FANCG Research Articles

Molecular analysis of Fanconi anemia: the experience of the Bone Marrow Failure Study Group of the Italian Association of Pediatric Onco-Hematology

Fanconi anemia is an inherited disease characterized by congenital malformations, pancytopenia, cancer predisposition, and sensitivity to cross-linking agents. The molecular diagnosis of Fanconi anemia is relatively complex for several aspects including genetic heterogeneity with mutations in at least 16 different genes. In this paper, we report the mutations identified in 100 unrelated probands enrolled into the National Network of the Italian Association of Pediatric Hematoly and Oncology. In approximately half of these cases, mutational screening was carried out after retroviral complementation analyses or protein analysis. In the other half, the analysis was performed on the most frequently mutated genes or using a next generation sequencing approach. We identified 108 distinct variants of the FANCA, FANCG, FANCC, FANCD2, and FANCB genes in 85, 9, 3, 2, and 1 families, respectively. Despite the relatively high number of private mutations, 45 of which are novel Fanconi anemia alleles, 26% of the FANCA alleles are due to 5 distinct mutations. Most of the mutations are large genomic deletions and nonsense or frameshift mutations, although we identified a series of missense mutations, whose pathogenetic role was not always certain. The molecular diagnosis of Fanconi anemia is still a tiered procedure that requires identifying candidate genes to avoid useless sequencing. Introduction of next generation sequencing strategies will greatly improve the diagnostic process, allowing a rapid analysis of all the genes.

Fanconi anaemia in black South African patients heterozygous for the FANCG c.637-643delTACCGCC founder mutation

Fanconi anaemia (FA) is an autosomal recessive, genetically heterogeneous disorder, characterised by interstrand crosslink-induced chromosome breaks, congenital abnormalities and predisposition to malignancies. It has a prevalence of about 1/40 000 in black South Africans (SAs). A founder mutation in the FANCG gene occurs in the homozygous state in 77.5% of southern African blacks. To locate additional pathogenic mutations in the FANCG gene of black FA patients who were heterozygous for the founder mutation. Methods. Further mutation analysis of the FANCG gene was undertaken in 7 patients clinically suspected of having FA. The parents of two of the patients were tested for the presence of the founder mutation to determine true heterozygosity in the patients. To clarify whether or not previously unreported variants were pathogenic, 58 random black SA individuals were screened. Three novel single base pair deletions, resulting in frameshift mutations (c.247delA, c.179delT and c.899delT) were identified in 3/7 patients. A fourth patient was found to have a single base substitution resulting in a splice site mutation (c.1636+1G>A). The remaining three patients were not found to harbour any pathogenic mutations. Two non-pathogenic variants were also identified among the seven patients. The results of this small sample suggest that a second common mutation in the FANCG gene is unlikely in this population. However, FANCG sequencing should be performed on patients heterozygous for the common founder mutation to attempt to confirm their diagnosis.

Expression of FANCG gene in acute myeloid leukemia

This study was purposed to investigate the relationship between expression of the FANCG gene and adult sporadic acute myeloid leukemia (AML), real-time PCR with SYBR Green I technique was used for detecting FANCG gene expression level in bone marrow mononuclear cells of 54 newly diagnosed AML patients, 46 AML patients in complete remission (CR) and 36 control samples. β-actin gene was used as internal reference. Relative changes of FANCG gene expression level were detected by 2(-ΔΔCT) method in newly diagnosed AML patients and control samples, in newly diagnosed AML and patient in CR, as well as in AML patients in CR and control samples. The results showed that the relative expression level of FANCG mRNA was 0.56 ± 0.27 in newly diagnosed group, 0.75 ± 0.54 in AML CR group, and 0.85 ± 0.45 in control group. The expression level of FANCG mRNA in newly diagnosed group was significantly lower than that in control and AML CR groups (P < 0.05). There was no statistically significant deference in comparison of AML CR group with the control group (P > 0.05). It is concluded that the expression of FANCG gene decrease in the newly diagnosed AML patients. There is no significant difference between AML CR group and control group, which indicated that FANCG gene may be related with the onset and the prognosis of AML, and may provide a clinical value for evaluating effect of chemotherapy.

