Search

Bloom syndrome (BS) is a rare genetic disorder caused by biallelic inactivation of the BLM gene, which usually manifests in childhood by significant growth retardation, immune deficiency, characteristic skin lesions, cancer predisposition and other distinguishable disease features. To our knowledge, all prior instances of BS have been identified via intentional analysis of patients with clinical suspicion for this disease or DNA testing of members of affected pedigrees. We describe an incidental finding of BS, which occurred upon routine germline DNA analysis of consecutive breast cancer patients. The person with the biallelic pathogenic BLM c.1642C>T (p.Gln548Ter) variant remained clinically healthy for 38 years until she developed breast cancer. Detailed examination of this woman, which was carried out after the genetic diagnosis, revealed mild features of BS. A sister chromatid exchange (SCE) test confirmed the presence of this syndrome. The tumor exhibited triple-negative receptor status, a high proliferation rate, a low tumor mutation burden (TMB), and a moderate level of chromosomal instability (homologous recombination deficiency (HRD) score = 29). The patient showed normal tolerability to radiotherapy and several regimens of cytotoxic therapy. Thus, some BS patients may remain undiagnosed due to the mild phenotype of their disease. BLM should be incorporated in gene panels utilized for germline DNA testing of cancer patients., (© 2024. The Author(s), under exclusive licence to Springer Nature B.V.)

Introduction: Bloom syndrome (BS) is a rare autosomal recessive disorder caused by a loss-of-function mutation in the BLM gene encoding an RecQ helicase involved in DNA repair and maintenance of chromosomal stability. In patients with BS, significant sensitivity to both DNA-damaging chemotherapy (CT) and ionizing radiation complicates the management of neoplasms by exacerbating comorbidities and predisposing to toxicities and poor outcomes., Case Report: A 30-year-old female patient diagnosed with BS who presented with early-stage triple-negative breast cancer was treated with four cycles of doxorubicin (60 mg/m 2 ) and cyclophosphamide (600 mg/m 2 ) followed by weekly paclitaxel (80 mg/m 2 ) for 12 weeks as the chemotherapy protocol and a total of 5000 cGy curative radiotherapy (RT). Due to pancytopenia 8 months after completion of therapy, bone marrow biopsy and aspiration were performed, and a diagnosis of myelodysplastic syndrome with excess blasts 2 (MDS-EB2) was made. Two courses of the azacitidine (75 mg/m 2 ) protocol were administered every 28 days in the hematology clinic. Two weeks after CT the patient was transferred from the emergency department to the hematology clinic with the diagnosis of pancytopenia and febrile neutropenia. She died at the age of 33 due to sepsis that developed during follow-up., Conclusion: Due to the rarity of BS, there is no prospective trial in patients with cancer and no evidence base upon which to design treatment programs. For these reasons, it is strongly recommended that patients receive multidisciplinary care, with precise assessment and discussion of the indication and an adequate dose of DNA-damaging agents such as chemotherapy and ionizing radiation., (© 2024. The Author(s).)

Ribosomal DNA (rDNA) encodes the ribosomal RNA genes and represents an intrinsically unstable genomic region. However, the underlying mechanisms and implications for genome integrity remain elusive. Here, we use Bloom syndrome (BS), a rare genetic disease characterized by DNA repair defects and hyper-unstable rDNA, as a model to investigate the mechanisms leading to rDNA instability. We find that in Bloom helicase (BLM) proficient cells, the homologous recombination (HR) pathway in rDNA resembles that in nuclear chromatin; it is initiated by resection, replication protein A (RPA) loading and BRCA2-dependent RAD51 filament formation. However, BLM deficiency compromises RPA-loading and BRCA1/2 recruitment to rDNA, but not RAD51 accumulation. RAD51 accumulates at rDNA despite depletion of long-range resection nucleases and rDNA damage results in micronuclei when BLM is absent. In summary, our findings indicate that rDNA is permissive to RAD51 accumulation in the absence of BLM, leading to micronucleation and potentially global genomic instability., (© 2024. The Author(s).)

Generation of O 6 -methylguanine (O 6 -meG) by DNA-alkylating agents such as N-methyl N-nitrosourea (MNU) activates the multiprotein mismatch repair (MMR) complex and the checkpoint response involving ATR/CHK1 and ATM/CHK2 kinases, which may in turn trigger cell cycle arrest and apoptosis. The Bloom syndrome DNA helicase BLM interacts with the MMR complex, suggesting functional relevance to repair and checkpoint responses. We observed a strong interaction of BLM with MMR proteins in HeLa cells upon treatment with MNU as evidenced by co-immunoprecipitation as well as colocalization in the nucleus as revealed by dual immunofluorescence staining. Knockout of BLM sensitized HeLa MR cells to MNU-induced cell cycle disruption and enhanced expression of the apoptosis markers cleaved caspase-9 and PARP1. MNU-treated BLM-deficient cells also exhibited a greater number of 53BP1 foci and greater phosphorylation levels of H2AX at S139 and RPA32 at S8, indicating the accumulation of DNA double-strand breaks. These findings suggest that BLM prevents double-strand DNA breaks during the MMR-dependent DNA damage response and mitigates O 6 -meG-induced apoptosis., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Ryosuke Fujikane reports financial support was provided by JSPS KAKENHI. Masumi Hidaka reports financial support was provided by JSPS KAKENHI. Masumi Hidaka reports financial support was provided by Promotion and Mutual Aid Corporation for Private Schools of Japan. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

James German's work to establish the natural history and cancer risk associated with Bloom syndrome (BS) has had a strong influence on the generation of scientists and clinicians working to understand other RECQ deficiencies and heritable cancer predisposition syndromes. I summarize work by us and others below, inspired by James German's precedents with BS, to understand and compare BS with the other heritable RECQ deficiency syndromes with a focus on Werner syndrome (WS). What we know, unanswered questions and new opportunities are discussed, as are potential ways to treat or modify WS-associated disease mechanisms and pathways.

