The genetics of Fanconi's anaemia

Case Report: A Novel Homozygous Variant in the SLX4 Gene Causes Fanconi Anemia

Background: Fanconi anemia (FA) is a rare genetic disorder that affects multiple systems in the body and is the most prevalent congenital syndrome, leading to bone marrow failure. Twenty-two genes have been identified as contributors to the disease. Significant advancements have been made in the past 2 decades in understanding the genetic and pathophysiological processes involved. Whole exome sequencing (WES) is employed to diagnose rare Mendelian disorders when standard tests fail to provide a definitive pathological diagnosis. However, WES has the potential to reveal pathogenic variants that may complicate the diagnostic process. In this study, the method was chosen to examine SLX4/FANCP. Aims: The goal of our research was to suggest that the new potentially harmful genetic mutation, c.4921dup A>AC (p.Val1641GlyfsTer15), could lead to the development of FA. Methods and Result: This patient was analyzed by performing the WES test, and a homozygous pathogenic variant in the SLX4 gene (c.4921dupA>AC - chr16-3633329-p.Val1641GlyfsTer15) was identified in this patient. The candidate variant was confirmed by Sanger sequencing. The parent of the patient and the fetus of this family were also examined using Sanger sequencing, and they were determined to be carriers and heterozygous. Conclusion: Our research has uncovered a new form of pathogenic genetic variation in the SLX4 gene, providing new insights into the molecular causes of this condition. To date, the c.4921dup A>AC (p.Val1641GlyfsTer15) pathogenic variant has not been observed or reported worldwide. These findings could be valuable for investigating the mechanisms of FA and may offer insights for preventing, diagnosing, and managing the risks associated with this disease.

Ligase IV syndrome can present with microcephaly and radial ray anomalies similar to Fanconi anaemia plus fatal kidney malformations

Ligase IV (LIG4) syndrome is a rare disorder of DNA damage repair caused by biallelic, pathogenic variants in LIG4. This is a phenotypically heterogeneous condition with clinical presentation varying from lymphoreticular malignancies in developmentally normal individuals to significant microcephaly, primordial dwarfism, radiation hypersensitivity, severe combined immunodeficiency and early mortality. Renal defects have only rarely been described as part of the ligase IV disease spectrum.

We identified a consanguineous family where three siblings presenting with antenatal growth retardation, microcephaly, severe renal anomalies and skeletal abnormalities, including radial ray defects. Autozygosity mapping and exome sequencing identified a novel homozygous frameshift variant in LIG4, c.597_600delTCAG, p.(Gln200LysfsTer33), which segregated in the family. LIG4 is encoded by a single exon and so this frameshift variant is predicted to result in a protein truncated by 678 amino acids. This is the shortest predicted LIG4 protein product reported and correlates with the most severe clinical phenotype described to date. We note the clinical overlap with Fanconi anemia and suggest that LIG4 syndrome is considered in the differential diagnosis of this severe developmental disorder.

Fanconi Anemia: Overview of the Disease and the Role of Hematopoietic Transplantation

Fanconi anemia (FA) is an inherited bone marrow failure syndrome characterized by congenital abnormalities and chromosomal breakages with the occurrence of hematological and solid malignancies. FA is the most common type of inherited bone marrow failure and poses tremendous challenges. FA patients are uniquely hypersensitive to hematopoietic stem cell transplantation (HSCT) conditioning agents due to the underling chromosomal instability. HSCT has shown important progress in the last years, especially after the introduction of fludarabine and the reduction of cyclophosphamide in the preparative regimen. For patients with HLA-identical-related donors HSCT should be performed as first-line therapy, for patients with alternative donors HSCT remains a therapy with increased morbidity and mortality.

Cytogenetic assessment of Fanconi anemia in children with aplastic anemia in Tunisia

BACKGROUND

Chromosome breakage hypersensitivity to alkylating agents is the gold standard test for Fanconi anemia (FA) diagnosis. The aim of the present study was to assess the proportion of FA cases among aplastic anemia (AA) in Tunisian pediatric patients.

