Genetic heterogeneity among Fanconi anemia heterozygotes and risk of cancer

Carotenoids as modulators of the PI3K/Akt/mTOR pathway: innovative strategies in cancer therapy

Cancer progression is primarily driven by the uncontrolled activation of cellular signaling pathways, with the PI3K/Akt/mTOR (PAMT) pathway playing a central role. This pathway significantly contributes to the proliferation and survival of cancer cells, and its hyperactivity is a major challenge in managing several types of malignancies. This article delves into the promising potential of carotenoids, natural pigments found in abundance in fruits and vegetables, as a novel therapeutic strategy for cancer treatment. By specifically targeting and inhibiting the PAMT pathway, carotenoids may effectively disrupt the growth and survival of cancer cells. The article examines the complex mechanisms underlying these interactions and highlights the obstacles faced in cancer treatment. It proposes a compelling approach to developing therapies that leverage natural products to target this critical pathway, offering a fresh perspective on cancer treatment. Further research is essential to enhance the therapeutic efficacy of these compounds.

Prediction of Cancer Proneness under Influence of X-rays with Four DNA Mutability and/or Three Cellular Proliferation Assays

Context: Although carcinogenesis is a multi-factorial process, the mutability and the capacity of cells to proliferate are among the major features of the cells that contribute together to the initiation and promotion steps of cancer formation. Particularly, mutability can be quantified by hyper-recombination rate assessed with specific plasmid assay, hypoxanthine-guanine phosphoribosyltransferase (HPRT) mutations frequency rate, or MRE11 nuclease activities. Cell proliferation can be assessed by flow cytometry by quantifying G2/M, G1 arrests, or global cellular evasion.

METHODS

All these assays were applied to skin untransformed fibroblasts derived from eight major cancer syndromes characterized by their excess of relative cancer risk (ERR).

RESULTS

Significant correlations with ERR were found between hyper-recombination assessed by the plasmid assay and G2/M arrest and described a third-degree polynomial ERR function and a sigmoidal ERR function, respectively. The product of the hyper-recombination rate and capacity of proliferation described a linear ERR function that permits one to better discriminate each cancer syndrome.

CONCLUSIONS

Hyper-recombination and cell proliferation were found to obey differential equations that better highlight the intrinsic bases of cancer formation. Further investigations to verify their relevance for cancer proneness induced by exogenous agents are in progress.

Germline variants in acquired aplastic anemia: current knowledge and future perspectives

Aplastic anemia (AA) is a disease characterized by failure of hematopoiesis, bone marrow aplasia, and pancytopenia. It can be inherited or acquired. Although acquired AA is believed to be immune-mediated and random, new evidence suggests an underlying genetic predisposition. Besides confirmed genomic mutations that contribute to inherited AA (such as pathogenic mutations of TERT and TERC), germline variants, often in heterozygous states, also play a not negligible role in the onset and progression of acquired AA. These variants, associated with inherited bone marrow failure syndromes and inborn errors of immunity, contribute to the disease, possibly through mechanisms including gene homeostasis, DNA repair, and immune injury. This article explores the nuanced association between acquired AA and germline variants, detailing the clinical significance of germline variants in diagnosing and managing this condition. More work is encouraged to better understand the role of immunogenic pathogenic variants and whether somatic mutations participate as secondary "hits" in the development of bone marrow failure.

First report of familial mixed phenotype acute leukemia: shared clinical characteristics, Philadelphia translocation, and germline variants

While our understanding of the molecular basis of mixed phenotype acute leukemia (MPAL) has progressed over the decades, our knowledge is limited and the prognosis remains poor. Investigating cases of familial leukemia can provide insights into the role of genetic and environmental factors in leukemogenesis. Although familial cases and associated mutations have been identified in some leukemias, familial occurrence of MPAL has never been reported. Here, we report the first cases of MPAL in a family. A 68-year-old woman was diagnosed with MPAL and received haploidentical stem cell transplantation from her 44-year-old son. In four years, the son himself developed MPAL. Both cases exhibited similar characteristics such as biphenotypic leukemia with B/myeloid cell antigens, Philadelphia translocation (BCR-ABL1 mutation), and response to acute lymphoblastic leukemia-type chemotherapy. These similarities suggest the presence of hereditary factors contributing to the development of MPAL. Targeted sequencing identified shared germline variants in these cases; however, in silico analyses did not strongly support their pathogenicity. Intriguingly, when the son developed MPAL, the mother did not develop donor-derived leukemia and remained in remission. Our cases provide valuable insights to guide future research on familial MPAL.

Liver abnormalities are frequent and persistent in patients with Fanconi anemia

ABSTRACT

Liver disease has not been well described in patients with Fanconi anemia (FA). Improvements in outcomes of transplant mean that more individuals with FA are reaching adulthood and new features of the FA phenotype are being discovered. We performed a retrospective review of liver function in a cohort of 97 patients with FA followed-up for at least 10 years at a single center. We identified a high frequency of transaminitis (n = 31, 32%) without elevation of bilirubin and with no evidence of structural hepatic abnormality in patients with FA. Transaminitis was persistent in many cases, sometimes lasting more than a decade without clinical manifestation, although 2 patients with prolonged transaminitis are deceased from liver failure, indicating important long-term clinical consequences. Transaminitis was found in patients who had and had not received transplant but was more frequent in recipients of transplant. Exposure to total body irradiation increased risk (odds ratio, 15.5 [95% confidence interval, 2.44-304.54]; P = .01), whereas treatment with androgens did not. Review of limited numbers of liver biopsies and autopsy material showed a cholestatic pattern of liver injury, with progressive fibrosis, in the majority of patients. Occurrence in cases without transplant as well as cases with transplant argues against a potential diagnosis of atypical liver graft-versus-host disease. Limited data regarding therapy suggest no benefit from treatment with steroids or other immune suppressive medications or ursodeoxycholic acid. Our data show that liver disease is common in patients with FA, and because most children with FA now reach adulthood, end-stage liver disease in young adulthood means systematic testing of potential therapies is urgently needed.

Most Fanconi anemia heterozygotes are not at increased cancer risk: A genome-first DiscovEHR cohort population study

PURPOSE

Fanconi anemia (FA) is a bone marrow failure and cancer predisposition syndrome caused primarily by biallelic pathogenic variants in 1 of 22 genes involved in DNA interstrand cross-link repair. An enduring question concerns cancer risk of those with a single pathogenic FA gene variant. To investigate all FA genes, this study utilized the DiscovEHR cohort of 170,503 individuals with exome sequencing and electronic health data.

METHODS

5822 subjects with a single pathogenic variant in an FA gene were identified. Two control groups were used in primary analysis deriving cancer risk signals. Secondary exploratory analysis was conducted using the UK Biobank and The Cancer Genome Atlas.

RESULTS

Signals for elevated cancer risk were found in all 5 known cancer predisposition genes. Among the remaining 15 genes associated with autosomal recessive inheritance cancer risk signals were found for 4 cancers across 3 genes in the primary cohort but were not validated in secondary cohorts.

