Telomere-lengthening germline variants predispose to a syndromic papillary thyroid cancer subtype.

Papillary thyroid cancer (PTC) is the most common endocrine malignancy. 10% to 15% of individuals show familial clustering with three or more affected members, but the factors underlying this risk are unknown. In a group of recently studied individuals with POT1 pathogenic variants and ultra-long telomere length, PTC was the second most common solid tumor. We tested whether variants in POT1 and four other telomere-maintenance genes associated with familial cancer underlie PTC susceptibility. Among 470 individuals, we identified pathogenic or likely pathogenic variants in three genes encoding telomere-binding proteins: POT1, TINF2, and ACD. They were found in 4.5% and 1.5% of familial and unselected cases, respectively. Individuals harboring these variants had ultra-long telomere length, and 15 of 18 (83%) developed other cancers, of which melanoma, lymphoma, and sarcoma were most common. Among individuals with PTC and melanoma, 22% carried a deleterious germline variant, suggesting that a long telomere syndrome might be clinically recognizable. Successive generations had longer telomere length than their parents and, at times, developed more cancers at younger ages. Tumor sequencing identified a single oncogenic driver, BRAF p.Val600Glu, in 10 of 10 tumors studied, but no telomere-maintenance mechanism, including at the TERT promoter. These data identify a syndromic subset of PTCs with locus heterogeneity and telomere lengthening as a convergent mechanism. They suggest these germline variants lower the threshold to cancer by obviating the need for an acquired telomere-maintenance mechanism in addition to sustaining the longevity of oncogenic mutations.

Familial Clonal Hematopoiesis in a Long Telomere Syndrome.

BACKGROUND: Telomere shortening is a well-characterized cellular aging mechanism, and short telomere syndromes cause age-related disease. However, whether long telomere length is advantageous is poorly understood. METHODS: We examined the clinical and molecular features of aging and cancer in persons carrying heterozygous loss-of-function mutations in the telomere-related gene POT1 and noncarrier relatives. RESULTS: A total of 17 POT1 mutation carriers and 21 noncarrier relatives were initially included in the study, and a validation cohort of 6 additional mutation carriers was subsequently recruited. A majority of the POT1 mutation carriers with telomere length evaluated (9 of 13) had long telomeres (>99th percentile). POT1 mutation carriers had a range of benign and malignant neoplasms involving epithelial, mesenchymal, and neuronal tissues in addition to B- and T-cell lymphoma and myeloid cancers. Five of 18 POT1 mutation carriers (28%) had T-cell clonality, and 8 of 12 (67%) had clonal hematopoiesis of indeterminate potential. A predisposition to clonal hematopoiesis had an autosomal dominant pattern of inheritance, as well as penetrance that increased with age; somatic DNMT3A and JAK2 hotspot mutations were common. These and other somatic driver mutations probably arose in the first decades of life, and their lineages secondarily accumulated a higher mutation burden characterized by a clocklike signature. Successive generations showed genetic anticipation (i.e., an increasingly early onset of disease). In contrast to noncarrier relatives, who had the typical telomere shortening with age, POT1 mutation carriers maintained telomere length over the course of 2 years. CONCLUSIONS: POT1 mutations associated with long telomere length conferred a predisposition to a familial clonal hematopoiesis syndrome that was associated with a range of benign and malignant solid neoplasms. The risk of these phenotypes was mediated by extended cellular longevity and by the capacity to maintain telomeres over time. (Funded by the National Institutes of Health and others.).

T cell immune deficiency rather than chromosome instability predisposes patients with short telomere syndromes to squamous cancers.

Patients with short telomere syndromes (STS) are predisposed to developing cancer, believed to stem from chromosome instability in neoplastic cells. We tested this hypothesis in a large cohort assembled over the last 20 years. We found that the only solid cancers to which patients with STS are predisposed are squamous cell carcinomas of the head and neck, anus, or skin, a spectrum reminiscent of cancers seen in patients with immunodeficiency. Whole-genome sequencing showed no increase in chromosome instability, such as translocations or chromothripsis. Moreover, STS-associated cancers acquired telomere maintenance mechanisms, including telomerase reverse transcriptase (TERT) promoter mutations. A detailed study of the immune status of patients with STS revealed a striking T cell immunodeficiency at the time of cancer diagnosis. A similar immunodeficiency that impaired tumor surveillance was documented in mice with short telomeres. We conclude that STS patients' predisposition to solid cancers is due to T cell exhaustion rather than autonomous defects in the neoplastic cells themselves.

