characterized by ‘T+BNK’ severe combined immunodeficiency and bone marrow failure. He underwent sibling bone marrow transplantation using a conditioning regimen (fludarabine, rabbit antithymocyte globulin, low-dose melphalan) selected according to the HHS/DC phenotype. This was associated with low toxicity, prompt engraftment with adequate immune reconstitution and full donor haemopoiesis.