CONCLUSION

To our knowledge, this is the first and largest FA heterozygote study to use genomic ascertainment and validates well-established cancer predispositions in 5 genes, whereas finding insufficient evidence of predisposition in 15 others. Our findings inform clinical surveillance given how common pathogenic FA variants are in the population.

Grade 5 Radiation Necrosis After Whole-Brain Radiation Therapy

Whole-brain radiation treatment is often considered for patients with leptomeningeal disease. There are limited reports of the development of radiation necrosis after whole-brain radiation treatment and fewer associating the presence of germline mutations with risk. We present a case report to highlight the need for consideration of radiosensitizing mutations when recommending radiation therapy.

Prevalence of germline mutations in cancer susceptibility genes in Chinese patients with renal cell carcinoma

Background

Germline pathogenic variants are estimated to affect 3-5% of patients with renal cell carcinoma (RCC). The identification of patients with hereditary RCC is important for cancer screening and treatment guidance.

Methods

Whole-exome sequencing (WES) (n=69) or gene panel sequencing containing 139 genes (n=54) related to germline cancer predisposition was used to analyze germline mutations in 123 patients with RCC admitted to Department of Urology, The Third Medical Center of Chinese PLA General Hospital. Chi-square test (χ²) was used to analyze relationship between clinicopathologic parameters and germline mutations.

Results

A total of 13 (10.57%) patients carried pathogenic or likely pathogenic germline mutations in 10 cancer predisposition genes, including VHL, FH, FLCN, SDHB, MUTYH, RAD51C, NBN, RAD50, FANCI, and FANCM. A total of 6 of these 10 cancer predisposition genes were associated with maintenance of genomic stability and DNA repair. Patients harboring pathogenic germline mutations tended to have an earlier RCC onset. The prevalence of deleterious mutations was higher in patients with bilateral or multifocal RCC compared to patients without bilateral or multifocal RCC. Patients with non-clear cell RCC (nccRCC) were significantly more likely to have RCC-associated gene mutations.

Conclusions

To our knowledge, this is the first report of pathogenic germline mutations in the FANCI and FANCM genes and heterozygous germline missense mutation in exon 5 of the FH gene c.563A>T:p.N188I in RCC. Young RCC patients, patients with bilateral or multifocal RCC, or patients with nccRCC are more likely to have pathogenic/potentially pathogenic germline mutations.

Molecular Genetic Characteristics of FANCI, a Proposed New Ovarian Cancer Predisposing Gene

FANCI was recently identified as a new candidate ovarian cancer (OC)-predisposing gene from the genetic analysis of carriers of FANCI c.1813C>T; p.L605F in OC families. Here, we aimed to investigate the molecular genetic characteristics of FANCI, as they have not been described in the context of cancer. We first investigated the germline genetic landscape of two sisters with OC from the discovery FANCI c.1813C>T; p.L605F family (F1528) to re-affirm the plausibility of this candidate. As we did not find other conclusive candidates, we then performed a candidate gene approach to identify other candidate variants in genes involved in the FANCI protein interactome in OC families negative for pathogenic variants in BRCA1, BRCA2, BRIP1, RAD51C, RAD51D, and FANCI, which identified four candidate variants. We then investigated FANCI in high-grade serous ovarian carcinoma (HGSC) from FANCI c.1813C>T carriers and found evidence of loss of the wild-type allele in tumour DNA from some of these cases. The somatic genetic landscape of OC tumours from FANCI c.1813C>T carriers was investigated for mutations in selected genes, copy number alterations, and mutational signatures, which determined that the profiles of tumours from carriers were characteristic of features exhibited by HGSC cases. As other OC-predisposing genes such as BRCA1 and BRCA2 are known to increase the risk of other cancers including breast cancer, we investigated the carrier frequency of germline FANCI c.1813C>T in various cancer types and found overall more carriers among cancer cases compared to cancer-free controls (p = 0.007). In these different tumour types, we also identified a spectrum of somatic variants in FANCI that were not restricted to any specific region within the gene. Collectively, these findings expand on the characteristics described for OC cases carrying FANCI c.1813C>T; p.L605F and suggest the possible involvement of FANCI in other cancer types at the germline and/or somatic level.

Application of Multigene Panels Testing for Hereditary Cancer Syndromes

BACKGROUND

Approximately 5-10% of all cancers are associated with hereditary cancer predisposition syndromes (HCPS). Early identification of HCPS is facilitated by widespread use of next-generation sequencing (NGS) and brings significant benefits to both the patient and their relatives. This study aims to evaluate the landscape of genetic variants in patients with personal and/or family history of cancer using NGS-based multigene panel testing.

MATERIALS AND METHODS

The study cohort included 1117 probands from Russia: 1060 (94.9%) patients with clinical signs of HCPS and 57 (5.1%) healthy individuals with family history of cancer. NGS analysis of 76 HCPS genes was performed using a custom Roche NimbleGen enrichment panel.

RESULTS

Pathogenic/likely pathogenic variants were identified in 378 of 1117 individuals (33.8%). The predominant number (59.8%) of genetic variants was identified in BRCA1/BRCA2 genes. CHEK2 was the second most commonly altered gene with a total of 28 (7.4%) variants, and 124 (32.8%) genetic variants were found in other 35 cancer-associated genes with variable penetrance.

CONCLUSIONS

Multigene panel testing allows for a differential diagnosis and identification of high-risk group for oncological diseases. Our results demonstrate that inclusion of non-coding gene regions into HCPS gene panels is highly important for the identification of rare spliceogenic variants with high penetrance.

Fanconi anemia and dyskeratosis congenita/telomere biology disorders: Two inherited bone marrow failure syndromes with genomic instability

Inherited bone marrow failure syndromes (IBMFS) are a complex and heterogeneous group of genetic diseases. To date, at least 13 IBMFS have been characterized. Their pathophysiology is associated with germline pathogenic variants in genes that affect hematopoiesis. A couple of these diseases also have genomic instability, Fanconi anemia due to DNA damage repair deficiency and dyskeratosis congenita/telomere biology disorders as a result of an alteration in telomere maintenance. Patients can have extramedullary manifestations, including cancer and functional or structural physical abnormalities. Furthermore, the phenotypic spectrum varies from cryptic features to patients with significantly evident manifestations. These diseases require a high index of suspicion and should be considered in any patient with abnormal hematopoiesis, even if extramedullary manifestations are not evident. This review describes the disrupted cellular processes that lead to the affected maintenance of the genome structure, contrasting the dysmorphological and oncological phenotypes of Fanconi anemia and dyskeratosis congenita/telomere biology disorders. Through a dysmorphological analysis, we describe the phenotypic features that allow to make the differential diagnosis and the early identification of patients, even before the onset of hematological or oncological manifestations. From the oncological perspective, we analyzed the spectrum and risks of cancers in patients and carriers.

