Intensive immunosuppression therapy for aplastic anemia associated with dyskeratosis congenita

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.

Telomere biology: from disorders to hematological diseases

Variations in the length of telomeres and pathogenic variants involved in telomere length maintenance have been correlated with several human diseases. Recent breakthroughs in telomere biology knowledge have contributed to the identification of illnesses named "telomeropathies" and revealed an association between telomere length and disease outcome. This review emphasizes the biology and physiology aspects of telomeres and describes prototype diseases in which telomeres are implicated in their pathophysiology. We also provide information on the role of telomeres in hematological diseases ranging from bone marrow failure syndromes to acute and chronic leukemias.

Telomere biology disorders: time for moving towards the clinic?

Telomere biology disorders (TBDs) are a group of rare diseases caused by mutations that impair telomere maintenance. Mutations that cause reduced levels of TERC/hTR, the telomerase RNA component, are found in most TBD patients and include loss-of-function mutations in hTR itself, in hTR-binding proteins [NOP10, NHP2, NAF1, ZCCHC8, and dyskerin (DKC1)], and in proteins required for hTR processing (PARN). These patients show diverse clinical presentations that most commonly include bone marrow failure (BMF)/aplastic anemia (AA), pulmonary fibrosis, and liver cirrhosis. There are no curative therapies for TBD patients. An understanding of hTR biogenesis, maturation, and degradation has identified pathways and pharmacological agents targeting the poly(A) polymerase PAPD5, which adds 3'-oligoadenosine tails to hTR to promote hTR degradation, and TGS1, which modifies the 5'-cap structure of hTR to enhance degradation, as possible therapeutic approaches. Critical next steps will be clinical trials to establish the effectiveness and potential side effects of these compounds in TBD patients.

Treatment of telomeropathies

Telomeropathies or telomere biology disorders (TBDs) are a group of rare diseases characterised by altered telomere maintenance. Most patients with TBDs show pathogenic variants of genes that encode factors involved in the prevention of telomere shortening. Particularly in adults, TBDs mostly present themselves with heterogeneous clinical features that often include bone marrow failure, hepatopathies, interstitial lung disease and other organ sites. Different degrees of severity are also observed among patients with TBDs, ranging from very severe syndromes manifesting themselves in early childhood, such as Revesz syndrome, Hoyeraal-Hreidarsson syndrome, and Coats plus disease, to dyskeratosis congenita (DKC) and adult-onset "cryptic" forms of TBD, which often affect fewer organ systems. Overall, the most relevant clinical complications of TBD are bone marrow failure, lung fibrosis, and liver cirrhosis. In this review, we summarise recent advances in the management and treatment of TBD and provide a brief overview of the various treatment approaches.

A case report of familial dyskeratosis congenital. Case report

Dyskeratosis congenita (DC) is a hereditary syndrome of bone marrow failure, which develops because of telomeres defects and combines with cancer predisposition. Its classical clinical features are skin pigmentation, nail dystrophy, oral leukoplakia (skin-mucosa triad). The goal is to describe the algorithm of diagnosis, clinical specificities of DC and specific treatment for cases of DC in one family. The present report includes descriptions of diagnosis and treatment of family members diagnosed for the first time as having a DC. The report shows an importance of all diagnostic stages: from a medical history and clinical picture to an application of modern high-tech diagnostic methods (flow-FISH, NGS). The report underlines an importance of diagnosis of all family members for excluding an asymptomatic form after a case of DC has been already detected in that family. A high frequency of a toxicity and secondary neoplasia makes it necessary to realize an individual approach at treatment of each patient with DC (the earliest start of androgen treatment, prompt decision of implementation of allogenic hematopoietic stem cell transplantation). The knowledge of pathogenesis, clinical features and principles of diagnosis and therapy of this disease is relevant to pediatricians and hematologists.