The Bloom syndrome (BLM) helicase is critical for alternative lengthening of telomeres (ALT), a homology-directed repair (HDR)-mediated telomere maintenance mechanism that is prevalent in cancers of mesenchymal origin. The DNA substrates that BLM engages to direct telomere recombination during ALT remain unknown. Here, we determine that BLM helicase acts on lagging strand telomere intermediates that occur specifically in ALT-positive cells to assemble a replication-associated DNA damage response. Loss of ATRX was permissive for BLM localization to ALT telomeres in S and G2, commensurate with the appearance of telomere C-strand-specific single-stranded DNA (ssDNA). DNA2 nuclease deficiency increased 5'-flap formation in a BLM-dependent manner, while telomere C-strand, but not G-strand, nicks promoted ALT. These findings define the seminal events in the ALT DNA damage response, linking aberrant telomeric lagging strand DNA replication with a BLM-directed HDR mechanism that sustains telomere length in a subset of human cancers., Competing Interests: Declaration of interests R.A.G. is a co-founder and scientific advisory board member of RADD Pharmaceuticals and a scientific advisory board member for Dong-A ST Co. Neither engagement directly relates to the substance of this study., (Copyright © 2024 Elsevier Inc. All rights reserved.)

Bloom syndrome (BS) is an autosomal recessive genetic disorder caused by variants in the BLM gene. BS is characterized by distinct facial features, elongated limbs, and various dermatological complications including photosensitivity, poikiloderma, and telangiectatic erythema. The BLM gene encodes a RecQ helicase critical for genome maintenance, stability, and repair, and a deficiency in functional BLM protein leads to genomic instability and high predisposition to various types of cancers, particularly hematological and gastrointestinal malignancies. Here, we report a case of BS with a previously unreported variant in the BLM gene. The patient was a 34-year-old woman who presented with short stature, prominent facial features, and a history of malignancies, including lymphoma, breast cancer, and myelodysplastic syndromes (MDS). She was initially treated with azacitidine for MDS and showed transient improvement, but eventually died at age of 35 due to progression of MDS. Genetic screening revealed compound heterozygous variants in the BLM gene, with a recurrent variant previously reported in BS in one allele and a previously unreported variant in the other allele. Based on her characteristic clinical features and the presence of heterozygous variants in the BLM gene, she was diagnosed with BS harboring compound heterozygous BLM variants., (© 2024. Japanese Society of Hematology.)

Bloom syndrome (BS) is a rare autosomal recessive inherited disorder. Patients with BS have photosensitivity, telangiectatic facial erythema, and stunted growth. They usually have mild microcephaly, and distinctive facial features such as a narrow, slender face, micrognathism, and a prominent nose. Kostmann disease (KD) is a subgroup of severe congenital neutropenias. The diagnosis of severe congenital neutropenia is based on clinical symptoms, bone marrow findings, and genetic mutation. Here, we report a female patient with a triangular face, nasal prominence, and protruding ears presenting with recurrent infections and severe neutropenia. Molecular genetic testing revealed a compound heterozygous variant in the HCLS-1-associated protein X-1 gene [(c.130_131insA) p.(trp44*), c.430 dup(p.Val144fs)] and a new homozygous variant in Bloom Syndrome RecQ like helicase gene [c.2074+2T>C p.(?)]. She was diagnosed with both BS and KD. To the best of our knowledge, this is the first case of coexisting BS and KD in a patient ever reported., Competing Interests: The authors have no conflicts of interest to declare., (Copyright © 2023 Wolters Kluwer Health, Inc. All rights reserved.)

Bloom syndrome (BSyn) is an autosomal recessive disorder caused by variants in the BLM gene, which is involved in genome stability. Patients with BSyn present with poor growth, sun sensitivity, mild immunodeficiency, diabetes, and increased risk of cancer, most commonly leukemias. Interestingly, patients with BSyn do not have other signs of premature aging such as early, progressive hair loss and cataracts. We set out to determine epigenetic age in BSyn, which can be a better predictor of health and disease over chronological age. Our results show for the first time that patients with BSyn have evidence of accelerated epigenetic aging across several measures in blood lymphocytes, as compared to carriers. Additionally, homozygous Blm mice exhibit accelerated methylation age in multiple tissues, including brain, blood, kidney, heart, and skin, according to the brain methylation clock. Overall, we find that Bloom syndrome is associated with accelerated epigenetic aging effects in multiple tissues and more generally a strong effect on CpG methylation levels., (© 2023 The Authors. Aging Cell published by Anatomical Society and John Wiley & Sons Ltd.)

Bloom syndrome helicase (BLM) is a RecQ-family helicase implicated in a variety of cellular processes, including DNA replication, DNA repair, and telomere maintenance. Mutations in human BLM cause Bloom syndrome (BS), an autosomal recessive disorder that leads to myriad negative health impacts including a predisposition to cancer. BS-causing mutations in BLM often negatively impact BLM ATPase and helicase activity. While BLM mutations that cause BS have been well characterized both in vitro and in vivo, there are other less studied BLM mutations that exist in the human population that do not lead to BS. Two of these non-BS mutations, encoding BLM P868L and BLM G1120R, when homozygous, increase sister chromatid exchanges in human cells. To characterize these naturally occurring BLM mutant proteins in vitro, we purified the BLM catalytic core (BLMcore, residues 636-1298) with either the P868L or G1120R substitution. We also purified a BLMcore K869A K870A mutant protein, which alters a lysine-rich loop proximal to the P868 residue. We found that BLMcore P868L and G1120R proteins were both able to hydrolyze ATP, bind diverse DNA substrates, and unwind G-quadruplex and duplex DNA structures. Molecular dynamics simulations suggest that the P868L substitution weakens the DNA interaction with the winged-helix domain of BLM and alters the orientation of one lobe of the ATPase domain. Because BLMcore P868L and G1120R retain helicase function in vitro, it is likely that the increased genome instability is caused by specific impacts of the mutant proteins in vivo. Interestingly, we found that BLMcore K869A K870A has diminished ATPase activity, weakened binding to duplex DNA structures, and less robust helicase activity compared to wild-type BLMcore. Thus, the lysine-rich loop may have an important role in ATPase activity and specific binding and DNA unwinding functions in BLM., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Cueny et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Pathogenic variants affecting the BLM gene are responsible for the manifestation of extremely rare cancer‑predisposing Bloom syndrome. The present study reports on a case of an infant with a congenital hypotrophy, short stature and abnormal facial appearance. Initially she was examined using a routine molecular diagnostic algorithm, including the cytogenetic analysis of her karyotype, microarray analysis and methylation‑specific MLPA, however, she remained undiagnosed on a molecular level. Therefore, she and her parents were enrolled in the project of trio‑based exome sequencing (ES) using Human Core Exome kit. She was revealed as a carrier of an extremely rare combination of causative sequence variants altering the BLM gene (NM_000057.4), c.1642C>T and c.2207_2212delinsTAGATTC in the compound heterozygosity, resulting in a diagnosis of Bloom syndrome. Simultaneously, a mosaic loss of heterozygosity of chromosome 11p was detected and then confirmed as a borderline imprinting center 1 hypermethylation on chromosome 11p15. The diagnosis of Bloom syndrome and mosaic copy‑number neutral loss of heterozygosity of chromosome 11p increases a lifetime risk to develop any types of malignancy. This case demonstrates the trio‑based ES as a complex approach for the molecular diagnostics of rare pediatric diseases.