OBSERVATION

Investigation of mitomycin C-induced chromosomal breakage was carried out in 163 pediatric patients with AA and siblings of the cases where diagnosis of FA was confirmed. We identified 31 patients with FA whose percentage of unstable mitoses ranges from 65% to 100%. Among 18 siblings who were investigated for chromosomal instability, 3 were incidentally found to be affected.

CONCLUSIONS

FA is an important cause of AA in Tunisia. Our report is the first study in North Africa that explored cytogenetic and phenotypic findings in FA children. It also showed the importance of mitomycin C sensitivity screening in all FA siblings.

Fanconi's anaemia and unilateral thumb polydactyly--don't miss it

Fanconi's anaemia (FA) is a rare, life threatening inherited syndrome. Patients usually present late in the first decade of life with aplastic anaemia or acute myeloid leukaemia. FA children are also at high risk of solid organ tumours, anogenital squamous cancers, and endocrinopathies. These patients can present with unilateral radial abnormalities including thumb duplication. Hand surgeons can help achieve early diagnosis and improved survival in this group by early referral for screening. In a retrospective study of 202 children with radial ray anomalies seen over a 20 year period seven children had FA. Of these seven with FA, four had bilateral thumb hypoplasia and three had unilateral thumb anomalies--two unilateral thumb hypoplasias and one thumb duplication. The three children with unilateral anomalies were diagnosed late, presenting with bone marrow failure. All three have subsequently died following late bone marrow transplants. This study highlights the link between unilateral radial anomalies, including thumb duplication and FA and the importance of early genetic referral for diagnosis and surveillance.

Fatal course of tonsillar squamous cell carcinoma associated with Fanconi anaemia: a mini review

Fanconi anaemia (FA) is a rare genetic syndrome characterized by progressive pancytopenia, variably expressed congenital abnormalities and susceptibility, amongst others, to solid tumours. Early detection by oral health professionals of a pathological process can have a critical impact on the clinical course of that condition. In this paper we report the case of a 27-year-old male patient with tonsillar squamous cell carcinoma (cT4 cN2b cM0 G3) associated with FA. Due to the locally advanced growth of the tumour and the poor systemic condition we ruled out primary surgery and settled for primary radio- and chemotherapy. Given the poor clinical course a focus on the aspect of secondary prevention is reasonable, given that it is known that patients with FA are at higher risk of developing malignancy than the general population. A multi-disciplinary approach is necessary in which the prevention of, surveillance for and the treatment of malignancies are important aspects of management and may improve disease-free survival.

Salivary flow rate, calcium, urea, total protein, and amylase levels in fanconi anemia

OBJECTIVES

Fanconi anemia (FA) is a genetic disease characterized by a chromosomal instability that develops a progressive pancitopenia, leukemia, and/or solid tumors. Nevertheless, it is unknown if this illness induces changes on the salivary gland parenchyma and function. The aim of this study was to assess the stimulated salivary flow rate (SSFR) and calcium, urea, total protein, and amylase levels in saliva of FA patients.

METHODS

Stimulated whole saliva was collected from 34 randomly selected FA patients and 34 age-matched and sex-matched controls. Both samples were analyzed for salivary flow rate, calcium, urea, total proteins, and amylase. The SSFR was analyzed by gravimetric method and calcium, urea, total protein, and amylase concentrations were realized by chemistry tests.

RESULTS

Mean values of SSFR for experimental and control groups were, respectively, 0.5 mL/min and 0.8 mL/min (P<0.05). Calcium concentration was 36% (P<0.05) and urea concentration was 21% (P<0.01) lower in the FA group saliva compared with saliva from the controls. The saliva concentration of amylase was almost equal in both groups.

CONCLUSIONS

FA patients may exhibit significant changes in SSFR, calcium, and urea concentration of saliva.