An update on the biology and management of dyskeratosis congenita and related telomere biology disorders

Introduction: Telomere biology disorders (TBDs) encompass a group of illnesses caused by germline mutations in genes regulating telomere maintenance, resulting in very short telomeres. Possible TBD manifestations range from complex multisystem disorders with onset in childhood such as dyskeratosis congenita (DC), Hoyeraal-Hreidarsson syndrome, Revesz syndrome and Coats plus to adults presenting with one or two DC-related features.Areas covered: The discovery of multiple genetic causes and inheritance patterns has led to the recognition of a spectrum of clinical features affecting multiple organ systems. Patients with DC and associated TBDs are at high risk of bone marrow failure, cancer, liver and pulmonary disease. Recently, vascular diseases, including pulmonary arteriovenous malformations and gastrointestinal telangiectasias, have been recognized as additional manifestations. Diagnostics include detection of very short leukocyte telomeres and germline genetic testing. Hematopoietic cell transplantation and lung transplantation are the only current therapeutic modalities but are complicated by numerous comorbidities. This review summarizes the pathophysiology underlying TBDs, associated clinical features, management recommendations and therapeutic options.Expert opinion: Understanding TBDs as complex, multisystem disorders with a heterogenous genetic background and diverse phenotypes, highlights the importance of clinical surveillance and the urgent need to develop new therapeutic strategies to improve health outcomes.

Evaluation and Management of Hematopoietic Failure in Dyskeratosis Congenita

Dyskeratosis congenita (DC) is a rare, inherited bone marrow failure (BMF) syndrome characterized by variable manifestations and ages of onset, and predisposition to cancer. DC is one of a spectrum of diseases caused by mutations in genes regulating telomere maintenance, collectively referred to as telomere biology disorders (TBDs). Hematologic disease is common in children with DC/TBD. Timely diagnosis of underlying TBD in patients with BMF affects treatment and has been facilitated by increased awareness and availability of diagnostic tests in recent years. This article summarizes the pathophysiology, evaluation, and management of hematopoietic failure in patients with DC and other TBDs.

How I diagnose and manage individuals at risk for inherited myeloid malignancies

Although inherited hematopoietic malignancies have been reported clinically since the early twentieth century, the molecular basis for these diseases has only recently begun to be elucidated. Growing utilization of next-generation sequencing technologies has facilitated the rapid discovery of an increasing number of recognizable heritable hematopoietic malignancy syndromes while also deepening the field's understanding of the molecular mechanisms that underlie these syndromes. Because individuals with inherited hematopoietic malignancies continue to be underdiagnosed and are increasingly likely to be encountered in clinical practice, clinicians need to have a high index of suspicion and be aware of the described syndromes. Here, we present the methods we use to identify, test, and manage individuals and families suspected of having a hereditary myeloid malignancy syndrome. Finally, we address the areas of ongoing research in the field and encourage clinicians and researchers to contribute and collaborate.

Response to androgen therapy in patients with dyskeratosis congenita

Dyskeratosis congenita (DC) is an inherited bone marrow failure syndrome and telomere biology disorder characterized by dysplastic nails, reticular skin pigmentation and oral leucoplakia. Androgens are a standard therapeutic option for bone marrow failure in those patients with DC who are unable to undergo haematopoietic stem cell transplantation, but there are no systematic data on its use in those patients. We evaluated haematological response and side effects of androgen therapy in 16 patients with DC in our observational cohort study. Untreated DC patients served as controls. Seventy percent of treated DC patients had a haematological response with red blood cell and/or platelet transfusion independence. The expected age-related decline in telomere length was noted in androgen-treated patients. All treated DC patients had at least one significant lipid abnormality. Additional treatment-related findings included a significant decrease in thyroid binding globulin, accelerated growth in pre-pubertal children and splenic peliosis in two patients. Liver enzymes were elevated in both androgen-treated and untreated patients, suggesting underlying liver involvement in DC. This study suggests that androgen therapy can be effectively used to treat bone marrow failure in DC, but that side effects need to be closely monitored.