Bloom syndrome (BS) is a rare autosomal recessive disorder characterized by genomic instability that leads to various complications, including cancer. Given the low prevalence of BS in Japan, we conducted a nationwide survey. We recruited eight patients with BS, three of whom exhibited intellectual disability. The 631delCAA mutation in the BLM gene was detected in 9 out of 16 alleles. To investigate neuronal development in patients with BS, we generated induced pluripotent stem cells derived from one of these patients (BS-iPSCs). We examined the phenotypes of the induced cortical neurons derived from the generated BS-iPSCs using a previously reported protocol; the generated BS-iPSCs showed an approximately 10-times higher frequency of sister-chromatid exchange (SCE) than the control iPSCs. Immunocytochemistry revealed shorter axons and higher proliferative potential in BS-iPSC-derived cortical neurons compared with control iPSCs. To our knowledge, our study is the first to clarify the abnormality of the cortical neuron phenotypes derived from patients with BS. Our findings may help identify the pathogenesis of neuronal differentiation in BS and aid in the development of novel therapeutic agents., (© 2023. The Author(s), under exclusive licence to The Japan Society of Human Genetics.)

The homologous recombination repair (HRR) pathway is critical for repairing double-strand breaks (DSB). Inhibition of the HRR pathway is usually considered a promising strategy for anticancer therapy. The Bloom's Syndrome Protein (BLM), a DNA helicase, is essential for promoting the HRR pathway. Previously, we discovered quinazolinone derivative 9h as a potential BLM inhibitor, which suppressed the proliferation of colorectal cancer (CRC) cell HCT116. Herein, a new series of quinazolinone derivatives with N3-substitution was designed and synthesized to improve the anticancer activity and explore the structure-activity relationship (SAR). After evaluating their BLM inhibitory activity, the SAR was discussed, leading to identifying compound 21 as a promising BLM inhibitor. 21 exhibited the potent BLM-dependent cytotoxicity against the CRC cells but weak against normal cells. Further evaluation revealed that 21 could disrupt the HRR level while inhibiting BLM located on the DSB site and trigger DNA damage in the CRC cells. This compound effectively suppressed the proliferation and invasion of CRC cells, along with cell cycle arrest and apoptosis. Consequently, 21 might be a promising candidate for treating CRC, and the BLM might be a new potential therapeutic target for CRC., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Masson SAS. All rights reserved.)

Rothmund-Thomson syndrome, a heterogeneous genodermatosis with autosomal recessive hereditary pattern, is an uncommon cancer susceptibility genetic syndrome. To date, only 400 cases have been reported in the literature, and the severity of the features varies among individuals with the condition. Here, we describe a 55-year-old male who had been diagnosed with Bloom Syndrome during childhood due to the suggestive physical features such as short stature, chronic facial erythema, poikiloderma in face and extremities, microtia and microcephaly. However, the genetic test demonstrated that the patient carried two pathogenic variants resulting in compound heterozygous in the RECQL4 gene (c.2269C>T and c.2547_2548delGT). He subsequently developed a calcaneal osteosarcoma, which was successfully treated, and has currently been oncologic disease-free for 3 years., (© 2022. The Author(s), under exclusive licence to Springer Nature B.V.)

Prostate cancer (PCa) is a common cancer and a major cause of cancer-related death worldwide in men, necessitating novel targets for cancer therapy. High expression of Bloom's syndrome protein (BLM) helicase is associated with the occurrence and development of PCa. Therefore, the identification and development of new BLM inhibitors may be a new direction for the treatment of PCa. Here, we identified a novel inhibitor by molecular docking and put it to systematic evaluation via various experiments, AO/854, which acted as a competitive inhibitor that blocked the BLM-DNA interaction. Cellular evaluation indicated that AO/854-suppressed tumor growth and metastasis in PC3 cells by enhancing DNA damage, phosphorylating Chk1/Chk2, and altering the p53 signaling pathway. Collectively, the study highlights the potential of BLM as a therapeutic target in PCa and reveals a distinct mechanism by which AO/854 competitively inhibits the function of BLM.

Bloom syndrome protein (BLM) is a conserved RecQ family helicase involved in the maintenance of genome stability. BLM has been widely recognized as a genome "caretaker" that processes structured DNA. In contrast, our knowledge of how BLM behaves on single-stranded (ss) DNA is still limited. Here, we demonstrate that BLM possesses the intrinsic ability for phase separation and can co-phase separate with ssDNA to form dynamically arrested protein/ssDNA co-condensates. The introduction of ATP potentiates the capability of BLM to condense on ssDNA, which further promotes the compression of ssDNA against a resistive force of up to 60 piconewtons. Moreover, BLM is also capable of condensing replication protein A (RPA)- or RAD51-coated ssDNA, before which it generates naked ssDNA by dismantling these ssDNA-binding proteins. Overall, our findings identify an unexpected characteristic of a DNA helicase and provide a new angle of protein/ssDNA co-condensation for understanding the genomic instability caused by BLM overexpression under diseased conditions., (© 2022 Wiley-VCH GmbH.)