The Role of Telomeres in Human Disease.

Telomere biology was first studied in maize, ciliates, yeast, and mice, and in recent decades, it has informed understanding of common disease mechanisms with broad implications for patient care. Short telomere syndromes are the most prevalent premature aging disorders, with prominent phenotypes affecting the lung and hematopoietic system. Less understood are a newly recognized group of cancer-prone syndromes that are associated with mutations that lengthen telomeres. A large body of new data from Mendelian genetics and epidemiology now provides an opportunity to reconsider paradigms related to the role of telomeres in human aging and cancer, and in some cases, the findings diverge from what was interpreted from model systems. For example, short telomeres have been considered potent drivers of genome instability, but age-associated solid tumors are rare in individuals with short telomere syndromes, and T cell immunodeficiency explains their spectrum. More commonly, short telomeres promote clonal hematopoiesis, including somatic reversion, providing a new leukemogenesis paradigm that is independent of genome instability. Long telomeres, on the other hand, which extend the cellular life span in vitro, are now appreciated to be the most common shared germline risk factor for cancer in population studies. Through this contemporary lens, I revisit here the role of telomeres in human aging, focusing on how short and long telomeres drive cancer evolution but through distinct mechanisms.

Telomere-mediated lung disease.

Parenchymal lung disease is the fourth leading cause of death in the United States; among the top causes, it continues on the rise. Telomeres and telomerase have historically been linked to cellular processes related to aging and cancer, but surprisingly, in the recent decade genetic discoveries have linked the most apparent manifestations of telomere and telomerase dysfunction in humans to the etiology of lung disease: both idiopathic pulmonary fibrosis (IPF) and emphysema. The short telomere defect is pervasive in a subset of IPF patients, and human IPF is the phenotype most intimately tied to germline defects in telomere maintenance. One-third of families with pulmonary fibrosis carry germline mutations in telomerase or other telomere maintenance genes, and one-half of patients with apparently sporadic IPF have short telomere length. Beyond explaining genetic susceptibility, short telomere length uncovers clinically relevant syndromic extrapulmonary disease, including a T-cell immunodeficiency and a propensity to myeloid malignancies. Recognition of this subset of patients who share a unifying molecular defect has provided a precision medicine paradigm wherein the telomere-mediated lung disease diagnosis provides more prognostic value than histopathology or multidisciplinary evaluation. Here, we critically evaluate this progress, emphasizing how the genetic findings put forth a new pathogenesis paradigm of age-related lung disease that links telomere abnormalities to alveolar stem senescence, remodeling, and defective gas exchange.

The Role of Genetic Testing in Pulmonary Fibrosis: A Perspective From the Pulmonary Fibrosis Foundation Genetic Testing Work Group.

Patients with familial pulmonary fibrosis represent a subset of patients with pulmonary fibrosis in whom inherited gene variation predisposes them to disease development. In the appropriate setting, genetic testing allows for personalized assessment of disease, recognition of clinically relevant extrapulmonary manifestations, and assessing susceptibility in unaffected relatives. However currently, the use of genetic testing is inconsistent, partly because of the lack of guidance regarding high-yield scenarios in which the results of genetic testing can inform clinical decision-making. To address this, the Pulmonary Fibrosis Foundation commissioned a genetic testing work group comprising pulmonologists, geneticists, and genetic counselors from the United States to provide guidance on genetic testing in patients with pulmonary fibrosis. This CHEST special feature presents a concise review of these proceedings and reviews pulmonary fibrosis susceptibility, clinically available genetic testing methods, and clinical scenarios in which genetic testing should be considered.

Somatic reversion impacts myelodysplastic syndromes and acute myeloid leukemia evolution in the short telomere disorders.