A Case Report of Fanconi Anemia Diagnosed by Genetic Testing Followed by Prenatal Diagnosis

Fanconi anemia (FA) is a rare genetic disorder affecting multiple body systems. Genetic testing, including prenatal testing, is a prerequisite for the diagnosis of many clinical conditions. However, genetic testing is complicated for FA because there are often many genes that are associated with its development, and large deletions, duplications, or sequence variations are frequently found in some of these genes. This study describes successful genetic testing for molecular diagnosis, and subsequent prenatal diagnosis, of FA in a patient and his family in Korea. We analyzed all exons and flanking regions of the FANCA, FANCC, and FANCG genes for mutation identification and subsequent prenatal diagnosis. Multiplex ligation-dependent probe amplification analysis was performed to detect large deletions or duplications in the FANCA gene. Molecular analysis revealed two mutations in the FANCA gene: a frameshift mutation c.2546delC and a novel splice-site mutation c.3627-1G>A. The FANCA mutations were separately inherited from each parent, c.2546delC was derived from the father, whereas c.3627-1G>A originated from the mother. The amniotic fluid cells were c.3627-1G>A heterozygotes, suggesting that the fetus was unaffected. This is the first report of genetic testing that was successfully applied to molecular diagnosis of a patient and subsequent prenatal diagnosis of FA in a family in Korea.

Abstract 2597: Identification of new genes for hereditary breast cancer

Abstract Major hereditary breast cancer (BC) genes, BRCA1 and BRCA2, contribute to no more than 20-25% of familial BC clustering; therefore the majority of BC-predisposing mutations remain to be identified. We have selected for the study 95 BC cases, which showed accumulation of clinical signs of the genetic disease (e.g., occurrence of BC among multiple relatives and/or bilaterality and/or young age at onset), but could not be explained either by BRCA1/2 sequence alterations or by Russian founder mutations in CHEK2 (c.1100delC, c.444+1G&amp;gt;A, del5395) or NBN (657del5) genes. The entire coding regions of DNA repair genes were examined using high resolution melting (HRM) analysis and DNA sequencing. Three of 16 genes selected for the study (CHEK2, NBN, PALB2, BRIP1, BARD1, RAD51C, BLM, FANCG, CHEK1, PARP1, PARP2, ERCC1, XPE, BRD7, RNF8, RAD51A) contained potentially deleterious mutations. Two patients carried inactivating lesion in the PALB2 gene (p.R414X and p.Q921X); both these carriers had the bilateral form of BC disease. 1 woman harbored mutation in the FANCG gene (c.520_524delTCTAinsC), which resulted in the loss of serine at position 174 and lysine to glutamine substitution at position 175. The analysis of the BLM gene revealed two heterozygous carriers of the c.1642 C&amp;gt;T (Q548X) allele. This mutation was subjected to the extended study, which confirmed its recurrent character and strong association with BC risk: BLM c.1642 C&amp;gt;T (Q548X) heterozygotes were detected in 17/1,498 (1.1%) BC patients as compared to 2/1,093 (0.2%) healthy females (p = 0.004). As expected for BC-predisposing gene, the BLM 1670 C&amp;gt;T allele tended to be associated with first-degree family history of BC, early onset and bilateral appearance of the disease. This is the first demonstration of the role of the BLM heterozygosity in the determination of BC risk. The impact of constitutional BLM mutations in hereditary cancer predisposition deserves to be tested in other ethnic groups as well as in other tumor types. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2597. doi:1538-7445.AM2012-2597

Relevance of the Fanconi anemia pathway in the response of human cells to trabectedin

