Autosomal Dominant Dyskeratosis Congenita Research Articles

HuR regulates telomerase activity through TERC methylation

Telomerase consists of the catalytic protein TERT and the RNA TERC. Mutations in TERC are linked to human diseases, but the underlying mechanisms are poorly understood. Here we report that the RNA-binding protein HuR associates with TERC and promotes the assembly of the TERC/TERT complex by facilitating TERC C106 methylation. Dyskeratosis congenita (DC)-related TERC U100A mutation impair the association of HuR with TERC, thereby reducing C106 methylation. Two other TERC mutations linked to aplastic anemia and autosomal dominant DC, G107U, and GC107/108AG, likewise disrupt methylation at C106. Loss-of-HuR binding and hence lower TERC methylation leads to decreased telomerase activity and telomere shortening. Furthermore, HuR deficiency or mutation of mTERC HuR binding or methylation sites impair the renewal of mouse hematopoietic stem cells, recapitulating the bone marrow failure seen in DC. Collectively, our findings reveal a novel function of HuR, linking HuR to telomerase function and TERC-associated DC.

Bilateral Retinal Vasculopathy Associated with Autosomal Dominant Dyskeratosis Congenita

To report a case of autosomal dominant dyskeratosis congenita (AD-DC) complicated by bilateral retinal vasculopathy and proliferative retinopathy with vitreous hemorrhage in the right eye, in the absence of pancytopenia. We report a 32-year-old woman who presented with floaters in her right eye. She underwent complete ophthalmic examination and fundus fluorescein angiography. Funduscopic examination revealed vascular sheathing in the temporal periphery of both eyes and a vitreous hemorrhage in the right eye. Fluorescein angiography showed retinal neovascularization in the right eye and bilateral temporal peripheral capillary nonperfusion. Treatment consisted of laser photocoagulation directed to the areas of capillary nonperfusion in both eyes. A point mutation in the TERC gene confirmed the diagnosis of AD-DC. Autosomal dominant dyskeratosis congenita is a rare form of inherited bone marrow failure and its presentation is milder than seen in patients with X-linked and autosomal recessive mutations. These patients may lack the classic clinical triad, so it is important to have a high index of suspicion and to be aware of retinal vasculopathy as a complication of dyskeratosis congenita as it may severely compromise vision. Appropriate treatment includes prompt laser photocoagulation to areas of retinal nonperfusion.

Non-telomeric epigenetic and genetic changes are associated with the inheritance of shorter telomeres in mice

Studies using human and mouse cells have revealed some changes to non-telomeric chromatin and gene expression in response to abnormally short telomeres. To investigate this further, we studied the effect of inheriting shorter telomeres on transcription and genetic stability at non-telomeric sites in the mouse. Using multiple generations of Terc knockout mice, we show that inheriting shorter telomeres from one parent increases the likelihood of transcriptional silencing at a non-telomeric green fluorescent protein (GFP) transgene inherited from the other parent. In these cases, silencing must occur at or after zygote formation. In grand-offspring from a G3 Terc (-/-) parent, transgene expression was further reduced and associated with increased DNA methylation and, surprisingly, reduced copy number at the transgene array. In these cases, the transgene had been passed through the germline of a Terc-compromised parent, providing an opportunity for meiotic events. Furthermore, genome-wide microarray analysis of copy number variations revealed greater genetic instability in G3 Terc (-/-) mice than detected in wild-type mice of the same genetic background. Our results have implications for the molecular mechanisms underlying premature-ageing syndromes, such as dyskeratosis congenita. In autosomal-dominant dyskeratosis congenita, progressive telomere shortening is seen as it passes down the generations, and this is associated with anticipation, i.e. the disease becomes more severe earlier. The underlying mechanism is not known, but has been considered to be simply associated with decreases in telomere length. Epigenetic and/or genetic changes at non-telomeric regions could, in theory, be involved.