BACKGROUNDGermline mutations in telomerase and other telomere maintenance genes manifest in the premature aging short telomere syndromes. Myelodysplastic syndromes and acute myeloid leukemia (MDS/AML) account for 75% of associated malignancies, but how these cancers overcome the inherited telomere defect is unknown.METHODSWe used ultra-deep targeted sequencing to detect somatic reversion mutations in 17 candidate telomere lengthening genes among controls and patients with short telomere syndromes with and without MDS/AML, and we tested the functional significance of these mutations.RESULTSWhile no controls carried somatic mutations in telomere maintenance genes, 29% (16 of 56) of adults with germline telomere maintenance defects carried at least 1 (P < 0.001), and 13% (7 of 56) had 2 or more. In addition to TERT promoter mutations, which were present in 19%, another 13% of patients carried a mutation in POT1 or TERF2IP. POT1 mutations impaired telomere binding in vitro and some mutations were identical to ones seen in familial melanoma associated with longer telomere length. Exclusively in patients with germline defects in telomerase RNA (TR), we identified somatic mutations in nuclear RNA exosome genes RBM7, SKIV2L2, and DIS3, where loss-of-function upregulates mature TR levels. Somatic reversion events in 6 telomere-related genes were more prevalent in patients who were MDS/AML-free (P = 0.02, RR 4.4, 95% CI 1.2-16.7), and no patient with MDS/AML had more than 1 reversion mutation.CONCLUSIONOur data indicate that diverse adaptive somatic mutations arise in the short telomere syndromes. Their presence may alleviate the telomere crisis that promotes transformation to MDS/AML.FUNDINGThis work was supported by the NIH, the Commonwealth Foundation, the S&R Foundation Kuno Award, the Williams Foundation, the Vera and Joseph Dresner Foundation, the MacMillan Pathway to Independence Award, the American Society of Hematology Scholar Award, the Johns Hopkins Research Program for Medical Students, and the Turock Scholars Fund.

Synonymous Mutation in DKC1 Causes Telomerase RNA Insufficiency Manifesting as Familial Pulmonary Fibrosis.

BACKGROUND: Idiopathic pulmonary fibrosis (IPF) is the most common of short telomere phenotypes. Familial clustering of IPF is common, but the genetic basis remains unknown in more than one-half of cases. We identified a 65-year-old man with familial IPF, short telomere length, and low telomerase RNA levels. He was diagnosed with a short telomere syndrome after developing hematologic complications post-lung transplantation, but no mutations were identified in a clinical testing pipeline. RESEARCH QUESTION: What is the molecular basis underlying the familial IPF and low telomerase RNA levels in this patient? STUDY DESIGN AND METHODS: We analyzed whole-genome sequence data and performed functional molecular studies on cells derived from the patient and his family. RESULTS: We identified a previously unreported synonymous variant c.942G>A p.K314K in DKC1, the gene encoding the dyskerin ribonucleoprotein, which is required for telomerase RNA biogenesis. The mutation created a competing de novo exonic splicing enhancer, and the misspliced product was degraded by nonsense-mediated decay causing an overall dyskerin deficiency in mutation carriers. In silico tools identified other rare silent DKC1 variants that warrant functional evaluation if found in patients with short telomere-mediated disease. INTERPRETATION: Our data point to silent mutation in telomere maintenance genes as a mechanism of familial pulmonary fibrosis. In contrast to DKC1 missense mutations, which primarily manifest in children as dyskeratosis congenita, hypomorphic mutations affecting dyskerin levels likely have a predilection to presenting in adults as pulmonary fibrosis.

Cancer and myeloid clonal evolution in the short telomere syndromes.

The short telomere syndromes are considered the most common premature aging disorders. Although studies in genetically modified cells and animal models have suggested telomere dysfunction may promote genome instability, only a minority of humans with inherited loss-of-function mutations in telomerase and related genes develop cancer. Solid tumors are overall rare, and the vast majority of cancers are bone marrow-derived with myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) comprising three-quarter of cases. In contrast to young short telomere syndrome patients who develop aplastic anemia, MDS and AML are usually diagnosed in adults who have milder short telomere defects. Here, we dissect the mechanisms by which these two bone marrow failure states, aplastic anemia and MDS-AML, evolve in the setting of varying degrees of telomere shortening. We discuss the implications of these observations for patient care as well as for understanding the genetics and biology of age-related myeloid clonal evolution.