Rare germline alterations of myeloperoxidase predispose to myeloid neoplasms

Myeloperoxidase (MPO) gene alterations with variable clinical penetrance have been found in hereditary MPO deficiency, but their leukemia association in patients and carriers has not been established. Germline MPO alterations were found to be significantly enriched in myeloid neoplasms: 28 pathogenic/likely pathogenic variants were identified in 100 patients. The most common alterations were c.2031-2 A > C, R569W, M519fs* and Y173C accounting for about half of the cases. While functional experiments showed that the marrow stem cell pool of Mpo^-/- mice was not increased, using competitive repopulation demonstrated that Mpo^-/- grafts gained growth advantage over MPO wild type cells. This finding also correlated with increased clonogenic potential after serial replating in the setting of H₂O₂-induced oxidative stress. Furthermore, we demonstrated that H₂O₂-induced DNA damage and activation of error-prone DNA repair may result in secondary genetic damage potentially predisposing to leukemia leukemic evolution. In conclusion, our study for the first time demonstrates that germline MPO variants may constitute risk alleles for MN evolution.

XRCC2 reduced the sensitivity of NSCLC to radio-chemotherapy by arresting the cell cycle

OBJECTIVE

This study aimed to reveal the role and mechanism of X-ray repair cross complementing 2 (XRCC2) and bevacizumab combined with radiotherapy in the treatment of non-small cell lung cancer (NSCLC).

METHODS

Gene Expression Profiling Interactive Analysis (GEPIA) database and Starbase database were used to predict the expression level of XRCC2 in NSCLC tissues and the survival time of patients diagnosed with NSCLC, respectively. Besides, qRT-PCR (quantitative real time polymerase chain reaction) and immunoblotting were conducted to confirm the expression of XRCC2 NSCLC tissues and cells. Moreover, cell viability and colony formation were measured by CCK-8 (cell counting kit-8) assay. Cell migration and invasion capabilities were determined by transwell assay. Flow cytometry analysis was employed to detect cell cycle.

RESULTS

XRCC2 was highly expressed in NSCLC tissues and cells. Additionally, bevacizumab combined with radiotherapy significantly inhibited NSCLC cell proliferation, migration and invasion. Knockdown of XRCC2 further aggravated the role of bevacizumab and radiotherapy in NSCLC, while XRCC2 overexpression reversed these effects efficiently. Furthermore, XRCC2 silence exacerbated the arrest of cell cycle induced by bevacizumab combined with radiotherapy in NSCLC cells, whereas overexpression of XRCC2 alleviated the arrest remarkably.

CONCLUSION

Collectively, our research revealed that XRCC2 inhibited the sensitivity of NSCLC to bevacizumab combined with radiotherapy by decreasing cell cycle arrest.

A cross-sectional survey of genetic counselors providing carrier screening regarding GBA variants and Parkinson disease susceptibility

PURPOSE

Adult-onset disease risks associated with carriers of recessive disease have and will continue to be identified. As carrier screening becomes more broadly utilized, providers face the dilemma of whether they should discuss these risks during discussions with prospective parents. This study aimed to understand whether preconception/prenatal genetic counselors (PPGCs) were aware of the risk of Parkinson disease in carriers of, and persons with, Gaucher disease and the reasons behind choosing whether to discuss this risk with patients.

METHODS

Eligible participants included board-certified or board-eligible genetic counselors who had counseled preconception/prenatal patients within the past 3 years. An online survey was distributed via the National Society of Genetic Counselors in November of 2017.

RESULTS

One hundred twenty genetic counselors completed the quantitative survey, distributed in Fall of 2017. While the majority of respondents knew of the Gaucher-related Parkinson's link (n = 78; 65%), just over one-third reported discussing it in preconception/prenatal settings (n = 30; 38.5%). Respondents reported discussing these links more consistently when disclosing positive results or when the patient/family approached the topic. Respondents cited the lack of professional guidelines as one of the main reasons for not discussing the link.

CONCLUSION

These results highlight an inconsistency in PPGCs' discussions of the Parkinson's risk in Gaucher disease carriers, and the need to develop guidelines regarding these issues to help standardize the care and education of patients.

Identification and prioritization of myeloid malignancy germline variants in a large cohort of adult patients with AML

Inherited predisposition to myeloid malignancies is more common than previously appreciated. We analyzed the whole-exome sequencing data of paired leukemia and skin biopsy samples from 391 adult patients from the Beat AML 1.0 consortium. Using the 2015 American College of Medical Genetics and Genomics (ACMG) guidelines for variant interpretation, we curated 1547 unique variants from 228 genes. The pathogenic/likely pathogenic (P/LP) germline variants were identified in 53 acute myeloid leukemia (AML) patients (13.6%) in 34 genes, including 6.39% (25/391) of patients harboring P/LP variants in genes considered clinically actionable (tier 1). 41.5% of the 53 patients with P/LP variants were in genes associated with the DNA damage response. The most frequently mutated genes were CHEK2 (8 patients) and DDX41 (7 patients). Pathogenic germline variants were also found in new candidate genes (DNAH5, DNAH9, DNMT3A, and SUZ12). No strong correlation was found between the germline mutational rate and age of AML onset. Among 49 patients who have a reported history of at least one family member affected with hematological malignancies, 6 patients harbored known P/LP germline variants and the remaining patients had at least one variant of uncertain significance, suggesting a need for further functional validation studies. Using CHEK2 as an example, we show that three-dimensional protein modeling can be one of the effective methodologies to prioritize variants of unknown significance for functional studies. Further, we evaluated an in silico approach that applies ACMG curation in an automated manner using the tool for assessment and (TAPES) prioritization in exome studies, which can minimize manual curation time for variants. Overall, our findings suggest a need to comprehensively understand the predisposition potential of many germline variants in order to enable closer monitoring for disease management and treatment interventions for affected patients and families.

The neglected members of the family: non-BRCA mutations in the Fanconi anemia/BRCA pathway and reproduction

BACKGROUND

BReast CAncer (BRCA) genes are extensively studied in the context of fertility and reproductive aging. BRCA proteins are part of the DNA repair Fanconi anemia (FA)/BRCA pathway, in which more than 20 proteins are implicated. According to which gene is mutated and which interactions are lost owing to the mutation, carriers and patients with monoallelic or biallelic FA/BRCA mutations exhibit very different phenotypes, from overt FA to cancer predisposition or no pathological implications. The effect of the so far neglected non-BRCA FA mutations on fertility also deserves consideration.

OBJECTIVE AND RATIONALE

As improved treatments allow a longer life expectancy in patients with biallelic FA mutations and overt FA, infertility is emerging as a predominant feature. We thus reviewed the mechanisms for such a manifestation, as well as whether they also occur in monoallelic carriers of FA non-BRCA mutations.

SEARCH METHODS

Electronic databases PUBMED, EMBASE and CENTRAL were searched using the following term: 'fanconi' OR 'FANC' OR 'AND' 'fertility' OR 'pregnancy' OR 'ovarian reserve' OR 'spermatogenesis' OR 'hypogonadism'. All pertinent reports in the English-language literature were retrieved until May 2021 and the reference lists were systematically searched in order to identify any potential additional studies.