High resolution melting analysis for the identification of novel mutations in DKC1 and TERT genes in patients with dyskeratosis congenita

Dyskeratosis congenita (DC) is a rare inherited bone-marrow failure syndrome with high clinical heterogeneity. Cells derived from DC patients present short telomeres at early ages, as a result of mutations in genes encoding components of the telomerase complex (DKC1, TERC, TERT, NHP2 and NOP10), or the shelterin complex (TINF2). However, mutations have been identified only in around 50% of the cases, indicating that other genes could be involved in the development of this disease. Indeed, mutations in TCBA1 or chromosome segment C16orf57 have been described recently. We have used HRM technology to perform genetic analysis in the above mentioned genes, in Spanish patients showing both, some clinical features of DC and short telomeres. The mutations have been identified by PCR amplification of DC genes followed by high resolution melting (HRM) and direct DNA sequencing analysis. We have identified seven new families with DC, three with X-linked DC and four with autosomal dominant DC, in which we have found two novel mutations in DKC1 (p.His68Arg and p.Lys390del) and four novel mutations in TERT gene (p.Pro530Leu, p.Arg698Trp, p.Arg971His and p.Arg698Gln). The results show that the use of HRM analysis enables a rapid and inexpensive identification of mutations in dyskeratosis congenita associated genes.

389 Transition of murine leukemic cells to epithelial-like cells under different growth conditions

Dyskeratosis congenita (DC) is a rare bone marrow failure syndrome that displays marked clinical and genetic heterogeneity. The identification of dyskeratosis congenita gene 1 (DKC1) mutations in X-linked recessive patients initially suggested that DC is a defective pseudouridylation disorder. The subsequent identification of mutations in the telomerase RNA component (TERC) of autosomal dominant DC patients together with the discovery that both TERC and the DKC1-encoded protein, dyskerin, are closely associated in the telomerase complex have suggested that the pathophysiology of DC predominantly relates to defective telomere maintenance. Recent discoveries have shown that autosomal dominant DC exhibits disease anticipation and that this is associated with progressive telomere shortening owing to the haplo-insufficiency of TERC.

Telomere elongation in induced pluripotent stem cells from dyskeratosis congenita patients

Patients with dyskeratosis congenita (DC), a disorder of telomere maintenance, suffer degeneration of multiple tissues1–3. Patient-specific induced pluripotent stem (iPS) cells4 represent invaluable in vitro models for human degenerative disorders like DC. A cardinal feature of iPS cells is acquisition of indefinite self-renewal capacity, which is accompanied by induction of telomerase reverse transcriptase (TERT)5–7. We investigated whether defects in telomerase function would limit derivation and maintenance of iPS cells from patients with DC. Here we show that reprogrammed DC cells overcome a critical limitation in telomerase RNA component (TERC) levels to restore telomere maintenance and self-renewal. We discovered that TERC upregulation is a feature of the pluripotent state, that multiple telomerase components are targeted by pluripotency-associated transcription factors, and that in autosomal dominant DC, transcriptional silencing accompanies a 3' deletion at the TERC locus. Our results demonstrate that reprogramming restores telomere elongation in DC cells despite genetic lesions affecting telomerase, and suggest that strategies to increase TERC expression may be therapeutically beneficial in DC patients.

Telomere Elongation in Dyskeratosis Congenita Induced Pluripotent Stem Cells.

Abstract 497Patients with dyskeratosis congenita (DC), a disorder of telomere maintenance, suffer premature degeneration of multiple tissues. Bone marrow failure is the principal cause of mortality, and allogeneic stem cell transplantation is limited by increased treatment-related mortality. Somatic cells can be reprogrammed using defined genetic and chemical factors, yielding “induced pluripotent stem” (iPS) cell lines which have the capacity to differentiate into any tissue. Patient-specific iPS cells therefore hold promise as therapeutic agents and disease models for human degenerative disorders like DC. A cardinal feature of iPS cells is acquisition of indefinite self-renewal capacity, and we have found that telomere length is increased in human iPS cells relative to the normal primary somatic cells from which they are derived. Here we investigated whether defects in telomerase function would limit derivation or self-renewal of iPS cells from patients with DC. We reprogrammed primary fibroblasts from patients with X-linked and autosomal dominant DC, caused by mutations in the genes encoding dyskerin and telomerase RNA component (TERC), respectively. We were able to establish multiple DC-specific iPS lines showing all hallmarks of pluripotency, including the formation of hematopoietic progenitors in vitro. Unexpectedly, DC-specific iPS cells were able to sustain continual proliferation in vitro, in contrast to the premature senescence displayed by the DC fibroblasts. Although early passage DC iPS cells had shorter telomeres than donor fibroblasts, we found that telomere length in DC iPS cells increased with continued passage in culture. To explain this finding, we discovered that steady state levels of TERC, which are critically limiting in several forms of DC, are upregulated in normal and DC iPS cells. We found that TERC upregulation is a feature of the pluripotent state, that the TERC locus is a target of pluripotency-associated transcription factors, and that transcriptional silencing accompanies a 3' deletion at the TERC locus in autosomal dominant DC. Our results demonstrate that reprogramming restores self-renewal capacity in DC cells despite genetic lesions affecting telomerase, and suggest that strategies to enhance endogenous TERC expression may be feasible and therapeutically beneficial in DC patients. The studies demonstrate the value of patient-specific iPS cells for basic and translational discovery, and further the rationale for autologous iPS based cellular therapy of genetic hematologic disorders. Disclosures:Daley:MPM Capital: Consultancy; Solasia: Consultancy; Epizyme: Consultancy; iPierian: Consultancy, Equity Ownership.

