Short telomeres in pulmonary fibrosis: from genetics to clinical significance.

Pulmonary fibrosis has been linked molecularly and pathophysiologically by abnormal telomere maintenance. Short telomere lengths are commonly found in both the familial and sporadic forms, telomerase mutations being the most common identifiable genetic cause of the disease. Telomeres are repeated nucleotide sequences that cap the ends of chromosomes and protect them from damage. Telomeres are eroded with cell division and shorten with age. Telomere integrity is mediated by the telomerase complex, a specialized polymerase that adds sequences to the ends of chromosomes. Mutations in the genes encoding telomerase (TERT and TERC) cause pulmonary fibrosis through low telomerase activity, accelerated telomere shortening and exhaustion of lung stem cells. Mutations in TERTor TERC account for only 19% of familial pulmonary fibrosis cases, and it is likely that additional environmental, genetic and epigenetic factors contribute to telomere erosion and to disease phenotype. Identification of short telomeres has potential clinical implications in pulmonary fibrosis: it may be a marker for an increased predisposition toward the development of the disease, it might affect risk stratification as it has been associated with lower survival rates and post-transplant complications that reflect the syndromic nature of this molecular defect.