TINF2 mutations result in very short telomeres: analysis of a large cohort of patients with dyskeratosis congenita and related bone marrow failure syndromes. Blood. 2008;112:3594-3600. [PMID: 18669893 PMCID: PMC2572788 DOI: 10.1182/blood-2008-05-153445]

An algorithmic approach towards diagnosis of patients with hereditary reticulate pigmentary disorders: a narrative review

Hereditary reticulate pigmentary disorders include a group of genetic disorders, with netlike pigmentation as their predominant presentation. Many of these hereditary reticulate pigmentary disorders have a wide array of cutaneous presentations with overlapping features. Furthermore, some of these disorders also have systemic manifestations. The overlapping features often add confusion and cause delay in diagnosis. Based on a literature search, we propose an easy-to-follow and concise diagnostic algorithm for diagnosis. This algorithm would aid in ordering a definitive genetic test. A thorough data search was done using the PubMed database with the following keywords: ('inherit*' OR 'genetic') AND ('reticulate AND pigment*'). Thereafter, a search for individual diseases was done using the keywords 'Dowling-Degos disease', 'dyschromatosis hereditaria symmetrica', 'acropigmentation of Kitamura', 'dyschromatosis universalis hereditaria', 'Naegeli-Franceschetti-Jadassohn syndrome', 'X-linked reticulate pigmentary disorder' and 'dyskeratosis congenita'. The search included case reports, case series, observational studies, narrative and systematic reviews, and clinical trials. Acquired pigmentary disorders were excluded. In total, 1994 articles were retrieved. Finally, 625 articles were included for the review. The articles were narrative reviews (40), case series (23), observational studies (44) and case reports (518). An easy-to-follow clinical diagnostic algorithm was prepared based on age of onset, distribution and other parameters. This algorithm will aid in reaching a provisional diagnosis. Furthermore, this approach will help in the genetic investigations of a case of hereditary reticulate pigmentary disorder.

Telomere function and regulation from mouse models to human ageing and disease

Telomeres protect the ends of chromosomes but shorten following cell division in the absence of telomerase activity. When telomeres become critically short or damaged, a DNA damage response is activated. Telomeres then become dysfunctional and trigger cellular senescence or death. Telomere shortening occurs with ageing and may contribute to associated maladies such as infertility, neurodegeneration, cancer, lung dysfunction and haematopoiesis disorders. Telomere dysfunction (sometimes without shortening) is associated with various diseases, known as telomere biology disorders (also known as telomeropathies). Telomere biology disorders include dyskeratosis congenita, Høyeraal-Hreidarsson syndrome, Coats plus syndrome and Revesz syndrome. Although mouse models have been invaluable in advancing telomere research, full recapitulation of human telomere-related diseases in mice has been challenging, owing to key differences between the species. In this Review, we discuss telomere protection, maintenance and damage. We highlight the differences between human and mouse telomere biology that may contribute to discrepancies between human diseases and mouse models. Finally, we discuss recent efforts to generate new 'humanized' mouse models to better model human telomere biology. A better understanding of the limitations of mouse telomere models will pave the road for more human-like models and further our understanding of telomere biology disorders, which will contribute towards the development of new therapies.

Inherited Telomere Biology Disorders: Pathophysiology, Clinical Presentation, Diagnostics, and Treatment

Background

Telomeres are the end-capping structures of all eukaryotic chromosomes thereby protecting the genome from damage and degradation. During the aging process, telomeres shorten continuously with each cell division until critically short telomeres prevent further proliferation whereby cells undergo terminal differentiation, senescence, or apoptosis. Premature aging due to critically short telomere length (TL) can also result from pathogenic germline variants in the telomerase complex or related genes that typically counteract replicative telomere shortening in germline and certain somatic cell populations, e.g., hematopoetic stem cells. Inherited diseases that result in altered telomere maintenance are summarized under the term telomere biology disorder (TBD).

Summary

Since TL both reflects but more importantly restricts the replicative capacity of various human tissues, a sufficient telomere reserve is particularly important in cells with high proliferative activity (e.g., hematopoiesis, immune cells, intestinal cells, liver, lung, and skin). Consequently, altered telomere maintenance as observed in TBDs typically results in premature replicative cellular exhaustion in the respective organ systems eventually leading to life-threatening complications such as bone marrow failure (BMF), pulmonary fibrosis, and liver cirrhosis.

Key Messages

The recognition of a potential congenital origin in approximately 10% of adult patients with clinical BMF is of utmost importance for the proper diagnosis, appropriate patient and family counseling, to prevent the use of inefficient treatment and to avoid therapy-related toxicities including appropriate donor selection when patients have to undergo stem cell transplantation from related donors. This review summarizes the current state of knowledge about TBDs with particular focus on the clinical manifestation patterns in children (termed early onset TBD) compared to adults (late-onset TBD) including typical treatment- and disease course-related complications as well as their prognosis and adequate therapy. Thereby, it aims to raise awareness for a disease group that is currently still highly underdiagnosed particularly when it first manifests itself in adulthood.

Germline variants in acquired aplastic anemia: current knowledge and future perspectives

Aplastic anemia (AA) is a disease characterized by failure of hematopoiesis, bone marrow aplasia, and pancytopenia. It can be inherited or acquired. Although acquired AA is believed to be immune-mediated and random, new evidence suggests an underlying genetic predisposition. Besides confirmed genomic mutations that contribute to inherited AA (such as pathogenic mutations of TERT and TERC), germline variants, often in heterozygous states, also play a not negligible role in the onset and progression of acquired AA. These variants, associated with inherited bone marrow failure syndromes and inborn errors of immunity, contribute to the disease, possibly through mechanisms including gene homeostasis, DNA repair, and immune injury. This article explores the nuanced association between acquired AA and germline variants, detailing the clinical significance of germline variants in diagnosing and managing this condition. More work is encouraged to better understand the role of immunogenic pathogenic variants and whether somatic mutations participate as secondary "hits" in the development of bone marrow failure.

Late-onset and long-lasting neutropenias in the young: A new entity anticipating immune-dysregulation disorders

This study identifies a new chronic form of immune neutropenia in the young with or without detectable indirect anti-neutrophil antibodies, characterized by mild/moderate neutropenia low risk of severe infection (14%), tendency to develop autoimmune phenomena over the course of the disease (cumulative incidence of 58.6% after 20 years of disease duration), leukopenia, progressive reduction of absolute lymphocyte count and a T- and B-cell profile similar to autoimmune disorders like Sjogren syndrome, rheumatoid arthritis, and systemic lupus erythematosus (increased HLADR+ and CD3 + TCRγδ cells, reduced T regulatory cells, increased double-negative B and a tendency to reduced B memory cells). In a minority of patients, P/LP variants related to primary immuno-regulatory disorders were found. This new form may fit the group of "Likely acquired neutropenia," a provisional category included in the recent International Guidelines on Diagnosis and Management of Neutropenia of EHA and EUNET INNOCHRON ACTION 18233. The early recognition of this form of neutropenia would help clinicians to delineate better specific monitoring plans, genetic counseling, and potentially targeted therapies.