OUTCOMES

Biallelic FA mutations causing overt FA disease are associated with premature ovarian insufficiency (POI) occurring in the fourth decade in women and with primary non-obstructive azoospermia (NOA) in men. Hypogonadism in FA patients seems mainly associated with a defect in primordial germ cell proliferation in fetal life. In recent small, exploratory whole-exome sequencing studies, biallelic clinically occult mutations in the FA complementation group A (Fanca) and M (Fancm) genes were found in otherwise healthy patients with isolated NOA or POI, and also monoallelic carrier status for a loss-of-function mutation in Fanca has been implicated as a possible cause for POI. In those patients with known monoallelic FA mutations undergoing pre-implantation genetic testing, poor assisted reproduction outcomes are reported. However, the mechanisms underlying the repeated failures and the high miscarriage rates observed are not fully known.

WIDER IMPLICATIONS

The so far 'neglected' members of the FA/BRCA family will likely emerge as a relevant focus of investigation in the genetics of reproduction. Several (rather than a single) non-BRCA genes might be implicated. State-of-the-art methods, such as whole-genome/exome sequencing, and further exploratory studies are required to understand the prevalence and mechanisms for occult FA mutations in infertility and recurrent miscarriage.

Risk of cancer in heterozygous relatives of patients with Fanconi anemia

PURPOSE

Fanconi anemia (FA) is a cancer-prone inherited bone marrow failure syndrome caused by biallelic pathogenic variants in one of >22 genes in the FA/BRCA DNA repair pathway. A major concern is whether the risk of cancer is increased in individuals with a single pathogenic FA gene variant.

METHODS

We evaluated the risk of cancer in the relatives of patients with FA in the National Cancer Institute Inherited Bone Marrow Failure Syndrome cohort. We genotyped all available relatives and determined the rates, types of cancer and the age of patients at cancer diagnosis. We calculated the observed-to-expected (O/E) cancer ratios using data from the Surveillance, Epidemiology, and End Results Program adjusted for age, sex, and birth cohort.

RESULTS

The risk of cancer was not increased among all FA relatives and FA heterozygotes (O/E ratios of 0.78 and 0.79, respectively). In particular, the risk of cancer was not increased among FANCA or FANCC heterozygotes (O/E ratios of 0.92 and 0.71, respectively). Relatives did not have typical FA cancers, and age at cancer diagnosis was not younger than expected.

CONCLUSION

Understanding the risk of cancer in individuals with single pathogenic FA variants is critical for counseling and management. We did not find increased risk of cancer in these individuals. These findings do not extend to the known cancer predisposition autosomal dominant FA genes, namely BRCA1, BRCA2, PALB2, BRIP1, and RAD51C.

Fanconi anemia gene-associated germline predisposition in aplastic anemia and hematologic malignancies

Whether Fanconi anemia (FA) heterozygotes are predisposed to bone marrow failure and hematologic neoplasm is a crucial but unsettled issue in cancer prevention and family consulting. We retrospectively analyzed rare possibly significant variations (PSVs) in the five most obligated FA genes, BRCA2, FANCA, FANCC, FANCD2, and FANCG, in 788 patients with aplastic anemia (AA) and hematologic malignancy. Sixty-eight variants were identified in 66 patients (8.38%). FANCA was the most frequently mutated gene (n = 29), followed by BRCA2 (n = 20). Compared with that of the ExAC East Asian dataset, the overall frequency of rare PSVs was higher in our cohort (P = 0.016). BRCA2 PSVs showed higher frequency in acute lymphocytic leukemia (P = 0.038), and FANCA PSVs were significantly enriched in AA and AML subgroups (P = 0.020; P = 0.008). FA-PSV-positive MDS/AML patients had a higher tumor mutation burden, higher rate of cytogenetic abnormalities, less epigenetic regulation, and fewer spliceosome gene mutations than those of FA-PSV-negative MDS/AML patients (P = 0.024, P = 0.029, P = 0.024, and P = 0.013). The overall PSV enrichment in our cohort suggests that heterozygous mutations of FA genes contribute to hematopoietic failure and leukemogenesis.

Feasibility of breast radiation therapy in a Fanconi Anemia patient diagnosed with breast cancer: A case report and review of literature

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We present the journey of an FA patient who developed metachronous bilateral breast cancers and was successfully treated with breast conserving therapy with no significant treatment related toxicity.

Fanconi Anemia (FA) is a rare inherited autosomal recessive disease that results in impaired double stranded DNA repair. This leads to both increased susceptibility to various cancers, as well as hypersensitivity to radiotherapy and systemic therapy; thus, increasing the complexity of oncological treatment paradigm.

Here, we present an FA patient who initially developed invasive breast cancer for which she received breast conserving treatment with no significant treatment related toxicity. This was followed by a diagnosis of high-grade ductal carcinoma-in-situ in the contralateral breast, which was managed successfully by surgery and meticulously planned adjuvant radiotherapy, with no treatment interruptions.

Impact of MDM2 promoter SNP55 (rs2870820) on risk of endometrial and ovarian cancer

BACKGROUND

While large GWAS analyses have not found convincing associations between MDM2 promoter SNP55 and gynaecological cancers, SNP55 is in linkage disequilibrium with two other functional SNPs in the same promoter, likely to obscure associations between single SNPs and cancer risk. Here, we assessed the impact of SNP55 on risk of endometrial and ovarian cancer, including sub-analyses stratified for other functional SNPs in the region.

MATERIAL AND METHODS

Using a custom LightSNiP assay, we genotyped SNP55 in two large hospital-based cohorts of patients with ovarian (n = 1,332) and endometrial (n = 1,363) cancer and compared genotypes to healthy female controls (n = 1,858).

RESULTS

Among individuals harbouring the SNP309TT genotype, the minor SNP55T-allele was associated with a reduced risk of endometrial (dominant model: OR = 0.63; CI = 0.45-0.88; p = 0.01). Regardless of the genotype in neighbouring SNPs, the SNP55T-allele was also associated with a reduced risk of endometrial cancer before 50 years of age (dominant model: OR = 0.56; CI = 0.34-0.90; p = 0.02). No association between SNP55 status and ovarian cancer risk was observed.

CONCLUSIONS

MDM2 SNP55T-allele may correlate with reduced risk for endometrial cancer in a SNP309T-, but not SNP309G, context.

Nationwide germline whole genome sequencing of 198 consecutive pediatric cancer patients reveals a high incidence of cancer prone syndromes

PURPOSE

Historically, cancer predisposition syndromes (CPSs) were rarely established for children with cancer. This nationwide, population-based study investigated how frequently children with cancer had or were likely to have a CPS.

METHODS

Children (0-17 years) in Denmark with newly diagnosed cancer were invited to participate in whole-genome sequencing of germline DNA. Suspicion of CPS was assessed according to Jongmans'/McGill Interactive Pediatric OncoGenetic Guidelines (MIPOGG) criteria and familial cancer diagnoses were verified using population-based registries.

