Clinical manifestations of telomere biology disorders in adults

Telomeres consist of (TTAGGG)_n nucleotide repeats and a protein complex at chromosome ends that protect against loss of protein-encoding DNA during cell replication and are thus essential for genome stability.¹  Telomeres shorten with each cell division, and over time critically short telomeres trigger cellular senescence or apoptosis.^1,2  Telomere biology disorders (TBDs) represent a heterogeneous group of multi-organ diseases caused by pathogenic germline variants in genes encoding key telomere biology proteins. The best known subtype is classic dyskeratosis congenita (DC), which typically manifests during childhood with the mucocutaneous triad of nail dysplasia, abnormal skin pigmentation, and oral leukoplakia, but can also present in adults.³  The TBD designation encompasses phenotypes also called cryptic DC, which may manifest in adulthood with one or two isolated features such as bone marrow failure (BMF), interstitial lung disease (ILD), head and neck squamous cell carcinoma (HNSCC), or liver fibrosis. Underdiagnosis of TBDs impacts clinical outcome, since affected patients need specific surveillance measures and treatment considerations.

The biology connecting the spectrum of TBDs is impaired telomere maintenance resulting in short telomeres for age.^2,4  Currently, pathogenic variants in at least 17 genes involved in telomere biology are associated with TBDs (Table 1).^2,5  All modes of inheritance have been reported in TBDs, including X-linked recessive (XLR), autosomal recessive (AR), and autosomal dominant (AD). Patients with de novo germline variants have also been reported. TBD-causing variants show both variable expressivity and incomplete penetrance as the result of several factors, including but not limited to somatic genetic rescue mechanisms such as acquisition of variants in the TERT promoter region.^2,6  Genetic anticipation with shorter telomeres and earlier onset clinical manifestations has been reported in successive generations.²  All these phenomena add to TBD pleiotropy, making them frequently challenging to recognize in adults.

The presented individuals participated in the National Cancer Institute IRB-approved Inherited Bone Marrow Failure Syndromes study (NCT00027274) or the Aachen TBD registry (EK206/09, Aachen, Germany). The patients or their legal guardians signed informed consent.

Case 1: A 16-year-old male presented with portal hypertension without alcohol use history or infectious causes. Banding of esophageal varices and a transjugular intrahepatic portosystemic shunt was performed for progressive portal hypertension (Figure 1A). At age 26 years, mild pancytopenia was noted without evidence of myelodysplastic syndrome (MDS) on bone marrow exam, and was interpreted in the context of liver disease. Hepatic diffuse large B-cell lymphoma was diagnosed at 35 years of age. Prolonged pancytopenia with several severe infections occurred during chemotherapy, leading to dose reductions and discontinuation after 4 cycles. The patient later became transfusion dependent for platelets at 36 years of age. He had no mucocutaneous manifestations consistent with DC. He also had a history of a malabsorption syndrome with growth retardation and severe periodontitis with loss of several teeth. There was no family history of TBD-related features. Bone marrow biopsy after chemotherapy showed persistent hypocellularity (Figure 1B), and liver biopsy revealed signs of cirrhosis.

Case 2: A 42-year-old woman presented with persistent cytopenias. Mild thrombocytopenia was first noted at age 18 years, followed by leukocytopenia and macrocytic anemia. Light ridging of fingernails and lacy skin pigmentation were found on physical exam. Additional features included early graying at age 14 and two skin squamous cell carcinomas in her thirties. Family history was notable for transfusion-dependent cytopenias and pulmonary fibrosis (PF) in the patient's mother and mild thrombocytopenia and dysplastic fingernails in the patient's child. The patient's bone marrow biopsy revealed hypocellularity without significant dysplasia.

The phenotypic spectrum associated with aberrant telomere function is broad, and consensus diagnostic criteria for TBDs have not been established. However, there are clinical findings in adults that are suspicious for an underlying TBD (Figure 2).

