In humans, germline homozygous RTEL1 mutations result in severe telomere-related disorders, including Dyskeratosis congenita (DKC) and Hoyeraal-Hreidarsson syndrome (HHS) [31–33], while heterozygous RTEL1 mutations are associated with familial pulmonary fibrosis with no hematologic phenotypes [34, 35]. This evidence concerns the gene RTEL1 and Hoyeraal-Hreidarsson syndrome.