Bloom syndrome (BS) is an autosomal recessive disease clinically characterized by primary microcephaly, growth deficiency, immunodeficiency and predisposition to cancer. It is mainly caused by biallelic loss-of-function mutations in the BLM gene, which encodes the BLM helicase, acting in DNA replication and repair processes. Here, we describe the gene expression profiles of three BS fibroblast cell lines harboring causative, biallelic truncating mutations obtained by single-cell (sc) transcriptome analysis. We compared the scRNA transcription profiles from three BS patient cell lines to two age-matched wild-type controls and observed specific deregulation of gene sets related to the molecular processes characteristically affected in BS, such as mitosis, chromosome segregation, cell cycle regulation and genomic instability. We also found specific upregulation of genes of the Fanconi anemia pathway, in particular FANCM, FANCD2 and FANCI, which encode known interaction partners of BLM. The significant deregulation of genes associated with inherited forms of primary microcephaly observed in our study might explain in part the molecular pathogenesis of microcephaly in BS, one of the main clinical characteristics in patients. Finally, our data provide first evidence of a novel link between BLM dysfunction and transcriptional changes in condensin complex I and II genes. Overall, our study provides novel insights into gene expression profiles in BS on an sc level, linking specific genes and pathways to BLM dysfunction., (© The Author(s) 2022. Published by Oxford University Press.)

Purpose: This study aimed to describe the spectrum of cancers observed in Bloom Syndrome and the observed survival and age of first cancer diagnosis in Bloom syndrome as these are not well-defined., Methods: Data from the Bloom Syndrome Registry (BSR) was used for this study. Cancer history, ages of first cancer diagnosis, and ages of death were compiled from the BSR and analyzed., Results: Among the 290 individuals in the BSR, 155 (53%) participants developed 251 malignant neoplasms; 100 (65%) were diagnosed with 1 malignancy, whereas the remaining 55 (35%) developed multiple malignancies. Of the 251 neoplasms, 83 (33%) were hematologic and 168 (67%) were solid tumors. Hematologic malignancies (leukemia and lymphoma) were more common than any of the solid tumors. The most commonly observed solid tumors were colorectal, breast, and oropharyngeal. The cumulative incidence of any malignancy by age 40 was 83%. The median survival for all participants in the BSR was 36.2 years. There were no significant differences in time to first cancer diagnosis or survival by genotype among the study participants., Conclusion: We describe the spectrum of cancers observed in Bloom syndrome and the observed survival and age of first cancer diagnosis in Bloom syndrome. We also highlight the significant differences in survival and age of diagnosis seen among different tumor types and genotypes., Competing Interests: Conflict of Interest The authors declare no conflicts of interest., (Copyright © 2022 American College of Medical Genetics and Genomics. Published by Elsevier Inc. All rights reserved.)

Bloom syndrome (BS) is an autosomal recessive disorder with characteristic clinical features of primary microcephaly, growth deficiency, cancer predisposition, and immunodeficiency. Here, we report the clinical and molecular findings of eight patients from six families diagnosed with BS. We identified causative pathogenic variants in all families including three different variants in BLM and one variant in RMI1. The homozygous c.581_582delTT;p.Phe194* and c.3164G>C;p.Cys1055Ser variants in BLM have already been reported in BS patients, while the c.572_573delGA;p.Arg191Lysfs*4 variant is novel. Additionally, we present the detailed clinical characteristics of two cases with BS in which we previously identified the biallelic loss-of-function variant c.1255_1259delAAGAA;p.Lys419Leufs*5 in RMI1. All BS patients had primary microcephaly, intrauterine growth delay, and short stature, presenting the phenotypic hallmarks of BS. However, skin lesions and upper airway infections were observed only in some of the patients. Overall, patients with pathogenic BLM variants had a more severe BS phenotype compared to patients carrying the pathogenic variants in RMI1, especially in terms of immunodeficiency, which should be considered as one of the most important phenotypic characteristics of BS., (© 2022 The Authors. Clinical Genetics published by John Wiley & Sons Ltd.)

RecQ helicases-also known as the "guardians of the genome"-play crucial roles in genome integrity maintenance through their involvement in various DNA metabolic pathways. Aside from being conserved from bacteria to vertebrates, their importance is also reflected in the fact that in humans impaired function of multiple RecQ helicase orthologs are known to cause severe sets of problems, including Bloom, Werner, or Rothmund-Thomson syndromes. Our aim was to create and characterize a zebrafish (Danio rerio) disease model for Bloom syndrome, a recessive autosomal disorder. In humans, this syndrome is characterized by short stature, skin rashes, reduced fertility, increased risk of carcinogenesis, and shortened life expectancy brought on by genomic instability. We show that zebrafish blm mutants recapitulate major hallmarks of the human disease, such as shortened lifespan and reduced fertility. Moreover, similarly to other factors involved in DNA repair, some functions of zebrafish Blm bear additional importance in germ line development, and consequently in sex differentiation. Unlike fanc genes and rad51, however, blm appears to affect its function independent of tp53. Therefore, our model will be a valuable tool for further understanding the developmental and molecular attributes of this rare disease, along with providing novel insights into the role of genome maintenance proteins in somatic DNA repair and fertility., (© 2022. The Author(s).)