The splicing factor Prpf31 is required for hematopoietic stem and progenitor cell expansion during zebrafish embryogenesis

Pre-mRNA splicing is a precise regulated process and is crucial for system development and homeostasis maintenance. Mutations in spliceosomal components have been found in various hematopoietic malignancies (HMs) and have been considered as oncogenic derivers of HMs. However, the role of spliceosomal components in normal and malignant hematopoiesis remains largely unknown. Pre-mRNA processing factor 31 (PRPF31) is a constitutive spliceosomal component, which mutations are associated with autosomal dominant retinitis pigmentosa. PRPF31 was found to be mutated in several HMs, but the function of PRPF31 in normal hematopoiesis has not been explored. In our previous study, we generated a prpf31 knockout (KO) zebrafish line and reported that Prpf31 regulates the survival and differentiation of retinal progenitor cells by modulating the alternative splicing of genes involved in mitosis and DNA repair. In this study, by using the prpf31 KO zebrafish line, we discovered that prpf31 KO zebrafish exhibited severe defects in hematopoietic stem and progenitor cell (HSPC) expansion and its sequentially differentiated lineages. Immunofluorescence results showed that Prpf31-deficient HSPCs underwent malformed mitosis and M phase arrest during HSPC expansion. Transcriptome analysis and experimental validations revealed that Prpf31 deficiency extensively perturbed the alternative splicing of mitosis-related genes. Collectively, our findings elucidate a previously undescribed role for Prpf31 in HSPC expansion, through regulating the alternative splicing of mitosis-related genes.

Genome stability from the perspective of telomere length

Telomeres and their associated proteins protect the ends of chromosomes to maintain genome stability. Telomeres undergo progressive shortening with each cell division in mammalian somatic cells without telomerase, resulting in genome instability. When telomeres reach a critically short length or are recognized as a damage signal, cells enter a state of senescence, followed by cell cycle arrest, programmed cell death, or immortalization. This review provides an overview of recent advances in the intricate relationship between telomeres and genome instability. Alongside well-established mechanisms such as chromosomal fusion and telomere fusion, we will delve into the perspective on genome stability by examining the role of retrotransposons. Retrotransposons represent an emerging pathway to regulate genome stability through their interactions with telomeres.

When to consider inherited marrow failure syndromes in adults

The inherited bone marrow failure syndromes (IBMFS) are a heterogenous group of disorders caused by germline mutations in related genes and characterized by bone marrow failure (BMF), disease specific organ involvement, and, in most cases, predisposition to malignancy. Their distinction from immune marrow failure can often be challenging, particularly when presentations occur in adulthood or are atypical. A combination of functional (disease specific assays) and genetic testing is optimal in assessing all new BMF patients for an inherited etiology. However, genetic testing is costly and may not be available worldwide due to resource constraints; in such cases, clinical history, standard laboratory testing, and the use of algorithms can guide diagnosis. Interpretation of genetic results can be challenging and must reflect assessment of pathogenicity, inheritance pattern, clinical phenotype, and specimen type used. Due to the progressive use of genomics, new IBMFS continue to be identified, widening the spectrum of these disorders.

Genetic Counseling and Family Screening Recommendations in Patients with Telomere Biology Disorders

PURPOSE OF REVIEW

Telomere biology disorders (TBDs) encompass a spectrum of genetic diseases with a common pathogenesis of defects in telomerase function and telomere maintenance causing extremely short telomere lengths. Here, we review the current literature surrounding genetic testing strategies, cascade testing, reproductive implications, and the role of genetic counseling.

RECENT FINDINGS

The understanding of the genetic causes and clinical symptoms of TBDs continues to expand while genetic testing and telomere length testing are nuanced tools utilized in the diagnosis of this condition. Access to genetic counseling is becoming more abundant and is valuable in supporting patients and their families in making informed decisions. Patient resources and support groups are valuable to this community. Defining which populations should be offered genetic counseling and testing is imperative to provide proper diagnoses and medical management for not only the primary patient, but also their biological relatives.

Telomeres: Dysfunction, Maintenance, Aging and Cancer

Aging has emerged at the forefront of scientific research due to the growing social and economic costs associated with the growing aging global population. The defining features of aging involve a variety of molecular processes and cellular systems, which are interconnected and collaboratively contribute to the aging process. Herein, we analyze how telomere dysfunction potentially amplifies or accelerates the molecular and biochemical mechanisms underpinning each feature of aging and contributes to the emergence of age-associated illnesses, including cancer and neurodegeneration, via the perspective of telomere biology. Furthermore, the recently identified novel mechanistic actions for telomere maintenance offer a fresh viewpoint and approach to the management of telomeres and associated disorders. Telomeres and the defining features of aging are intimately related, which has implications for therapeutic and preventive approaches to slow aging and reduce the prevalence of age-related disorders.

Hematopoietic stem cell transplantation of aplastic anemia by relative with mutations and normal telomere length: A case report

BACKGROUND

Immunosuppressive therapy and matched sibling donor hematopoietic stem cell transplantation (MSD-HSCT) are the preferred treatments for aplastic anemia (AA).

CASE SUMMARY

In this report, we describe a 43-year-old male patient with severe AA who carried BRIP1 (also known as FANCJ), TINF2, and TCIRG1 mutations. Screening of the family pedigree revealed the same TINF2 mutation in his mother and older brother, with his older brother also carrying the BRIP1 variant and demonstrating normal telomere length and hematopoietic function. The patient was successfully treated with oral cyclosporine A, eltrombopag, and acetylcysteine, achieving remission 4 years after receiving MSD-HSCT from his older brother.

CONCLUSION

This case provides a valuable clinical reference for individuals with suspected pathogenic gene mutations, normal telomere length, and hematopoietic function, highlighting them as potential donors for patients with AA.

A Well-Curated Cost-Effective Next-Generation Sequencing Panel Identifies a Diverse Landscape of Pathogenic and Novel Germline Variants in a Bone Marrow Failure Cohort in a Resource-Constraint Setting

The current study is a 4-year experience in diagnosis and screening of inherited and immune bone marrow failure cases using a targeted sequencing panel. A total of 171 cases underwent targeted next-generation sequencing and were categorized as suspected inherited bone marrow failure syndrome (IBMFS) group (106; 62%) and immune/idiopathic aplastic anemia (IAA) group (65; 38%) based on clinical and laboratory criteria. A total of 110 (64%) were pediatric (aged 0 to 12 years) patients and 61 (36%) were adolescent and adult (aged 13 to 47 years) patients. In suspected IBMFS group, 47 (44%), and in IAA group, 8 (12%) revealed a likely germline pathogenic variation. Whole-exome sequencing performed in 15 of 59 suspected IBMFS group cases was negative on targeted panel, and revealed a clinically important variation in 3 (20%) cases. A total of 11 novel variants were identified. The targeted panel helped establish a diagnosis in 44% (27/61) of unclassified bone marrow failure syndrome cases and led to amendment of clinical diagnosis in 5 (4.7%) cases. Overall, diagnostic yield of this well-curated small panel was comparable to Western studies with larger gene panels. Moreover, this was achievable at a much lower cost, making it suitable for resource-constraint settings. In addition, high frequency (>10%) of cryptic pathogenic IBMFS gene variations in IAA cohort suggests routine incorporation of targeted next-generation sequencing screening in these cases.

Links between telomere dysfunction and hallmarks of aging

Aging is characterized by the gradual loss of physiological integrity, leading to impaired function and increased risk of death. This deterioration is the main risk factor for the great majority of chronic diseases, which account for most of the morbidity, death and medical expenses. The hallmarks of aging comprise diverse molecular mechanisms and cell systems, which are interrelated and coordinated to drive the aging process. This review focuses on telomere to analyze the interrelationships between telomere dysfunction and other aging hallmarks and their relative contributions to the initiation and progression of age-related diseases (such as neurodegeneration, cardiovascular disease, and cancer), which will contribute to determine drug targets, improve human health in the aging process with minimal side effects and provide information for the prevention and treatment of age-related diseases.

