Dyskeratosis congenita (DC) is a multisystem inherited syndrome exhibiting 
marked clinical and genetic heterogeneity. In its classic form, it is 
characterized by mucocutaneous abnormalities, BM failure, and a predisposition 
to cancer. BM failure is the principal cause of premature mortality. Studies 
over the last 15 years have led to significant advances, with 8 DC genes (DKC1, 
TERC, TERT, NOP10, NHP2, TIN2, C16orf57, and TCAB1) having been characterized. 
Seven of these are important in telomere maintenance either because they encode 
components of the telomerase enzyme complex (DKC1, TERC, TERT, NOP10, NHP2, and 
TCAB1) or the shelterin complex (TINF2). DC is therefore principally a disease 
of defective telomere maintenance and patients usually have very short 
telomeres. The genetic advances have led to the unification of DC with several 
other disorders, including the severe multisystem disorders Hoyeraal-Hreidarsson 
and Revesz syndromes, as well as a subset of patients with aplastic anemia, 
myelodysplasia, leukemia, and idiopathic pulmonary fibrosis. This wide spectrum 
of diseases ranging from classic DC to aplastic anemia can be regarded as 
disorders of defective telomere maintenance-"the telomereopathies." These 
advances have increased our understanding of normal hematopoiesis and 
highlighted the important role of telomerase and telomeres in human biology. 
They are also facilitating the diagnosis (especially when presentation is 
atypical) and management of DC.