RESULTS

198 of 235 (84.3%) eligible patients participated, of whom 94/198 (47.5%) carried pathogenic variants (PVs) in a CPS gene or had clinical features indicating CPS. Twenty-nine of 198 (14.6%) patients harbored a CPS, of whom 21/198 (10.6%) harbored a childhood-onset and 9/198 (4.5%) an adult-onset CPS. In addition, 23/198 (11.6%) patients carried a PV associated with biallelic CPS. Seven of the 54 (12.9%) patients carried two or more variants in different CPS genes. Seventy of 198 (35.4%) patients fulfilled the Jongmans' and/or MIPOGG criteria indicating an underlying CPS, including two of the 9 (22.2%) patients with an adult-onset CPS versus 18 of the 21 (85.7%) patients with a childhood-onset CPS (p = 0.0022), eight of the additional 23 (34.8%) patients with a heterozygous PV associated with biallelic CPS, and 42 patients without PVs. Children with a central nervous system (CNS) tumor had family members with CNS tumors more frequently than patients with other cancers (11/44, p = 0.04), but 42 of 44 (95.5%) cases did not have a PV in a CPS gene.

CONCLUSION

These results demonstrate the value of systematically screening pediatric cancer patients for CPSs and indicate that a higher proportion of childhood cancers may be linked to predisposing germline variants than previously supposed.

Prevalence and clinical implications of germline predisposition gene mutations in patients with acute myeloid leukemia

Acute myeloid leukemia (AML) is one of the most common types of leukemia. With the recent advances in sequencing technology and the growing body of knowledge on the genetics of AML, there is increasing concern about cancer predisposing germline mutations as well as somatic mutations. As familial cases sharing germline mutations are constantly reported, germline predisposition gene mutations in patients with AML are gaining attention. We performed genomic sequencing of Korean patients diagnosed with AML to identify the prevalence and characteristics of germline predisposition mutations. Among 180 patients, germline predisposition mutations were identified in 13 patients (13/180, 7.2%, eight adults and five children). Germline mutations of BLM, BRCA1, BRCA2, CTC1, DDX41, ERCC4, ERCC6, FANCI, FANCM, PALB2, and SBDS were identified. Most of the mutations are in genes involved in DNA repair and genomic stability maintenance. Patients harboring germline mutations tended to have earlier onset of AML (p = 0.005), however, the presence of germline mutations did not showed significant association with other clinical characteristics or treatment outcome. Since each mutation was rare, further study with a larger number of cases would be needed to establish the effect of the mutations.

Management of Fanconi Anemia patients with head and neck carcinoma: Diagnosis and treatment adaptation

Fanconi anemia (FA) is a rare genetic disease that is mostly transmitted, according to a recessive model with biallelic germline alterations in one of the 22 genes of the FA pathway, or monoallelic alteration of the 23rd FA gene (RAD51). The FA pathway is implicated in interstrand DNA crosslink repair, induces genome stability, and is a potent driver of tumorigenesis. Patients with FA have a 500 to 1000-fold increased risk of developing head and neck squamous cell carcinoma (HNSCC). Patients with FA developing an HNSCC, usually have severe radiation toxicities. In this context, the modalities of radiation therapy should be adapted. Some patients with FA present a milder phenotype, especially in the case of medullary FA gene spontaneous reversion. Therefore, in an unusual context of HNSCC, such as no risk factors or a young age, it may be very useful to search anemia or development abnormalities, that may unravel a yet undiagnosed FA disease. Besides, in some young patients with HNSCC who did not suffer from FA, a monoallelic germline alteration in an FA gene could be combined with a second risk factor such as HPV infection or APOBEC alteration. Although several in vitro studies showed that normal cells with monoallelic FA gene alteration may have a particular radiosensitivity, these observations have not been confirmed in vivo in FA heterozygotes patients. Finally, some somatic activating alterations have also been found in HSNCC tumor samples and could be associated with radioresistance.

Fanconi Anemia Pathway: Mechanisms of Breast Cancer Predisposition Development and Potential Therapeutic Targets

The maintenance of genomic stability is crucial for species survival, and its failure is closely associated with tumorigenesis. The Fanconi anemia (FA) pathway, involving 22 identified genes, plays a central role in repairing DNA interstrand cross-links. Importantly, a germline defect in any of these genes can cause Fanconi's anemia, a heterogeneous genetic disorder, characterized by congenital growth abnormalities, bone marrow failure, and predisposition to cancer. On the other hand, the breast cancer susceptibility genes, BRCA1 and BRCA2, also known as FANCS and FANCD1, respectively, are involved in the FA pathway; hence, researchers have studied the association between the FA pathway and cancer predisposition. Here, we mainly focused on and systematically reviewed the clinical and mechanistic implications of the predisposition of individuals with abnormalities in the FA pathway to cancer, especially breast cancer.

Exploring the Role of Mutations in Fanconi Anemia Genes in Hereditary Cancer Patients

Fanconi anemia (FA) is caused by biallelic mutations in FA genes. Monoallelic mutations in five of these genes (BRCA1, BRCA2, PALB2, BRIP1 and RAD51C) increase the susceptibility to breast/ovarian cancer and are used in clinical diagnostics as bona-fide hereditary cancer genes. Increasing evidence suggests that monoallelic mutations in other FA genes could predispose to tumor development, especially breast cancer. The objective of this study is to assess the mutational spectrum of 14 additional FA genes (FANCA, FANCB, FANCC, FANCD2, FANCE, FANCF, FANCG, FANCI, FANCL, FANCM, FANCP, FANCQ, FANCR and FANCU) in a cohort of hereditary cancer patients, to compare with local cancer-free controls as well as GnomAD. A total of 1021 hereditary cancer patients and 194 controls were analyzed using our next generation custom sequencing panel. We identified 35 pathogenic variants in eight genes. A significant association with the risk of breast cancer/breast and ovarian cancer was found for carriers of FANCA mutations (odds ratio (OR) = 3.14 95% confidence interval (CI) 1.4–6.17, p = 0.003). Two patients with early-onset cancer showed a pathogenic FA variant in addition to another germline mutation, suggesting a modifier role for FA variants. Our results encourage a comprehensive analysis of FA genes in larger studies to better assess their role in cancer risk.

Genetic Predisposition to Breast and Ovarian Cancers: How Many and Which Genes to Test?

Breast and ovarian cancers are some of the most common tumors in females, and the genetic predisposition is emerging as one of the key risk factors in the development of these two malignancies. BRCA1 and BRCA2 are the best-known genes associated with hereditary breast and ovarian cancer. However, recent advances in molecular techniques, Next-Generation Sequencing in particular, have led to the identification of many new genes involved in the predisposition to breast and/or ovarian cancer, with different penetrance estimates. TP53, PTEN, STK11, and CDH1 have been identified as high penetrance genes for the risk of breast/ovarian cancers. Besides them, PALB2, BRIP1, ATM, CHEK2, BARD1, NBN, NF1, RAD51C, RAD51D and mismatch repair genes have been recognized as moderate and low penetrance genes, along with other genes encoding proteins involved in the same pathways, possibly associated with breast/ovarian cancer risk. In this review, we summarize the past and more recent findings in the field of cancer predisposition genes, with insights into the role of the encoded proteins and the associated genetic disorders. Furthermore, we discuss the possible clinical utility of genetic testing in terms of prevention protocols and therapeutic approaches.

