BLM heterozygosity and the risk of colorectal cancer

Functions of the Bloom syndrome helicase N-terminal intrinsically disordered region

Bloom syndrome helicase (Blm) is a RecQ family helicase involved in DNA repair, cell cycle progression, and development. Pathogenic variants in human BLM cause the autosomal recessive disorder Bloom Syndrome, characterized by predisposition to numerous types of cancer. Prior studies of Drosophila Blm mutants lacking helicase activity or protein have shown sensitivity to DNA damaging agents, defects in repairing DNA double-strand breaks (DSBs), female sterility, and improper segregation of chromosomes in meiosis. Blm orthologs have a well-conserved and highly structured RecQ helicase domain, but more than half of the protein, particularly in the N-terminus, is predicted to be intrinsically disordered. Because this region is poorly conserved across metazoa, we compared closely related species to identify regions of conservation that might be associated with important functions. We deleted 2 Drosophila-conserved regions in Drosophila melanogaster using CRISPR/Cas9 gene editing and assessed the effects on several Blm functions. Each deletion had distinct effects. Deletion of either conserved region 1 (CR1) or CR2 compromised DSB repair through synthesis-dependent strand annealing and resulted in increased mitotic crossovers. In contrast, CR2 is critical for embryonic development, but CR1 is less important. Loss of CR1 leads to defects in meiotic crossover designation and patterning but does not impact meiotic chromosome segregation, whereas deletion of CR2 does not result in significant meiotic defects. Thus, while the 2 regions have overlapping functions, there are distinct roles facilitated by each. These results provide novel insights into functions of the N-terminal region of Blm helicase.

The Diagnostic Yield of Panel Versus Exome Sequencing to Identify Hereditary Cancer Disorders in Pediatric Cancer

This study aimed to assess whether targeted exome sequencing (TES) outperforms next- generation sequencing (NGS) panels in detecting clinically actionable cancer predisposition syndromes (CPS) in pediatric cancer patients. Patients with cancer underwent genetic counseling and NGS panel testing (27 or 64 genes). Simultaneously, a 616-gene targeted exome, including the NGS panel genes and 552 additional potential cancer-related genes, was conducted on the patients and their parents. Of 42 patients undergoing both tests, NGS panels identified an APC risk allele (RA) in a patient with ganglioglioma and a pathogenic RB1 variant in a patient with retinoblastoma. In addition to the variants found by NGS panels, TES detected a pathogenic MUTYH variant in a patient with acute lymphoblastic leukemia (ALL) and a likely pathogenic (LP) BLM variant in another patient with ALL. TES also revealed a variant in candidate CPS genes, MC1R (RA) and EXT2 (LP), in a patient with embryonal rhabdomyosarcoma and Ewing sarcoma, respectively. Despite identifying variants in candidate CPS genes ( MC1R , EXT2 ) not included on common NGS panels and known CPS genes ( MUTYH , BLM ) absent from this study's panels, the diagnostic yield of clinically actionable CPS variants did not substantially increase with TES compared with standard NGS panels in pediatric cancer patients. In conclusion, for most cases, panel testing remains appropriate for CPS diagnosis in pediatric cancer within typical clinical settings.

Functions of the Bloom Syndrome Helicase N-terminal Intrinsically Disordered Region

Bloom Syndrome helicase (Blm) is a RecQ family helicase involved in DNA repair, cell-cycle progression, and development. Pathogenic variants in human BLM cause the autosomal recessive disorder Bloom Syndrome, characterized by predisposition to numerous types of cancer. Prior studies of Drosophila Blm mutants lacking helicase activity or protein have shown sensitivity to DNA damaging agents, defects in repairing DNA double-strand breaks (DSBs), female sterility, and improper segregation of chromosomes in meiosis. Blm orthologs have a well conserved and highly structured RecQ helicase domain, but more than half of the protein, particularly in the N-terminus, is predicted to be unstructured. Because this region is poorly conserved across multicellular organisms, we compared closely related species to identify regions of conservation, potentially indicating important functions. We deleted two of these Drosophila-conserved regions in D. melanogaster using CRISPR/Cas9 gene editing and assessed the effects on different Blm functions. Each deletion had distinct effects on different Blm activities. Deletion of either conserved region 1 (CR1) or conserved region 2 (CR2) compromised DSB repair through synthesis-dependent strand annealing and resulted in increased mitotic crossovers. In contrast, CR2 is critical for embryonic development but CR1 is not as important. CR1 deletion allows for proficient meiotic chromosome segregation but does lead to defects in meiotic crossover designation and patterning. Finally, deletion of CR2 does not lead to significant meiotic defects, indicating that while each region has overlapping functions, there are discreet roles facilitated by each. These results provide novel insights into functions of the N-terminal disordered region of Blm.

Founder pathogenic variants in colorectal neoplasia susceptibility genes in Ashkenazi Jews undergoing colonoscopy

BACKGROUND

Colorectal neoplasia is one of the most common tumors affecting Western populations.

METHODS

In this study we used a custom amplicon sequencing platform and an in-house bioinformatic pipeline to study constitutional DNA from two different case series of Ashkenazi Jews undergoing colonoscopy (n = 765). The first series all had pathologically confirmed colorectal adenomas and/or carcinoma. The second series consisted of persons who had undergone a colonoscopy within the five years prior to ascertainment, regardless of findings. Ninety-one percent of all patients were asymptomatic at the time of colonoscopy.