The Effects of a Remote-based Weight Loss Program on Adipocytokines, Metabolic Markers, and Telomere Length in Breast Cancer Survivors: the POWER-Remote Trial.

PURPOSE: We initiated a clinical trial to determine the proportion of breast cancer survivors achieving ≥5% weight loss using a remotely delivered weight loss intervention (POWER-remote) or a self-directed approach, and to determine the effects of the intervention on biomarkers of cancer risk including metabolism, inflammation, and telomere length. EXPERIMENTAL DESIGN: Women with stage 0-III breast cancer, who completed local therapy and chemotherapy, with a body mass index ≥25 kg/m2 were randomized to a 12-month intervention (POWER-remote) versus a self-directed approach. The primary objective was to determine the number of women who achieved at least 5% weight loss at 6 months. We assessed baseline and 6-month change in a panel of adipocytokines (adiponectin, leptin, resistin, HGF, NGF, PAI1, TNFα, MCP1, IL1ß, IL6, and IL8), metabolic factors (insulin, glucose, lipids, hs-CRP), and telomere length in peripheral blood mononuclear cells. RESULTS: From 2013 to 2015, 96 women were enrolled, and 87 were evaluable for the primary analysis; 45 to POWER-remote and 42 to self-directed. At 6 months, 51% of women randomized to POWER-remote lost ≥5% of their baseline body weight, compared with 12% in the self-directed arm [OR, 7.9; 95% confidence interval (CI), 2.6-23.9; P = 0.0003]; proportion were similar at 12 months (51% vs 17%, respectively, P = 0.003). Weight loss correlated with significant decreases in leptin, and favorable modulation of inflammatory cytokines and lipid profiles. There was no significant change in telomere length at 6 months. CONCLUSIONS: A remotely delivered weight loss intervention resulted in significant weight loss in breast cancer survivors, and favorable effects on several biomarkers.

Cancer spectrum and outcomes in the Mendelian short telomere syndromes.

Short telomeres have been linked to cancer risk, yet other evidence supports them being tumor suppressive. Here, we report cancer outcomes in individuals with germline mutations in telomerase and other telomere-maintenance genes. Among 180 individuals evaluated in a hospital-based setting, 12.8% had cancer. Solid tumors were rare (2.8%); nearly all were young male DKC1 mutation carriers, and they were generally resectable with good short-term outcomes. Myelodysplastic syndrome (MDS) was most common, followed by acute myeloid leukemia (AML); they accounted for 75% of cancers. Age over 50 years was the biggest risk factor, and MDS/AML usually manifested with marrow hypoplasia and monosomy 7, but the somatic mutation landscape was indistinct from unselected patients. One- and 2-year survival were 61% and 39%, respectively, and two-thirds of MDS/AML patients died of pulmonary fibrosis and/or hepatopulmonary syndrome. In one-half of the cases, MDS/AML patients showed a recurrent peripheral blood pattern of acquired, granulocyte-specific telomere shortening. This attrition was absent in age-matched mutation carriers who did not have MDS/AML. We tested whether adult short telomere patients without MDS/AML also had evidence of clonal hematopoiesis of indeterminate potential-related mutations and found that 30% were affected. These patients also primarily suffered morbidity from pulmonary fibrosis during follow-up. Our data show that the Mendelian short telomere syndromes are associated with a relatively narrow cancer spectrum, primarily MDS and AML. They suggest that short telomere length is sufficient to drive premature age-related clonal hematopoiesis in these inherited disorders.

ZCCHC8, the nuclear exosome targeting component, is mutated in familial pulmonary fibrosis and is required for telomerase RNA maturation.

