Differences in Disease Severity but Similar Telomere Lengths in Genetic Subgroups of Patients with Telomerase and Shelterin Mutations

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Diminished Telomeric 3′ Overhangs Are Associated with Telomere Dysfunction in Hoyeraal-Hreidarsson Syndrome

BACKGROUND:Eukaryotic chromosomes end with telomeres, which in most organisms are composed of tandem DNA repeats associated with telomeric proteins. These DNA repeats are synthesized by the enzyme telomerase, whose activity in most human tissues is tightly regulated, leading to gradual telomere shortening with cell divisions. Shortening beyond a critical length causes telomere uncapping, manifested by the activation of a DNA damage response (DDR) and consequently cell cycle arrest. Thus, telomere length limits the number of cell divisions and provides a tumor-suppressing mechanism. However, not only telomere shortening, but also damaged telomere structure, can cause telomere uncapping. Dyskeratosis Congenita (DC) and its severe form Hoyeraal-Hreidarsson Syndrome (HHS) are genetic disorders mainly characterized by telomerase deficiency, accelerated telomere shortening, impaired cell proliferation, bone marrow failure, and immunodeficiency. METHODOLOGY/PRINCIPAL FINDINGS:We studied the telomere phenotypes in a family affected with HHS, in which the genes implicated in other cases of DC and HHS have been excluded, and telomerase expression and activity appears to be normal. Telomeres in blood leukocytes derived from the patients were severely short, but in primary fibroblasts they were normal in length. Nevertheless, a significant fraction of telomeres in these fibroblasts activated DDR, an indication of their uncapped state. In addition, the telomeric 3' overhangs are diminished in blood cells and fibroblasts derived from the patients, consistent with a defect in telomere structure common to both cell types. CONCLUSIONS/SIGNIFICANCE:Altogether, these results suggest that the primary defect in these patients lies in the telomere structure, rather than length. We postulate that this defect hinders the access of telomerase to telomeres, thus causing accelerated telomere shortening in blood cells that rely on telomerase to replenish their telomeres. In addition, it activates the DDR and impairs cell proliferation, even in cells with normal telomere length such as fibroblasts. This work demonstrates a telomere length-independent pathway that contributes to a telomere dysfunction disease

Lung transplantation for pulmonary fibrosis in dyskeratosis congenita: Case Report and systematic literature review

<p>Abstract</p> <p>Background</p> <p>Dyskeratosis congenita (DC) is a progressive, multi-system, inherited disorder of telomere biology with high risks of morbidity and mortality from bone marrow failure, hematologic malignancy, solid tumors and pulmonary fibrosis. Hematopoietic stem cell transplantation (HSCT) can cure the bone marrow failure, but it does not eliminate the risks of other complications, for which life-long surveillance is required. Pulmonary fibrosis is a progressive and lethal complication of DC.</p> <p>Case presentation</p> <p>In this report, we describe a patient with DC who developed pulmonary fibrosis seven years after HSCT for severe aplastic anemia, and was successfully treated with bilateral lung transplantation. We also performed a systematic literature review to understand the burden of pulmonary disease in patients with DC who did or did not receive an HSCT. Including our patient, we identified 49 DC patients with pulmonary disease (12 after HSCT and 37 without HSCT), and 509 with no reported pulmonary complications.</p> <p>Conclusion</p> <p>Our current case and literature review indicate that pulmonary morbidity is one of the major contributors to poor quality of life and reduced long-term survival in DC. We suggest that lung transplantation be considered for patients with DC who develop pulmonary fibrosis with no concurrent evidence of multi-organ failure.</p

Telomere Lengths, Pulmonary Fibrosis and Telomerase (TERT) Mutations

mutations. mutation carriers demonstrate reduced life expectancy, with a mean age of death of 58 and 67 years for males and females, respectively. mutation have shorter telomere lengths than controls, demonstrating epigenetic inheritance of a shortened parental telomere length set-point

The Clinical Impact of Copy Number Variants in Inherited Bone Marrow Failure Syndromes

Inherited bone marrow failure syndromes (IBMFSs) comprise a genetically heterogeneous group of diseases with hematopoietic failure and a wide array of physical malformations. Copy number variants (CNVs) were reported in some IBMFSs. It is unclear what impact CNVs play in patients evaluated for a suspected diagnosis of IBMFS. Clinical and genetic data of 323 patients from the Canadian Inherited Marrow Failure Registry from 2001 to 2014, who had a documented genetic work-up, were analyzed. Cases with pathogenic CNVs (at least 1 kilobasepairs) were compared to cases with other mutations. Genotype-phenotype correlations were performed to assess the impact of CNVs. Pathogenic nucleotide-level mutations were found in 157 of 303 tested patients (51.8%). Genome-wide CNV analysis by single nucleotide polymorphism arrays or comparative genomic hybridization arrays revealed pathogenic CNVs in 11 of 67 patients tested (16.4%). In four of these patients, identification of CNV was crucial for establishing the correct diagnosis as their clinical presentation was ambiguous. Eight additional patients were identified to harbor pathogenic CNVs by other methods. Of the 19 patients with pathogenic CNVs, four had compound-heterozygosity of a CNV with a nucleotide-level mutation. Pathogenic CNVs were associated with more extensive non-hematological organ system involvement

Molecular characterization of glucose-6-phosphate dehydrogenase deficiency in Jeddah, Kingdom of Saudi Arabia