A de novo TINF2, R282C Mutation in a Case of Dyskeratosis Congenital Founded by Next-Generation Sequencing

Background

Dyskeratosis congenita (DC), an inherited and rare disease prevalent in males, is clinically manifested by reticulate hyperpigmentation, nail dystrophy, and leukoplakia. DC is associated with the increased risk of malignancy and other potentially lethal complications such as bone marrow failure, as well as lung and liver diseases. Mutations in 19 genes were found to be correlated with DC. Herein, we report a 12-year-old boy carrying a de novo mutation in TINF2 gene.

Methods

Whole exome sequencing (WES) was performed on DNA sample of the proband, and the variant was investigated in the family by Sanger sequencing. Population and bioinformatics analysis were performed.

Results

The NM_ 001099274.3(TINF2): c.844C>T (p.Arg282Cys) mutation was found by WES.

Conclusion

There was no history of the disease in the family, and the variant was classified as a de novo mutation.

Genetics of human telomere biology disorders

Telomeres are specialized nucleoprotein structures at the ends of linear chromosomes that prevent the activation of DNA damage response and repair pathways. Numerous factors localize at telomeres to regulate their length, structure and function, to avert replicative senescence or genome instability and cell death. In humans, Mendelian defects in several of these factors can result in abnormally short or dysfunctional telomeres, causing a group of rare heterogeneous premature-ageing diseases, termed telomeropathies, short-telomere syndromes or telomere biology disorders (TBDs). Here, we review the TBD-causing genes identified so far and describe their main functions associated with telomere biology. We present molecular aspects of TBDs, including genetic anticipation, phenocopy, incomplete penetrance and somatic genetic rescue, which underlie the complexity of these diseases. We also discuss the implications of phenotypic and genetic features of TBDs on fundamental aspects related to human telomere biology, ageing and cancer, as well as on diagnostic, therapeutic and clinical approaches.

Truncating TINF2 p.Tyr312Ter variant and inherited breast cancer susceptibility

TINF2 is a critical subunit of the shelterin complex, which protects and maintains the length of telomeres. Pathogenic missense and truncating TINF2 mutations are causative for dyskeratosis congenita (DC), a rare, dominantly inherited bone marrow failure syndrome characterized by mucocutaneous abnormalities and cancer predisposition. Recent reports indicate that specific TINF2 truncating mutations act as high penetrance cancer predisposition alleles outside DC context, including breast cancer in their tumor spectrum. Here, we have evaluated the role of germline mutations in TINF2 and other shelterin genes in inherited breast cancer susceptibility using exome sequencing data from 98 Northern Finnish breast cancer cases with indication of inherited disease predisposition as a discovery cohort. A single protein truncating variant, TINF2 p.Tyr312Ter, was identified in one of the cases (1/98), and four more carriers were observed in the subsequently genotyped unselected breast cancer cohort (4/1904). None of the carriers were reported to have DC. TINF2 p.Tyr312Ter resulted in stable short form of mRNA transcript, and normal telomere length has been indicated by a recent report. Although recurrent in cases (total of 5/2095), TINF2 p.Tyr312Ter is also present in Finnish population controls (8/12,517), and the observed 4-fold higher frequency in cases falls at most into the range of moderate breast cancer risk alleles (OR 3.74, 95% CI 1.22-11.45, p = 0.029). Current results indicate that not all TINF2 truncating variants are high cancer risk alleles and add further evidence that different TINF2 mutations can have very diverse effects on the disease phenotype.

Dyskeratosis congenita and telomere biology disorders

Numerous genetic discoveries and the advent of clinical telomere length testing have led to the recognition of a spectrum of telomere biology disorders (TBDs) beyond the classic dyskeratosis congenita (DC) triad of nail dysplasia, abnormal skin pigmentation, and oral leukoplakia occurring with pediatric bone marrow failure. Patients with DC/TBDs have very short telomeres for their age and are at high risk of bone marrow failure, cancer, pulmonary fibrosis (PF), pulmonary arteriovenous malformations, liver disease, stenosis of the urethra, esophagus, and/or lacrimal ducts, avascular necrosis of the hips and/or shoulders, and other medical problems. However, many patients with TBDs do not develop classic DC features; they may present in middle age and/or with just 1 feature, such as PF or aplastic anemia. TBD-associated clinical manifestations are progressive and attributed to aberrant telomere biology caused by the X-linked recessive, autosomal dominant, autosomal recessive, or de novo occurrence of pathogenic germline variants in at least 18 different genes. This review describes the genetics and clinical manifestations of TBDs and highlights areas in need of additional clinical and basic science research.

Role of angiotensin II in aging

Aging is an inevitable progressive decline in physiological organ function that increases the chance of disease and death. The renin-angiotensin system (RAS) is involved in the regulation of vasoconstriction, fluid homeostasis, cell growth, fibrosis, inflammation, and oxidative stress. In recent years, unprecedented advancement has been made in the RAS study, particularly with the observation that angiotensin II (Ang II), the central product of the RAS, plays a significant role in aging and chronic disease burden with aging. Binding to its receptors (Ang II type 1 receptor - AT1R in particular), Ang II acts as a mediator in the aging process by increasing free radical production and, consequently, mitochondrial dysfunction and telomere attrition. In this review, we examine the physiological function of the RAS and reactive oxygen species (ROS) sources in detail, highlighting how Ang II amplifies or drives mitochondrial dysfunction and telomere attrition underlying each hallmark of aging and contributes to the development of aging and age-linked diseases. Accordingly, the Ang II/AT1R pathway opens a new preventive and therapeutic direction for delaying aging and reducing the incidence of age-related diseases in the future.

Novel TINF2 gene mutation in dyskeratosis congenita with extremely short telomeres: A case report

BACKGROUND

Dyskeratosis congenita is a rare disease characterized by bone marrow failure and a clinical triad of oral leukoplakia, nail dystrophy, and abnormal skin pigmentation. The genetics of dyskeratosis congenita include mutations in genes involved in telomere maintenance, including TINF2.

CASE SUMMARY

Here, we report a female patient who presented thrombocytopenia, anemia, reticulate hyperpigmentation, dystrophy in fingernails and toenails, and leukoplakia on the tongue. A histopathological study of the skin showed dyskeratocytes; however, a bone marrow biopsy revealed normal cell morphology. The patient was diagnosed with dyskeratosis congenita, but her family history did not reveal significant antecedents. Whole-exome sequencing showed a novel heterozygous punctual mutation in exon 6 from the TINF2 gene, namely, NM_001099274.1:c.854delp.(Val285Alafs*32). An analysis of telomere length showed short telomeres relative to the patient’s age.

CONCLUSION

The disease in this patient was caused by a germline novel mutation of TINF2 in one of her parents.

Autoimmune Neutropenia and Immune-Dysregulation in a Patient Carrying a TINF2 Variant

In recent years, the knowledge about the immune-mediated impairment of bone marrow precursors in immune-dysregulation and autoimmune disorders has increased. In addition, immune-dysregulation, secondary to marrow failure, has been reported as being, in some cases, the most evident and early sign of the disease and making the diagnosis of both groups of disorders challenging. Dyskeratosis congenita is a disorder characterized by premature telomere erosion, typically showing marrow failure, nail dystrophy and leukoplakia, although incomplete genetic penetrance and phenotypes with immune-dysregulation features have been described. We report on a previously healthy 17-year-old girl, with a cousin successfully treated for acute lymphoblastic leukemia, who presented with leukopenia and neutropenia. The diagnostic work-up showed positive anti-neutrophil antibodies, leading to the diagnosis of autoimmune neutropenia, a slightly low NK count and high TCR-αβ+-double-negative T-cells. A next-generation sequencing (NGS) analysis showed the 734C>A variant on exon 6 of the TINF2 gene, leading to the p.Ser245Tyr. The telomere length was short on the lymphocytes and granulocytes, suggesting the diagnosis of an atypical telomeropathy showing with immune-dysregulation. This case underlines the importance of an accurate diagnostic work-up of patients with immune-dysregulation, who should undergo NGS or whole exome sequencing to identify specific disorders that deserve targeted follow-up and treatment.