Genes on the long arm of the Drosophila melanogaster 4th chromosome are difficult to study because the chromosome lacks mitotic and meiotic recombination. Without recombination numerous standard methods of genetic analysis are impossible. Here, we report new resources for the 4th. For mitotic recombination, we generated a chromosome with an FRT very near the centromere in 101F and a derivative that carries FRT101F with a distal ubiquitously expressed GAL80 transgene. This pair of chromosomes enables both unmarked and MARCM clones. For meiotic recombination, we demonstrate that a Bloom syndrome helicase and recombination defective double mutant genotype can create recombinant 4th chromosomes via female meiosis. All strains will be available to the community via the Bloomington Drosophila Stock Center. Additional resources for studies of the 4th are in preparation and will also be made available. The goal of the 4th Chromosome Resource Project is to accelerate the genetic analysis of protein-coding genes on the 4th, including the 44 genes with no demonstrated function. Studies of these previously inaccessible but largely conserved genes will close longstanding gaps in our knowledge of metazoan development and physiology., (© The Author(s) 2022. Published by Oxford University Press on behalf of Genetics Society of America.)

The RecQ-like helicase BLM cooperates with topoisomerase IIIα, RMI1, and RMI2 in a heterotetrameric complex (the "Bloom syndrome complex") for dissolution of double Holliday junctions, key intermediates in homologous recombination. Mutations in any component of the Bloom syndrome complex can cause genome instability and a highly cancer-prone disorder called Bloom syndrome. Some heterozygous carriers are also predisposed to breast cancer. To understand how the activities of BLM helicase and topoisomerase IIIα are coupled, we purified the active four-subunit complex. Chemical cross-linking and mass spectrometry revealed a unique architecture that links the helicase and topoisomerase domains. Using biochemical experiments, we demonstrated dimerization mediated by the N terminus of BLM with a 2:2:2:2 stoichiometry within the Bloom syndrome complex. We identified mutations that independently abrogate dimerization or association of BLM with RMI1, and we show that both are dysfunctional for dissolution using in vitro assays and cause genome instability and synthetic lethal interactions with GEN1/MUS81 in cells. Truncated BLM can also inhibit the activity of full-length BLM in mixed dimers, suggesting a putative mechanism of dominant-negative action in carriers of BLM truncation alleles. Our results identify critical molecular determinants of Bloom syndrome complex assembly required for double Holliday junction dissolution and maintenance of genome stability., Competing Interests: Competing interest statement: A.J.D. is the recipient of research funding from Tessellate Biosciences and Pfizer unrelated to the work presented. These companies have had no influence on the content of the manuscript., (Copyright © 2022 the Author(s). Published by PNAS.)

Bloom's syndrome is caused by inactivation of the BLM helicase, which functions with TOP3A and RMI1-2 (BTR complex) to dissolve recombination intermediates and avoid somatic crossing-over. We show here that crossover avoidance by BTR further requires the activity of cyclin-dependent kinase-1 (CDK1), Polo-like kinase-1 (PLK1), and the DDR mediator protein TOPBP1, which act in the same pathway. Mechanistically, CDK1 phosphorylates BLM and TOPBP1 and promotes the interaction of both proteins with PLK1. This is amplified by the ability of TOPBP1 to facilitate phosphorylation of BLM at sites that stimulate both BLM-PLK1 and BLM-TOPBP1 binding, creating a positive feedback loop that drives rapid BLM phosphorylation at the G 2 -M transition. In vitro, BLM phosphorylation by CDK/PLK1/TOPBP1 stimulates the dissolution of topologically linked DNA intermediates by BLM-TOP3A. Thus, we propose that the CDK1-TOPBP1-PLK1 axis enhances BTR-mediated dissolution of recombination intermediates late in the cell cycle to suppress crossover recombination and curtail genomic instability.

Bloom syndrome (BS) is a genomic and chromosomal instability disorder with prodigious cancer predisposition caused by pathogenic variants in BLM. We report the clinical and genetic details of a boy who first presented with infantile fibrosarcoma (IFS) at the age of 6 months and subsequently was diagnosed with BS at the age of 9 years. Molecular analysis identified the pathogenic germline BLM sequence variants (c.1642C>T and c.2207_2212delinsTAGATTC). This is the first report of IFS related to BS, for which we show that both BLM alleles are maintained in the tumor and demonstrate a TPM3-NTKR1 fusion transcript in the IFS. Our communication emphasizes the importance of long-term follow up after treatment for pediatric neoplastic conditions, as clues to important genetic entities might manifest later, and the identification of a heritable tumor predisposition often leads to changes in patient surveillance and management., (© 2020. The Author(s).)

Bloom Syndrome (BS) is a genetic DNA repair disorder, caused by mutations in the BLM gene. The clinical phenotype includes growth retardation, immunodeficiency and a strong predisposition to different types of malignancies. Treatment of malignancies in BS patients with radiotherapy or chemotherapy is believed to be associated with increased toxicity, but clinical and laboratory data are lacking. We collected clinical data of two Dutch BS patients with solid tumors. Both were treated with radiotherapy before the diagnosis BS was made and tolerated this treatment well. In addition, we collected fibroblasts from BS patients to perform in vitro clonogenic survival assays to determine radiosensitivity. BS fibroblasts showed less radiosensitivity than the severely radiosensitive Artemis fibroblasts. Moreover, studies of double strand break kinetics by counting 53BP1 foci after irradiation showed similar patterns compared to healthy controls. In combination, the clinical cases and laboratory experiments are valuable information in the discussion whether radiotherapy is absolutely contraindicated in BS, which is the Case in other DNA repair syndromes like Ataxia Telangiectasia and Artemis., (Copyright © 2021 The Authors. Published by Elsevier Masson SAS.. All rights reserved.)

Homology-directed repair (HDR), a critical DNA repair pathway in mammalian cells, is complex, leading to multiple outcomes with different impacts on genomic integrity. However, the factors that control these different outcomes are often not well understood. Here we show that SWS1-SWSAP1-SPIDR controls distinct types of HDR. Despite their requirement for stable assembly of RAD51 recombinase at DNA damage sites, these proteins are not essential for intra-chromosomal HDR, providing insight into why patients and mice with mutations are viable. However, SWS1-SWSAP1-SPIDR is critical for inter-homolog HDR, the first mitotic factor identified specifically for this function. Furthermore, SWS1-SWSAP1-SPIDR drives the high level of sister-chromatid exchange, promotes long-range loss of heterozygosity often involved with cancer initiation, and impels the poor growth of BLM helicase-deficient cells. The relevance of these genetic interactions is evident as SWSAP1 loss prolongs Blm-mutant embryo survival, suggesting a possible druggable target for the treatment of Bloom syndrome., (© 2021. The Author(s).)