Trabectedin (Yondelis; ET-743) is a potent anticancer drug that binds to DNA by forming a covalent bond with a guanine in one strand and one or more hydrogen bonds with the opposite strand. Using a fluorescence-based melting assay, we show that one single trabectedin-DNA adduct increases the thermal stability of the double helix by >20 degrees C. As deduced from the analysis of phosphorylated H2AX and Rad51 foci, we observed that clinically relevant doses of trabectedin induce the formation of DNA double-strand breaks in human cells and activate homologous recombination repair in a manner similar to that evoked by the DNA interstrand cross-linking agent mitomycin C (MMC). Because one important characteristic of this drug is its marked cytotoxicity on cells lacking a functional Fanconi anemia (FA) pathway, we compared the response of different subtypes of FA cells to MMC and trabectedin. Our data clearly show that human cells with mutations in FANCA, FANCC, FANCF, FANCG, or FANCD1 genes are highly sensitive to both MMC and trabectedin. However, in marked contrast to MMC, trabectedin does not induce any significant accumulation of FA cells in G2-M. The critical relevance of FA proteins in the response of human cells to trabectedin reported herein, together with observations showing the role of the FA pathway in cancer suppression, strongly suggest that screening for mutations in FA genes may facilitate the identification of tumors displaying enhanced sensitivity to this novel anticancer drug.

Role of the Fancg gene in protecting cells from particulate chromate-induced chromosome instability

Particulate hexavalent chromium (Cr(VI)) is a known human lung carcinogen. Cr(VI)-induced tumors exhibit chromosome instability (CIN), but the mechanisms underlying these effects are unknown. We investigated a possible role for the Fanconi anemia (FA) pathway in particulate Cr(VI)-induced chromosomal damage by focusing on the Fancg gene, which plays an important role in cellular resistance to DNA interstrand crosslinks. We used the isogenic Chinese hamster ovary (CHO) KO40 fancg mutant compared with parental and gene-complemented cells. We found that fancg cells treated with lead chromate had lower intracellular Cr ion levels than control cell lines. Accounting for differences of Cr ion levels between cell lines, we discovered that fancg cells treated with lead chromate had increased cytotoxicity and chromosomal aberrations, which was not observed after restoring the Fancg gene. Chromosomal damage was manifest as increased total chromosome damage and percent metaphases with damage, specifically an increase in chromatid and isochromatid breaks. We conclude that Fancg protects cells from particulate Cr(VI)-induced cytotoxicity and chromosome damage, which is consistent with the known sensitivity of fancg cells to crosslinking damage and the ability of Cr(VI) to produce crosslinks.

Targeted Disruption of FANCC and FANCG in Human Cancer Provides a Preclinical Model for Specific Therapeutic Options

How specifically to treat pancreatic and other cancers harboring Fanconi anemia gene mutations has raised great interest recently, yet preclinical studies have been hampered by the lack of well-controlled human cancer models. We endogenously disrupted FANCC and FANCG in a human adenocarcinoma cell line and determined the impact of these genes on drug sensitivity, irradiation sensitivity, and genome maintenance. FANCC and FANCG disruption abrogated FANCD2 monoubiquitination, confirming an impaired Fanconi anemia pathway function. On treatment with DNA interstrand-cross-linking agents, FANCC and FANCG disruption caused increased clastogenic damage, G2/M arrest, and decreased proliferation. The extent of hypersensitivity varied among agents, with ratios of inhibitory concentration 50% ranging from 2-fold for oxaliplatin to 14-fold for melphalan, a drug infrequently used in solid tumors. No hypersensitivity was observed on gemcitabine, etoposide, 3-aminobenzamide, NU1025, or hydrogen peroxide. FANCC and FANCG disruption also resulted in increased clastogenic damage on irradiation, but only FANCG disruption caused a subsequent decrease in relative survival. Finally, FANCC and FANCG disruption increased spontaneous chromosomal breakage, supporting the role of these genes in genome maintenance and likely explaining why they are mutated in sporadic cancer. Our human cancer cell model provides optimal controls to elucidate fundamental biologic features of individual Fanconi anemia gene defects and facilitates preclinical studies of therapeutic options. The impact of Fanconi gene defects on drug and irradiation sensitivity renders these genes promising targets for a specific, genotype-based therapy for individual cancer patients, providing a strong rationale for clinical trials.