The role of the Fanconi anemia network in the response to DNA replication stress

Fanconi anemia is a genetically heterogeneous disorder associated with chromosome instability and a highly elevated risk for developing cancer. The mutated genes encode proteins involved in the cellular response to DNA replication stress. Fanconi anemia proteins are extensively connected with DNA caretaker proteins, and appear to function as a hub for the coordination of DNA repair with DNA replication and cell cycle progression. At a molecular level, however, the raison d'être of Fanconi anemia proteins still remains largely elusive. The thirteen Fanconi anemia proteins identified to date have not been embraced into a single and defined biological process. To help put the Fanconi anemia puzzle into perspective, we begin this review with a summary of the strategies employed by prokaryotes and eukaryotes to tolerate obstacles to the progression of replication forks. We then summarize what we know about Fanconi anemia with an emphasis on biochemical aspects, and discuss how the Fanconi anemia network, a late acquisition in evolution, may function to permit the faithful and complete duplication of our very large vertebrate chromosomes.

The fanconi anemia core complex acts as a transcriptional co-regulator in hairy enhancer of split 1 signaling

Mutations in one of the 13 Fanconi anemia (FA) genes cause a progressive bone marrow failure disorder associated with developmental abnormalities and a predisposition to cancer. Although FA has been defined as a DNA repair disease based on the hypersensitivity of patient cells to DNA cross-linking agents, FA patients develop various developmental defects such as skeletal abnormalities, microphthalmia, and endocrine abnormalities that may be linked to transcriptional defects. Recently, we reported that the FA core complex interacts with the transcriptional repressor Hairy Enhancer of Split 1 (HES1) suggesting that the core complex plays a role in transcription. Here we show that the FA core complex contributes to transcriptional regulation of HES1-responsive genes, including HES1 and the cyclin-dependent kinase inhibitor p21(cip1/waf1). Chromatin immunoprecipitation studies show that the FA core complex interacts with the HES1 promoter but not the p21(cip1/waf1) promoter. Furthermore, we show that the FA core complex interferes with HES1 binding to the co-repressor transducin-like-Enhancer of Split, suggesting that the core complex affects transcription both directly and indirectly. Taken together these data suggest a novel function of the FA core complex in transcriptional regulation.

Correlation of thyroid and growth hormones to chromosomal instability in Egyptian Fanconi anemia patients

OBJECTIVE

Fanconi anemia (FA) is a rare inherited genomic instability syndrome and usually associated with endocrine dysfunctions. We aimed to assess the diagnostic standards of chromosomal instability in FA and to correlate the breakage frequency with the severity of endocrinal dysfunctions.

METHODS

Twenty seven FA patients were randomly selected from Hematology Unit of Mansoura University Children's Hospital; their mean age 8.8 yr. Sixteen normal children matched for age and sex were used as controls. Cytogenetic studies included peripheral blood lymphocyte cultures using phytohemagglutinin to obtain chromosomal spreads. Chromosomal breakage was induced by (i) Diepoxybutane 0.1 mug/ml. (ii) Mitomycin C 0.1 microg/ml. (iii) Irradiation of cultures to four radiation doses; 75, 150, 300 and 400 rads (rad1, rad2, rad3 and rad4 respectively). Chromosomal aberrations were scored from the previous 6 cultures besides a culture for spontaneous chromosomal breakage; then mean chromosomal breakage was calculated for the seven cultures. Endocrinal evaluation included quantitative determination of thyroid stimulating hormone (TSH) and tetraiodothyronine (T4), serum growth hormone (GH), insulin like growth factor-1 (IGF-1) and insulin levels.

RESULTS

Chromosomal breakage was found to be significantly higher in patients than control when induced by Diepoxybutane (p = 0.003), Mitomycin (p = 0.001), rad3 (p = 0.043) and rad4 (p = 0.001). Mean chromosomal breakage was significantly negative correlated to head circumference (r = -0.57) and GH level (r = -0.50), with no significant correlation to other hormonal parameters. Mitomycin and rad4 were found more accurate than DEB test for diagnosis of FA in suspected cases.