Autosomal hereditary recessive diseases characterized by genetic instability are often associated with cancer predisposition. Bloom syndrome (BS), a rare genetic disorder, with <300 cases reported worldwide, combines both. Indeed, patients with Bloom's syndrome are 150 to 300 times more likely to develop cancers than normal individuals. The wide spectrum of cancers developed by BS patients suggests that early initial events occur in BS cells which may also be involved in the initiation of carcinogenesis in the general population and these may be common to several cancers. BS is caused by mutations of both copies of the BLM gene, encoding the RecQ BLM helicase. This review discusses the different aspects of BS and the different cellular functions of BLM in genome surveillance and maintenance through its major roles during DNA replication, repair, and transcription. BLM's activities are essential for the stabilization of centromeric, telomeric and ribosomal DNA sequences, and the regulation of innate immunity. One of the key objectives of this work is to establish a link between BLM functions and the main clinical phenotypes observed in BS patients, as well as to shed new light on the correlation between the genetic instability and diseases such as immunodeficiency and cancer. The different potential implications of the BLM helicase in the tumorigenic process and the use of BLM as new potential target in the field of cancer treatment are also debated., (Copyright © 2019. Published by Elsevier Inc.)

Bloom syndrome is a rare autosomal recessive disorder with less than 300 cases reported in the literature. Bloom syndrome is characterized by chromosome instability, physical stigmata, growth deficiency, immunodeficiency, and a predisposition to cancer, most commonly leukemias, although solid tumors are reported as well. Bloom syndrome occurs in multiple ethnic groups with a higher incidence in persons of Ashkenazi Jewish origin. Few patients of Hispanic ethnicity have been reported. We report here a Mexican American family with a BLM pathogenic variant, c.2506&#95;2507delAG, previously reported in a single patient from Mexico. In this family of four siblings, three have phenotypic features of Bloom syndrome, and BLM gene mutation was homozygous in these affected individuals. Our proband developed a rhabdomyosarcoma. Analysis of surrounding markers in the germline DNA revealed a common haplotype, suggesting a previously unrecognized founder mutation in the Hispanic population of Mexican origin., (© 2021 Sybouts et al.; Published by Cold Spring Harbor Laboratory Press.)

The Bloom syndrome complex is a DNA damage repair machine. It consists of several protein components which are functional in isolation, but interdependent in cells for the maintenance of accurate homologous recombination. Mutations to any of the genes encoding these proteins cause numerous physical and developmental markers as well as phenotypes of genome instability, infertility, and cancer predisposition. Here we review the published structural and biochemical data on each of the components of the complex: the helicase BLM, the type IA topoisomerase TOP3A, and the OB-fold-containing RMI and RPA subunits. We describe how each component contributes to function, interacts with each other, and the DNA that it manipulates/repairs., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

The treatment of malignancy in cancer predisposition syndromes that also confer exquisite sensitivity to standard chemotherapy and radiation regimens remains a challenge. Bloom syndrome is one such disorder that is caused by a defect in DNA repair, predisposing to the development of early-onset age-related medical conditions and malignancies. We report on two patients with Bloom syndrome who responded well to chemotherapy despite significant alterations to standard protocols necessitated by hypersensitivity. Both patients experienced severe toxicities and exacerbation of endocrine comorbidities during chemotherapy. A multidisciplinary team of oncologists and endocrinologists is best suited to care for this patient population., (© 2020 Wiley Periodicals LLC.)

Pathogenic biallelic variants in the BLM/RECQL3 gene cause a rare autosomal recessive disorder called Bloom syndrome (BS). This syndrome is characterized by severe growth delay, immunodeficiency, dermatological manifestations and a predisposition to a wide variety of cancers, often multiple and very early in life. Literature shows that the main mode of BLM inactivation is protein translation termination. We expanded the molecular spectrum of BS by reporting the first deep intronic variant causing intron exonisation. We describe a patient with a clinical phenotype of BS and a strong increase in sister chromatid exchanges (SCE), who was found to be compound heterozygous for a novel nonsense variant c.3379C>T, p.(Gln1127Ter) in exon 18 and a deep intronic variant c.3020-258A>G in intron 15 of the BLM gene. The deep intronic variant creates a high-quality de novo donor splice site, which leads to retention of two intron segments. Both pseudo-exons introduce a premature stop codon into the reading frame and abolish BLM protein expression, confirmed by Western Blot analysis. These findings illustrate the role of non-coding variation in Mendelian disorders and herewith highlight an unmet need in routine testing of Mendelian disorders, being the added value of RNA-based approaches to provide a complete molecular diagnosis., (© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

The Bloom syndrome helicase BLM interacts with topoisomerase IIIα (TOP3A), RMI1 and RMI2 to form the BTR complex, which dissolves double Holliday junctions to produce non-crossover homologous recombination (HR) products. BLM also promotes DNA-end resection, restart of stalled replication forks, and processing of ultra-fine DNA bridges in mitosis. How these activities of the BTR complex are regulated in cells is still unclear. Here, we identify multiple conserved motifs within the BTR complex that interact cooperatively with the single-stranded DNA (ssDNA)-binding protein RPA. Furthermore, we demonstrate that RPA-binding is required for stable BLM recruitment to sites of DNA replication stress and for fork restart, but not for its roles in HR or mitosis. Our findings suggest a model in which the BTR complex contains the intrinsic ability to sense levels of RPA-ssDNA at replication forks, which controls BLM recruitment and activation in response to replication stress.

