We describe an African American family with Hoyeraal-Hreidarrson syndrome (HHS) in which 2 TERT mutations (causing P530L and A880T amino acid changes) and two in the DKC1 variants (G486R and A487A) were segregating. Both genes are associated with dyskeratosis congenita and HHS. It was important to determine the importance of these mutations in disease pathogenesis to counsel family members. From genetic analysis of family members, telomere length and X-inactivation studies we concluded that compound heterozygosity for the TERT mutations was the major cause of HHS and the DKC1 G486R variant is a rare African variant unlikely to cause disease.