CONCLUSION

Correction of the frequently associated hormonal dysfunction (reduced GH and T4) should be considered in the treatment discipline of FA patients to improve their final height.

Hyperbaric oxygen should not be used in the management of hemorrhagic cystitis in patients with Fanconi anemia

Hemorrhagic cystitis (HC) is a common complication after stem cell transplantation (SCT) that occurs more frequently in patients with Fanconi anemia (FA) because of hypersensitivity of their cells to the agents used in the preparation for SCT (chemo and radiation). Many HC cases respond to therapy with hyperhydration and maintenance of adequate platelet counts, but refractory cases may require additional measures such as the use of prostaglandins, alum, or hyperbaric oxygen (HBO). We report here an unusual complication to HBO therapy in a FA patient consisting of generalized edema mimicking capillary leak syndrome but with no pulmonary edema or ascites.

An overview of isolated and syndromic oesophageal atresia

Oesophageal atresia (OA) and/or tracheo-oesophageal fistula (TOF) are frequent malformations observed in approximately one in 3500 births. OA/TOF can be divided clinically into isolated OA (IOA) and syndromic OA (SOA) when associated with other features, the most frequent being cardiac, limb and vertebral malformations or anal atresia. SOA is observed in 50% of patients and can be subdivided into several causative groups comprising environmental agents, chromosomal disorders, malformative associations (CHARGE syndrome and VATER/VACTERL association), and other multiple congenital anomaly disorders. The observation of chromosomal disorders with SOA, as well as mouse models of OA provide support for the involvement of genetic factors in OA. Yet, epidemiological data (twin and family studies) do not support the major role of genetic factors in the majority of cases of IOA but rather a multifactorial model. However, several genes involved in SOA have been recently identified, namely N-MYC, SOX2, and CHD7 involved in Feingold (MIM 164280), anophthalmia-oesophageal-genital (MIM 600992) and CHARGE syndromes respectively (MIM 214800), suggesting that OA/TOF, at least in their syndromic forms, may be a highly genetically heterogeneous group.

Oesophageal atresia, tracheo-oesophageal fistula, and the VACTERL association: review of genetics and epidemiology

Oesophageal atresia and/or tracheo-oesophageal fistula are relatively common malformations occurring in approximately 1 in 3500 births. In around half of the cases (syndromic oesophageal atresia), there are associated anomalies, with cardiac malformations being the most common. In the remainder (non-syndromic cases), oesophageal atresia/tracheo-oesophageal fistula occur in isolation. Data from twin and family studies suggest that genetic factors do not play a major role, and yet there are well-defined instances of this malformation where genetic factors clearly are important. This is highlighted by the recent identification of no fewer than three separate genes with a role in the aetiology of oesophageal atresia: those for Feingold syndrome (N-MYC), anophthalmia-oesophageal-genital (AEG) syndrome (SOX2), and CHARGE syndrome (CHD7). Additional support for genetic factors in this malformation comes from chromosomal studies and mouse models. This paper reviews current knowledge of the genetics and epidemiology of the different oesophageal atresia/tracheo-oesophageal fistula syndromes and associations.

Individualized risks of first adverse events in patients with Fanconi anemia

Fanconi anemia (FA) is an autosomal recessive condition associated with bone marrow failure (BMF) leading to death or hematopoietic stem cell transplantation, acute myeloid leukemia (AML), and solid tumors (STs). It is unclear which patients are most likely to develop each outcome. From a cohort of 144 North American patients with FA, we calculated individualized risks of each outcome, given the presence or absence of readily diagnosed congenital abnormalities that occur frequently in FA. Abnormal radii and a 5-item congenital abnormality score were significant risk factors for BMF. The cumulative incidence of BMF by age 10 years varied from 18% in the lowest BMF risk group to 83% in the highest. Because of competing risks, patients in the lowest BMF risk group were most likely to live long enough to develop AML or ST, and, conversely, patients in the highest BMF risk group were least likely to live long enough to develop AML or ST. By age 40, the cumulative incidence of ST ranged from 0.6% to 29% in the highest and lowest BMF risk groups, respectively. Abnormal radii are the strongest predictor of early BMF in FA; a congenital abnormality score separates patients with normal radii into distinct prognostic groups.