Skin findings: The classic TBD feature is the mucocutaneous triad of nail dysplasia, reticulated skin pigmentation, and mucosal leukoplakia.^5,7  However, triad features may not be present or may be subtle; the mucocutaneous triad often progresses with age.⁸  For adult patients another nonspecific, yet suspicious, clue is premature graying (<30 years).⁸ 

Pulmonary disease: Individuals with familial PF (FPF), or PF with findings suggestive of TBDs in their personal or family history, should be evaluated for TBDs.⁹  TBDs can manifest with different forms of ILD, with idiopathic PF being the most frequent. There also appears to be a predisposition to severe smoking-related emphysema.¹⁰  PF is the leading manifestation of adult-onset TBDs, and pathogenic variants in TBD-related genes are found in 30% to 35% of FPF and 10% of sporadic PF cases.¹⁰  PF in the context of TBDs is rapidly progressive and associated with high morbidity and mortality.^7,11,12  PF patients present with mainly a restrictive pattern on spirometry, decreased diffusion capacity for carbon monoxide (D_LCO), and commonly a pattern consistent with usual interstitial pneumonia on high-resolution computed tomography (HRCT).¹²  Important additional pulmonary manifestations include hepatopulmonary syndrome (HPS) and/or pulmonary arteriovenous malformations (PAVMs), both of which may co-occur with PF, and are associated with early-onset telomere disease, including young adults.^13,14  PAVMs have been reported in the absence of overt HPS. However, it is not clear if PAVMs develop independently or if their diagnosis is connected with existing or developing HPS/liver disease and therefore are the component of one symptom complex.¹⁴ 

Hematopoietic manifestations: Screening for TBDs is recommended for individuals of all ages with BMF and for those younger than 50 years of age with MDS.^3,15  A recent study of a reportedly acquired aplastic anemia cohort found that approximately 2% of individuals had an unrecognized TBD by germline genetic testing.¹⁶  Additionally, MDS is a frequent manifestation of TBDs with an increased risk of 145-fold to 500-fold compared with the general population.^15,17 

Liver disease: Cryptogenic liver fibrosis and/or cirrhosis, unexplained through lifestyle or infectious causes, or idiopathic portal hypertension can be a clue for a TBD. TBD-related hepatic involvement is variable and may first present as an asymptomatic liver enzyme elevation, nonspecific ultrasound abnormalities, and/or nodular regenerative hyperplasia on biopsy.^18,19  TBD liver disease is progressive and should be considered part of the differential diagnosis for patients with nonalcoholic/noninfectious liver fibrosis/cirrhosis, idiopathic portal hypertension, and HPS.^13,18-20 

Cancer susceptibility: Cancer presenting at a younger than expected age, especially HNSCC, may indicate an underlying TBD. Patients with TBDs have a 4-fold increased risk for development of malignancies compared with the general population.¹⁵  Telomeres may play a role in cancer development due to chromosomal instability (short telomeres) or accumulation of somatic DNA changes (long telomeres).^21,22  T-cell exhaustion was recently proposed as an additional contributor to solid tumor development in TBDs.²³  Acute myeloid leukemia (AML) and HNSCC are the predominant cancer entities associated with TBDs, with each having an estimated 70-fold (observed/expected) increased risk in TBDs compared with the general population.¹⁵  Other frequent malignancies include anal and cutaneous squamous cell carcinomas.^15,17  The median age at MDS/acute myeloid leukemia diagnosis is usually younger than the general population.¹⁷  HNSCCs also show an unusually early age at onset in TBDs (<40 years of age) and predominantly affect the tongue.^15,17 

Family history: Pedigree construction often yields important clues for an adult-onset TBD since each of above-mentioned organ manifestations may present in isolation or precede development of other features.^7,20,24  Consideration should be given to the fact that the complex pathophysiological background of TBDs leads to both a variety of affected organs and variable time of disease onset, even within members of the same family. However, de novo occurrence of variants is possible, reported most frequently in TINF2 and DKC1.