Telomere Dysfunction in Bone Marrow Failure.

Abstract SCI-12In order to distinguish a normal telomere from a double strand break, a minimum number of telomere repeats must “cap” each chromosome end. The length of each repeat array will reflect a unique history of addition and losses. Telomere losses are known to occur sporadic as well as with every replication cycle. Losses of telomeric DNA are countered by the telomerase enzyme containing telomerase RNA (encoded by the TERC gene) and a reverse transcriptase protein (encoded by TERT gene) as minimal components. Telomerase levels are high in cells of the germline and immortal cellines and the telomere length is typically maintained in such cells. In contrast, telomerase activity is limiting in most human somatic (stem) cells and as a result the average length of telomere repeats in most somatic cells shows a highly significant decline with age. The hypothesis that loss of telomere repeats acts as a “mitotic clock” and a tumor suppressor mechanism in stem cells is strongly supported by recent studies of patients with mild telomerase deficiency resulting from haplo-insufficiency for either the TERC or TERT gene. Such genetic defects can give rise to various disorders including autosomal dominant Dyskeratosis Congenita (DKC), aplastic anemia, liver fibrosis and pulmonary fibrosis. Other recent studies have revealed that amplification of the hTERT gene is one of the most common genetic abnormalities in various cancers. Paradoxically, it is becoming clear that SNPs within the TERT locus are among the most reproducible risk factors for the development of different types of cancer including lung cancer, acute myeloid leukemia and chronic lymphocytic leukemia. The links between hypo- and hyperproliferative consequences of inborn telomerase deficiencies and SNP's in the TERT gene are poorly understood. It seems plausible that the increased risk of leukemia development in aplastic anemia, myelodysplastic syndrome and Dyskeratosis Congenita, results from stem cell failure. Could reduced stem cell numbers by itself provide a risk factor for tumor development? More direct measures of stem cell numbers in vivo are needed to examine this possibility and the relationship between stem cell numbers and tumor development in patients with defective telomere maintenance as well as in normal individuals as a function of age. Measurements of the average telomere length as well as the length of telomere repeats at individual chromosome ends in specific cells and tissues will further calrify the involvement of telomeres in bone marrow failure, normal aging and tumor biology. DisclosuresLansdorp:Repeat Diagnostics Inc.: Equity Ownership.

Single-molecule analysis of the human telomerase RNA.dyskerin interaction and the effect of dyskeratosis congenita mutations.

It has been proposed that human telomerase RNA (hTR) interacts with dyskerin, prior to assembly of the telomerase holoenzyme. The direct interaction of dyskerin and hTR has not been demonstrated and is an experimentally challenging research problem because of difficulties in expressing and purifying dyskerin in quantities that are useful for biophysical analysis. By orthogonally labeling dyskerin and hTR, we have been able to employ single-molecule two-color coincidence detection (TCCD) to observe directly the formation of a dyskerin·hTR complex. By systematic deletion of hTR subdomains, we have gained insights into the RNA sites required for interaction with dyskerin. We then investigated mutated forms of hTR and dyskerin that are associated with dyskeratosis congenita (DC), on the basis of clinical genetics studies, for their effects on the dyskerin·hTR interaction. Dyskerin mutations associated with X-linked DC resulted in significant impairment of the dyskerin·hTR interaction, whereas mutations in hTR associated with autosomal dominant (AD) DC did not affect the interaction. We propose that disruption of the dyskerin·hTR interaction may contribute to X-linked DC.