RESULTS

In the first group (n = 438), we identified 65 founder variants (56 in APC, 2 in GREM1, 3 in MSH2 and 4 in BLM). In the second group (n = 327), the findings were 30, nothing, 1 and 1, respectively, as well as 2 MSH6 variants.

CONCLUSIONS

Overall, we found that 10 to 15% of Ashkenazi Jewish persons undergoing colonoscopy harbor variants of interest in colorectal and/or polyposis predisposition. This includes pathogenic variants in MSH6, which is associated with colorectal cancer but not with polyposis. We identified no pathogenic variants in more recently discovered polyposis predisposition genes (POLE, POLD1 or NTHL1), rendering the presence of such founder variants rare.

Prenatal Testing for Variants in Genes Associated with Hereditary Cancer Risk: Laboratory Experience and Considerations

Prenatal molecular genetic testing for familial variants that cause inherited disorders has been performed for decades and is accepted as standard of care. However, the spectrum of genes considered for prenatal testing is expanding because of genetic testing for hereditary cancer risk (HCR) and inclusion of conditions with associated cancer risk in carrier screening panels. A few of these disorders, such as ataxia telangiectasia and Bloom syndrome, include increased cancer risk as part of the phenotype, already meet professional guidelines for prenatal testing, and may be associated with increased cancer risk in heterozygous carriers. In addition, recent studies implicate heterozygosity for variants in lysosomal storage disease genes in HCR etiology. Currently, there is no specific professional guidance regarding prenatal testing for HCR. To determine the prevalence of such testing, we reviewed 1345 consecutive prenatal specimens received in our laboratory for familial variant-specific testing and identified 65 (4.8%) with a known or likely HCR component, plus 210 (15.6%) for lysosomal storage disease. These specimens were classified into five distinct categories for clarity and to enable evaluation. Our experience assessing prenatal specimens for variants associated with HCR, with or without a constitutional phenotype, provides metrics for and contributes to the points to consider in prenatal testing for HCR.

TFIP11 promotes replication fork reversal to preserve genome stability

Replication fork reversal, a critical protective mechanism against replication stress in higher eukaryotic cells, is orchestrated via a series of coordinated enzymatic reactions. The Bloom syndrome gene product, BLM, a member of the highly conserved RecQ helicase family, is implicated in this process, yet its precise regulation and role remain poorly understood. In this study, we demonstrate that the GCFC domain-containing protein TFIP11 forms a complex with the BLM helicase. TFIP11 exhibits a preference for binding to DNA substrates that mimic the structure generated at stalled replication forks. Loss of either TFIP11 or BLM leads to the accumulation of the other protein at stalled forks. This abnormal accumulation, in turn, impairs RAD51-mediated fork reversal and slowing, sensitizes cells to replication stress-inducing agents, and enhances chromosomal instability. These findings reveal a previously unidentified regulatory mechanism that modulates the activities of BLM and RAD51 at stalled forks, thereby impacting genome integrity.

Increased Frequency of Clonal Hematopoiesis of Indeterminate Potential in Bloom Syndrome Probands and Carriers

Background

Bloom Syndrome (BSyn) is an autosomal recessive disorder caused by biallelic germline variants in BLM, which functions to maintain genomic stability. BSyn patients have poor growth, immune defects, insulin resistance, and a significantly increased risk of malignancies, most commonly hematologic. The malignancy risk in carriers of pathogenic variants in BLM (BLM variant carriers) remains understudied. Clonal hematopoiesis of indeterminate potential (CHIP) is defined by presence of somatic mutations in leukemia-related genes in blood of individuals without leukemia and is associated with increased risk of leukemia. We hypothesize that somatic mutations driving clonal expansion may be an underlying mechanism leading to increased cancer risk in BSyn patients and BLM variant carriers.

Methods

To determine whether de novo or somatic variation is increased in BSyn patients or carriers, we performed and analyzed exome sequencing on BSyn and control trios.

Results

We discovered that both BSyn patients and carriers had increased numbers of low-frequency, putative somatic variants in CHIP genes compared to controls. Furthermore, BLM variant carriers had increased numbers of somatic variants in DNA methylation genes compared to controls. There was no statistical difference in the numbers of de novo variants in BSyn probands compared to control probands.

Conclusion

Our findings of increased CHIP in BSyn probands and carriers suggest that one or two germline pathogenic variants in BLM could be sufficient to increase the risk of clonal hematopoiesis. These findings warrant further studies in larger cohorts to determine the significance of CHIP as a potential biomarker of aging, cancer, cardiovascular disease, morbidity and mortality.

BLM mutation is associated with increased tumor mutation burden and improved survival after immunotherapy across multiple cancers

BACKGROUND

BLM encodes a RecQ DNA helicase that regulates genomic stability, and its mutations are associated with increased cancer susceptibility. Here, we show a multifaceted role of BLM mutations in tumorigenesis and immunotherapy.

METHODS AND RESULTS

A total of 10,967 cancer samples from the cancer genome atlas database were analyzed, 1.6% of which harbored BLM somatic mutations. BLM mutation was found to be associated with increased tumor mutation burden and more immune-active tumor microenvironment in these patients. Moreover, clinical data of 2785 patients from nine immunotherapy studies were analyzed to study BLM mutations' impact on immunotherapy. Among them, 69 patients harbored BLM mutations, and interestingly, they had significantly higher survival probability than patients without BLM mutations. Cancer patients with BLM mutations had higher complete response and partial response rates, but lower progressive disease rate than BLM nonmutant patients.