In vivoTherapeutic Responses Contingent on Fanconi Anemia/BRCA2 Status of the Tumor

BRCA2, FANCC, and FANCG gene mutations are present in a subset of pancreatic cancer. Defects in these genes could lead to hypersensitivity to interstrand cross-linkers in vivo and a more optimal treatment of pancreatic cancer patients based on the genetic profile of the tumor. Two retrovirally complemented pancreatic cancer cell lines having defects in the Fanconi anemia pathway, PL11 (FANCC-mutated) and Hs766T (FANCG-mutated), as well as several parental pancreatic cancer cell lines with or without mutations in the Fanconi anemia/BRCA2 pathway, were assayed for in vitro and in vivo sensitivities to various chemotherapeutic agents. A distinct dichotomy of drug responses was observed. Fanconi anemia-defective cancer cells were hypersensitive to the cross-linking agents mitomycin C (MMC), cisplatin, chlorambucil, and melphalan but not to 5-fluorouracil, gemcitabine, doxorubicin, etoposide, vinblastine, or paclitaxel. Hypersensitivity to cross-linking agents was confirmed in vivo; FANCC-deficient xenografts of PL11 and BRCA2-deficient xenografts of CAPAN1 regressed on treatment with two different regimens of MMC whereas Fanconi anemia-proficient xenografts did not. The MMC response comprised cell cycle arrest, apoptosis, and necrosis. Xenografts of PL11 also regressed after a single dose of cyclophosphamide whereas xenografts of genetically complemented PL11(FANCC) did not. MMC or other cross-linking agents as a clinical therapy for pancreatic cancer patients with tumors harboring defects in the Fanconi anemia/BRCA2 pathway should be specifically investigated.

A common Fanconi anemia mutation in black populations of sub-Saharan Africa

AbstractFanconi anemia (FA) is a genetically heterogeneous chromosomal instability syndrome associated with multiple congenital abnormalities, aplastic anemia, and cancer. We report that a deletion mutation in the FANCG gene (c.637_643delTACCGCC) was present in 82% of FA patients in the black populations of Southern Africa. These patients originated from South Africa, Swaziland, Mozambique, and Malawi. The mutation was found on the same haplotype and was present in 1% of controls from the black South African population. These data indicate that the birth incidence of FA in this population is higher than 1 in 40 000, which is much higher than previously supposed, and suggest that the FANCG deletion is an ancient founder mutation in Bantu-speaking populations of sub-Saharan Africa. Diagnostic screening is now possible by means of a simple DNA test.

Hyperoxia Induces Defective Epo-Induced Signal Transduction and Loss of Expansion Capacity in Fanca- and Fancg-Deficient Erythroid Progenitors.

Fanconi anemia (FA) is characterized by chromosomal instability and bone marrow hypoplasia. To explore the mechanism of FA-related bone marrow failure, we studied erythropoietin (Epo)-dependent proliferation and differentiation of erythroid progenitors expanded from mice lacking the Fanca or Fancg gene. Erythroid progenitors can be expanded in serum-free medium supplemented with Epo, Stem Cell Factor (SCF) and glucocorticoids. The expansion capacity of Fanca−/− and Fancg−/− erythroid progenitors was reduced and the progenitors differentiated to mature erythrocytes instead after 10 days of culture. When Epo-induced signal transduction was compared between progenitors expanded for 6 days from fetal livers of Fanca−/−, Fancg−/− and wt littermates, Epo-induced phosphorylation of STAT5 and ERK1/2 appeared to be severely reduced and delayed in progenitors lacking Fanca or Fancg. Both in wt, Fanca−/− and Fancg−/− progenitors the phosphorylation of STAT5 and ERK1/2 increased with rising Epo-concentrations, but at low concentrations 4-fold more Epo was required to obtained comparable Stat5 phosphorylation in FancA−/− or FancG−/− cells, while efficient phosphorylation at high concentrations was never achieved in Fanca or Fancg-deficient cells. As a consequence, the regulation of Epo-target genes like p21WAF, Gilz, SOCS3, Spi2.1 and BclXL was impaired. In contrast to downstream signaling intermediates, Epo-induced phosphorylation of the Epo-receptor and its associated kinase JAK2 was not affected. Stem Cell Factor-induced c-Kit activation and downstream Erk1/2 phosphorylation was also equally efficient in wt, Fanca−/− and Fancg−/− progenitors. Thus, the signaling defect specifically seems to affect targets downstream of Jak2. Surprisingly, Epo-induced activation of Stat5 was unaffected in freshly isolated bone marrow cells. Comparison of Epo-induced Stat5 phosphorylation in erythroid progenitors cultured at atmospheric (20%) and physiologic (3%) oxygen revealed that Stat5 phosphorylation was only lost upon expansion of the progenitors at atmospheric (hyperoxic) conditions. Hyperoxia can damage many biomolecules among which DNA. In contrast to wt cells, Fanca−/− and Fancg−/− progenitors may not be able to repair DNA-damage induced by atmospheric oxygen. To examine whether increased DNA damage could impair Epo-induced signal transduction, we expanded erythroid progenitors from fetal livers of mice lacking the DNA-repair enzyme Ercc1. Ercc1 is directly involved in repair of DNA crosslinks, while a defective FA pathway renders cells hypersensitive to DNA-crosslinks. Epo-induced phosphorylation of Stat5 was impaired in Ercc1−/− progenitors, indicating that deficient repair of DNA damage, rather than FA-pathway specific mechanisms may cause the observed signaling defect. To substantiate this finding we treated wt and p53−/− progenitors with increasing concentrations of mitomycin C (MMC). Sublethal concentrations of MMC abrogated the renewal capacity and impaired Epo-induced phosporylation of Stat5 and Erk1/2 in wt but not in p53−/− erythroid progenitors. Together the data suggest that impaired progenitor expansion and Stat5 phosphorylation is not a specific aspect of cells lacking the fanconi pathway, but a general aspect of a p53-dependent response to genomic stress.