Editing TINF2 as a potential therapeutic approach to restore telomere length in dyskeratosis congenita

Mutations in the TINF2 gene, encoding the shelterin protein TIN2, cause telomere shortening and the inherited bone marrow (BM) failure syndrome dyskeratosis congenita (DC). A lack of suitable model systems limits the mechanistic understanding of telomere shortening in the stem cells and thus hinders the development of treatment options for BM failure. Here, we endogenously introduced TIN2-DC mutations in human embryonic stem cells (hESCs) and human hematopoietic stem and progenitor cells (HSPCs) to dissect the disease mechanism and identify a gene-editing strategy that rescued the disease phenotypes. The hESCs with the T284R disease mutation exhibited the short telomere phenotype observed in DC patients. Yet, telomeres in mutant hESCs did not trigger DNA damage responses at telomeres or show exacerbated telomere shortening when differentiated into telomerase-negative cells. Disruption of the mutant TINF2 allele by introducing a frameshift mutation in exon 2 restored telomere length in stem cells and the replicative potential of differentiated cells. Similarly, we introduced TIN2-DC disease variants in human HSPCs to assess the changes in telomere length and proliferative capacity. Lastly, we showed that editing at exon 2 of TINF2 that restored telomere length in hESCs could be generated in TINF2-DC patient HSPCs. Our study demonstrates a simple genetic intervention that rescues the TIN2-DC disease phenotype in stem cells and provides a versatile platform to assess the efficacy of potential therapeutic approaches in vivo.

The biology and management of dyskeratosis congenita and related disorders of telomeres

BACKGROUND

Dyskeratosis congenita (DC) is a multisystem syndrome characterized by mucocutaneous abnormalities, bone marrow failure, and predisposition to cancer. Studies over the last 25 years have led to the identification of 18 disease genes. These have a principal role in telomere maintenance, and patients usually have very short/abnormal telomeres. The advances have also led to the unification of DC with a number of other diseases, now collectively referred to as the telomeropathies or telomere biology disorders.

WHAT IS COVERED

Clinical features, genetics, and biology of the different subtypes. Expert view on diagnosis, treatment of the hematological complications and future.

EXPERT VIEW

As these are very pleotropic disorders affecting multiple organs, a high index of suspicion is necessary to make the diagnosis. Telomere length measurement and genetic analysis of the disease genes have become useful diagnostic tools. Although hematological defects can respond to danazol/oxymetholone, the only current curative treatment for these is hematopoietic stem cell transplantation (HSCT) using fludarabine-based conditioning protocols. New therapies are needed where danazol/oxymetholone is ineffective and HSCT is not feasible.

de novo TINF2 C.845G>A: Pathogenic Variant in Patient with Dyskeratosis Congenita

Dyskeratosis congenita (DC) is a clinically and genetically heterogeneous, multisystem inherited syndrome with a very high risk for bone marrow failure (BMF) and cancer predisposition. The classical clinical form of DC is characterized by abnormal skin pigmentation, nail dystrophy, and oral leukoplakia. Bone marrow failure is considered to be an important and major complication of DC and the leading cause of death which develops in around 85% of cases. A number of genes involved in telomere maintenance are associated with DC, such as genes that encode the components of the telomerase complex (TERT, DKC1, TERC, NOP10, and NHP2), T-loop assembly protein (RTEL1), telomere capping (CTC1), telomere shelterin complex (TINF2), and telomerase trafficking protein (TCAB1). Mutations in TINF2 have been reported in 11–20% of all patients with DC and have been associated with bone marrow failure. Here we report on a 19-month old boy with very early presentation of bone marrow failure as a first clinical manifestation of DC. Upon first admission, the patient presented with thrombocytopenia and macrocytic anemia. Soon after, his blood counts deteriorated with the development of pancytopenia and aplastic anemia. Four months later, he developed nail dystrophy and skin hyperpigmentation. A de novo heterozygous pathogenic variant c.845G>A, p.(Arg282His) was located in exon 6 of TINF2 gene and was identified via clinical exome sequencing. The findings confirmed the diagnosis of DC. This is the first case with DC due to TINF2 pathogenic variant reported in North Macedonia.

Disease progression and clinical outcomes in telomere biology disorders

Dyskeratosis congenita related telomere biology disorders (DC/TBDs) are characterized by very short telomeres caused by germline pathogenic variants in telomere biology genes. Clinical presentations can affect all organs, and inheritance patterns include autosomal dominant (AD), autosomal recessive (AR), X-linked (XLR), or de novo. This study examined the associations between mode of inheritance with phenotypes and long-term clinical outcomes. Two hundred thirty-one individuals with DC/TBDs (144 male, 86.6% known genotype, median age at diagnosis 19.4 years [range 0 to 71.6]), enrolled in the National Cancer Institute's Inherited Bone Marrow Failure Syndrome Study, underwent detailed clinical assessments and longitudinal follow-up (median follow-up 5.2 years [range 0 to 36.7]). Patients were grouped by inheritance pattern, considering AD-nonTINF2, AR/XLR, and TINF2 variants separately. Severe bone marrow failure (BMF), severe liver disease, and gastrointestinal telangiectasias were more prevalent in AR/XLR or TINF2 disease, whereas pulmonary fibrosis developed predominantly in adults with AD disease. After adjusting for age at DC/TBD diagnosis, we observed the highest cancer risk in AR/XLR individuals. At last follow-up, 42% of patients were deceased with a median overall survival (OS) of 52.8 years (95% confidence interval [CI] 45.5-57.6), and the hematopoietic cell or solid organ transplant-free median survival was 45.3 years (95% CI 37.4-52.1). Significantly better OS was present in AD vs AR/XLR/TINF2 disease (P < .01), while patients with AR/XLR and TINF2 disease had similar survival probabilities. This long-term study of the clinical manifestations of DC/TBDs creates a foundation for incorporating the mode of inheritance into evidence-based clinical care guidelines and risk stratification in patients with DC/TBDs. This trial was registered at www.clinicaltrials.gov as #NCT00027274.

TIN2 deficiency leads to ALT-associated phenotypes and differentiation defects in embryonic stem cells

Telomere integrity is critical for embryonic development, and core telomere-binding proteins, such as TIN2, are key to maintaining telomere stability. Here, we report that homozygous Tin2^S341X resulted in embryonic lethality in mice and reduced expression of Tin2 in the derived mouse embryonic stem cells (mESCs). Homozygous mutant mESCs were able to self-renew and remain undifferentiated but displayed many phenotypes associated with alternative lengthening of telomeres (ALT), including excessively long and heterogeneous telomeres, increased ALT-associated promyelocytic leukemia (PML) bodies, and unstable chromosomal ends. These cells also showed upregulation of Zscan4 expression and elevated targeting of DAXX/ATRX and H3K9me3 marks on telomeres. Furthermore, the mutant mESCs were impeded in their differentiation capacity. Upon differentiation, DAXX/ATRX and PML bodies disassociated from telomeres in these cells, where elevated DNA damage was also apparent. Our results reveal differential responses to telomere dysfunction in mESCs versus differentiated cells and highlight the critical role of TIN2 in embryonic development.