Short telomere syndromes manifest as familial idiopathic pulmonary fibrosis; they are the most common premature aging disorders. We used genome-wide linkage to identify heterozygous loss of function of ZCCHC8, a zinc-knuckle containing protein, as a cause of autosomal dominant pulmonary fibrosis. ZCCHC8 associated with TR and was required for telomerase function. In ZCCHC8 knockout cells and in mutation carriers, genomically extended telomerase RNA (TR) accumulated at the expense of mature TR, consistent with a role for ZCCHC8 in mediating TR 3' end targeting to the nuclear RNA exosome. We generated Zcchc8-null mice and found that heterozygotes, similar to human mutation carriers, had TR insufficiency but an otherwise preserved transcriptome. In contrast, Zcchc8-/- mice developed progressive and fatal neurodevelopmental pathology with features of a ciliopathy. The Zcchc8-/- brain transcriptome was highly dysregulated, showing accumulation and 3' end misprocessing of other low-abundance RNAs, including those encoding cilia components as well as the intronless replication-dependent histones. Our data identify a novel cause of human short telomere syndromes-familial pulmonary fibrosis and uncover nuclear exosome targeting as an essential 3' end maturation mechanism that vertebrate TR shares with replication-dependent histones.

Long telomeres and cancer risk: the price of cellular immortality.

The distribution of telomere length in humans is broad, but it has finite upper and lower boundaries. Growing evidence shows that there are disease processes that are caused by both short and long telomere length extremes. The genetic basis of these short and long telomere syndromes may be linked to mutations in the same genes, such as the telomerase reverse transcriptase (TERT), but through differential effects on telomere length. Short telomere syndromes have a predominant degenerative phenotype marked by organ failure that most commonly manifests as pulmonary fibrosis and are associated with a relatively low cancer incidence. In contrast, insights from studies of cancer-prone families as well as genome-wide association studies (GWAS) have identified both rare and common variants that lengthen telomeres as being strongly associated with cancer risk. We have hypothesized that these cancers represent a long telomere syndrome that is associated with a high penetrance of cutaneous melanoma and chronic lymphocytic leukemia. In this Review, we will synthesize the clinical and human genetic observations with data from mouse models to define the role of telomeres in cancer etiology and biology.

Impaired Cytomegalovirus Immunity in Idiopathic Pulmonary Fibrosis Lung Transplant Recipients with Short Telomeres.

RATIONALE: Cytomegalovirus (CMV)-related morbidities remain one of the most common complications after lung transplantation and have been linked to allograft dysfunction, but the factors that predict high risk for CMV complications and effective immunity are incompletely understood. OBJECTIVES: To determine if short telomeres in idiopathic pulmonary fibrosis (IPF) lung transplant recipients (LTRs) predict the risk for CMV-specific T-cell immunity and viral control. METHODS: We studied IPF-LTRs (n = 42) and age-matched non-IPF-LTRs (n = 42) and assessed CMV outcomes. We measured lymphocyte telomere length and DNA sequencing, and assessed CMV-specific T-cell immunity in LTRs at high risk for CMV events, using flow cytometry and fluorescence in situ hybridization. MEASUREMENTS AND MAIN RESULTS: We identified a high prevalence of relapsing CMV viremia in IPF-LTRs compared with non-IPF-LTRs (69% vs. 31%; odds ratio, 4.98; 95% confidence interval, 1.95-12.50; P < 0.001). Within this subset, IPF-LTRs who had short telomeres had the highest risk of CMV complications (P < 0.01) including relapsing-viremia episodes, end-organ disease, and CMV resistance to therapy, as well as shorter time to viremia versus age-matched non-IPF control subjects (P < 0.001). The short telomere defect in IPF-LTRs was associated with significantly impaired CMV-specific proliferative responses, T-cell effector functions, and induction of the major type-1 transcription factor T-bet (T-box 21;TBX21). CONCLUSIONS: Because the short telomere defect has been linked to the pathogenesis of IPF in some cases, our data indicate that impaired CMV immunity may be a systemic manifestation of telomere-mediated disease in these patients. Identifying this high-risk subset of LTRs has implications for risk assessment, management, and potential strategies for averting post-transplant CMV morbidities.