Human telomeres and telomere biology disorders

Telomeres consist of long nucleotide repeats and a protein complex at chromosome ends essential for chromosome stability. Telomeres shorten with each cell division and thus are markers of cellular age. Dyskeratosis congenita (DC) is a cancer-prone inherited bone marrow failure syndrome caused by germ-line mutations in key telomere biology genes that result in extremely short telomeres. The triad of nail dysplasia, abnormal skin pigmentation, and oral leukoplakia is diagnostic of DC but highly variable. Patients with DC may also have but numerous other medical problems, including pulmonary fibrosis, liver abnormalities, avascular necrosis of the hips, and stenosis of the esophagus, lacrimal ducts, and/or urethra. All modes of inheritance have been reported in DC and de novo mutations are common. Broad phenotypic heterogeneity occurs within DC. Clinically severe variants of DC are Hoyeraal-Hreidarsson syndrome and Revesz syndrome. Coats plus syndrome joined the spectrum of DC with the discovery that it is caused by mutations in a telomere-capping gene. Less clinically severe variants, such as subsets of apparently isolated aplastic anemia or pulmonary fibrosis, have also been recognized. These patients may not have the DC-associated mucocutaneous triad or complicated medical features, but they do have the same underlying genetic etiology. This has led to the use of the descriptive term telomere biology disorder (TBD). This chapter will review the connection between telomere biology and human disease through the examples of DC and its related TBDs.

Updates on the biology and management of dyskeratosis congenita and related telomere biology disorders

Dyskeratosis congenita (DC) is a cancer-prone inherited bone marrow failure syndrome caused by aberrant telomere biology. The mucocutaneous triad of nail dysplasia, abnormal skin pigmentation and oral leukoplakia is diagnostic, but is not always present; DC can also be diagnosed by the presence of very short leukocyte telomeres. Patients with DC are at high risk of bone marrow failure, pulmonary fibrosis, liver disease, cancer and other medical problems. Germline mutations in one of nine genes associated with telomere maintenance are present in approximately 60% of patients. DC is one among the group of clinically and biologically related telomere biology disorders, including Hoyeraal-Hreidarsson syndrome, Revesz syndrome, Coats plus (also known as cranioretinal microangiopathy with calcifications and cysts) and subsets of aplastic anemia, pulmonary fibrosis, nonalcoholic and noninfectious liver disease and leukemia. The authors review the pathobiology that connects DC and the related telomere biology disorders, methods of diagnosis and management modalities.

Cytokine production by bone marrow mononuclear cells in inherited bone marrow failure syndromes

Fanconi anaemia (FA), dyskeratosis congenita (DC), Diamond-Blackfan anaemia (DBA), and Shwachman-Diamond syndrome (SDS) are characterized by the progressive development of bone marrow failure. Overproduction of tumour necrosis factor-α (TNF-α) from activated bone marrow T-cells has been proposed as a mechanism of FA-related aplasia. Whether such overproduction occurs in the other syndromes is unknown. We conducted a comparative study on bone marrow mononuclear cells to examine the cellular subset composition and cytokine production. We found lower proportions of haematopoietic stem cells in FA, DC, and SDS, and a lower proportion of monocytes in FA, DC, and DBA compared with controls. The T- and B-lymphocyte proportions were similar to controls, except for low B-cells in DC. We did not observe overproduction of TNF-α or IFN-γ by T-cells in any patients. Induction levels of TNF-α, interleukin (IL)-6, IL-1β, IL-10, granulocyte colony-stimulating factor, and granulocyte-macrophage colony-stimulating factor in monocytes stimulated with high-dose lipopolysaccharide (LPS) were similar at 4 h but lower at 24 h when compared to controls. Unexpectedly, patient samples showed a trend toward higher cytokine level in response to low-dose (0·001 μg/ml) LPS. Increased sensitivity to LPS may have clinical implications and could contribute to the development of pancytopenia by creating a chronic subclinical inflammatory micro-environment in the bone marrow.