Multisystemic Manifestations in Rare Diseases: The Experience of Dyskeratosis Congenita

Dyskeratosis congenital (DC) is the first genetic syndrome described among telomeropathies. Its classical phenotype is characterized by the mucocutaneous triad of reticulated pigmentation of skin lace, nail dystrophy and oral leukoplakia. The clinical presentation, however, is heterogeneous and serious clinical complications include bone marrow failure, hematological and solid tumors. It may also involve immunodeficiencies, dental, pulmonary and liver disorders, and other minor complication. Dyskeratosis congenita shows marked genetic heterogeneity, as at least 14 genes are responsible for the shortening of telomeres characteristic of this disease. This review discusses clinical characteristics, molecular genetics, disease evolution, available therapeutic options and differential diagnosis of dyskeratosis congenita to provide an interdisciplinary and personalized medical assessment that includes family genetic counseling.

Molecular insight of dyskeratosis congenita: Defects in telomere length homeostasis

BACKGROUND

Dyskeratosis congenita (DC) is a rare disease and is a heterogenous disorder, with its inheritance patterns as autosomal dominant, autosomal recessive, and X-linked recessive. This disorder occurs due to faulty maintenance of telomeres in stem cells. This congenital condition is diagnosed with three symptoms: oral leukoplakia, nail dystrophy, and abnormal skin pigmentation. However, because it has a wide range of symptoms, it may have phenotypes similar to other diseases. For this reason, it is necessary to use methods of measuring the Telomere Length (TL) and determining the shortness of the telomere in these patients so that it can be distinguished from other diseases. Today, the Next Generation Sequencing technique accurately detects mutations in the target genes.

AIM

This work aims to review and summarize how each of the DC genes is involved in TL, and how to diagnose and differentiate the disease using clinical signs and methods to measure TL. It also offers treatments for DC patients, such as Hematopoietic Stem Cell Transplantation and Androgen therapy.

RELEVANCE FOR PATIENTS

In DC patients, the genes involved in telomere homeostasis are mutated. Because these patients may have an overlapping phenotype with other diseases, it is best to perform whole-exome sequencing after genetics counseling to find the relevant mutation. As DC is a multi-systemic disease, we need to monitor patients frequently through annual lung function tests, ultrasounds, gynecological examinations, and skin examinations.

Association of leukocyte telomere length with chronic kidney disease in East Asians with type 2 diabetes: a Mendelian randomization study

Background

Chronic kidney disease (CKD) is common among people with type 2 diabetes (T2D), and increases the risk of kidney failure and cardiovascular diseases. Shorter leukocyte telomere length (LTL) is associated with CKD in patients with T2D. We previously reported single-nucleotide polymorphisms (SNPs) associated with LTL in an Asian population. In this study, we elucidated the association of these SNPs with CKD in patients with T2D using the Mendelian randomization (MR) approach.

Methods

The cross-sectional association of 16 LTL SNPs with CKD, defined as an estimated glomerular filtration rate of <60 mL/min/1.73 m², was assessed among 4768 (1628 cases and 3140 controls) participants in the Singapore Study of Macro-angiopathy and Micro-vascular Reactivity in T2D and Diabetic Nephropathy cohorts. MR analysis was performed using the random-effect inverse-variance weighted (IVW) method, the weighted median, MR-Egger and Radial MR adjusted for age and sex-stratified by cohorts and ethnicity (Chinese and Malays), then meta-analyzed.

Results

Genetically determined shorter LTL was associated with increased risk of CKD in patients with T2D (meta-IVW adjusted odds ratio = 1.51, 95% confidence interval 1.12–2.12, P = 0.007, P_het = 0.547). Similar results were obtained following sensitivity analysis. MR-Egger analysis (intercept) suggested no evidence of horizontal pleiotropy (β = 0.010, P = 0.751).

Conclusions

Our findings suggest that genetically determined LTL is associated with CKD in patients with T2D. Further studies are warranted to elucidate the causal role of telomere length in CKD progression.

Differential impact of a dyskeratosis congenita mutation in TPP1 on mouse hematopoiesis and germline

A TPP1 mutation known to cause telomere shortening and bone marrow failure in humans recapitulates telomere loss but results in severe germline defects in mice without impacting murine hematopoiesis.

Telomerase extends chromosome ends in somatic and germline stem cells to ensure continued proliferation. Mutations in genes critical for telomerase function result in telomeropathies such as dyskeratosis congenita, frequently resulting in spontaneous bone marrow failure. A dyskeratosis congenita mutation in TPP1 (K170∆) that specifically compromises telomerase recruitment to telomeres is a valuable tool to evaluate telomerase-dependent telomere length maintenance in mice. We used CRISPR-Cas9 to generate a mouse knocked in for the equivalent of the TPP1 K170∆ mutation (TPP1 K82∆) and investigated both its hematopoietic and germline compartments in unprecedented detail. TPP1 K82∆ caused progressive telomere erosion with increasing generation number but did not induce steady-state hematopoietic defects. Strikingly, K82∆ caused mouse infertility, consistent with gross morphological defects in the testis and sperm, the appearance of dysfunctional seminiferous tubules, and a decrease in germ cells. Intriguingly, both TPP1 K82∆ mice and previously characterized telomerase knockout mice show no spontaneous bone marrow failure but rather succumb to infertility at steady-state. We speculate that telomere length maintenance contributes differently to the evolutionary fitness of humans and mice.

Tissue-specific telomere shortening and degenerative changes in a patient with TINF2 mutation and dyskeratosis congenita

Dyskeratosis congenita is a disease of impaired tissue maintenance downstream of telomere dysfunction. Characteristically, patients present with the clinical triad of nail dystrophy, oral leukoplakia, and skin pigmentation defects, but the disease involves degenerative changes in multiple organs. Mutations in telomere-binding proteins such as TINF2 (TRF1-interacting nuclear factor 2) or in telomerase, the enzyme that counteracts age related telomere shortening, are causative in dyskeratosis congenita. We present a patient who presented with severe hypoxemia at age 13. The patient had a history of myelodysplastic syndrome treated with bone marrow transplant at the age of 5. At age 18 she was hospitalized for an acute pneumonia progressing to respiratory failure, developed renal failure and ultimately, she and her family opted to withdraw support as she was not a candidate for a lung transplant. Sequencing of the patient's TINF2 locus revealed a heterozygous mutation (c.844C > T, Arg282Cys) which has previously been reported in a subset of dyskeratosis congenita patients. Tissue sections from multiple organs showed degenerative changes including disorganized bone remodeling, diffuse alveolar damage and small vessel proliferation in the lung, and hyperkeratosis with hyperpigmentation of the skin. Autopsy samples revealed a bimodal distribution of telomere length, with telomeres from donor hematopoietic tissues being an age-appropriate length and those from patient tissues showing pathogenic shortening, with the shortest telomeres in lung, liver, and kidney. We report for the first time a survey of degenerative changes and telomere lengths in multiple organs in a patient with dyskeratosis congenita.

Hallmarks of Cancers: Primary Antibody Deficiency Versus Other Inborn Errors of Immunity

Inborn Errors of Immunity (IEI) comprise more than 450 inherited diseases, from which selected patients manifest a frequent and early incidence of malignancies, mainly lymphoma and leukemia. Primary antibody deficiency (PAD) is the most common form of IEI with the highest proportion of malignant cases. In this review, we aimed to compare the oncologic hallmarks and the molecular defects underlying PAD with other IEI entities to dissect the impact of avoiding immune destruction, genome instability, and mutation, enabling replicative immortality, tumor-promoting inflammation, resisting cell death, sustaining proliferative signaling, evading growth suppressors, deregulating cellular energetics, inducing angiogenesis, and activating invasion and metastasis in these groups of patients. Moreover, some of the most promising approaches that could be clinically tested in both PAD and IEI patients were discussed.