Human RecQ helicases play diverse roles in the maintenance of genomic stability. Inactivating mutations in 3 of the 5 human RecQ helicases are responsible for the pathogenesis of Werner syndrome (WS), Bloom syndrome (BS), Rothmund-Thomson syndrome (RTS), RAPADILINO, and Baller-Gerold syndrome (BGS). WS, BS, and RTS patients are at increased risk for developing many age-associated diseases including cancer. Mutations in RecQL1 and RecQL5 have not yet been associated with any human diseases so far. In terms of disease outcome, RecQL4 deserves special attention because mutations in RecQL4 result in 3 autosomal recessive syndromes (RTS type II, RAPADILINO, and BGS). RecQL4, like other human RecQ helicases, has been demonstrated to play a crucial role in the maintenance of genomic stability through participation in diverse DNA metabolic activities. Increased incidence of osteosarcoma in RecQL4-mutated RTS patients and elevated expression of RecQL4 in sporadic cancers including osteosarcoma suggest that loss or gain of RecQL4 expression is linked with cancer susceptibility. In this review, current and future perspectives are discussed on the potential use of RecQL4 as a novel cancer therapeutic target., (© 2021 S. Karger AG, Basel.)

Objective: To analyze the clinical features and genetic variants in a 13-month-old child with Bloom syndrome., Methods: Clinical data of the child was collected. Genetic variants were detected by high-throughput sequencing and Sanger sequencing., Results: The child was born at full term but was small for gestational age. His clinical features included loss of appetite, severe growth retardation, microcephaly, and small mandible. Genetic testing found that he had carried compound heterozygous c.1068+3A>C and c.1069-1G>C variants of the BLM gene, both of which were unreported previously., Conclusion: Bloom syndrome is mainly characterized by severe growth retardation in infancy. The novel variants have expanded the variant spectrum of the BLM gene.

Werner Syndrome (WS) and Bloom Syndrome (BS) are disorders of DNA damage repair caused by biallelic disruption of the WRN or BLM DNA helicases respectively. Both are commonly associated with insulin resistant diabetes, usually accompanied by dyslipidemia and fatty liver, as seen in lipodystrophies. In keeping with this, progressive reduction of subcutaneous adipose tissue is commonly observed. To interrogate the underlying cause of adipose tissue dysfunction in these syndromes, CRISPR/Cas9 genome editing was used to generate human pluripotent stem cell (hPSC) lacking either functional WRN or BLM helicase. No deleterious effects were observed in WRN -/- or BLM -/- embryonic stem cells, however upon their differentiation into adipocyte precursors (AP), premature senescence emerged, impairing later stages of adipogenesis. The resulting adipocytes were also found to be senescent, with increased levels of senescent markers and senescence-associated secretory phenotype (SASP) components. SASP components initiate and reinforce senescence in adjacent cells, which is likely to create a positive feedback loop of cellular senescence within the adipocyte precursor compartment, as demonstrated in normal ageing. Such a scenario could progressively attenuate adipose mass and function, giving rise to "lipodystrophy-like" insulin resistance. Further assessment of pharmacological senolytic strategies are warranted to mitigate this component of Werner and Bloom syndromes.

Background: Bloom syndrome (BS) is a rare autosomal recessive chromosome instability disorder. The main clinical manifestations are growth deficiency, telangiectasic facial erythema, immunodeficiency, and increased risk to develop neoplasias at early age. Cytogenetic test for sister chromatid exchanges (SCEs) is used as a diagnostic marker for BS. In addition, most patients also present mutations in the BLM gene, related to defects in the DNA repair mechanism. However, the molecular mechanism behind the pathogenicity of BS is still not completely understood., Methods: We describe two patients confirmed with BS by SCE and molecular analysis. Also, we performed the gene expression profile by the RNA-seq methodology in mRNA transcripts for differential gene expression analysis using as a biological condition for comparison BS versus health controls., Results: We detected 216 differentially expressed genes related to immunological pathways such as positive regulation and activation of B cells, immune effector process and absence of difference of DNA repair genes expression. In addition; we also observed differentially expressed genes associated with apoptosis control, such as BCL2L1, CASP7, CDKN1A, E2F2, ITPR, CD274, TNFAIP6, TNFRSF25, TNFRSF13C, and TNFRSF17., Conclusion: Our results suggest that the combination of altered expression of genes involved in signaling pathways of immune response and apoptosis control may contribute directly to the main characteristics observed in BS, such as recurrent infections, growth failure, and high risk of cancer. Transcriptome studies of other instability syndromes could allow a more accurate analysis of the relevant gene interactions associated with the destabilization of the genome. This is a first description of the profile of differential gene expression related to immunological aspects detected in patients with BS by RNA-seq., (© 2020 The Authors. Molecular Genetics & Genomic Medicine published by Wiley Periodicals, Inc.)

Bloom syndrome is characterized by severe pre- and postnatal growth deficiency, immune abnormalities, sensitivity to sunlight, insulin resistance, and a high risk for many cancers that occur at an early age. The diagnosis is established on characteristic clinical features and/or presence of biallelic pathogenic variants in the BLM gene. An increased frequency of sister-chromatid exchanges is also observed and can be useful to diagnose BS patients with weak or no clinical features. For the first time, we derived an induced pluripotent cell line from a Bloom syndrome patient retaining the specific sister-chromatid exchange feature as a unique tool to model the pathology., Competing Interests: Declaration of Competing Interest None, (Copyright © 2019. Published by Elsevier B.V.)

Bloom helicase (BLM) and its orthologs are essential for the maintenance of genome integrity. BLM defects represent the underlying cause of Bloom Syndrome, a rare genetic disorder that is marked by strong cancer predisposition. BLM deficient cells accumulate extensive chromosomal aberrations stemming from dysfunctions in homologous recombination (HR). BLM participates in several HR stages and helps dismantle potentially harmful HR intermediates. However, much remains to be learned about the molecular mechanisms of these BLM-mediated regulatory effects. Here, we use DNA curtains to directly visualize the activity of BLM helicase on single molecules of DNA. Our data show that BLM is a robust helicase capable of rapidly (∼70-80 base pairs per second) unwinding extensive tracts (∼8-10 kilobases) of double-stranded DNA (dsDNA). Importantly, we find no evidence for BLM activity on single-stranded DNA (ssDNA) that is bound by replication protein A (RPA). Likewise, our results show that BLM can neither associate with nor translocate on ssDNA that is bound by the recombinase protein RAD51. Moreover, our data reveal that the presence of RAD51 also blocks BLM translocation on dsDNA substrates. We discuss our findings within the context of potential regulator roles for BLM helicase during DNA replication and repair., (© The Author(s) 2019. Published by Oxford University Press on behalf of Nucleic Acids Research.)