Additional phenotypes: With more study, the clinical spectrum associated with telomere dysfunction is growing. Vascular disease, including PAVMs and gastrointestinal telangiectasias, were recently recognized as an important cause of morbidity in TBDs, with gastrointestinal hemorrhage being noted as an initial manifestation of TBDs in children or young adults even in the absence of overt portal hypertension.²⁵  While abnormal immune status is predominantly associated with childhood-onset TBDs, T-cell immunodeficiency has been reported in adult TBDs even in the absence of BMF.²⁶  Signs of impaired immune response may therefore be an additional clue for an underlying TBD.

The presentation with one feature of a TBD (liver disease), as highlighted in case 1, illustrates the complex diagnostic journey of such patients. It wasn't until his disease progressed and other evaluations were not diagnostic that a TBD was suspected (Table 2). Adult patients may initially not present to the hematologist but to other subspecialties, illustrating the importance of interdisciplinary clinical care. The patient in case 2 presented with BMF as a classic TBD feature, but her cutaneous phenotype was subtle. The early graying was an additional hint, yet the most important clue in her case was the family history (Table 2).

Traditionally, classic DC was diagnosed by the presence of mucocutaneous triad or a combination of 1 triad feature plus BMF. The addition of telomere length testing as a diagnostic tool and germline genetic testing have greatly improved diagnostics and expanded the phenotypic spectrum of TBDs.^3,5 

Telomere testing: Lymphocyte telomere length (LTL) testing by fluorescent in situ hybridization and flow cytometry (flow FISH) measures mean telomere length and is a powerful tool in diagnosing individuals with TBDs.^27-29  In the clinical setting it is currently considered the primary diagnostic test for TBDs yet is labor intensive and only established in specialized laboratories.^3,28,29 

The recently established high-throughput single telomere length analysis (HT-STELA), which determines the distribution of telomere length, has been implemented as a diagnostic tool for TBD in the United Kingdom and may identify asymptomatic individuals with TBD not readily detected with other methods.^4,29  Other measurement approaches, including quantitative PCR or telomere shortest length assay (TeSLA), are useful in research but not validated in the clinical setting.^29,30 

Interpreting TL results in adults can be challenging and complicated by a few factors: First, due to normal age-associated telomere attrition, LTL must be interpreted as age adjusted.^3,27,28  Telomeres shorten more slowly in middle age than in childhood, making the diagnostic window between normal for age and critically short telomeres sometimes challenging to interpret in adults.²⁸  Second, some genotypes are associated with short but not very short telomeres. Childhood-onset TBDs typically exhibit TL below the 1st percentile for age whereas adult-onset disease may exhibit telomeres between the 1st and 10th percentile.^24,28  Therefore in a clinically suspected adult TBD case, the detection of LTL <10th percentile for age should trigger genetic workup.³  Of note, variants in DCLRE1B/Apollo, which are to date solely reported in childhood-onset TBD, are not associated with a global TL reduction.³¹  Third, granulocyte TL is often routinely measured with LTL. While LTL less than the first percentile is sensitive and highly specific for TBDs, very short granulocyte TL lack specificity for TBDs and may also be observed in acquired aplastic anemia or clonal myeloid disorders.^27,32 

Genetic testing: Genetic testing of the patient and their family members is helpful for both clinical guidance and family counseling. In cases of LTL <10th percentile, detecting a pathogenic germline variant can confirm a TBD diagnosis.³  The TBD-associated genetic spectrum continues to expand, with pathogenic variants in at least 17 different genes associated with disease reported to date (Table 1). However, in approximately 20% of TBD cases, an underlying genetic cause cannot be identified, and newly discovered or rare TBD genes may not yet be included in clinical gene panels.^2,5,7,29,33  While potentially uncovering unrecognized TBDs, the implementation of panel or exome sequencing in routine diagnostics has also led to increased detection of variants of unknown significance, which are difficult to interpret in the absence of an obvious TBD phenotype. Additionally, in rare cases relatives from yet unidentified TBD patients may inherit short telomeres and exhibit TBD symptoms despite their wild-type genotype, a phenomenon called phenocopy.²  These patients would be missed by exclusive genetic testing. LTL can sometimes be helpful in assessing the functional impact of the identified variant, but additional basic science studies are often required.