Retinal vasculopathy in a family with autosomal dominant dyskeratosis congenita

Background: Dyskeratosis congenita is a rare multisystem bone marrow failure genetic disorder characterized by reticular skin hyperpigmentation, nail dystrophy, and oral leukoplakia. Clinical ophthalmic features in these patients include retinal hemorrhages, retinal vasculopathy, telangiectasia, and macular exudates.Methods: Complete family medical history, clinical examination, complete blood profile, ophthalmologic examination, fundus color photography and fundus fluorescein angiography, and optical coherence tomography.Results: We report a case of a young white adult male with a family history of clinically diagnosed autosomal dominant dyskeratosis congenita, who presented with retinal edema and peripheral retinal ischemia. The sister had milder manifestations and the father had very subtle manifestations.Conclusions: This case is consistent with the previously reported observations of genetic anticipation and variable expressivity in the retinal findings of dyskeratosis congenita.

TINF2 mutations in children with severe aplastic anemia

To the Editor: Dyskeratosis congenita (DC), a bone marrow failure (BMF) syndrome associated with skin abnormalities, dystrophic nails, and leukoplakia, has been linked to mutations in genes that encode components of telomerase (dyskerin, TERC, TERT, NHP2, and NOP10). Recently, one of the components of the shelterin complex, TIN2, which is encoded by the TINF2 gene, was found to be mutated in some patients with autosomal dominant DC and in sporadic cases of DC [1,2]. Autosomal dominant forms of DC caused by mutations in TERT or TERC are often mild; many of these patients present with only BMF and are indistinguishable from individuals with idiopathic severe aplastic anemia (SAA) or myelodysplastic syndrome (MDS). In a recent issue of the journal, Pigullo et al. [3] hypothesized that mutations in NOLA1 (also known as GAR1), which encodes another component of the telomerase complex, might account for some cases of aplastic anemia (AA) in children. Of 108 patients with AA screened, none had a pathogenic mutation [3]. We postulated that TINF2 mutations might underlie some cases of idiopathic AA in childhood. To address this, we analyzed DNA samples from an anonymous registry [4] of pediatric patients who underwent unrelated donor hematopoietic stem cell transplantation (UD-HSCT) for SAA (n = 109) or MDS (n =137). We focused our mutational analysis on exon 6 of the gene, the site of all known TINF2 mutations linked to DC [1,2]. We identified potentially pathogenic mutations in 6 of 109 patients with SAA. A 2-year-old Caucasian male and a 10-year-old Caucasian male were heterozygous for TINF2 G845A (R282H), a mutation previously shown to cause DC with early onset AA [1,2]. A 6-year-old Caucasian female and a 17-year-old Caucasian male were heterozygous for C844T (R282C), another missense mutation linked to DC [2]. A 7-year-old Hispanic boy was heterozygous for a single nucleotide insertion that alters the TIN2 sequence beginning at residue 290 and introduces a stop codon (F290R291N292 → P290L291X). The remaining patient, a 4-year-old Hispanic girl, was heterozygous for the missense mutation T862C (F288L). The phenylalanine residue at position 288 of human TIN2 is conserved in chimpanzee, rat, and dog, whereas mouse and cow have a leucine residue at this position [1]. Therefore, it is unclear whether the F288L substitution is deleterious. No TINF2 mutations were detected in patients with MDS (P <0.01). Previously, 298 healthy control individuals of diverse ethnicities were screened for TINF2 mutations [1]; none had a TIN2 sequence change near amino acid 282 (P <0.001). We conclude that a significant proportion of patients who underwent UD-HSCT for SAA harbored mutations in TINF2 and may have had occult DC. Among pediatric patients with SAA in the registry, TINF2 mutations were more common than TERC mutations (5.5% vs. 0%, P <0.01) [4]. In pedigrees with DC due to mutation of TERC, signs and symptoms of the disease usually present in adulthood. Our findings, coupled with those of other investigators [1,2], suggest that mutation of TINF2 is more likely to manifest during childhood as SAA. In contrast, TERC and TERT gene mutations are associated with MDS and possibly acute myelogenous leukemia later in life.