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.

Rare variants in FANCA induce premature ovarian insufficiency

Premature ovarian insufficiency (POI) is a major cause of reduced female fertility and affects approximately 1% women under 40 years of age. Recent advances emphasize the genetic heterogeneity of POI. Fanconi anemia (FA) genes, traditionally known for their essential roles in DNA repair and cytogenetic instability, have been demonstrated to be involved in meiosis and germ cell development. Here, we conducted whole-exome sequencing (WES) in 50 Han Chinese female patients with POI. Rare missense variants were identified in FANCA (Fanconi anemia complementation group A): c.1772G > A (p.R591Q) and c.3887A > G (p.E1296G). Both variants are heterozygous in the patients and very rare in the human population. In vitro functional studies further demonstrated that these two missense variants of FANCA exhibited reduced protein expression levels compared with the wild type, suggesting the partial loss of function. Moreover, mono-ubiquitination levels of FANCD2 upon mitomycin C stimulation were significantly reduced in cells overexpressing FANCA variants. Furthermore, a loss-of-function mutation of Fanca was generated in C57BL/6 mice for in vivo functional assay. Consistently, heterozygous mutated female mice (Fanca^+/−) showed reduced fertility and declined numbers of follicles with aging when compared with the wild-type female mice. Collectively, our results suggest that heterozygous pathogenic variants in FANCA are implicated in non-syndromic POI in Han Chinese women, provide new insights into the molecular mechanisms of POI and highlight the contribution of FANCA variants in female subfertility.

Targeted sequencing identifies the mutational signature of double primary and metastatic malignancies: a case report

BACKGROUND

The accurate identification of the tissue of origin is critical for optimal management of cancer patients particularly those who develop multiple malignancies; however, conventional diagnostic methods at times may fail to provide conclusive diagnosis of the origin of the malignancy. Herein, we describe the use of targeted sequencing in distinguishing the primary and metastatic tumors in a patient with metachronous malignancies in the lung, colon and kidney.

CASE PRESENTATION

In December 2016, a 55-year-old Chinese male was diagnosed with stage IB lung adenosquamous carcinoma and treated with left lower lobectomy and 4 cycles of platinum-based chemotherapy. After being disease-free for 3.5 months, three colonic polyps were discovered and were diagnosed as invasive adenocarcinoma after polypectomy. Within 5.4 months from the polypectomy, squamous cell renal carcinoma was identified and was managed by radical nephrectomy. Immunohistochemistry results were inconclusive on the origin of the kidney tumor. Hence, the three archived surgical tissue samples were sequenced using a targeted panel with 520 cancer-related genes. Analysis revealed similar mutational signature between the lung and kidney tumors and a distinct mutational profile for the colon tumor, suggesting that the lung and colon malignancies were primary tumors, while the kidney tumor originated from the lung, revealing a diagnosis of metastatic double primary cancer - lung carcinoma with renal cell metastasis and second primary colon carcinoma.

CONCLUSION

Mutational profiling using targeted sequencing is valuable not only for the detection of actionable mutations, but also in the identification of the origin of tumors. This diagnostic approach should be considered in similar scenarios.

Two truncating variants in FANCC and breast cancer risk

Fanconi anemia (FA) is a genetically heterogeneous disorder with 22 disease-causing genes reported to date. In some FA genes, monoallelic mutations have been found to be associated with breast cancer risk, while the risk associations of others remain unknown. The gene for FA type C, FANCC, has been proposed as a breast cancer susceptibility gene based on epidemiological and sequencing studies. We used the Oncoarray project to genotype two truncating FANCC variants (p.R185X and p.R548X) in 64,760 breast cancer cases and 49,793 controls of European descent. FANCC mutations were observed in 25 cases (14 with p.R185X, 11 with p.R548X) and 26 controls (18 with p.R185X, 8 with p.R548X). There was no evidence of an association with the risk of breast cancer, neither overall (odds ratio 0.77, 95%CI 0.44-1.33, p = 0.4) nor by histology, hormone receptor status, age or family history. We conclude that the breast cancer risk association of these two FANCC variants, if any, is much smaller than for BRCA1, BRCA2 or PALB2 mutations. If this applies to all truncating variants in FANCC it would suggest there are differences between FA genes in their roles on breast cancer risk and demonstrates the merit of large consortia for clarifying risk associations of rare variants.

Inherited variants in XRCC2 and the risk of breast cancer

Background

XRCC2 participates in homologous recombination and in DNA repair. XRCC2 has been reported to be a breast cancer susceptibility gene and is now included in several breast cancer susceptibility gene panels.

Methods

We sequenced XRCC2 in 617 Polish women with familial breast cancer and found a founder mutation. We then genotyped 12,617 women with breast cancer and 4599 controls for the XRCC2 founder mutation.

Results

We identified a recurrent truncating mutation of XRCC2 (c.96delT, p.Phe32fs) in 3 of 617 patients with familial breast cancer who were sequenced. The c.96delT mutation was then detected in 29 of 12,617 unselected breast cancer cases (0.23%) compared to 11 of 4599 cancer-free women (0.24%) (OR = 0.96; 95% CI 0.48–1.93). The mutation frequency in 1988 women with familial breast cancer was 0.2% (OR = 0.84, 95% CI 0.27–2.65). Breast cancers in XRCC2 mutation carriers and non-carriers were similar with respect to age of diagnosis and clinical characteristics. Loss of the wild-type XRCC2 allele was observed only in one of the eight breast cancers from patients who carried the XRCC2 mutation. No cancer type was more common in first- or second-degree relatives of XRCC2 mutation carriers than in relatives of the non-carriers.

Conclusion

XRCC2 c.96delT is a protein-truncating founder variant in Poland. There is no evidence that this mutation predisposes to breast cancer (and other cancers). It is premature to consider XRCC2 as a breast cancer-predisposing gene.

Hematological Malignancies in Adults With a Family Predisposition

BACKGROUND

Some hematological malignancies arise in persons with a hereditary predisposition. The hereditary nature of these diseases often goes unrecognized, particularly when symptoms begin in adulthood.

METHODS

This review is based on pertinent publications retrieved by a selective search in PubMed.

RESULTS

Many rare germline mutations have been identified that lead to acute leukemia and myelodysplastic syndromes. They differ from one another with respect to their penetrance, the age of onset of disease, and the clinical manifestations. In view of this heterogeneity, no uniform recommendations have yet been formulated for their diagnosis and treatment. The most common types of hematological malig- nancy with a hereditary predisposition are traceable to an underlying disturbance of DNA damage response and repair mechanisms and to mutations of hematological transcription factors. With regard to the selection of patients for testing, the con- sensus is that cytogenetic and molecular-genetic findings that are suspect for a hereditary predisposition, such as CEBPA and RUNX1 mutations, call for further investigation, as do any clinical features that are typical of tumor syndromes, or a positive family history. The knowledge that a hereditary predisposition may be present is highly stressful for patients; testing should only be carried out after the patient has received genetic counseling. The confirmation of a germline mutation always requires a comparison with healthy tissue. A fibroblast culture is recom- mended as the gold standard for this purpose.