Involvement of Fanconi Anemia (FA) Genes FANCG and FANCA in Human DNA Replication, Mitosis and Chromosome Segregation: A Gene Expression Profiling Study.

FA is an autosomal recessive disorder with diverse clinical symptoms, including developmental anomalies, progressive bone marrow failure, and a predisposition to the development of malignancies. FA cells are hypersensitive to DNA cross-linking agents, and display chromosomal instability and defective DNA repair. FANCG-deficient pts accounts for 10% of all FA pts, and are a high risk FA population for acute myeloblastic leukemia. FANCG protein is part of the FA nuclear core complex, interacting with FANCA and FANCF. It can also interact with FANCD1, RAD51, and CYP2E1, suggesting roles in homologous recombination DNA repair and oxidative DNA-damage protection. However, FANCG lack apparent homology to other proteins involved in such processes. To address whether FANCG mRNA expression level was associated with some microarray-based functional signatures using Affymetrix HG-U133A Genechips, we first used a dataset including 111 T-acute lymphoblastic leukemia (T-ALL) samples. This large series was selected because FA pts do not usually develop T-ALL (risk of FANC gene mutation/inactivation low), FANCG is highly expressed in thymus and lymphoblasts, FANCG gene expression was significantly varying across these samples. We first selected samples having the lowest (FANCGlow) and highest (FANCGhigh) FANCG expression levels (n=15 per group, median expression values: 36 vs. 329), and identified genes differentially expressed between these 2 groups using SAM (fold change>3; qvalue<1%). Among the 368 probesets (308 known genes) significantly up-regulated in FANCGhigh group (likely to be co-expressed/regulated with FANCG), 55 were correlated to FANCG expression profile (>.75) when analyzing all 111 T-ALL samples. These genes were mainly involved in cell proliferation, mitotic cell cycle and its regulation (DNA replication, traversing Start control point, G2/M transition, chromosome segregation and cytokinesis), and were also representing cellular components involved in such processes (kinesin complex, spindle, and kinetochore). FANCA, RAD51, RAD51C, and PIR51 were also among the genes having expression patterns close to FANCG one. In addition, 11 of these 55 genes, all involved in DNA replication, were also correlated with FANCA (>.75). A robust regression analysis identified CKS1B, CCNB2, RFC5, MELK, STK18, and CENPF as the genes most significantly associated with FANCG expression profile (p<.0001, power=100%). Finally, we compared normal fibroblasts (CCL153) to primary fibroblasts from 2 FANCG-deficient pts grown under normal conditions or with MMC 100 nM for 36 hours (PD829, PD352). Fifty-eight of the 585 probesets down-regulated in FANCG-deficient fibroblasts (fold change>2; qvalue<1%) were also present in the FANCGhigh list of genes, and were mainly involved in DNA replication, mitotic chromosomal positioning and segregation, as well as in cytokinesis. Among these genes, GMNN (DNA replication inhibition by preventing MCM complex incorporation), MCM10 (DNA replication initiation), POLE2 (DNA replication and repair), and RRM2 (DNA synthesis) were also correlated with FANCA expression pattern. Of note, FANCC, FANCE, FANCF, FANCD1/BRCA2, and FANCL expression patterns were not significantly correlated with the one of FANCG or FANCA.Conclusion: these results suggest that the FA core complex, and especially FANCG and FANCA, is involved in DNA replication and mitosis.