International audienceABSTRACT: BACKGROUND: The development of polymerase chain reaction (PCR)-based methods for the detection of known mutations has facilitated detecting specific red blood cell (RBC) enzyme deficiencies. We carried out a study on glucose-6-phosphate dehydrogenase (G6PD) deficient subjects in Jeddah to evaluate the molecular characteristics of this enzyme deficiency and the frequency of nucleotide1311 and IVS-XI-93 polymorphisms in the glucose-6-phosphate dehydrogenase gene. RESULTS: A total of 1584 unrelated Saudis (984 neonates and 600 adults) were screened for glucose-6-phosphate dehydrogenase deficiency. The prevalence of glucose-6-phosphate dehydrogenase deficiency was 6.9% (n=110). G6PD Mediterranean mutation was observed in 98 (89.1%) cases, G6PD Aures in 11 (10.0%) cases, and G6PD Chatham in 1 (0.9%) case. None of the samples showed G6PD A mutation. Samples from 29 deficient subjects (25 males and 4 females) were examined for polymorphism. The association of two polymorphisms of exon/intron 11 (c.1311T/IVS XI 93C) was observed in 14 (42.4%) of 33 chromosomes studied. This association was found in 9 (31.0%) carriers of G6PD Mediterranean and in 4 (13.8%) carriers of G6PD Aures. CONCLUSIONS: The majority of mutations were G6PD Mediterranean, followed by G6PD Aures and <1% G6PD Chatham. We conclude that 1311T is a frequent polymorphism in subjects with G6PD Mediterranean and Aures variants in Jeddah

Telomere and telomerase in stem cells

Telomeres, guanine-rich tandem DNA repeats of the chromosomal end, provide chromosomal stability, and cellular replication causes their loss. In somatic cells, the activity of telomerase, a reverse transcriptase that can elongate telomeric repeats, is usually diminished after birth so that the telomere length is gradually shortened with cell divisions, and triggers cellular senescence. In embryonic stem cells, telomerase is activated and maintains telomere length and cellular immortality; however, the level of telomerase activity is low or absent in the majority of stem cells regardless of their proliferative capacity. Thus, even in stem cells, except for embryonal stem cells and cancer stem cells, telomere shortening occurs during replicative ageing, possibly at a slower rate than that in normal somatic cells. Recently, the importance of telomere maintenance in human stem cells has been highlighted by studies on dyskeratosis congenital, which is a genetic disorder in the human telomerase component. The regulation of telomere length and telomerase activity is a complex and dynamic process that is tightly linked to cell cycle regulation in human stem cells. Here we review the role of telomeres and telomerase in the function and capacity of the human stem cells

Zebrafish Models for Dyskeratosis Congenita Reveal Critical Roles of p53 Activation Contributing to Hematopoietic Defects through RNA Processing

Dyskeratosis congenita (DC) is a rare bone marrow failure syndrome in which hematopoietic defects are the main cause of mortality. The most studied gene responsible for DC pathogenesis is DKC1 while mutations in several other genes encoding components of the H/ACA RNP telomerase complex, which is involved in ribosomal RNA(rRNA) processing and telomere maintenance, have also been implicated. GAR1/nola1 is one of the four core proteins of the H/ACA RNP complex. Through comparative analysis of morpholino oligonucleotide induced knockdown of dkc1 and a retrovirus insertion induced mutation of GAR1/nola1 in zebrafish, we demonstrate that hematopoietic defects are specifically recapitulated in these models and that these defects are significantly reduced in a p53 null mutant background. We further show that changes in telomerase activity are undetectable at the early stages of DC pathogenesis but rRNA processing is clearly defective. Our data therefore support a model that deficiency in dkc1 and nola1 in the H/ACA RNP complex likely contributes to the hematopoietic phenotype through p53 activation associated with rRNA processing defects rather than telomerase deficiency during the initial stage of DC pathogenesis

Two Pathways Recruit Telomerase to Saccharomyces cerevisiae Telomeres

The catalytic subunit of yeast telomerase, Est2p, is a telomere associated throughout most of the cell cycle, while the Est1p subunit binds only in late S/G2 phase, the time of telomerase action. Est2p binding in G1/early S phase requires a specific interaction between telomerase RNA (TLC1) and Ku80p. Here, we show that in four telomerase-deficient strains (cdc13-2, est1Ä, tlc1-SD, and tlc1-BD), Est2p telomere binding was normal in G1/early S phase but reduced to about 40–50% of wild type levels in late S/G2 phase. Est1p telomere association was low in all four strains. Wild type levels of Est2p telomere binding in late S/G2 phase was Est1p-dependent and required that Est1p be both telomere-bound and associated with a stem-bulge region in TLC1 RNA. In three telomerase-deficient strains in which Est1p is not Est2p-associated (tlc1-SD, tlc1-BD, and est2Ä), Est1p was present at normal levels but its telomere binding was very low. When the G1/early S phase and the late S/G2 phase telomerase recruitment pathways were both disrupted, neither Est2p nor Est1p was telomere-associated. We conclude that reduced levels of Est2p and low Est1p telomere binding in late S/G2 phase correlated with an est phenotype, while a WT level of Est2p binding in G1 was not sufficient to maintain telomeres. In addition, even though Cdc13p and Est1p interact by two hybrid, biochemical and genetic criteria, this interaction did not occur unless Est1p was Est2p-associated, suggesting that Est1p comes to the telomere only as part of the holoenzyme. Finally, the G1 and late S/G2 phase pathways for telomerase recruitment are distinct and are likely the only ones that bring telomerase to telomeres in wild-type cells