CONCLUSION

Our study shows that BLM mutation is related to improved survival after immunotherapy across multiple cancers.

Bloom syndrome patients and mice display accelerated epigenetic aging

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.

Biochemical Properties of Naturally Occurring Human Bloom Helicase Variants

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 (BLM core , residues 636-1298) with either the P868L or G1120R substitution. We also purified a BLM core K869A K870A mutant protein, which alters a lysine-rich loop proximal to the P868 residue. We found that BLM core 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 BLM core 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 BLM core K869A K870A has diminished ATPase activity, weakened binding to duplex DNA structures, and less robust helicase activity compared to wild-type BLM core . Thus, the lysine-rich loop may have an important role in ATPase activity and specific binding and DNA unwinding functions in BLM.

RecQ Helicase Somatic Alterations in Cancer

Named the “caretakers” of the genome, RecQ helicases function in several pathways to maintain genomic stability and repair DNA. This highly conserved family of enzymes consist of five different proteins in humans: RECQL1, BLM, WRN, RECQL4, and RECQL5. Biallelic germline mutations in BLM, WRN, and RECQL4 have been linked to rare cancer-predisposing syndromes. Emerging research has also implicated somatic alterations in RecQ helicases in a variety of cancers, including hematological malignancies, breast cancer, osteosarcoma, amongst others. These alterations in RecQ helicases, particularly overexpression, may lead to increased resistance of cancer cells to conventional chemotherapy. Downregulation of these proteins may allow for increased sensitivity to chemotherapy, and, therefore, may be important therapeutic targets. Here we provide a comprehensive review of our current understanding of the role of RecQ DNA helicases in cancer and discuss the potential therapeutic opportunities in targeting these helicases.

BRCA1 and BRCA2 pathogenic variants and prostate cancer risk: systematic review and meta-analysis

BACKGROUND

BRCA1 and BRCA2 pathogenic variants (PVs) are associated with prostate cancer (PCa) risk, but a wide range of relative risks (RRs) has been reported.

METHODS

We systematically searched PubMed, Embase, MEDLINE and Cochrane Library in June 2021 for studies that estimated PCa RRs for male BRCA1/2 carriers, with no time or language restrictions. The literature search identified 27 studies (BRCA1: n = 20, BRCA2: n = 21).

RESULTS

The heterogeneity between the published estimates was high (BRCA1: I2 = 30%, BRCA2: I2 = 83%); this could partly be explained by selection for age, family history or aggressive disease, and study-level differences in ethnicity composition, use of historical controls, and location of PVs within BRCA2. The pooled RRs were 2.08 (95% CI 1.38-3.12) for Ashkenazi Jewish BRCA2 carriers, 4.35 (95% CI 3.50-5.41) for non-Ashkenazi European ancestry BRCA2 carriers, and 1.18 (95% CI 0.95-1.47) for BRCA1 carriers. At ages <65 years, the RRs were 7.14 (95% CI 5.33-9.56) for non-Ashkenazi European ancestry BRCA2 and 1.78 (95% CI 1.09-2.91) for BRCA1 carriers.

CONCLUSIONS

These PCa risk estimates will assist in guiding clinical management. The study-level subgroup analyses indicate that risks may be modified by age and ethnicity, and for BRCA2 carriers by PV location within the gene, which may guide future risk-estimation studies.

Bloom syndrome helicase contributes to germ line development and longevity in zebrafish

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.

RQC helical hairpin in Bloom's syndrome helicase regulates DNA unwinding by dynamically intercepting nascent nucleotides

The RecQ family of helicases are important for maintenance of genomic integrity. Although functions of constructive subdomains of this family of helicases have been extensively studied, the helical hairpin (HH) in the RecQ-C-terminal domain (RQC) has been underappreciated and remains poorly understood. Here by using single-molecule fluorescence resonance energy transfer, we found that HH in the human BLM transiently intercepts different numbers of nucleotides when it is unwinding a double-stranded DNA. Single-site mutations in HH that disrupt hydrogen bonds and/or salt bridges between DNA and HH change the DNA binding conformations and the unwinding features significantly. Our results, together with recent clinical tests that correlate single-site mutations in HH of human BLM with the phenotype of cancer-predisposing syndrome or Bloom's syndrome, implicate pivotal roles of HH in BLM's DNA unwinding activity. Similar mechanisms might also apply to other RecQ family helicases, calling for more attention to the RQC helical hairpin.