The Fanconi Anemia Proteins Functionally Interact with the Protein Kinase Regulated by RNA (PKR)

Protein kinase regulated by RNA (PKR) plays critical roles in cell growth and apoptosis and is implicated as a potential pathogenic factor of Alzheimer's, Parkinson's, and Huntington's diseases. Here we report that this proapoptotic kinase is also involved in Fanconi anemia (FA), a disease characterized by bone marrow (BM) failure and leukemia. We have used a BM extract to show that three FA proteins, FANCA, FANCC, and FANCG, functionally interact with the PKR kinase, which in turn regulates translational control. By using a combined immunoprecipitation and reconstituted kinase assay, in which an active PKR kinase complex was captured from a normal cell extract, we demonstrated functional interactions between the FA proteins and the PKR kinase. In primary human BM cells, mutations in the FANCA, FANCC, and FANCG genes markedly increase the amount of PKR bound to FANCC, and this PKR accumulation is correlated with elevated PKR activation and hypersensitivity of BM progenitor cells to growth repression mediated by the inhibitory cytokines interferon-gamma and tumor necrosis factor-alpha. Specific inhibition of PKR by 2-aminopurine in these FA BM cells attenuates PKR activation and apoptosis induction. In lymphoblasts derived from an FA-C patient, overexpression of a dominant negative mutant PKR (PKRK296R) suppressed PKR activation and apoptosis induced by interferon-gamma and tumor necrosis factor-alpha. Furthermore, by using genetically matched wild-type and PKR-null cells, we demonstrated that forced expression of a patient-derived FA-C mutant (FANCCL554P) augmented double-stranded RNA-induced PKR activation and cell death. Thus, inappropriate activation of PKR as a consequence of certain FA mutations might play a role in bone marrow failure that frequently occurred in FA.

Characterization of the hamster FancG/Xrcc9 gene and mutations in CHO UV40 and NM3.

The human FANCG/XRCC9 gene, which is defective in Fanconi anemia complementation group G (FA-G) cells, was first cloned by genetic complementation of the mitomycin C (MMC) sensitivity of CHO mutant UV40. The CHO NM3 mutant was subsequently assigned to the same complementation group. The parental AA8 CHO cells are hemizygous at the FancG locus, and we identified frameshift mutations that result in N-terminal truncations of the protein in both UV40 and NM3. Hypersensitivity to DNA cross-linking agents, such as MMC, typically characterizes FA cells. By introducing the native CHO FancG gene into mutant NM3, we demonstrate that hamster FancG fully corrects the 3-fold sensitivity to methyl methanesulfonate (MMS) as well as the 10-fold sensitivity to MMC, whereas resistance to ionizing radiation did not increase appreciably. In contrast, hamster cDNA transformants showed incomplete correction for both MMC and MMS sensitivity. The constitutively expressed FancG protein is present in the cytoplasmic, nuclear and chromatin fractions. FancG protein levels and subcellular localization do not change appreciably as a function of cell cycle position. Our results are consistent with roles of FancG in both the nuclear and cytoplasmic compartments to maintain genomic stability in response to various genotoxic agents.

Molecular characterization of three novel Fanconi anemia mutations in Israeli Arabs.