Outcomes of allogeneic hematopoietic cell transplantation in patients with dyskeratosis congenita

We describe outcomes after allogeneic transplantation in 34 patients with dyskeratosis congenita who underwent transplantation between 1981 and 2009. The median age at transplantation was 13 years (range, 2 to 35). Approximately 50% of transplantations were from related donors. Bone marrow was the predominant source of stem cells (24 of 34). The day-28 probability of neutrophil recovery was 73% and the day-100 platelet recovery was 72%. The day-100 probability of grade II to IV acute GVHD and the 3-year probability of chronic graft-versus-host disease were 24% and 37%, respectively. The 10-year probability of survival was 30%; 14 patients were alive at last follow-up. Ten deaths occurred within 4 months from transplantation because of graft failure (n = 6) or other transplantation-related complications; 9 of these patients had undergone transplantation from mismatched related or from unrelated donors. Another 10 deaths occurred after 4 months; 6 of them occurred more than 5 years after transplantation, and 4 of these were attributed to pulmonary failure. Transplantation regimen intensity and transplantations from mismatched related or unrelated donors were associated with early mortality. Transplantation of grafts from HLA-matched siblings with cyclophosphamide-containing nonradiation regimens was associated with early low toxicity. Late mortality was attributed mainly to pulmonary complications and likely related to the underlying disease.

Telomere biology in hematopoiesis and stem cell transplantation

Telomeres are long (TTAGGG)(n) nucleotide repeats and an associated protein complex located at the end of the chromosomes. They shorten with every cell division and, thus are markers for cellular aging, senescence, and replicative capacity. Telomere dysfunction is linked to several bone marrow disorders, including dyskeratosis congenita, aplastic anemia, myelodysplastic syndrome, and hematopoietic malignancies. Hematopoietic stem cell transplantation (HSCT) provides an opportunity in which to study telomere dynamics in a high cell proliferative environment. Rapid telomere shortening of donor cells occurs in the recipient shortly after HSCT; the degree of telomere attrition does not appear to differ by graft source. As expected, telomeres are longer in recipients of grafts with longer telomeres (e.g., cord blood). Telomere attrition may play a role in, or be a marker of, long term outcome after HSCT, but these data are limited. In this review, we discuss telomere biology in normal and abnormal hematopoiesis, including HSCT.

The genetics and clinical manifestations of telomere biology disorders

Telomere biology disorders are a complex set of illnesses defined by the presence of very short telomeres. Individuals with classic dyskeratosis congenita have the most severe phenotype, characterized by the triad of nail dystrophy, abnormal skin pigmentation, and oral leukoplakia. More significantly, these individuals are at very high risk of bone marrow failure, cancer, and pulmonary fibrosis. A mutation in one of six different telomere biology genes can be identified in 50–60% of these individuals. DKC1, TERC, TERT, NOP10, and NHP2 encode components of telomerase or a telomerase-associated factor and TINF2, a telomeric protein. Progressively shorter telomeres are inherited from generation to generation in autosomal dominant dyskeratosis congenita, resulting in disease anticipation. Up to 10% of individuals with apparently acquired aplastic anemia or idiopathic pulmonary fibrosis also have short telomeres and mutations in TERC or TERT. Similar findings have been seen in individuals with liver fibrosis or acute myelogenous leukemia. This report reviews basic aspects of telomere biology and telomere length measurement, and the clinical and genetic features of those disorders that constitute our current understanding of the spectrum of illness caused by defects in telomere biology. We also suggest a grouping schema for the telomere disorders.

Dyskeratosis congenita

Dyskeratosis congenita (DC) is an inheritable bone marrow failure syndrome characterized by reticulated hyperpigmentation, dystrophic nails and oral leukoplakia. Another name for the condition is Zinsser-Cole-Engman syndrome. Hematologic manifestations usually do not appear in childhood but later in early adulthood. Patients are also prone to carcinomas, particularly of the head and neck. The disease has X-linked or autosomal dominant/recessive inheritance. Early childhood variants (Hoyeraal-Hreidarsson syndrome) are associated with immunological abnormalities in the form of low T- and B-cell numbers. Four genes, namely DKC1 (codes for dyskerin), TERC and TERT (code for telomerase) and NOP10, have been implicated in the pathogenesis; the short telomeres provide a marker for genetic linkage studies. Androgens, with or without granulocyte colony stimulating factor, have been tried in the treatment of the conditions with variable results. Stem cell transplantation from matched sibling donor is currently the treatment of choice. It requires modified nonmyeloablative conditioning protocols, since the patients with DC are prone to pulmonary and hepatic complications.