Homologous Recombination Deficiency: Cancer Predispositions and Treatment Implications

Homologous recombination (HR) is a highly accurate DNA repair mechanism. Several HR genes are established cancer susceptibility genes with clinically actionable pathogenic variants (PVs). Classically, BRCA1 and BRCA2 germline PVs are associated with significant breast and ovarian cancer risks. Patients with BRCA1 or BRCA2 PVs display worse clinical outcomes but respond better to platinum-based chemotherapies and poly-ADP ribose polymerase inhibitors, a trait termed "BRCAness." With the advent of whole-exome sequencing and multigene panels, PVs in other HR genes are increasingly identified among familial cancers. As such, several genes such as PALB2 are reclassified as cancer predisposition genes. But evidence for cancer risks remains unclear for many others. In this review, we will discuss cancer predispositions and treatment implications beyond BRCA1 and BRCA2, with a focus on 24 HR genes: 53BP1, ATM, ATR, ATRIP, BARD1, BLM, BRIP1, DMC1, MRE11A, NBN, PALB2, RAD50, RAD51, RAD51B, RAD51C, RAD51D, RIF1, RMI1, RMI2, RPA1, TOP3A, TOPBP1, XRCC2, and XRCC3. IMPLICATIONS FOR PRACTICE: This review provides a comprehensive reference for readers to quickly identify potential cancer predisposing homologous recombination (HR) genes, and to generate research questions for genes with inconclusive evidence. This review also evaluates the "BRCAness" of each HR member. Clinicians can refer to these discussions to identify potential candidates for future clinical trials.

CDX2 inducible microRNAs sustain colon cancer by targeting multiple DNA damage response pathway factors

Meta-analysis of transcripts in colon adenocarcinoma patient tissues led to the identification of a DNA damage responsive miR signature called DNA damage sensitive miRs (DDSMs). DDSMs were experimentally validated in the cancerous colon tissues obtained from an independent cohort of colon cancer patients and in multiple cellular systems with high levels of endogenous DNA damage. All the tested DDSMs were transcriptionally upregulated by a common intestine-specific transcription factor, CDX2. Reciprocally, DDSMs were repressed via the recruitment of HDAC1/2-containing complexes onto the CDX2 promoter. These miRs downregulated multiple key targets in the DNA damage response (DDR) pathway, namely BRCA1, ATM, Chk1 (also known as CHEK1) and RNF8. CDX2 directly regulated the DDSMs, which led to increased tumor volume and metastasis in multiple preclinical models. In colon cancer patient tissues, the DDSMs negatively correlated with BRCA1 levels, were associated with decreased probability of survival and thereby could be used as a prognostic biomarker. This article has an associated First Person interview with the first author of the paper.

Bloom syndrome and the underlying causes of genetic instability

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.

Functions of BLM Helicase in Cells: Is It Acting Like a Double-Edged Sword?

DNA damage repair response is an important biological process involved in maintaining the fidelity of the genome in eukaryotes and prokaryotes. Several proteins that play a key role in this process have been identified. Alterations in these key proteins have been linked to different diseases including cancer. BLM is a 3′−5′ ATP-dependent RecQ DNA helicase that is one of the most essential genome stabilizers involved in the regulation of DNA replication, recombination, and both homologous and non-homologous pathways of double-strand break repair. BLM structure and functions are known to be conserved across many species like yeast, Drosophila, mouse, and human. Genetic mutations in the BLM gene cause a rare, autosomal recessive disorder, Bloom syndrome (BS). BS is a monogenic disease characterized by genomic instability, premature aging, predisposition to cancer, immunodeficiency, and pulmonary diseases. Hence, these characteristics point toward BLM being a tumor suppressor. However, in addition to mutations, BLM gene undergoes various types of alterations including increase in the copy number, transcript, and protein levels in multiple types of cancers. These results, along with the fact that the lack of wild-type BLM in these cancers has been associated with increased sensitivity to chemotherapeutic drugs, indicate that BLM also has a pro-oncogenic function. While a plethora of studies have reported the effect of BLM gene mutations in various model organisms, there is a dearth in the studies undertaken to investigate the effect of its oncogenic alterations. We propose to rationalize and integrate the dual functions of BLM both as a tumor suppressor and maybe as a proto-oncogene, and enlist the plausible mechanisms of its deregulation in cancers.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund–Thomson syndrome (RTS), Baller–Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Human RecQ Helicases in DNA Double-Strand Break Repair

RecQ DNA helicases are a conserved protein family found in bacteria, fungus, plants, and animals. These helicases play important roles in multiple cellular functions, including DNA replication, transcription, DNA repair, and telomere maintenance. Humans have five RecQ helicases: RECQL1, Bloom syndrome protein (BLM), Werner syndrome helicase (WRN), RECQL4, and RECQL5. Defects in BLM and WRN cause autosomal disorders: Bloom syndrome (BS) and Werner syndrome (WS), respectively. Mutations in RECQL4 are associated with three genetic disorders, Rothmund-Thomson syndrome (RTS), Baller-Gerold syndrome (BGS), and RAPADILINO syndrome. Although no genetic disorders have been reported due to loss of RECQL1 or RECQL5, dysfunction of either gene is associated with tumorigenesis. Multiple genetically independent pathways have evolved that mediate the repair of DNA double-strand break (DSB), and RecQ helicases play pivotal roles in each of them. The importance of DSB repair is supported by the observations that defective DSB repair can cause chromosomal aberrations, genomic instability, senescence, or cell death, which ultimately can lead to premature aging, neurodegeneration, or tumorigenesis. In this review, we will introduce the human RecQ helicase family, describe in detail their roles in DSB repair, and provide relevance between the dysfunction of RecQ helicases and human diseases.