In a previous study, we investigated the molecular basis of Fanconi anemia (FA) in 13 unrelated Israeli Jewish FA patients and identified four ethnicity specific mutations. In the present study we extended our study to Israeli Arab patients. We studied three consanguineous families with nine FA patients and an additional unrelated patient. DNA single-strand conformation polymorphism of each exon of the FANCA and FANCG genes was followed by sequence analysis of the aberrantly migrating fragments and by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis of the splice-site mutations identified. Three unique disease-causing mutations were identified: (i) FANCA gross deletion of exons 6-31; (ii) FANCA splice-site mutation IVS 42-2A>C; (iii) FANCG splice-site mutation IVS4+3A>G. Sequence analysis of the FANCA gross deletion revealed recombination between two highly homologous Alu elements. cDNA analysis of the two splice mutations suggested intron 42 retention in FANCA IVS 42-2A>C and exon 4 skipping in FANCG IVS4+3A>G. The clinical condition of eight patients with FANCA mutations was severe. Two unique FANCA mutations and one FANCG mutation were identified in Israeli Arab FA patients. Deletion of FANCA exon 6-31 as in previously described gross deletions was within introns rich in Alu repeats. To the best of our knowledge, the FANCA IVS 42-2A>C mutation is the first in this gene to result in intron retention. Further analysis of FA mutations will enable prenatal diagnosis and a rational therapeutic approach including frequent monitoring and early bone marrow transplantation.

The Genetics of FANCC and FANCG in Familial Pancreatic Cancer

Patients with Fanconi anemia (FA) display a wide variety of defects including bone marrow failure and a high risk of developing cancer. Multiple Fanconi genes exist whose proteins form a complex that along with BRCA1 is important for the translocalization of FANCD2 to nuclear foci 1. With BRCA2 and RAD51, this complex is thought to have a role in the repair of DNA double strand breaks. The genetic basis of another form of Fanconi anemia- FANCD1, was recently identified as the result of biallelic inactivating mutations of the BRCA2 gene 2. Since carriers of germline BRCA2 gene mutations have an increased risk of developing pancreatic cancer, the FA pathway has been investigated as a tumor suppressor pathway in pancreatic cancer. Recently van der Heijden et al. identified FANCC and FANCG gene mutations in patients with young-onset pancreatic cancer 3. Here, we determined the role of germline FA gene mutations in kindred in which several family members had pancreatic cancer. Sequence analysis of 38 individuals with familial pancreatic cancer enrolled in the National Familial Pancreatic Tumor Registry (NFPTR) revealed previously identified polymorphisms within two exons and one intron of FANCC, and in three introns of FANCG. In addition, an unaffected relative from one family contained an exonic polymorphism within the FANCC gene. These and published data suggest the possibility that although germline and somatic mutations in FANCC and FANCG may contribute to the occurrence of pancreatic cancers, the pancreatic cancers that arise do so in an apparent sporadic fashion rather than with a phenotype of familial pancreatic cancer. FANCC and FANCG mutations may have low penetrance for the pancreatic cancer phenotype. Summary: Sequencing of the FANCC and FANCG genes from 38 familial pancreatic cancer patients revealed polymorphisms within the introns and exons of these genes. These sequence variations do not appear to contribute to familial pancreatic cancer.

Spectrum of sequence variation in the FANCG gene: An International Fanconi Anemia Registry (IFAR) study

Spectrum of sequence variation in the FANCG gene: An International Fanconi Anemia Registry (IFAR) study

Spectrum of sequence variation in the FANCG gene: an International Fanconi Anemia Registry (IFAR) study.

Fanconi anemia (FA) is a genetically heterogeneous autosomal recessive syndrome associated with chromosomal instability, hypersensitivity to DNA cross-linking agents, and predisposition to malignancy. The gene for FA complementation group G (FANCG) was the third FA gene to be cloned, and was found to be identical with human XRCC9, which maps to 9p13. The cDNA is predicted to encode a polypeptide of 622 amino acids, with no sequence similarities to any other known protein or motifs that could point to a molecular function for FANCG/XRCC9. We used single strand conformational polymorphism analysis (SSCP) to screen genomic DNA from a panel of 307 racially and ethnically diverse unrelated FA patients from the International Fanconi Anemia Registry (IFAR) for variants in FANCG. Twenty-seven abnormal SSCP patterns were found; 18 of these variants appear to be pathogenic mutations while nine are likely to be nonpathogenic polymorphisms. Direct sequencing of genomic DNA from seven FA-G probands with one mutant allele not detected in the SSCP study and three additional probands assigned to the FA-G complementation group by retroviral correction with FANCG resulted in the detection of nine additional pathogenic mutations and two common SNPs. Conditions for rapid screening for these mutations by DHPLC for use in a clinical laboratory setting were established. The most common FANCG mutations in the IFAR population were: IVS8-2A>G (seven Portuguese-Brazilian probands), IVS11+1G>C (seven French-Acadian probands), 1794_1803del10 (seven European probands), and IVS3+1G>C (five Korean or Japanese probands). Our data suggest that the Portuguese-Brazilian, French-Acadian, and Korean/Japanese mutations were likely to have been present in a founding member of each of these populations.