Pathophysiology and management of inherited bone marrow failure syndromes

The inherited marrow failure syndromes are a diverse set of genetic disorders characterized by hematopoietic aplasia and cancer predisposition. The clinical phenotypes are highly variable and much broader than previously recognized. The medical management of the inherited marrow failure syndromes differs from that of acquired aplastic anemia or malignancies arising in the general population. Diagnostic workup, molecular pathogenesis, and clinical treatment are reviewed.

Dyskeratosis congenita: the first NIH clinical research workshop

Dyskeratosis congenita (DC) is a heterogeneous inherited bone marrow failure syndrome, characterized by abnormally short telomeres and mutations in telomere biology genes. The spectrum of telomere biology disorders is growing and the clinical management of these patients is complex. A DC-specific workshop was held at the NIH on September 19, 2008; participants included physicians, patients with DC, their family members, and representatives from other support groups. Data from the UK's DC Registry and the NCI's DC cohort were described. Updates on the function of the known DC genes were presented. Clinical aspects discussed included androgen therapy, stem cell transplant, cancer risk, and cancer screening. Families with DC met for the first time and formed a family support group (http://www.dcoutreach.com/). Ongoing, open collaboration between the clinical, scientific, and family communities is required for continued improvement in our understanding of DC and the clinical consequences of telomeric defects.

Dyskeratosis congenita

Dyskeratosis congenita (DC) is an inherited bone marrow failure syndrome characterized clinically by the triad of abnormal nails, reticular skin pigmentation, and oral leukoplakia, and is associated with high risk of developing aplastic anemia, myelodysplastic syndrome, leukemia, and solid tumors. Patients have very short germline telomeres, and approximately half have mutations in one of six genes encoding proteins that maintain telomere function. Accurate diagnosis of DC is critical to ensure proper clinical management, because patients who have DC and bone marrow failure do not respond to immunosuppressive therapy and may have increased morbidity and mortality associated with hematopoietic stem cell transplantation.

TINF2, a component of the shelterin telomere protection complex, is mutated in dyskeratosis congenita

Patients with dyskeratosis congenita (DC), a heterogeneous inherited bone marrow failure syndrome, have abnormalities in telomere biology, including very short telomeres and germline mutations in DKC1, TERC, TERT, or NOP10, but approximately 60% of DC patients lack an identifiable mutation. With the very short telomere phenotype and a highly penetrant, rare disease model, a linkage scan was performed on a family with autosomal-dominant DC and no mutations in DKCI, TERC, or TERT. Evidence favoring linkage was found at 2p24 and 14q11.2, and this led to the identification of TINF2 (14q11.2) mutations, K280E, in the proband and her five affected relatives and TINF2 R282H in three additional unrelated DC probands, including one with Revesz syndrome; a fifth DC proband had a R282S mutation. TINF2 mutations were not present in unaffected relatives, DC probands with mutations in DKC1, TERC, or TERT or 298 control subjects. We demonstrate that a fifth gene, TINF2, is mutated in classical DC and, for the first time, in Revesz syndrome. This represents the first shelterin complex mutation linked to human disease and confirms the role of very short telomeres as a diagnostic test for DC.

Telomere maintenance and human bone marrow failure

Acquired and congenital aplastic anemias recently have been linked molecularly and pathophysiologically by abnormal telomere maintenance. Telomeres are repeated nucleotide sequences that cap the ends of chromosomes and protect them from damage. Telomeres are eroded with cell division, but in hematopoietic stem cells, maintenance of their length is mediated by telomerase. Accelerated telomere shortening is virtually universal in dyskeratosis congenita, caused by mutations in genes encoding components of telomerase or telomere-binding protein (TERT, TERC, DKC1, NOP10, or TINF2). About one-third of patients with acquired aplastic anemia also have short telomeres, which in some cases associate with TERT or TERC mutations. These mutations cause low telomerase activity, accelerated telomere shortening, and diminished proliferative capacity of hematopoietic progenitors. As in other genetic diseases, additional environmental, genetic, and epigenetic modifiers must contribute to telomere erosion and ultimately to disease phenotype. Short telomeres also may cause genomic instability and malignant progression in these marrow failure syndromes. Identification of short telomeres has potential clinical implications: it may be useful in dyskeratosis congenita diagnosis, in suggesting mutations in patients with acquired aplastic anemia, and for selection of suitable hematopoietic stem cell family donors for transplantation in telomerase-deficient patients.