Heterozygous germline BLM mutations increase susceptibility to asbestos and mesothelioma

Rare biallelic BLM gene mutations cause Bloom syndrome. Whether BLM heterozygous germline mutations (BLM ^+/-) cause human cancer remains unclear. We sequenced the germline DNA of 155 mesothelioma patients (33 familial and 122 sporadic). We found 2 deleterious germline BLM ^+/- mutations within 2 of 33 families with multiple cases of mesothelioma, one from Turkey (c.569_570del; p.R191Kfs*4) and one from the United States (c.968A>G; p.K323R). Some of the relatives who inherited these mutations developed mesothelioma, while none with nonmutated BLM were affected. Furthermore, among 122 patients with sporadic mesothelioma treated at the US National Cancer Institute, 5 carried pathogenic germline BLM ^+/- mutations. Therefore, 7 of 155 apparently unrelated mesothelioma patients carried BLM ^+/- mutations, significantly higher (P = 6.7E-10) than the expected frequency in a general, unrelated population from the gnomAD database, and 2 of 7 carried the same missense pathogenic mutation c.968A>G (P = 0.0017 given a 0.00039 allele frequency). Experiments in primary mesothelial cells from Blm ^+/- mice and in primary human mesothelial cells in which we silenced BLM revealed that reduced BLM levels promote genomic instability while protecting from cell death and promoted TNF-α release. Blm ^+/- mice injected intraperitoneally with asbestos had higher levels of proinflammatory M1 macrophages and of TNF-α, IL-1β, IL-3, IL-10, and IL-12 in the peritoneal lavage, findings linked to asbestos carcinogenesis. Blm ^+/- mice exposed to asbestos had a significantly shorter survival and higher incidence of mesothelioma compared to controls. We propose that germline BLM ^+/- mutations increase the susceptibility to asbestos carcinogenesis, enhancing the risk of developing mesothelioma.

National recommendations of the French Genetics and Cancer Group - Unicancer on the modalities of multi-genes panel analyses in hereditary predispositions to tumors of the digestive tract

In case of suspected hereditary predisposition to digestive cancers, next-generation sequencing can analyze simultaneously several genes associated with an increased risk of developing these tumors. Thus, "Gastro Intestinal" (GI) gene panels are commonly used in French molecular genetic laboratories. Lack of international recommendations led to disparities in the composition of these panels and in the management of patients. To harmonize practices, the Genetics and Cancer Group (GGC)-Unicancer set up a working group who carried out a review of the literature for 31 genes of interest in this context and established a list of genes for which the estimated risks associated with pathogenic variant seemed sufficiently reliable and high for clinical use. Pancreatic cancer susceptibility genes have been excluded. This expertise defined a panel of 14 genes of confirmed clinical interest and relevant for genetic counseling: APC, BMPR1A, CDH1, EPCAM, MLH1, MSH2, MSH6, MUTYH, PMS2, POLD1, POLE, PTEN, SMAD4 and STK11. The reasons for the exclusion of the others 23 genes have been discussed. The paucity of estimates of the associated tumor risks led to the exclusion of genes, in particular CTNNA1, MSH3 and NTHL1, despite their implication in the molecular pathways involved in the pathophysiology of GI cancers. A regular update of the literature is planned to up-grade this panel of genes in case of new data on candidate genes. Genetic and epidemiological studies and international collaborations are needed to better estimate the risks associated with the pathogenic variants of these genes either selected or not in the current panel.

Investigating the Role of Telomere and Telomerase Associated Genes and Proteins in Endometrial Cancer

Endometrial cancer (EC) is the commonest gynaecological malignancy. Current prognostic markers are inadequate to accurately predict patient survival, necessitating novel prognostic markers, to improve treatment strategies. Telomerase has a unique role within the endometrium, whilst aberrant telomerase activity is a hallmark of many cancers. The aim of the current in silico study is to investigate the role of telomere and telomerase associated genes and proteins (TTAGPs) in EC to identify potential prognostic markers and therapeutic targets. Analysis of RNA-seq data from The Cancer Genome Atlas identified differentially expressed genes (DEGs) in EC (568 TTAGPs out of 3467) and ascertained DEGs associated with histological subtypes, higher grade endometrioid tumours and late stage EC. Functional analysis demonstrated that DEGs were predominantly involved in cell cycle regulation, while the survival analysis identified 69 DEGs associated with prognosis. The protein-protein interaction network constructed facilitated the identification of hub genes, enriched transcription factor binding sites and drugs that may target the network. Thus, our in silico methods distinguished many critical genes associated with telomere maintenance that were previously unknown to contribute to EC carcinogenesis and prognosis, including NOP56, WFS1, ANAPC4 and TUBB4A. Probing the prognostic and therapeutic utility of these novel TTAGP markers will form an exciting basis for future research.

Tumour predisposition and cancer syndromes as models to study gene-environment interactions

Cell division and organismal development are exquisitely orchestrated and regulated processes. The dysregulation of the molecular mechanisms underlying these processes may cause cancer, a consequence of cell-intrinsic and/or cell-extrinsic events. Cellular DNA can be damaged by spontaneous hydrolysis, reactive oxygen species, aberrant cellular metabolism or other perturbations that cause DNA damage. Moreover, several environmental factors may damage the DNA, alter cellular metabolism or affect the ability of cells to interact with their microenvironment. While some environmental factors are well established as carcinogens, there remains a large knowledge gap of others owing to the difficulty in identifying them because of the typically long interval between carcinogen exposure and cancer diagnosis. DNA damage increases in cells harbouring mutations that impair their ability to correctly repair the DNA. Tumour predisposition syndromes in which cancers arise at an accelerated rate and in different organs - the equivalent of a sensitized background - provide a unique opportunity to examine how gene-environment interactions influence cancer risk when the initiating genetic defect responsible for malignancy is known. Understanding the molecular processes that are altered by specific germline mutations, environmental exposures and related mechanisms that promote cancer will allow the design of novel and effective preventive and therapeutic strategies.