Functional analysis of patient-derived mutations in the Fanconi anemia gene, FANCG/XRCC9

Fanconi anemia (FA) is an autosomal-recessive cancer susceptibility syndrome with seven complementation groups. Six of the FA genes have been cloned (corresponding to subtypes A, C, D2, E, F, and G) and the encoded proteins interact in a common pathway. Patient-derived mutations in FA genes have been helpful in delineating functional domains of FA proteins. The purpose of this work was to subtype FA patient-derived cell lines in our repository and to identify FA gene mutations. We subtyped 62 FA patients as type A, G, C, or non-ACG by using a combination of retroviral gene transfer and immunoblot analysis. Among these FA patients, we identified six FA-G patients for further analysis. We used a strategy involving amplification of FANCG/XRCC9 exons and direct sequencing to identify novel FANCG mutations in cell lines derived from these FA-G patients. We functionally analyzed FANCG mutant alleles by transducing the corresponding cDNAs into a known FA-G indicator cell line and scoring correction of MMC sensitivity. Our results demonstrate a wide range of mutations in the FANCG gene (splice, nonsense, and missense mutations). Based on this mutational screen, a carboxy terminal functional domain of the FANCG protein appears to be required for complementation of FA-G cells and for normal assembly of the FANCA/FANCG/FANCC protein complex. The identification of patient-derived mutant alleles of FA genes can provide important insights to the function of FA proteins. FA subtyping is also a necessary precondition for gene therapy.

Café au lait spots: the pediatrician's perspective.

1. Mustafa Tekin, MD* 2. Joann N. Bodurtha, MD, MPH† 3. Vincent M. Riccardi, MD‡ 1. 2. *Clinical Genetics Fellow. 3. 4. †Associate Professor of Human Genetics, Pediatrics, Obstetrics and Gynecology, Virginia Commonwealth University/Medical College of Virginia Hospitals, Richmond, VA. 5. ‡President, The Neurofibromatosis Institute, La Crescenta, CA. Objectives After completing this article, readers should be able to: 1. Define cafe au lait spots typical of neurofibromatosis type 1 (NF1) and describe their frequency and variability in the normal population. 2. List three or more genetic disorders other than NF1 that are associated with cafe au lait spots. 3. Summarize three or more clinical manifestations and molecular bases of NF1 and NF2. 4. List the diagnostic criteria for NF1. 5. Summarize clinical findings of genetic disorders other than NF1 associated with cafe au lait spots. Every pediatrician faces the challenge of deciding if a patient who has cafe au lait (CAL) spots has an underlying genetic condition. CAL spots typical of neurofibromatosis type 1 (NF1) are discrete, round or oval, uniformly hyperpigmented skin patches. Their color varies from light to dark brown, and the border may be smooth or irregular. They usually are smaller in newborns, enlarge as children get older, and are less prominent in adults. The histologic basis of CAL spots is increased melanin content, with the presence of giant melanosomes in both melanocytes and basal keratinocytes and no melanocytic proliferation. The giant melanosomes in CAL spots are not unique to NF1; they can be seen in unaffected skin of adults who have NF1 and occasionally in normal skin of healthy individuals. Therefore, the presence of giant melanosomes is not helpful for diagnosing NF1. The frequency and number of CAL spots vary in the general population according to ethnic background and age. Sometimes otherwise healthy children who have red hair and often are of Irish or Welsh background have multiple areas of patchy hyperpigmentation. Similarly, multiple patchy areas of hyperpigmentation can occur in healthy children who have mixed ethnic backgrounds in which two parents have very different skin colors. CAL spots were noted in 0.3% of Caucasians and 18% of African-Americans …