Pulmonary fibrosis in dyskeratosis congenita: a case report with a PRISMA-compliant systematic review

Background

Dyskeratosis congenita (DC) is a rare genetic disorder of poor telomere maintenance. Pulmonary fibrosis (PF) related to DC is rarely reported.

Case presentation

A 23-year-old student presented with a four-year history of progressive cough and exertional dyspnea. Physical examination was remarkable for typical mucocutaneous abnormalities. Chest computerized tomography scan revealed interstitial fibrosis. Testing of peripheral blood leukocytes confirmed that his telomeres were 30th percentile of age-matched controls. A heterozygous missense mutation located in exon 22 of PARN gene was identified in the patient by whole exome sequencing. The patient refused danazol therapy and lung transplantation, and died of respiratory failure 2 years later. In addition, this case and 26 reported cases of DC-related PF identified through the comprehensive search of PubMed, Web of Science, WANFANG and CNKI were reviewed. Later-onset PF was observed in 11 patients (40.7%). Radiological usual interstitial pneumonia (UIP) pattern or possible UIP pattern was noted only in half of patients. However, histopathological UIP or probable UIP patterns were found in 63.6% of patients. Age at bone marrow failure (BMF) and the frequency of normal to mild thrombocytopenia in later-onset patients was significantly higher than in early-onset patients (p = 0.017 and p = 0.021, respectively). Age at PF and age at BMF in DC patients with TERC/TERT variants was significantly higher than in those with TINF2 variants or DKC1/NHP2 variants (p = 0.004 and p = 0.003, respectively). The patients with TERT/TERC/RTEL1/PARN variants had a significantly better transplant-free survival than those with TINF2 variants or DKC1/NHP2 variants (p < 0.05). Patients who underwent surgical lung biopsy had significantly worse transplant-free survival than those without lung biopsy (p = 0.042). Worse survival was found in patients with immunosuppression therapy than in those without (p = 0.012).

Conclusions

It is common for DC-associated PF to occur later in life without significant hematological manifestations. Mutations in the genes encoding different components of the telomere maintenance pathway were associated with clinical phenotypes and prognosis. PF caused by DC should be kept in mind by clinicians in the differential diagnosis of patients with unexplained PF and should be excluded before diagnostic surgical lung biopsy is undertaken or empirical immunosuppression therapy is prescribed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12890-021-01645-w.

Structure, dynamics, and regulation of TRF1-TIN2-mediated trans- and cis-interactions on telomeric DNA

TIN2 is a core component of the shelterin complex linking double-stranded telomeric DNA-binding proteins (TRF1 and TRF2) and single-strand overhang-binding proteins (TPP1-POT1). In vivo, the large majority of TRF1 and TRF2 exist in complexes containing TIN2 but lacking TPP1/POT1; however, the role of TRF1-TIN2 interactions in mediating interactions with telomeric DNA is unclear. Here, we investigated DNA molecular structures promoted by TRF1-TIN2 interaction using atomic force microscopy (AFM), total internal reflection fluorescence microscopy (TIRFM), and the DNA tightrope assay. We demonstrate that the short (TIN2S) and long (TIN2L) isoforms of TIN2 facilitate TRF1-mediated DNA compaction (cis-interactions) and DNA-DNA bridging (trans-interactions) in a telomeric sequence- and length-dependent manner. On the short telomeric DNA substrate (six TTAGGG repeats), the majority of TRF1-mediated telomeric DNA-DNA bridging events are transient with a lifetime of ~1.95 s. On longer DNA substrates (270 TTAGGG repeats), TIN2 forms multiprotein complexes with TRF1 and stabilizes TRF1-mediated DNA-DNA bridging events that last on the order of minutes. Preincubation of TRF1 with its regulator protein Tankyrase 1 and the cofactor NAD+ significantly reduced TRF1-TIN2 mediated DNA-DNA bridging, whereas TIN2 protected the disassembly of TRF1-TIN2 mediated DNA-DNA bridging upon Tankyrase 1 addition. Furthermore, we showed that TPP1 inhibits TRF1-TIN2L-mediated DNA-DNA bridging. Our study, together with previous findings, supports a molecular model in which protein assemblies at telomeres are heterogeneous with distinct subcomplexes and full shelterin complexes playing distinct roles in telomere protection and elongation.

Two Cases of Dyskeratosis Congenita with Clinically Distinct Presentations, Seen in National University Hospital, Singapore

Dyskeratosis congenita (DKC) is a genodermatosis of variable inheritance and is often characterised by the classical triad of nail dysplasia, reticulate hyperpigmentation of upper chest and neck, and oral leukoplakia. We report 2 cases of DKC from National University Hospital, Singapore, whose clinical presentations differed greatly from each other. Dermatologists should hold a high index of suspicion for DKC in young patients who present without the classical triad of features, as early dermatological care can be instituted through reinforcement of rigorous sun protection and regular surveillance for skin cancers. Early diagnosis also offers physicians the time to organise haematopoietic stem cell transplantation if necessary, as bone marrow failure is often inevitable. As a multisystemic disease with high morbidity and mortality particularly from haematological complications if left undetected and untreated in the early stages, the role of the dermatologist in diagnosing DKC is a crucial one.

External environmental agents influence telomere length and telomerase activity by modulating internal cellular processes: Implications in human aging

External environment affects cellular physiological processes and impact the stability of our genome. The most important structural components of our linear chromosomes which endure the impact by these agents, are the chromosomal ends called telomeres. Telomeres preserve the integrity of our genome by preventing end to end fusions and telomeric loss through by inhibiting DNA damage response (DDR) activation. This is accomplished by the presence of a six membered shelterin complex at telomeres. Further, telomeres cannot be replicated by normal DNA polymerase and require a special enzyme called telomerase which is expressed only in stem cells, few immune cells and germ cells. Telomeres are rich in guanine content and thus become extremely prone to damage arising due to physiological processes like oxidative stress and inflammation. External environmental factors which includes various physical, biological and chemical agents also affect telomere homeostasis by increasing oxidative stress and inflammation. In the present review, we highlight the effect of these external factors on telomerase activity and telomere length. We also discuss how the external agents affect the physiological processes, thus modulating telomere stability. Further, we describe its implication in the development of aging and its related pathologies.

High-throughput STELA provides a rapid test for the diagnosis of telomere biology disorders

Telomere biology disorders are complex clinical conditions that arise due to mutations in genes required for telomere maintenance. Telomere length has been utilised as part of the diagnostic work-up of patients with these diseases; here, we have tested the utility of high-throughput STELA (HT-STELA) for this purpose. HT-STELA was applied to a cohort of unaffected individuals (n = 171) and a retrospective cohort of mutation carriers (n = 172). HT-STELA displayed a low measurement error with inter- and intra-assay coefficient of variance of 2.3% and 1.8%, respectively. Whilst telomere length in unaffected individuals declined as a function of age, telomere length in mutation carriers appeared to increase due to a preponderance of shorter telomeres detected in younger individuals (< 20 years of age). These individuals were more severely affected, and age-adjusted telomere length differentials could be used to stratify the cohort for overall survival (Hazard Ratio = 5.6 (1.5-20.5); p < 0.0001). Telomere lengths of asymptomatic mutation carriers were shorter than controls (p < 0.0001), but longer than symptomatic mutation carriers (p < 0.0001) and telomere length heterogeneity was dependent on the diagnosis and mutational status. Our data show that the ability of HT-STELA to detect short telomere lengths, that are not readily detected with other methods, means it can provide powerful diagnostic discrimination and prognostic information. The rapid format, with a low measurement error, demonstrates that HT-STELA is a new high-quality laboratory test for the clinical diagnosis of an underlying telomeropathy.