Dominantly Inherited Hereditary Nonpolyposis Colorectal Cancer Not Caused by MMR Genes

In the past two decades, multiple studies have been undertaken to elucidate the genetic cause of the predisposition to mismatch repair (MMR)-proficient nonpolyposis colorectal cancer (CRC). Here, we present the proposed candidate genes according to their involvement in specific pathways considered relevant in hereditary CRC and/or colorectal carcinogenesis. To date, only pathogenic variants in RPS20 may be convincedly linked to hereditary CRC. Nevertheless, accumulated evidence supports the involvement in the CRC predisposition of other genes, including MRE11, BARD1, POT1, BUB1B, POLE2, BRF1, IL12RB1, PTPN12, or the epigenetic alteration of PTPRJ. The contribution of the identified candidate genes to familial/early onset MMR-proficient nonpolyposis CRC, if any, is extremely small, suggesting that other factors, such as the accumulation of low risk CRC alleles, shared environmental exposures, and/or gene-environmental interactions, may explain the missing heritability in CRC.

Germline BLM mutations and metastatic prostate cancer

BACKGROUND

Biallelic loss-of-function BLM mutations result in Bloom syndrome: a genetic disorder characterized by growth deficiencies, photosensitivity, and multiple cancer susceptibilities. There are conflicting reports about whether or not heterozygous BLM carriers are at a higher risk of various cancers. Without BLM protein functionality, there is evidence of increased sister chromatid exchange and chromosomal instability.

METHODS

Metastatic prostate cancer patients (N = 796) underwent germline genetic testing as part of routine care at three academic centers. Patients with heterozygous BLM mutations were identified. Tumor tissue was analyzed for somatic alterations in those patients who had a germline pathogenic mutation. Control data using a population sample were extracted from the Genome Aggregation Database.

RESULTS

Heterozygous BLM germline mutations in 5 of 796 patients (prevalence, 0.63%). All mutations were loss-of-function truncating alterations. None of the mutations were BLM^Ash . The control population (gnomAD) frequency of pathogenic or likely pathogenic BLM mutations was 0.18% (212 of 116 653). The relative risk (RR) of BLM mutations in metastatic prostate cancer patients was 3.4 (95% CI, 1.42-8.33; P < .0062) compared to gnomAD controls. Tumor DNA sequencing in the BLM carriers showed no evidence of somatic BLM mutations. Interestingly, 3 of 5 BLM germline carriers had bi-allelic BRCA2 inactivation evident on tumor sequencing. One patient had both germline and somatic mutations in BRCA2. Excluding the patient with the germline BRCA2 mutation (BLM prevalence, 4 of 796: 0.50%) still yielded a statistically significant finding vs the gnomAD controls (RR, 2.8; 95% CI, 1.02-7.39; P < .04).

CONCLUSION

Truncating BLM germline mutations occur at a higher frequency in patients with advanced prostate cancer as compared to control populations. Though no biallelic loss of BLM was no noted in cancers, a surprising number of the BLM germline heterozygotes had pathogenic BRCA2 mutations in their tumor.

Extreme intratumour heterogeneity and driver evolution in mismatch repair deficient gastro-oesophageal cancer

Mismatch repair deficient (dMMR) gastro-oesophageal adenocarcinomas (GOAs) show better outcomes than their MMR-proficient counterparts and high immunotherapy sensitivity. The hypermutator-phenotype of dMMR tumours theoretically enables high evolvability but their evolution has not been investigated. Here we apply multi-region exome sequencing (MSeq) to four treatment-naive dMMR GOAs. This reveals extreme intratumour heterogeneity (ITH), exceeding ITH in other cancer types >20-fold, but also long phylogenetic trunks which may explain the exquisite immunotherapy sensitivity of dMMR tumours. Subclonal driver mutations are common and parallel evolution occurs in RAS, PIK3CA, SWI/SNF-complex genes and in immune evasion regulators. MSeq data and evolution analysis of single region-data from 64 MSI GOAs show that chromosome 8 gains are early genetic events and that the hypermutator-phenotype remains active during progression. MSeq may be necessary for biomarker development in these heterogeneous cancers. Comparison with other MSeq-analysed tumour types reveals mutation rates and their timing to determine phylogenetic tree morphologies.

