Syndrome complex of bone marrow failure and pulmonary fibrosis predicts germline defects in telomerase

Abstract

Mutations in the essential telomerase components hTERT and hTR cause dyskeratosis congenita, a bone marrow failure syndrome characterized by mucocutaneous features. Some (~ 3%) sporadic aplastic anemia (AA) and idiopathic pulmonary fibrosis cases also carry mutations in hTERT and hTR. Even though it can affect clinical outcome, because the mutation frequency is rare, genetic testing is not standard. We examined whether the cooccurrence of bone marrow failure and pulmonary fibrosis in the same individual or family enriches for the presence of a telomerase mutation. Ten consecutive individuals with a total of 36 family members who fulfilled these criteria carried a germline mutant telomerase gene (100%). The mean age of onset for individuals with AA was significantly younger than that for those with pulmonary fibrosis (14 vs 51; P < .0001). Families displayed autosomal dominant inheritance and there was an evolving pattern of genetic anticipation, with the older generation primarily affected by pulmonary fibrosis and successive generations by bone marrow failure. The cooccurrence of AA and pulmonary fibrosis in a single patient or family is highly predictive for the presence of a germline telomerase defect. This diagnosis affects the choice of bone marrow transplantation preparative regimen and can prevent morbidity.

Figure 1

Evidence of both pulmonary fibrosis and bone marrow failure in individuals with mutant telomerase genes. (A-B) Representative CAT scan images showing typical peripheral honeycombing pattern in 2 individuals with idiopathic pulmonary fibrosis and pancytopenia. Both individuals had biopsy confirmation of the usual interstitial pneumonia. The scans are from individuals in families 2 and 6. (C) CAT scan image of the proband of family 7, who developed pulmonary fibrosis after bone marrow transplantation for AA. Biopsy confirmed nonspecific interstitial pneumonia. (D) For the 3 individuals with images shown, the percentage of bone marrow CD34⁺ cells by flow cytometry was decreased in the setting of pancytopenia, macrocytosis, and hypocellular/aplastic marrow. The 95% confidence interval for CD34⁺ percentage is 0.4%-1.8%.

Figure 2

Pedigrees of 10 probands with personal or family history of telomere-mediated disease. (A) Pedigrees showing males symbolized by squares, females by circles, and deceased individuals with a slash through them. The mutation is listed above each pedigree, and the shaded symbols indicate the diagnoses described in the key above the pedigrees. (B) Telomerase activity assay showing that mutations in hTERT or hTR decrease enzyme activity, as evident by the decreased intensity of the ladder repeat pattern compared with wild-type telomerase (WT). hTERT mutations are referred to by the residue number and the mutant residue. (C) Quantitation of telomerase activity based on at least 3 independent experiments. **P < .01 (2-sided Student t test). (D) Lymphocyte telomere length measured by flow-fluorescence in situ hybridization showing mutation carriers relative to healthy controls. The normal distribution is based on data from 400 controls. Both AA and pulmonary fibrosis probands had telomere length less than the first percentile compared with age-matched controls.