CONCLUSION

The detection of a hereditary predisposition to hematological neoplasia is often relevant to treatment and follow-up care: for example, it may motivate early allogeneic stem-cell transplantation. Counseling, predictive testing, and follow-up care are available to the patients' relatives as well.

Deleterious Mutations in DNA Repair Gene FANCC Exist in BRCA1/2-Negative Chinese Familial Breast and/or Ovarian Cancer Patients

Introduction: FANCC is reported as a novel susceptibility gene for breast cancer, however, its mutation remains unclear in Chinese population. We aimed to identify the germline mutations of FANCC in high-risk breast cancer patients in China. Methods: 255 BRCA1/2-negative Chinese familial breast and/or ovarian cancer (FBOC) patients were recruited for FANCC germline mutations screen. For whom 90 patients were detected by PCR-sequencing assay, and another 165 patients were detected by a 98-gene panel sequencing assay. The 98-gene panel sequencing assay was also used to screen other possible gene mutations for the patients with FANCC mutations detected by PCR-sequencing assay. Two hundred and fifty sporadic breast cancer (SBC) patients and 248 female non-cancer controls (FNCCs) were recruited for the genotyping analysis. Immunohistochemistry (IHC) analysis was used to evaluate the FANCC expression in patients with FANCC mutation. Results: We found one rare FANCC deleterious mutation (c.339G>A, p.W113X, 0.4%) and two novel non-synonymous variants (c.51G>C, p.Q17H, 0.4% and c.758C>A, p.A253E, 0.4%) in FBOC patients, whereas none of above mutations was identified in SBC patients or FNCCs. We also found that one novel synonymous variant (c.903A>G, p.A301A) existed in one FBOC patient. Additionally, two non-synonymous SNPs rs201407189 (c.973G>A, p.A325T) and rs1800367 (c.1345G>A, p.V449M), and two synonymous SNPs rs55719336 (c.816C>T, p.I272I) and rs79722116 (c.1407G>A, p.T469T) were identified in FBOC patients. Conclusion: FANCC deleterious mutations exist in Chinese FBOC patients and investigations on the penetrance and spectrum of FANCC mutations need to be further conducted.

Comprehensive Analysis of Germline Variants in Mexican Patients with Hereditary Breast and Ovarian Cancer Susceptibility

Hereditary breast and ovarian cancer syndrome (HBOC) represents 5⁻10% of all patients with breast cancer and is associated with high-risk pathogenic alleles in BRCA1/2 genes, but only for 25% of cases. We aimed to find new pathogenic alleles in a panel of 143 cancer-predisposing genes in 300 Mexican cancer patients with suspicion of HBOC and 27 high-risk patients with a severe family history of cancer, using massive parallel sequencing. We found pathogenic variants in 23 genes, including BRCA1/2. In the group of cancer patients 15% (46/300) had a pathogenic variant; 11% (33/300) harbored variants with unknown clinical significance (VUS) and 74% (221/300) were negative. The high-risk group had 22% (6/27) of patients with pathogenic variants, 4% (1/27) had VUS and 74% (20/27) were negative. The most recurrent mutations were the Mexican founder deletion of exons 9-12 and the variant p.G228fs in BRCA1, each found in 5 of 17 patients with alterations in this gene. Rare VUS with potential impact at the protein level were found in 21 genes. Our results show for the first time in the Mexican population a higher contribution of pathogenic alleles in other susceptibility cancer genes (54%) than in BRCA1/2 (46%), highlighting the high locus heterogeneity of HBOC and the necessity of expanding genetic tests for this disease to include broader gene panels.

Fanconi anaemia and cancer: an intricate relationship

Fanconi anaemia (FA) is a genetic disorder that is characterized by bone marrow failure (BMF), developmental abnormalities and predisposition to cancer. Together with other proteins involved in DNA repair processes and cell division, the FA proteins maintain genome homeostasis, and germline mutation of any one of the genes that encode FA proteins causes FA. Monoallelic inactivation of some FA genes, such as FA complementation group D1 (FANCD1; also known as the breast and ovarian cancer susceptibility gene BRCA2), leads to adult-onset cancer predisposition but does not cause FA, and somatic mutations in FA genes occur in cancers in the general population. Carcinogenesis resulting from a dysregulated FA pathway is multifaceted, as FA proteins monitor multiple complementary genome-surveillance checkpoints throughout interphase, where monoubiquitylation of the FANCD2-FANCI heterodimer by the FA core complex promotes recruitment of DNA repair effectors to chromatin lesions to resolve DNA damage and mitosis. In this Review, we discuss how the FA pathway safeguards genome integrity throughout the cell cycle and show how studies of FA have revealed opportunities to develop rational therapeutics for this genetic disease and for malignancies that acquire somatic mutations within the FA pathway.

Fanconi Anemia germline variants as susceptibility factors in aplastic anemia, MDS and AML

Using next generation sequencing we have systematically analyzed a large cohort of 489 patients with bone marrow failure (BMF), including myelodysplastic syndrome (MDS), acute myeloid leukemia (AML), aplastic anemia (AA), and related conditions for the presence of germline (GL) alterations in Fanconi Anemia (FA) and telomerase genes. We have detected an increased frequency of heterozygous FA gene mutations in MDS and to lesser degree in AML suggesting that the presence of one normal allele may not be completely protective and indeed heterozygous FA lesions may have a long latency period before hematologic manifestation. In contrast, GL telomerase gene mutations were not associated with increased disease risk. When compared to large control cohorts, we have not detected an increased frequency of damaging variants among telomerase complex genes, including those previously believed to be involved in the pathogenesis of AA. Our results may suggest that while low penetrance and delayed disease onset can confound identification of genetic predisposition factors, GL FA alterations can be also associated with MDS.

The genomics of inherited bone marrow failure: from mechanism to the clinic

The inherited bone marrow failure syndromes (IBMFS) typically present with significant cytopenias in at least one haematopoietic cell lineage that may progress to pancytopenia, and are associated with increased risk of cancer. Although the clinical features of the IBMFS are often diagnostic, variable disease penetrance and expressivity may result in diagnostic dilemmas. The discovery of the genetic aetiology of the IBMFS has been greatly facilitated by next-generation sequencing methods. This has advanced understanding of the underlying biology of the IBMFS and been essential in improving clinical management and genetic counselling for affected patients. Herein we review the clinical features, underlying biology, and new genomic discoveries in the IBMFS, including Fanconi anaemia, dyskeratosis congenita, Diamond Blackfan anaemia, Shwachman Diamond syndrome and some disorders of the myeloid and megakaryocytic lineages.