Implication of DNA repair genes in Lynch-like syndrome

Many colorectal cancers (CRCs) that exhibit microsatellite instability (MSI) are not explained by MLH1 promoter methylation or germline mutations in mismatch repair (MMR) genes, which cause Lynch syndrome (LS). Instead, these Lynch-like syndrome (LLS) patients have somatic mutations in MMR genes. However, many of these patients are young and have relatives with cancer, suggesting a hereditary entity. We performed germline sequence analysis in LLS patients and determined their tumor's mutational profiles using FFPE DNA. Six hundred and fifty-four consecutive CRC patients were screened for suspected LS using MSI and absence of MLH1 methylation. Suspected LS cases were exome sequenced to identify germline and somatic mutations. Single nucleotide variants were used to characterize mutational signatures. We identified 23 suspected LS cases. Germline sequence analysis of 16 available samples identified five cases with LS mutations and 11 cases without LS mutations, LLS. Most LLS tumors had a combination of somatic MMR gene mutation and loss of heterozygosity. LLS patients were relatively young and had excess first-degree relatives with cancer. Four of the 11 LLS patients had rare likely pathogenic variants in genes that maintain genome integrity. Moreover, tumors from this group had a distinct mutational signature compared to tumors from LLS patients lacking germline mutations in these genes. In summary, more than a third of the LLS patients studied had germline mutations in genes that maintain genome integrity and their tumors had a distinct mutational signature. The possibility of hereditary factors in LLS warrants further studies so counseling can be properly informed.

Inherited Variants in BLM and the Risk and Clinical Characteristics of Breast Cancer

Bloom Syndrome is a rare recessive disease which includes a susceptibility to various cancers. It is caused by homozygous mutations of the BLM gene. To investigate whether heterozygous carriers of a BLM mutation are predisposed to breast cancer, we sequenced BLM in 617 patients from Polish families with a strong family history of breast cancer. We detected a founder mutation (c.1642C>T, p.Gln548Ter) in 3 of the 617 breast cancer patients (0.49%) who were sequenced. Then, we genotyped 14,804 unselected breast cancer cases and 4698 cancer-free women for the founder mutation. It was identified in 82 of 14,804 (0.55%) unselected cases and in 26 of 4698 (0.55%) controls (OR = 1.0; 95%CI 0.6–1.6). Clinical characteristics of breast cancers in the BLM mutation carriers and non-carriers were similar. Loss of the wild-type BLM allele was not detected in cancers from the BLM mutation carriers. No cancer type was more common in the relatives of mutation carriers compared to relatives of non-carriers. The BLM founder mutation p.Gln548Ter, which in a homozygous state is a cause of Bloom syndrome, does not appear to predispose to breast cancer in a heterozygous state. The finding casts doubt on the designation of BLM as an autosomal dominant breast cancer susceptibility gene.

Chromosome instability syndromes

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.

BLM's balancing act and the involvement of FANCJ in DNA repair

Timely recruitment of DNA damage response proteins to sites of genomic structural lesions is very important for signaling mechanisms to activate appropriate cell cycle checkpoints but also repair the altered DNA sequence to suppress mutagenesis. The eukaryotic cell is characterized by a complex cadre of players and pathways to ensure genomic stability in the face of replication stress or outright genomic insult by endogenous metabolites or environmental agents. Among the key performers are molecular motor DNA unwinding enzymes known as helicases that sense genomic perturbations and separate structured DNA strands so that replacement of a damaged base or sugar-phosphate backbone lesion can occur efficiently. Mutations in the BLM gene encoding the DNA helicase BLM leads to a rare chromosomal instability disorder known as Bloom's syndrome. In a recent paper by the Sengupta lab, BLM's role in the correction of double-strand breaks (DSB), a particularly dangerous form of DNA damage, was investigated. Adding to the complexity, BLM appears to be a key ringmaster of DSB repair as it acts both positively and negatively to regulate correction pathways of high or low fidelity. The FANCJ DNA helicase, mutated in another chromosomal instability disorder known as Fanconi Anemia, is an important player that likely coordinates with BLM in the balancing act. Further studies to dissect the roles of DNA helicases like FANCJ and BLM in DSB repair are warranted.

Targeted sequencing of established and candidate colorectal cancer genes in the Colon Cancer Family Registry Cohort

The underlying genetic cause of colorectal cancer (CRC) can be identified for 5-10% of all cases, while at least 20% of CRC cases are thought to be due to inherited genetic factors. Screening for highly penetrant mutations in genes associated with Mendelian cancer syndromes using next-generation sequencing (NGS) can be prohibitively expensive for studies requiring large samples sizes. The aim of the study was to identify rare single nucleotide variants and small indels in 40 established or candidate CRC susceptibility genes in 1,046 familial CRC cases (including both MSS and MSI-H tumor subtypes) and 1,006 unrelated controls from the Colon Cancer Family Registry Cohort using a robust and cost-effective DNA pooling NGS strategy. We identified 264 variants in 38 genes that were observed only in cases, comprising either very rare (minor allele frequency <0.001) or not previously reported (n=90, 34%) in reference databases, including six stop-gain, three frameshift, and 255 non-synonymous variants predicted to be damaging. We found novel germline mutations in established CRC genes MLH1, APC, and POLE, and likely pathogenic variants in cancer susceptibility genes BAP1, CDH1, CHEK2, ENG, and MSH3. For the candidate CRC genes, we identified likely pathogenic variants in the helicase domain of POLQ and in the LRIG1, SH2B3, and NOS1 genes and present their clinicopathological characteristics. Using a DNA pooling NGS strategy, we identified novel germline mutations in established CRC susceptibility genes in familial CRC cases. Further studies are required to support the role of POLQ, LRIG1, SH2B3 and NOS1 as CRC susceptibility genes.