Transduction of hTR into Hematopoietic Stem Cells Increases Telomerase Activity

Background: Telomerase, an enzyme complex that adds telomere repeats to the ends of linear chromosomal DNA, is an important regulator of cellular senescence and replication. The human telomerase complex is composed of several factors including an RNA component (hTR) that acts as a template, a reverse transcriptase (hTERT), and dyskerin, a stabilizing nuclear protein. Telomerase activity is tightly regulated by hTERT and hTR levels. Several reports have shown that overexpression of hTERT by gene transfer can upregulate telomerase activity in somatic cells, though the effects of hTR gene transfer on telomerase activity in primary cells are unclear. Importantly, mutations in the major components of the telomerase complex cause dyskeratosis congenita (DC), a premature aging syndrome associated with defective hematopoiesis. Of note, our group has recently demonstrated correction of an abnormal phenotype in autosomal dominant (AD) DC fibroblasts by gene transfer of hTR. Additionally, hematopoietic stem cells (HSC) from several AD DC subjects were collected which could be used for future gene therapy studies. In anticipation of these studies, we hypothesized that a lentiviral vector-based gene transfer of hTR into normal hematopoietic stem cells (HSCs) might result in an upregulation of telomerase activity and a corresponding increase in replicative capacity.Methods: CD34 positively selected HSCs isolated from umbilical cord blood were expanded in cytokinesupplemented Stem Span media and counted periodically over a 14-day time course to determine proliferative capacity. Over this time course, cells were assessed for telomerase activity using the TRAP (telomeric repeat amplification protocol) assay. Additionally, cells were plated in a methylcellulose-based media in order to assess colony forming unit (CFU) formation. Transduction of HSCs was accomplished by infecting with a lentiviral (HIV) vector expressing GFP alone or GFP and hTR together. Transduced cells were assessed for GFP expression and then subjected to the same assessments as described above and comparisons were made to non-transduced cells.Results: HSCs cultured in Stem Span showed a 100 fold expansion of total nucleated cells over a 14-day time course. Two days post infection, transduction efficiency of 60% was achieved for CD34+ HSCs transduced with GFP alone, and 10% for hTR/GFP. At nine days post infection there was a similar percentage of GFP-expressing cells, suggesting retention of the construct in differentiated cells. Comparing transduced and non-transduced cells, minimal differences were observed in cell proliferation and colony formation, indicating that conditions used for viral gene transfer did not have a deleterious effect on HSCs. Telomerase activity was markedly increased in hTR-transduced cells at day 2 and 4 post-infection, compared to non-transduced and GFP-transduced cells (18 to 33 fold estimated increase). At later time points post-infection (6 to 10 days), telomerase activity in hTR-transduced cells decreased to levels similar to those of non-transduced cells. Additionally, an accelerated loss of CD34 expression was noted in hTR transduced cells.Conclusions: Lentiviral gene transfer of the hTR component of telomerase into normal HSCs results in an upregulation of telomerase activity without having any noticeable effect on cell proliferation or CFU formation but a possible alteration in differentiation. These studies indicate that transduction of hTR into HSCs may provide a means to upregulate telomerase and potentially correct the proliferative defects observed in bone marrow failure syndromes such as AD DC that are caused by prematurely shortened telomeres.

Ataxia and pancytopenia caused by a mutation in TINF2

The syndrome of ataxia-pancytopenia is an autosomal dominant disorder characterized by cerebellar ataxia, peripheral neuropathies, pancytopenia and a predilection to myelodysplastic syndrome and acute myeloid leukemia. The genetic basis of this condition is unknown. We describe a child who presented with ataxia and pancytopenia and was found to have a heterozygous mutation, c.845G>A (Arg282His) in TINF2, a gene recently reported to be mutated in a subset of patients with autosomal dominant dyskeratosis congenita. We propose that some cases of ataxia-pancytopenia may be affected by DC.

Expanding the clinical phenotype of autosomal dominant dyskeratosis congenita caused by TERT mutations

Dyskeratosis congenita (DC) is a hereditary disorder characterized by mucocutaneous manifestations, bone marrow failure, predisposition to malignancy, pulmonary and liver fibrosis and additional features.[1][1] X-linked recessive, autosomal recessive and autosomal dominant (AD) forms of inheritance

Complex inheritance pattern of dyskeratosis congenita in two families with 2 different mutations in the telomerase reverse transcriptase gene

AbstractHeterozygous mutations in the telomerase components TERT, the reverse transcriptase, and TERC, the RNA template, cause autosomal dominant dyskeratosis congenita due to telomere shortening. Anticipation, whereby the disease severity increases in succeeding generations due to inheritance of shorter telomeres, is a feature of this condition. Here we describe 2 families in which 2 TERT mutations are segregating. Both families contain compound heterozygotes. In one case the proband is homozygous for a novel mutation causing a P704S substitution, while his father's second allele encodes an H412Y mutation. The proband in the second family has mutant alleles Y846C and H876Q. Transfection studies show codominant expression of the mutated alleles with no evidence of a dominant negative effect or of intragenic complementation. Thus in these families the expression of both TERT alleles and the inherited telomere length contribute to the clinical phenotype.

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.