The role of telomere biology in bone marrow failure and other disorders

Telomeres, consisting of nucleotide repeats and a protein complex at chromosome ends, are essential in maintaining chromosomal integrity. Dyskeratosis congenita (DC) is the inherited bone marrow failure syndrome (IBMFS) that epitomizes the effects of abnormal telomere biology. Patients with DC have extremely short telomere lengths (<1st percentile) and many have mutations in telomere biology genes. Interpretation of telomere length in other IBMFSs is less straightforward. Abnormal telomere shortening has been reported in patients with apparently acquired hematologic disorders, including aplastic anemia, myeolodysplasia, paroxysmal nocturnal hemoglobinuria, and leukemia. In these disorders, the shortest-lived cells have the shortest telomeres, suggestive of increased hematopoietic stress. Telomeres are also markers of replicative and/or oxidative stress in other complex disease pathways, such as inflammation, stress, and carcinogenesis. The spectrum of related disorders caused by mutations in telomere biology genes extends beyond classical DC to include marrow failure that does not respond to immunosuppression, idiopathic pulmonary fibrosis, and possibly other syndromes. We suggest that such patients be categorized as having an inherited disorder of telomere biology. Longitudinal studies of patients with very short telomeres but without classical DC are necessary to further understand the long-term sequelae, such as malignancy, osteonecrosis/osteoporosis, and pulmonary and liver disease.

Very short telomere length by flow fluorescence in situ hybridization identifies patients with dyskeratosis congenita

Dyskeratosis congenita (DC) is an inherited bone marrow failure syndrome in which the known susceptibility genes (DKC1, TERC, and TERT) belong to the telomere maintenance pathway; patients with DC have very short telomeres. We used multicolor flow fluorescence in situ hybridization analysis of median telomere length in total blood leukocytes, granulocytes, lymphocytes, and several lymphocyte subsets to confirm the diagnosis of DC, distinguish patients with DC from unaffected family members, identify clinically silent DC carriers, and discriminate between patients with DC and those with other bone marrow failure disorders. We defined "very short" telomeres as below the first percentile measured among 400 healthy control subjects over the entire age range. Diagnostic sensitivity and specificity of very short telomeres for DC were more than 90% for total lymphocytes, CD45RA+/CD20- naive T cells, and CD20+ B cells. Granulocyte and total leukocyte assays were not specific; CD45RA- memory T cells and CD57+ NK/NKT were not sensitive. We observed very short telomeres in a clinically normal family member who subsequently developed DC. We propose adding leukocyte subset flow fluorescence in situ hybridization telomere length measurement to the evaluation of patients and families suspected to have DC, because the correct diagnosis will substantially affect patient management.

Diagnosis, genetics, and management of inherited bone marrow failure syndromes

The inherited bone marrow failure syndromes are traditionally considered to be pediatric disorders, but in fact, many of the patients now are diagnosed as adults, and many diagnosed as children now live to reach adulthood. The most common of these rare disorders include Fanconi anemia, dyskeratosis congenita, Shwachman-Diamond syndrome and amegakaryocytic thrombocytopenia, which often develop aplastic anemia and may evolve into myelodysplastic syndrome and acute myeloid leukemia; and Diamond-Blackfan anemia, severe congenital neutropenia, and thrombocytopenia absent radii, single cytopenias that rarely if ever become aplastic but have increased risks of leukemia. In addition, the first three syndromes have high risks of solid tumors: head and neck and anogenital squamous cell carcinoma in Fanconi anemia and dyskeratosis congenita, and osteogenic sarcoma in Diamond-Blackfan anemia. Diagnosis of a marrow failure syndrome requires recognition of characteristic physical abnormalities when present, and consideration of these disorders in the differential diagnosis of patients who present with "acquired" aplastic anemia, myelodysplastic syndrome, acute myeloid leukemia, or atypically early cancers of the types seen in the syndromes. Ultimate proof will come from identification of pathogenic mutations in genes associated with each syndrome.