Aberrant BLM cytoplasmic expression associates with DNA damage stress and hypersensitivity to DNA-damaging agents in colorectal cancer

BACKGROUND

Bloom syndrome is a rare and recessive disorder characterized by loss-of-function mutations of the BLM gene, which encodes a RecQ 3'-5' DNA helicase. Despite its putative tumor suppressor function, the contribution of BLM to human sporadic colorectal cancer (CRC) remains poorly understood.

METHODS

The transcriptional regulation mechanism underlying BLM and related DNA damage response regulation in independent CRC subsets and a panel of derived cell lines was investigated by bioinformatics analysis, the transcriptomic profile, a CpG island promoter methylation assay, Western blot, and an immunolocalization assay.

RESULTS

In silico analysis of gene expression data sets revealed that BLM is overexpressed in poorly differentiated CRC and exhibits a close connection with shorter relapse-free survival even after adjustment for prognostic factors and pathways that respond to DNA damage response through ataxia telangiectasia mutated (ATM) signaling. Functional characterization demonstrated that CpG island promoter hypomethylation increases BLM expression and associates with cytoplasmic BLM mislocalization and increased DNA damage response both in clinical CRC samples and in derived cancer cell lines. The DNA-damaging agent S-adenosylmethionine suppresses BLM expression, leading to the inhibition of cell growth following accumulation of DNA damage. In tumor specimens, cytoplasmic accumulation of BLM correlates with DNA damage and γH2AX and phosphorylated ATM foci and predicts long-term progression-free survival in metastatic patients treated with irinotecan.

CONCLUSIONS

Taken together, the findings of this study provide the first evidence that cancer-linked DNA hypomethylation and cytosolic BLM mislocalization might reflect compromised levels of DNA-repair activity and enhanced hypersensitivity to DNA-damaging agents in CRC patients.

First Two Cases of Bloom Syndrome in Russia: Lack of Skin Manifestations in a BLM c.1642C>T (p.Q548X) Homozygote as a Likely Cause of Underdiagnosis

Bloom syndrome (BS) is an exceptionally rare hereditary disease. Typical manifestations of BS usually include growth deficiency, a characteristic facial appearance, skin hypersensitivity to ultraviolet irradiation, and a strong predisposition to early-onset cancers. We have previously described a recurrent BLM c.1642C>T (p.Q548X) mutation, which is present in heterozygous state in 0.2-0.6% of individuals of Slavic origin. Despite the high occurrence of this founder allele, BS has not yet been described in patients of Slavic ethnicity. Here, we present 2 cases of BS, which were missed by standard genetic counseling and were eventually identified entirely due to chance. Our patients show the need for further investigations to confirm whether the atypical appearance of BS is indeed characteristic for biallelic carriers of the c.1642C>T (p.Q548X) allele and whether the absence of skin manifestations contributes to the underdiagnosis of the disease in Russia. Therefore, we suggest that all Slavic patients with only one single clinical feature of BS are to be screened for this allele and subjected to further analysis wherever appropriate. In addition to identifying new BS patients, this effort will help to clarify the frequency of "atypical BS" with incomplete phenotypic manifestations.

Bloom's syndrome: Why not premature aging?: A comparison of the BLM and WRN helicases

Genomic instability is a hallmark of cancer and aging. Premature aging (progeroid) syndromes are often caused by mutations in genes whose function is to ensure genomic integrity. The RecQ family of DNA helicases is highly conserved and plays crucial roles as genome caretakers. In humans, mutations in three RecQ genes - BLM, WRN, and RECQL4 - give rise to Bloom's syndrome (BS), Werner syndrome (WS), and Rothmund-Thomson syndrome (RTS), respectively. WS is a prototypic premature aging disorder; however, the clinical features present in BS and RTS do not indicate accelerated aging. The BLM helicase has pivotal functions at the crossroads of DNA replication, recombination, and repair. BS cells exhibit a characteristic form of genomic instability that includes excessive homologous recombination. The excessive homologous recombination drives the development in BS of the many types of cancers that affect persons in the normal population. Replication delay and slower cell turnover rates have been proposed to explain many features of BS, such as short stature. More recently, aberrant transcriptional regulation of growth and survival genes has been proposed as a hypothesis to explain features of BS.

Bloom's Syndrome: Clinical Spectrum, Molecular Pathogenesis, and Cancer Predisposition

Bloom's syndrome is an autosomal recessive disorder characterized by prenatal and postnatal growth deficiency, photosensitive skin changes, immune deficiency, insulin resistance, and a greatly increased risk of early onset of cancer and for the development of multiple cancers. Loss-of-function mutations of BLM, which codes for a RecQ helicase, cause Bloom's syndrome. The absence of a functional BLM protein causes chromosome instability, excessive homologous recombination, and a greatly increased number of sister chromatid exchanges that are pathognomonic of the syndrome. A common founder mutation designated blmAsh is present in about 1 in 100 persons of Eastern European Jewish ancestry, and there are additional recurrent founder mutations among other populations. Missense, nonsense, and frameshift mutations as well as multiexonic deletions have all been observed. Bloom's syndrome is a prototypical chromosomal instability syndrome, and the somatic mutations that occur as a result of that instability are responsible for the increased cancer risk. Although there is currently no treatment aimed at the underlying genetic abnormality, persons with Bloom's syndrome benefit from sun protection, aggressive treatment of infections, surveillance for insulin resistance, and early identification of cancer.