Chromosomal fragility in patients with triple A syndrome

Triple A syndrome is a rare, autosomal recessive disorder characterized by alacrima, achalasia, and adrenal insufficiency. Previous studies have shown that the triple A gene (AAAS) maps to chromosomal band 12q13. Mutations in the AAAS gene have been identified in triple A syndrome patients; however, the function of this gene is still obscure. We used classical and high-resolution chromosome analyses along with chromosome painting and DNA sequencing to study patients with triple A syndrome. We observed abnormalities in the heterochromatic region of chromosome 9 that included chromatid breaks, chromosome breaks, whole chromosome arm loss, and marker chromosomes, which occurred at unusually high frequencies in affected patients and heterozygotes. Our study raises the possibility of an association between chromosomal fragility in band 9q12 and triple A syndrome. Further investigation is necessary to understand the biologic basis of this finding in the context of triple A syndrome.

Fanconi anaemia

Fanconi anaemia (FA) is an autosomal recessive disease characterised by congenital abnormalities, defective haemopoiesis, and a high risk of developing acute myeloid leukaemia and certain solid tumours. Chromosomal instability, especially on exposure to alkylating agents, may be shown in affected subjects and is the basis for a diagnostic test. FA can be caused by mutations in at least seven different genes. Interaction pathways have been established, both between the FA proteins and other proteins involved in DNA damage repair, such as ATM, BRCA1 and BRCA2, thereby providing a link with other disorders in which defective DNA damage repair is a feature. This review summarises the clinical features of FA and the natural history of the disease, discusses diagnosis and management, and puts the recent molecular advances into the context of the cellular and clinical FA phenotype.

Analysis of the Fanconi anaemia complementation group A gene in acute myeloid leukaemia

Acute myeloid leukaemia (AML) is the most common acute leukaemia in adults. Around 10-15% of individuals with recessively inherited Fanconi anaemia (FA) develop AML. FA is one of a group of recessive syndromes characterized by excessive spontaneous chromosomal breakage in which heterozygote carriers appear to display an increased risk of cancer and there is some indirect evidence that FA carriers may also be at increased risk of AML. This suggests that FA genes may play a role in the development of AML in the wider context. To examine this proposition, further, we have screened samples from 79 AML patients for mutations in the major FA gene, FANCA. No truncating FANCA mutations were detected. One missense mutation previously designated as pathogenic and five novel missense mutations causing non-conservative amino acid substitutions were detected. The data suggests that while FANCA mutations are rare, FANCA mutations may contribute to the development of the disease in a subset of AML.

Somatic mosaicism and variable expressivity

For more than 50 years geneticists have assumed that variations in phenotypic expression are caused by alterations in genotype. Recent evidence shows that 'simple' mendelian disorders or monogenic traits are often far from simple, exhibiting phenotypic variation (variable expressivity) that cannot be explained entirely by a gene or allelic alteration. In certain cases of androgen insensitivity syndrome caused by identical mutations in the androgen receptor gene, phenotypic variability is caused by somatic mosaicism, that is, somatic mutations that occur only in certain androgen-sensitive cells. Recently, more than 30 other genetic conditions that exhibit variable expressivity have been linked to somatic mosaicism. Somatic mutations have also been identified in diseases such as prostate and colorectal cancer. Therefore, the concept of somatic mutations and mosaicism is likely to have far reaching consequences for genetics, in particular in areas such as genetic counseling.