Telomere biology disorders

Telomere biology disorders (TBD) are a heterogeneous group of diseases arising from germline mutations affecting genes involved in telomere maintenance. Telomeres are DNA-protein structures at chromosome ends that maintain chromosome stability; their length affects cell replicative potential and senescence. A constellation of bone marrow failure, pulmonary fibrosis, liver cirrhosis and premature greying is suggestive, however incomplete penetrance results in highly variable manifestations, with idiopathic pulmonary fibrosis as the most common presentation. Currently, the true extent of TBD burden is unknown as there is no established diagnostic criteria and the disorder often is unrecognised and underdiagnosed. There is no gold standard for measuring telomere length and not all TBD-related mutations have been identified. There is no specific cure and the only treatment is organ transplantation, which has poor outcomes. This review summarises the current literature and discusses gaps in understanding and areas of need in managing TBD.

Late-onset and long-lasting autoimmune neutropenia: an analysis from the Italian Neutropenia Registry

Primary autoimmune neutropenia (pAN) is typified by onset in early infancy and a mild/moderate phenotype that resolves within 3 years of diagnosis. In contrast, secondary AN is classically an adult disease associated with malignancy, autoimmunity, immunodeficiency, viral infection, or drugs. This study describes a cohort of 79 children from the Italian Registry who, although resembling pAN, did not fully match the criteria for pAN because neutropenia either appeared after age 5 years (LO-Np) or lasted longer than 3 years (LL-Np). These 2 categories compared with classical pAN showed a far inferior rate of resolution (P < .001), lower severity of neutropenia (P = .03), leukopenia (P < .001), lymphopenia (P < .001) with low B+ (P = .001), increased need of granulocyte colony-stimulating factor (P = .04), and increased frequency of autoimmunity over the disease course (P < .001). A paired comparison between LO-Np and LL-Np suggested that LO-Np had a lower rate of resolution (P < .001) and lower white blood cell (P < .001) and lymphocyte (P < .001) values, higher occurrence of apthae (P = .008), and a stronger association with autoimmune diseases/markers (P = .001) than LL-Np, thus suggesting a more pronounced autoimmune signature for LO-Np. A next-generation sequencing panel applied in a small subgroup of LO-Np and LL-Np patients identified variants related to immune dysregulations. Overall, these findings indicate that there are important differences among pAN LL-Np and LO-Np. Forms rising after 3 years of age, with low tendency to resolution, require tight monitoring and extensive immune investigations aimed to early identify underlying immunologic disease.

TPP1 mutagenesis screens unravel shelterin interfaces and functions in hematopoiesis

Telomerase catalyzes chromosome end replication in stem cells and other long-lived cells. Mutations in telomerase or telomere-related genes result in diseases known as telomeropathies. Telomerase is recruited to chromosome ends by the ACD/TPP1 protein (TPP1 hereafter), a component of the shelterin complex that protects chromosome ends from unwanted end joining. TPP1 facilitates end protection by binding shelterin proteins POT1 and TIN2. TPP1 variants have been associated with telomeropathies but remain poorly characterized in vivo. Disease variants and mutagenesis scans provide efficient avenues to interrogate the distinct physiological roles of TPP1. Here, we conduct mutagenesis in the TIN2- and POT1-binding domains of TPP1 to discover mutations that dissect TPP1's functions. Our results extend current structural data to reveal that the TPP1-TIN2 interface is more extensive than previously thought and highlight the robustness of the POT1-TPP1 interface. Introduction of separation-of-function mutants alongside known TPP1 telomeropathy mutations in mouse hematopoietic stem cells (mHSCs) lacking endogenous TPP1 demonstrated a clear phenotypic demarcation. TIN2- and POT1-binding mutants were unable to rescue mHSC failure resulting from end deprotection. In contrast, TPP1 telomeropathy mutations sustained mHSC viability, consistent with their selectively impacting end replication. These results highlight the power of scanning mutagenesis in revealing structural interfaces and dissecting multifunctional genes.

Gastrointestinal Hemorrhage: A Manifestation of the Telomere Biology Disorders

OBJECTIVE

To describe the clinical features, therapeutic interventions, and patient outcomes of gastrointestinal (GI) hemorrhage in individuals with a telomere biology disorder, including dyskeratosis congenita, Hoyeraal-Hreidarsson syndrome, Revesz syndrome, and Coats plus.

STUDY DESIGN

Clinical Care Consortium for Telomere Associated Ailments members were invited to contribute data on individuals with telomere biology disorders at their institutions who experienced GI bleeding. Patient demographic, laboratory, imaging, procedural, and treatment information and outcomes were extracted from the medical record.

RESULTS

Sixteen patients who experienced GI hemorrhage were identified at 11 centers. Among 14 patients who underwent genetic testing, 8 had mutations in TINF2, 4 had mutations in CTC1 or STN1, and 1 patient each had a mutation in TERC and RTEL1. Ten patients had a history of hematopoietic cell transplantation. The patients with Coats plus and those without Coats plus had similar clinical features and courses. Angiodysplasia of the stomach and/or small bowel was described in 8 of the 12 patients who underwent endoscopy; only 4 had esophageal varices. Various medical interventions were trialed. No single intervention was uniformly associated with cessation of bleeding, although 1 patient had a sustained response to treatment with bevacizumab. Recurrence was common, and the overall long-term outcome for affected patients was poor.

CONCLUSIONS

GI bleeding in patients with telomere biology disorders is associated with significant morbidity and with vascular ectasias rather than varices.

Diverse telomeres in trypanosomatids

Telomeres are the ends of linear eukaryotic chromosomes facilitating the resolution of the ‘end replication and protection’ problems, associated with linearity. At the nucleotide level, telomeres typically represent stretches of tandemly arranged telomeric repeats, which vary in length and sequence among different groups of organisms. Recently, a composition of the telomere-associated protein complex has been scrutinized in Trypanosoma brucei. In this work, we subjected proteins from that list to a more detailed bioinformatic analysis and delineated a core set of 20 conserved proteins putatively associated with telomeres in trypanosomatids. Out of these, two proteins (Ku70 and Ku80) are conspicuously missing in representatives of the genus Blastocrithidia, yet telomeres in these species do not appear to be affected. In this work, based on the analysis of a large set of trypanosomatids widely different in their phylogenetic position and life strategies, we demonstrated that telomeres of trypanosomatids are diverse in length, even within groups of closely related species. Our analysis showed that the expression of two proteins predicted to be associated with telomeres (those encoding telomerase and telomere-associated hypothetical protein orthologous to Tb927.6.4330) may directly affect and account for the differences in telomere length within the species of the Leishmania mexicana complex.

Molecular mechanisms of telomere biology disorders

Genetic mutations that affect telomerase function or telomere maintenance result in a variety of diseases collectively called telomeropathies. This wide spectrum of disorders, which include dyskeratosis congenita, pulmonary fibrosis, and aplastic anemia, is characterized by severely short telomeres, often resulting in hematopoietic stem cell failure in the most severe cases. Recent work has focused on understanding the molecular basis of these diseases. Mutations in the catalytic TERT and TR subunits of telomerase compromise activity, while others, such as those found in the telomeric protein TPP1, reduce the recruitment of telomerase to the telomere. Mutant telomerase-associated proteins TCAB1 and dyskerin and the telomerase RNA maturation component poly(A)-specific ribonuclease affect the maturation and stability of telomerase. In contrast, disease-associated mutations in either CTC1 or RTEL1 are more broadly associated with telomere replication defects. Yet even with the recent surge in studies decoding the mechanisms underlying these diseases, a significant proportion of dyskeratosis congenita mutations remain uncharacterized or poorly understood. Here we review the current understanding of the molecular basis of telomeropathies and highlight experimental data that illustrate how genetic mutations drive telomere shortening and dysfunction in these patients. This review connects insights from both clinical and molecular studies to create a comprehensive view of the underlying mechanisms that drive these diseases. Through this, we emphasize recent advances in therapeutics and pinpoint disease-associated variants that remain poorly defined in their mechanism of action. Finally, we suggest future avenues of research that will deepen our understanding of telomere biology and telomere-related disease.