Genotype-phenotype correlations: Typically, AR TBDs become evident in childhood or young adulthood, whereas AD pathogenic variants, except for those in TINF2, are primarily associated with symptom onset in adults (Figure 3).⁷  In general, genes found in adulthood include predominantly heterozygous pathogenic variants in TERT, TERC, RTEL1, or PARN.^3,24  In FPF cases AD TERT pathogenic changes are most frequent, followed by AD RTEL1 and AD PARN variants, while AD TERC changes are identified less often but present at a younger age.^11,34  In adult BMF, autosomal dominant (AD) TERC and TERT changes are predominant.^3,35  Of note, TINF2 and DKC1 TBDs commonly manifest in childhood, but DKC1-associated TBDs have been reported to present in late adulthood, and monoallelic TINF2 pathogenic germline variants have been observed in rare cases of adults with PF.^7,36 

In both clinical cases, very short LTL were detected (Figure 4) and monoallelic pathogenic TERC variants identified, fitting the common genotype spectrum in adult-onset TBDs.

Outcome analyses have found a better overall survival in AD compared with AR/XLR TBDs, possibly related to the older age at onset and fewer clinical features seen in non-TINF2 monoallelic TBDs.⁷  However, it is important to recognize that adult-onset TBDs are often accompanied by high morbidity and mortality due to progression of BMF, PF, liver disease, HNSCC, or other complications.^5,7 

Surveillance: Once a TBD diagnosis is established, regular surveillance is recommended (Table 3). This includes regular blood counts to monitor progression of cytopenias, and there should be a low threshold for a bone marrow aspirate and biopsy when blood counts change. Some providers recommend a bone marrow evaluation at diagnosis and annually. Abnormal pulmonary function tests are common in TBD patients and associated with development of significant pulmonary disease.¹²  Baseline pulmonary function tests are recommended at diagnosis and annually thereafter. Annual screening for oral cancer is recommended since it may detect HNSCC early, when still amenable to surgical resection. Additional specific screening recommendations are available in the TBD Diagnosis and Management Guidelines (https://teamtelomere.org).³⁷  Family members should be offered genetic counseling and testing based on the patient's genetic status. Related individuals with pathogenic variants causative of TBDs should be offered a clinical and diagnostic evaluation, even in the absence of symptoms, to establish a baseline given the considerable variation in respect to time of disease onset. Genetic counseling is essential for either the patient or family members and should address the possibility of genetic anticipation.

Therapy options: Research advances in telomere biology have led to a better understanding of the etiology of TBDs and their associated clinical manifestations. However, there are few therapeutic options. The only curative option for TBD-related lung, bone marrow, or hepatic disease is organ transplant. Each of these modalities can be complicated by the concomitant involvement of other organs and concerns for increased treatment- related toxicity.^38-40  This warrants close interdisciplinary care both pre- and posttransplant and highlights the importance of multicenter prospective trials in this setting. Implementation of reduced-intensity hematopoietic cell transplant (HCT) regimens and advancement in HCT donor matching have significantly improved its outcome in patients with TBDs.^40,41  After HCT, patients remain at high risk of PF, PAVM, liver disease, HNSCC, and/or gastrointestinal bleeding complications.^12,25,40,41  Lung transplant in TBD patients with PF has successfully been performed, yet patients are prone to complications and show inferior outcome compared with non-TBD lung transplant recipients.^10,38  A current collaborative effort by the Clinical Care Consortium of Telomere Associated Ailments (CCCTAA) is evaluating liver transplant outcomes in TBD patients. “Tandem” transplants of either lung/bone marrow or lung/liver have been considered as a possible therapeutic approach yet are restricted to a few specialized centers, and outcome data are sparse.⁴² 