Telomerase reverse-transcriptase homozygous mutations in autosomal recessive dyskeratosis congenita and Hoyeraal-Hreidarsson syndrome

Dyskeratosis congenita (DC) is a multisystem bone marrow failure syndrome characterized by a triad of mucocutaneous abnormalities and an increased predisposition to malignancy. X-linked DC is due to mutations in DKC1, while heterozygous mutations in TERC (telomerase RNA component) and TERT (telomerase reverse transcriptase) have been found in autosomal dominant DC. Many patients with DC remain uncharacterized, particularly families displaying autosomal recessive (AR) inheritance. We have now identified novel homozygous TERT mutations in 2 unrelated consanguineous families, where the index cases presented with classical DC or the more severe variant, Hoyeraal-Hreidarsson (HH) syndrome. These TERT mutations resulted in reduced telomerase activity and extremely short telomeres. As these mutations are homozygous, these patients are predicted to have significantly reduced telomerase activity in vivo. Interestingly, in contrast to patients with heterozygous TERT mutations or hemizygous DKC1 mutations, these 2 homozygous TERT patients were observed to have higher-than-expected TERC levels compared with controls. Collectively, the findings from this study demonstrate that homozygous TERT mutations, resulting in a pure but severe telomerase deficiency, produce a phenotype of classical AR-DC and its severe variant, the HH syndrome.

Dyskeratosis congenita: a genetic disorder of many faces

Dyskeratosis congenita (DC) is an inherited syndrome exhibiting marked clinical and genetic heterogeneity. It is characterized by multiple features including mucocutaneous abnormalities, bone marrow failure and an increased predisposition to cancer. Three genetic subtypes are recognized: X-linked recessive DC bears mutations in DKC1, the gene encoding dyskerin, a component of H/ACA small nucleolar ribonucleoprotein particles; autosomal dominant (AD) DC has heterozygous mutations in either TERC or TERT, the RNA and enzymatic components of telomerase, respectively, and autosomal recessive DC in which the genes involved remain largely elusive. Disease pathology is believed to be a consequence of chromosome instability because of telomerase deficiency due to mutations in DKC1, TERC and TERT; in patients with DKC1 mutations, defects in ribosomal RNA modification, ribosome biogenesis, translation control or mRNA splicing may also contribute to disease pathogenesis. The involvement of telomerase complex components in X-linked and AD forms and the presence of short telomeres in DC patients suggest that DC is primarily a disease of defective telomere maintenance. Treatment is variable and complicated by the development of secondary cancers but, being a monogenic disorder, it could potentially be treated by gene therapy. DC overlaps both clinically and genetically with several other diseases including Hoyeraal-Hreidarsson syndrome, aplastic anaemia and myelodysplasia, among others and its underlying telomeric defect has implications for a broader range of biological processes including ageing and many forms of cancer.

Splenic peliosis and rupture in patients with dyskeratosis congenita on androgens and granulocyte colony‐stimulating factor

Splenic peliosis and rupture in patients with dyskeratosis congenita on androgens and granulocyte colony‐stimulating factor

Functional characterization of novel telomerase RNA (TERC) mutations in patients with diverse clinical and pathological presentations

Functional characterization of heterozygous TERC (telomerase RNA component) and TERT (telomerase reverse transcriptase) mutations found in autosomal dominant dyskeratosis congenita (DC) and aplastic anemia (AA) shows that telomerase function is defective and that this is associated with short telomeres. This leads to reduced cell longevity with maximal impact on tissues with high proliferate potential. The aim of this study was to establish the role of TERC in the pathophysiology of uncharacterized patients with AA with some features of DC. The TERC gene was screened for mutations by denaturing high performance liquid chromatography. To determine the functional significance of TERC mutations telomerase activity was assessed in an in vitro (TRAP) assay and telomere length of patients' samples was determined using Southern blot analysis. RESULTS This study led to the identification of four novel TERC mutations (G178A, C180T, D52-86 and G2C) and a recurrent TERC mutation (D110-113GACT). Two of the de novo TERC mutations (G178A and C180T) found uniquely produce a clinical phenotype in the first generation, differing from previously published cases in which individuals in the first generation are usually asymptomatic. Curiously these mutations are located near the triple-helix domain of TERC. We also observed that the recurrent D110-113GACT can present with AA, myelodysplasia or leukemia. The D52-86 is associated with varied phenotypes including pulmonary disease (pulmonary fibrosis) as the first presentation. In summary, this study reports the functional characterization of several novel TERC mutations associated with varied hematologic and extra-hematologic presentations.