Utility of clinical comprehensive genomic characterization for diagnostic categorization in patients presenting with hypocellular bone marrow failure syndromes

Bone marrow failure (BMF) related to hypoplasia of hematopoietic elements in the bone marrow is a heterogeneous clinical entity with a broad differential diagnosis including both inherited and acquired causes. Accurate diagnostic categorization is critical to optimal patient care and detection of genomic variants in these patients may provide this important diagnostic and prognostic information. We performed real-time, accredited (ISO15189) comprehensive genomic characterization including targeted sequencing and whole exome sequencing in 115 patients with BMF syndrome (median age 24 years, range 3 months - 81 years). In patients with clinical diagnoses of inherited BMF syndromes, acquired BMF syndromes or clinically unclassifiable BMF we detected variants in 52% (12/23), 53% (25/47) and 56% (25/45) respectively. Genomic characterization resulted in a change of diagnosis in 30/115 (26%) including the identification of germline causes for 3/47 and 16/45 cases with pre-test diagnoses of acquired and clinically unclassifiable BMF respectively. The observed clinical impact of accurate diagnostic categorization included choice to perform allogeneic stem cell transplantation, disease-specific targeted treatments, identification of at-risk family members and influence of sibling allogeneic stem cell donor choice. Multiple novel pathogenic variants and copy number changes were identified in our cohort including in TERT, FANCA, RPS7 and SAMD9. Whole exome sequence analysis facilitated the identification of variants in two genes not typically associated with a primary clinical manifestation of BMF but also demonstrated reduced sensitivity for detecting low level acquired variants. In conclusion, genomic characterization can improve diagnostic categorization of patients presenting with hypoplastic BMF syndromes and should be routinely performed in this group of patients.

TINF2 is a haploinsufficient tumor suppressor that limits telomere length

Telomere shortening is a presumed tumor suppressor pathway that imposes a proliferative barrier (the Hayflick limit) during tumorigenesis. This model predicts that excessively long somatic telomeres predispose to cancer. Here, we describe cancer-prone families with two unique TINF2 mutations that truncate TIN2, a shelterin subunit that controls telomere length. Patient lymphocyte telomeres were unusually long. We show that the truncated TIN2 proteins do not localize to telomeres, suggesting that the mutations create loss-of-function alleles. Heterozygous knock-in of the mutations or deletion of one copy of TINF2 resulted in excessive telomere elongation in clonal lines, indicating that TINF2 is haploinsufficient for telomere length control. In contrast, telomere protection and genome stability were maintained in all heterozygous clones. The data establish that the TINF2 truncations predispose to a tumor syndrome. We conclude that TINF2 acts as a haploinsufficient tumor suppressor that limits telomere length to ensure a timely Hayflick limit.

Revesz syndrome revisited

Background

Revesz syndrome (RS) is an extremely rare variant of dyskeratosis congenita (DKC) with only anecdotal reports in the literature.

Methods

To further characterize the typical features and natural course of the disease, we screened the English literature and summarized the clinical and epidemiological features of previously published RS cases. In addition, we herein describe the first recorded patient in central Europe.

Results

The literature review included 18 children. Clinical features are summarized, indicating a low prevalence of the classical DKC triad. All patients experienced early bone marrow failure, in most cases within the second year of life (median age 1.5 years; 95% CI 1.4–1.6). Retinopathy occurred typically between 6 and 18 months of age (median age 1.1 years; 95% CI 0.7–1.5). The incidence of seizures was low and was present in an estimated 20% of patients. The onset of seizures was exclusively during early childhood. The Kaplan–Meier estimate of survival was dismal (median survival 6.5 years; 95% CI 3.6–9.4), and none of the patients survived beyond the age of 12 years. Stem cell transplantation (SCT) was performed in eight children, and after a median of 22 months from SCT four of these patients were alive at the last follow up visit.

Conclusion

RS is a severe variant of DKC with early bone marrow failure and retinopathy in all patients. Survival is dismal, but stem cell transplantation may be performed successfully and might improve prognosis in the future.

Dyskeratosis congenita: a literature review

Dyskeratosis congenita is a rare hereditary disease that occurs predominantly in males and manifests clinically as the classic triad of reticulate hyperpigmentation, nail dystrophy and leukoplakia. It increases the risk of malignancy and other potentially lethal complications such as bone marrow failure, lung and liver diseases. Mutations in 19 genes are associated with dyskeratosis congenita, and a fifth of the pathogenic mutations are found in DKC1, the gene coding for dyskerin. This review aims to address the clinical and genetic aspects of the disease.

Regulation of human telomerase in homeostasis and disease

Telomerase is a ribonucleoprotein complex, the catalytic core of which includes the telomerase reverse transcriptase (TERT) and the non-coding human telomerase RNA (hTR), which serves as a template for the addition of telomeric repeats to chromosome ends. Telomerase expression is restricted in humans to certain cell types, and telomerase levels are tightly controlled in normal conditions. Increased levels of telomerase are found in the vast majority of human cancers, and we have recently begun to understand the mechanisms by which cancer cells increase telomerase activity. Conversely, germline mutations in telomerase-relevant genes that decrease telomerase function cause a range of genetic disorders, including dyskeratosis congenita, idiopathic pulmonary fibrosis and bone marrow failure. In this Review, we discuss the transcriptional regulation of human TERT, hTR processing, assembly of the telomerase complex, the cellular localization of telomerase and its recruitment to telomeres, and the regulation of telomerase activity. We also discuss the disease relevance of each of these steps of telomerase biogenesis.

TERT and TERC mutations detected in cryptic dyskeratosis congenita suppress telomerase activity

INTRODUCTION

A cryptic form of dyskeratosis congenita (cDKC) has a gradual onset without the characteristic physical findings of DKC. cDKC is distinguished from other forms of bone marrow failure (BMF) through analysis of telomere shortening and gene mutations. Mutations in the telomerase reverse transcriptase (TERT) and telomere RNA component (TERC) genes have been detected in most Japanese cDKC patients. Therefore, we investigated the impact of each TERT and TERC mutation on telomerase activity.

METHODS

TERT and TERC mutants observed in DKC or cDKC patients were transfected into Saos-2 or VA13+TERT (TERT-expressing VA13 cells) cells to measure telomerase activity.

RESULTS

Telomerase activity in cells expressing a mutant detected in cDKC patients was significantly lower (P < .0001) than in cells expressing the wild-type genes. In addition, some TERT mutations seen in cDKC (p.P632R, p.T726M) caused weaker (P = .0013) suppression of telomerase activity than others (p.G106W and p.G682D). In contrast, telomerase activity in cells expressing a TERT or TERC mutant detected in DKC patients did not significantly differ from cells expressing the wild-type genes.

CONCLUSION

These findings suggest that TERT and TERC mutations detected in cDKC patients could potentially contribute to the pathogenesis of cDKC by blocking telomerase activity. However, TERT and TERC mutations detected in DKC patients did not affect telomerase activities, which means studying the telomerase activity of mutants are not always useful for the diagnosis of DKC.