Telomere Biology Disorder: A Focus on Gastrointestinal and Hepatic Manifestations

PURPOSE OF REVIEW

Telomere biology disorders (TBD) encompass several illnesses caused by underlying mutations in telomere maintenance leading to premature telomere attrition and telomere dysfunction. These disorders have unique features but share common disease manifestations including pulmonary fibrosis, cirrhosis, and bone marrow failure. The goals of this article are to provide an overview of the gastrointestinal and hepatic manifestations of TBD, focusing on their pathophysiology, clinical disease states, and current management strategies.

RECENT FINDINGS

Telomere shortening has been observed in patients with chronic liver disease and is associated with a higher risk of progression to cirrhosis and portal hypertension. While the directionality of the association between telomere dysfunction and senescence on liver disease is not fully understood, research in TBD may provide clarity and could lead to future therapies for this increasingly prevalent disease. While treatment options remain limited in TBD-associated liver disease, recent studies point to the safety and efficacy of liver transplantation among patients with end-stage liver disease.

Telomere length and cancer risk: finding Goldilocks

Telomeres are the nucleoprotein complex at chromosome ends essential in genomic stability. Baseline telomere length (TL) is determined by rare and common germline genetic variants but shortens with age and is susceptible to certain environmental exposures. Cellular senescence or apoptosis are normally triggered when telomeres reach a critically short length, but cancer cells overcome these protective mechanisms and continue to divide despite chromosomal instability. Rare germline variants in telomere maintenance genes cause exceedingly short telomeres for age (< 1st percentile) and the telomere biology disorders, which are associated with elevated risks of bone marrow failure, myelodysplastic syndrome, acute myeloid leukemia, and squamous cell carcinoma of the head/neck and anogenital regions. Long telomeres due to rare germline variants in the same or different telomere maintenance genes are associated with elevated risks of other cancers, such as chronic lymphocytic leukemia or sarcoma. Early epidemiology studies of TL in the general population lacked reproducibility but new methods, including creation of a TL polygenic score using common variants, have found longer telomeres associated with excess risks of renal cell carcinoma, glioma, lung cancer, and others. It has become clear that when it comes to TL and cancer etiology, not too short, not too long, but "just right" telomeres are important in minimizing cancer risk.

Adaptive and Maladaptive Clonal Hematopoiesis in Telomere Biology Disorders

PURPOSE OF REVIEW

Telomere biology disorders (TBDs) are germline-inherited conditions characterized by reduction in telomerase function, accelerated shortening of telomeres, predisposition to organ-failure syndromes, and increased risk of neoplasms, especially myeloid malignancies. In normal cells, critically short telomeres trigger apoptosis and/or cellular senescence. However, the evolutionary mechanism by which TBD-related telomerase-deficient cells can overcome this fitness constraint remains elusive.

RECENT FINDINGS

Preliminary data suggests the existence of adaptive somatic mosaic states characterized by variants in TBD-related genes and maladaptive somatic mosaic states that attempt to overcome hematopoietic fitness constraints by alternative methods leading to clonal hematopoiesis. TBDs are both rare and highly heterogeneous in presentation, and the association of TBD with malignant transformation is unclear. Understanding the clonal complexity and mechanisms behind TBD-associated molecular signatures that lead to somatic adaptation in the setting of defective hematopoiesis will help inform therapy and treatment for this set of diseases.

Implementation of a prospective screening strategy to identify adults with a telomere biology disorder among those undergoing lung transplant evaluation for interstitial lung disease

INTRODUCTION

Patients with interstitial lung disease (ILD) secondary to telomere biology disorders (TBD) experience increased morbidity after lung transplantation. Identifying patients with TBD may allow for personalized management to facilitate better outcomes. However, establishing a TBD diagnosis in adults is challenging.

METHODS

A TBD screening questionnaire was introduced prospectively into the lung transplant evaluation. Patients with ILD screening positive were referred for comprehensive TBD phenotyping and concurrent telomere length measurement and germline genetic testing.

RESULTS

Of 98 patients, 32 (33%) screened positive. Eight patients (8% of total; 25% of patients with a positive screen) met strict TBD diagnostic criteria, requiring either critically short lymphocyte telomeres (<1st percentile) (n = 4), a pathogenic variant in a TBD-associated gene (n = 1), or both (n = 3) along with a TBD clinical phenotype. Additional patients not meeting strict diagnostic criteria had histories consistent with TBD along with telomere lengths <10th percentile and/or rare variants in TBD-associated genes, highlighting a critical need to refine TBD diagnostic criteria for this patient population.