If lung transplant is not an option, antifibrotic agents such as nintedanib and pirfenidone could be considered. There are very few data on their use in TBDs, but overall reports suggest they are likely safe in TBD-related PF and may slow lung function decline.⁴³  Immunosuppressive therapy is not effective in TBD-related BMF. In lieu of HCT, androgen treatment can result in a hematologic response and transfusion independence for several years. Danazol is often used due to its somewhat more favorable side effect profile compared with nandrolone or oxymetholone. Their efficacy appears similar, but they have not been systematically studied in this setting.⁴⁴  In some studies androgens have been proposed to lengthen telomeres, but the effect has been inconsistent and the long-term risks or benefits of lengthening telomeres in TBDs is not known.^45-48  One study reported a potential positive effect of nandrolone on pulmonary function in TBD patients with ILD.⁴⁷  Solid tumors should be treated according to entity-specific recommendations with careful following for increased chemotherapy-related complications, especially for cytopenias. Patients with TBDs also have higher rates of complications from therapeutic radiation, including severe tissue reactions and avascular osteonecrosis.^7,49 

For both cases, screening measures as outlined in Table 3 were initiated. The progressive BMF in case 1 required treatment, and the patient was started on low-dose danazol because of the severe hepatopathy. His blood counts improved such that he no longer requires transfusions, and his liver disease has not worsened.

The patient in case 2 was started on androgen treatment for BMF and remained hematologically stable for more than 10 years. The first restrictive changes on pulmonary function tests and D_LCO reduction were noted at 52 years of age. PF was diagnosed 2 years later (Figure 1C) and was progressive, leading to oxygen dependency. Unfortunately, a suitable lung transplant donor could not be identified, and pirfenidone treatment did not lead to a significant improvement. She died due to respiratory failure at 59 years of age while awaiting a combined lung and bone marrow transplant. This clinical course sadly highlights 2 key problems of TBD patients: (1) the unavailability of suitable organs for transplants while experiencing rapid progression of disease and (2) the severe disease that can occur in several organs and limit therapeutic options.

Discovery of new genotypes: A growing understanding of telomere biology and the growth of next-generation sequencing has led to numerous discoveries of pathogenic variants in patients with TBDs. Most recently, germline variants involving both TYMS and ENOSF1 were reported to result in classic DC features in children and young adults and introduced the possibility of digenic inheritance of TBDs.⁵⁰  Consideration of variants in noncoding sequences, which may affect regulatory regions, or synonymous variants altering splicing may elucidate the genetic etiology in patients with TBDs and no currently known cause.

Emergence of new therapeutics: The development of therapeutic agents targeting disease-specific defects are required to expand treatment options and improve patient outcomes.⁵  Future targets may include pathways connected to telomere maintenance, telomerase-directed gene therapies, and/or CRISPR- Cas9 editing to elongate telomeres.^2,5,10,51,52  Major challenges in developing TBD-related therapeutics include their broad clinical spectrum and the multiple and variable genetic etiologies. Given the role telomeres play in genome integrity and potentially in carcinogenesis, long-term follow-up will also be required.

Until new therapies are discovered, early diagnosis of TBDs and careful surveillance for disease progression, including cancer, are essential to improve the health and well-being of all affected with TBDs.

We thank all the patients and families with TBDs for their invaluable contributions to science and medicine. Thank you to Dr. Neelam Giri, National Cancer Institute (NCI), for providing clinical insight and feedback on the patient cases.

M.R.N. receives support from the Gerdes Foundation. The work of F.B. is in part supported by a grant of the “Stiftung Lichterzellen.” The work of S.A.S. is supported by the intramural research program of the Division of Cancer Epidemiology and Genetics, National Cancer Institute.

Marena R. Niewisch: no competing financial interests to declare.

Fabian Beier: no competing financial interests to declare.

Sharon A. Savage: no competing financial interests to declare.

Marena R. Niewisch: Androgen-use in the context of telomere biology disorder related bone marrow failure.

Fabian Beier: Androgen-use in the context of telomere biology disorder related bone marrow failure.

Sharon A. Savage: Androgen-use in the context of telomere biology disorder related bone marrow failure.