Alpha-fetoprotein and Fanconi Anemia: Relevance to DNA Repair and Breast Cancer Susceptibility

Elevations of serum alpha-fetoprotein (sAFP) have been reported in fetal and infant states of anemia. Fanconi anemia (FA) belongs to a family of genetic instability disorders which lack the capability to repair DNA breaks. The lesion occurs at a checkpoint regulatory step of the G2 to mitotic transition, allowing FA cells to override cell-cycle arrest. FA DNA repair pathways contain complementation groups known as FANC proteins. FANC proteins form multi-protein complexes with BRCA proteins and are involved in homologous DNA repair. An impaired cascade in these events imparts an increased breast cancer susceptibility to female FA patients. Elevations of sAFP have availed this fetal protein to serve as a biomarker for FA disease. However, the origin of the synthesis of sAFA has not been determined in FA patients. We hypothesize that hematopoietic multipotent progenitor stem cells in the bone marrow are the source of sAFP production in FA patients.

Complementation of hypersensitivity to DNA interstrand crosslinking agents demonstrates that XRCC2 is a Fanconi anaemia gene

BACKGROUND

Fanconi anaemia (FA) is a heterogeneous inherited disorder clinically characterised by progressive bone marrow failure, congenital anomalies and a predisposition to malignancies.

OBJECTIVE

Determine, based on correction of cellular phenotypes, whether XRCC2 is a FA gene.

METHODS

Cells (900677A) from a previously identified patient with biallelic mutation of XRCC2, among other mutations, were genetically complemented with wild-type XRCC2.

RESULTS

Wild-type XRCC2 corrects each of three phenotypes characteristic of FA cells, all related to the repair of DNA interstrand crosslinks, including increased sensitivity to mitomycin C (MMC), chromosome breakage and G2-M accumulation in the cell cycle. Further, the p.R215X mutant of XRCC2, which is harboured by the patient, is unstable. This provides an explanation for the pathogenesis of this mutant, as does the fact that 900677A cells have reduced levels of other proteins in the XRCC2-RAD51B-C-D complex. Also, FANCD2 monoubiquitination and foci formation, but not assembly of RAD51 foci, are normal in 900677A cells. Thus, XRCC2 acts late in the FA-BRCA pathway as also suggested by hypersensitivity of 900677A cells to ionising radiation. These cells also share milder sensitivities towards olaparib and formaldehyde with certain other FA cells.

CONCLUSIONS

XRCC2/FANCU is a FA gene, as is another RAD51 paralog gene, RAD51C/FANCO. Notably, similar to a subset of FA genes that act downstream of FANCD2, biallelic mutation of XRCC2/FANCU has not been associated with bone marrow failure. Taken together, our results yield important insights into phenotypes related to FA and its genetic origins.

Defects in homologous recombination repair behind the human diseases: FA and HBOC

Hereditary breast and ovarian cancer (HBOC) syndrome and a rare childhood disorder Fanconi anemia (FA) are caused by homologous recombination (HR) defects, and some of the causative genes overlap. Recent studies in this field have led to the exciting development of PARP inhibitors as novel cancer therapeutics and have clarified important mechanisms underlying genome instability and tumor suppression in HR-defective disorders. In this review, we provide an overview of the basic molecular mechanisms governing HR and DNA crosslink repair, highlighting BRCA2, and the intriguing relationship between HBOC and FA.

MDM2 promoter SNP55 (rs2870820) affects risk of colon cancer but not breast-, lung-, or prostate cancer

Two functional SNPs (SNP285G > C; rs117039649 and SNP309T > G; rs2279744) have previously been reported to modulate Sp1 transcription factor binding to the promoter of the proto-oncogene MDM2, and to influence cancer risk. Recently, a third SNP (SNP55C > T; rs2870820) was also reported to affect Sp1 binding and MDM2 transcription. In this large population based case-control study, we genotyped MDM2 SNP55 in 10,779 Caucasian individuals, previously genotyped for SNP309 and SNP285, including cases of colon (n = 1,524), lung (n = 1,323), breast (n = 1,709) and prostate cancer (n = 2,488) and 3,735 non-cancer controls, as well as 299 healthy African-Americans. Applying the dominant model, we found an elevated risk of colon cancer among individuals harbouring SNP55TT/CT genotypes compared to the SNP55CC genotype (OR = 1.15; 95% CI = 1.01-1.30). The risk was found to be highest for left-sided colon cancer (OR = 1.21; 95% CI = 1.00-1.45) and among females (OR = 1.32; 95% CI = 1.01-1.74). Assessing combined genotypes, we found the highest risk of colon cancer among individuals harbouring the SNP55TT or CT together with the SNP309TG genotype (OR = 1.21; 95% CI = 1.00-1.46). Supporting the conclusions from the risk estimates, we found colon cancer cases carrying the SNP55TT/CT genotypes to be diagnosed at younger age as compared to SNP55CC (p = 0.053), in particular among patients carrying the SNP309TG/TT genotypes (p = 0.009).

Coordination of the recruitment of the FANCD2 and PALB2 Fanconi anemia proteins by an ubiquitin signaling network

Fanconi anemia (FA) is a chromosome instability syndrome and the 20 identified FA proteins are organized into two main arms which are thought to function at distinct steps in the repair of DNA interstrand crosslinks (ICLs). These two arms include the upstream FA pathway, which culminates in the monoubiquitination of FANCD2 and FANCI, and downstream breast cancer (BRCA)-associated proteins that interact in protein complexes. How, and whether, these two groups of FA proteins are integrated is unclear. Here, we show that FANCD2 and PALB2, as indicators of the upstream and downstream arms, respectively, colocalize independently of each other in response to DNA damage induced by mitomycin C (MMC). We also show that ubiquitin chains are induced by MMC and colocalize with both FANCD2 and PALB2. Our finding that the RNF8 E3 ligase has a role in recruiting FANCD2 and PALB2 also provides support for the hypothesis that the two branches of the FA-BRCA pathway are coordinated by ubiquitin signaling. Interestingly, we find that the RNF8 partner, MDC1, as well as the ubiquitin-binding protein, RAP80, specifically recruit PALB2, while a different ubiquitin-binding protein, FAAP20, functions only in the recruitment of FANCD2. Thus, FANCD2 and PALB2 are not recruited in a single linear pathway, rather we define how their localization is coordinated and integrated by a network of ubiquitin-related proteins. We propose that such regulation may enable upstream and downstream FA proteins to act at distinct steps in the repair of ICLs.

Interplay between Fanconi anemia and homologous recombination pathways in genome integrity

The Fanconi anemia (FA) pathway plays a central role in the repair of DNA interstrand crosslinks (ICLs) and regulates cellular responses to replication stress. Homologous recombination (HR), the error-free pathway for double-strand break (DSB) repair, is required during physiological cell cycle progression for the repair of replication-associated DNA damage and protection of stalled replication forks. Substantial crosstalk between the two pathways has recently been unravelled, in that key HR proteins such as the RAD51 recombinase and the tumour suppressors BRCA1 and BRCA2 also play important roles in ICL repair. Consistent with this, rare patient mutations in these HR genes cause FA pathologies and have been assigned FA complementation groups. Here, we focus on the clinical and mechanistic implications of the connection between these two cancer susceptibility syndromes and on how these two molecular pathways of DNA replication and repair interact functionally to prevent genomic instability.