CONCLUSION

A TBD phenotype screening questionnaire in patients with ILD undergoing lung transplant evaluation has a diagnostic yield of 25%. Additional gene discovery, rare variant functional testing, and refined TBD diagnostic criteria are needed to realize the maximum benefit of testing for TBD in patients undergoing lung transplantation.

Functional genomics for curation of variants in telomere biology disorder associated genes: A systematic review

PURPOSE

Patients with an underlying telomere biology disorder (TBD) have variable clinical presentations, and they can be challenging to diagnose clinically. A genomic diagnosis for patients presenting with TBD is vital for optimal treatment. Unfortunately, many variants identified during diagnostic testing are variants of uncertain significance. This complicates management decisions, delays treatment, and risks nonuptake of potentially curative therapies. Improved application of functional genomic evidence may reduce variants of uncertain significance classifications.

METHODS

We systematically searched the literature for published functional assays interrogating TBD gene variants. When possible, established likely benign/benign and likely pathogenic/pathogenic variants were used to estimate the assay sensitivity, specificity, positive predictive value, negative predictive value, and odds of pathogenicity.

RESULTS

In total, 3131 articles were screened and 151 met inclusion criteria. Sufficient data to enable a PS3/BS3 recommendation were available for TERT variants only. We recommend that PS3 and BS3 can be applied at a moderate and supportive level, respectively. PS3/BS3 application was limited by a lack of assay standardization and limited inclusion of benign variants.

CONCLUSION

Further assay standardization and assessment of benign variants are required for optimal use of the PS3/BS3 criterion for TBD gene variant classification.

Transient elastography in adult patients with cryptic dyskeratosis congenita reveals subclinical liver fibrosis: a retrospective analysis of the Aachen telomere biology disease registry

Background

Telomere biology disorders (TBD) such as dyskeratosis congenita (DKC) lead to progressive multi-organ failure as impaired telomere maintenance disturbs cellular proliferative capacity. A wide range of hepatic manifestations from asymptomatic liver enzyme elevation to overt liver fibrosis/cirrhosis can be observed in TBD patients. However, the incidence of hepatic involvement remains unknown. Non-invasive transient elastography (TE) predicts early fibrosis by measuring liver stiffness and may uncover subclinical liver damage in TBD patients.

Methods

Liver screening procedures of nine TBD patients from the Aachen TBD Registry are being presented retrospectively. Following clinical suspicion, TBD was diagnosed using flow-FISH with telomere length (TL) below the 1% percentile and confirmed by next-generation sequencing (NGS) detecting pathogenic mutations in telomere maintenance genes TERC or TERT.

Results

In all patients, TBD was first diagnosed in adulthood. Patients showed normal to slightly elevated liver function test parameters. Hepatic ultrasound revealed inhomogeneous parenchyma in seven (77.7%) and increased liver echogenicity in four patients (44.4%). Median liver stiffness was 10.7 kilopascal (kPa) (interquartile range 8.4, 15.7 kPa). Using 7.1 kPa as cut-off, 88.8% of patients were classified as moderate fibrosis to cirrhosis.

Conclusion

Subclinical chronic liver involvement is frequent in patients with adult-onset TBD. TE could have a valuable role in the routine work-up of patients with telomere disorders including DKC for early detection of patients at risk for liver function impairment.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02024-8.

A Case Series of TERC Variant Telomere Biology Disorders in Unrelated Families From Atlantic Canada

TERC variant telomere biology disorders (TBDs) are a rare, heterogenous group of disorders that arise from germline variants in TERC, a gene that encodes for the RNA component of telomerase. Variants in TERC lead to accelerated telomere attrition and can manifest as many different phenotypes. In this case series, we aimed to add to the literature describing TERC variant TBDs by reporting cases from two unrelated families from Atlantic Canada. The first case, a previously described germline TERC variant, n.107G>T (NR_001566.1), was identified in a young woman with myelodysplastic syndrome (MDS) and found to segregate with cytopenias in the family. This case represents a unique phenotypic presentation: this variant has not previously been described in patients with MDS and adds important segregation data to the literature. The second case, a novel TERC n.437T>G variant, was identified in a patient with both aplastic anemia and pulmonary fibrosis manifesting in his early 30s. We report these novel cases of germline TERC variants in order to help clinicians recognize TBDs, as well as to add important supporting information for the pathogenicity of these variants.