Fanconi anaemia (FA), ataxia telangiectasia (A-T), Nijmegen breakage syndrome (NBS) and Bloom syndrome (BS) are clinically distinct, chromosome instability (or breakage) disorders. Each disorder has its own pattern of chromosomal damage, with cells from these patients being hypersensitive to particular genotoxic drugs, indicating that the underlying defect in each case is likely to be different. In addition, each syndrome shows a predisposition to cancer. Study of the molecular and genetic basis of these disorders has revealed mechanisms of recognition and repair of DNA double-strand breaks, DNA interstrand crosslinks and DNA damage during DNA replication. Specialist clinics for each disorder have provided the concentration of expertise needed to tackle their characteristic clinical problems and improve outcomes. Although some treatments of the consequences of a disorder may be possible, for example, haematopoietic stem cell transplantation in FA and NBS, future early intervention to prevent complications of disease will depend on a greater understanding of the roles of the affected DNA repair pathways in development. An important realization has been the predisposition to cancer in carriers of some of these gene mutations.

DNA helicases of the RecQ family are conserved among the three domains of life and play essential roles in genome maintenance. Mutations in several human RecQ helicases lead to diseases that are marked by cancer predisposition. The Saccharomyces cerevisiae RecQ helicase Sgs1 is orthologous to human BLM, defects in which cause the cancer-prone Bloom's Syndrome. Here, we use single-molecule imaging to provide a quantitative mechanistic understanding of Sgs1 activities on single stranded DNA (ssDNA), which is a central intermediate in all aspects of DNA metabolism. We show that Sgs1 acts upon ssDNA bound by either replication protein A (RPA) or the recombinase Rad51. Surprisingly, we find that Sgs1 utilizes a novel motor mechanism for disrupting ssDNA intermediates bound by the recombinase protein Rad51. The ability of Sgs1 to disrupt Rad51-ssDNA filaments may explain some of the defects engendered by RECQ helicase deficiencies in human cells., (© The Author(s) 2019. Published by Oxford University Press on behalf of Nucleic Acids Research.)

Mutations in BLM helicase predispose Bloom syndrome (BS) patients to a wide spectrum of cancers. We demonstrate that MIB1-ubiquitylated BLM in G1 phase functions as an adaptor protein by enhancing the binding of transcription factor c-Jun and its E3 ligase, Fbw7α. BLM enhances the K48/K63-linked ubiquitylation on c-Jun, thereby enhancing the rate of its subsequent degradation. Functionally defective Fbw7α mutants prevalent in multiple human cancers are reactivated by BLM. However, BS patient-derived BLM mutants cannot potentiate Fbw7α-dependent c-Jun degradation. The decrease in the levels of c-Jun in cells expressing BLM prevents effective c-Jun binding to 2,584 gene promoters. This causes decreases in the transcript and protein levels of c-Jun targets in BLM-expressing cells, resulting in attenuated c-Jun-dependent effects during neoplastic transformation. Thus, BLM carries out its function as a tumor suppressor by enhancing c-Jun turnover and thereby preventing its activity as a proto-oncogene., (Copyright © 2018 The Author(s). Published by Elsevier Inc. All rights reserved.)

Objective: To expand the knowledge of the clinical and molecular characteristics of the children with Bloom syndrome. Methods: Clinical data of two siblings with classic Bloom syndrome of Shanghai Children's Medical Center from January 2009 to June 2017 were obtained and analyzed. The DNA of peripheral blood was collected from two Bloom syndrome siblings and their parents during 2015. The mutations were detected with high-throughput sequencing by Illumina sequencing platform. Results: The two siblings (probands) visited our department for short stature and growth retardation, they had full-term normal delivery after normal pregnancy of their mother. Both cases presented with feeding difficulties, malnutrition, microcephaly and mental retardation, repeated infection, symmetrical short stature and special faces. At first, the proband was an 8-year-3-month old girl, her height was 99.7 cm, body mass index (BMI) 12.07 kg/m(2), head circumference was 45.5 cm, and birth weight was 1.6 kg. Her younger brother was 3-year-11-month old, his height was 86.6 cm, BMI was 14 kg/m(2), birth weight was 1.95 kg, and the head circumference reached 36 cm at 16 months. No evidence of cancer and characteristic rash was detected at 8-year follow-up. Pathogenic complex heterozygous mutations c.772&#95;773delCT, p.Leu258Glufs*7 and c.959+ 2T>A in BLM gene were detected in both siblings, which were separately inherited from their unaffected parents. Besides , c.959 + 2T>A has not been reported previously. Conclusions: Children with Bloom syndrome are characterized by short stature, microcephaly, special faces, feeding difficulties, and immunodeficiency. And butterfly erythematous rash may be absent. The c.959+2T>A mutation detected in our patients maybe a novel pathogenic mutation.

Mutations in BLM in Bloom Syndrome patients predispose them to multiple types of cancers. Here we report that BLM is recruited in a biphasic manner to annotated DSBs. BLM recruitment is dependent on the presence of NBS1, MRE11 and ATM. While ATM activity is essential for BLM recruitment in early phase, it is dispensable in late phase when MRE11 exonuclease activity and RNF8-mediated ubiquitylation of BLM are the key determinants. Interaction between polyubiquitylated BLM and NBS1 is essential for the helicase to be retained at the DSBs. The helicase activity of BLM is required for the recruitment of HR and c-NHEJ factors onto the chromatin in S- and G1-phase, respectively. During the repair phase, BLM inhibits HR in S-phase and c-NHEJ in G1-phase. Consequently, inhibition of helicase activity of BLM enhances the rate of DNA alterations. Thus BLM utilizes its pro- and anti-repair functions to maintain genome stability.