Catherine Dubois d'Enghien

Evaluation of in silico splice tools for decision‐making in molecular diagnosis

It appears that all types of genomic nucleotide variations can be deleterious by affecting normal pre‐mRNA splicing via disruption/creation of splice site consensus sequences. As it is neither pertinent nor realistic to perform functional testing for all of these variants, it is important to identify those that could lead to a splice defect in order to restrict transcript analyses to the most appropriate cases. Web‐based tools designed to provide such predictions are available. We evaluated the performance of six of these tools (Splice Site Prediction by Neural Network [NNSplice], Splice‐Site Finder [SSF], MaxEntScan [MES], Automated Splice‐Site Analyses [ASSA], Exonic Splicing Enhancer [ESE] Finder, and Relative Enhancer and Silencer Classification by Unanimous Enrichment [RESCUE]‐ESE) using 39 unrelated retinoblastoma patients carrying different RB1 variants (31 intronic and eight exonic). These 39 patients were screened for abnormal splicing using puromycin‐treated cell lines and the results were compared to the predictions. As expected, 17 variants impacting canonical AG/GT splice sites were correctly predicted as deleterious. A total of 22 variations occurring at loosely defined positions (±60 nucleotides from an AG/GT site) led to a splice defect in 19 cases and 16 of them were classified as deleterious by at least one tool (84% sensitivity). In other words, three variants escaped in silico detection and the remaining three were correctly predicted as neutral. Overall our results suggest that a combination of complementary in silico tools is necessary to guide molecular geneticists (balance between the time and cost required by RNA analysis and the risk of missing a deleterious mutation) because the weaknesses of one in silico tool may be overcome by the results of another tool. Hum Mutat 29(7), 975–982, 2008.

Myelodysplasia and leukemia of Fanconi anemia are associated with a specific pattern of genomic abnormalities that includes cryptic RUNX1/AML1 lesions

Fanconi anemia (FA) is a genetic condition associated with bone marrow (BM) failure, myelodysplasia (MDS), and acute myeloid leukemia (AML). We studied 57 FA patients with hypoplastic or aplastic anemia (n = 20), MDS (n = 18), AML (n = 11), or no BM abnormality (n = 8). BM samples were analyzed by karyotype, high-density DNA arrays with respect to paired fibroblasts, and by selected oncogene sequencing. A specific pattern of chromosomal abnormalities was found in MDS/AML, which included 1q+ (44.8%), 3q+ (41.4%), -7/7q (17.2%), and 11q- (13.8%). Moreover, cryptic RUNX1/AML1 lesions (translocations, deletions, or mutations) were observed for the first time in FA (20.7%). Rare mutations of NRAS, FLT3-ITD, MLL-PTD, ERG amplification, and ZFP36L2-PRDM16 translocation, but no TP53, TET2, CBL, NPM1, and CEBPα mutations were found. Frequent homozygosity regions were related not to somatic copy-neutral loss of heterozygosity but to consanguinity, suggesting that homologous recombination is not a common progression mechanism in FA. Importantly, the RUNX1 and other chromosomal/genomic lesions were found at the MDS/AML stages, except for 1q+, which was found at all stages. These data have implications for staging and therapeutic managing in FA patients, and also to analyze the mechanisms of clonal evolution and oncogenesis in a background of genomic instability and BM failure.

Incidence, Presentation, and Prognosis of Malignancies in Ataxia-Telangiectasia: A Report From the French National Registry of Primary Immune Deficiencies

PURPOSE Biallelic mutations in ATM cause ataxia-telangiectasia (AT), a rare inherited disease with a high incidence of cancer. Precise estimates of the risk, presentation, and outcomes of cancer in patients with AT need to be addressed in large series. PATIENTS AND METHODS In this large retrospective cohort, 69 patients with cancers (24.5%) were identified among 279 patients with AT. Centralized review was performed on 60% of the lymphomas. Incidence rates were compared with the French population, and risk factors were analyzed. RESULTS Eight patients developed acute leukemias (including four T-cell acute lymphoblastic leukemias), 12 developed Hodgkin lymphoma (HL), 38 developed non-Hodgkin lymphoma (NHL), three developed T-cell prolymphocytic leukemia (T-PLL), and eight developed carcinoma at a median age of 8.3, 10.6, 9.7, 24.2, and 31.4 years, respectively (P < .001). The majority of NHLs were aggressive B-cell NHL. Epstein-Barr virus was associated with all of the HLs and 50% of the NHLs. Overall survival was shorter in patients with AT who developed cancer compared with those who did not develop cancer (15 v 24 years, respectively; P < .001). Survival was improved in patients who achieved a major response to treatment (3.46 v 0.87 years for major v minor responses, respectively; P = .011). Immunodeficiency was associated with increased risk of cancer. ATM mutation type was associated with a difference in survival in the entire cohort but not with cancer incidence or cancer survival. CONCLUSION B-cell NHL, HL, and acute lymphoblastic leukemia occur at a high rate and earlier age than carcinomas in AT. T-PLLs are rarer than initially reported. Prognosis is poor, but patients may benefit from treatment with an improved survival.

Underexpression and abnormal localization of ATM products in ataxia telangiectasia patients bearing ATM missense mutations

Ataxia telangiectasia (A-T) is a rare autosomal recessive disorder characterized by progressive cerebellar ataxia, oculocutaneous telangiectasia, immune defects and predisposition to malignancies. A-T is caused by biallelic inactivation of the ATM gene, in most cases by frameshift or nonsense mutations. More rarely, ATM missense mutations with unknown consequences on ATM function are found, making definitive diagnosis more challenging. In this study, a series of 15 missense mutations, including 11 not previously reported, were identified in 16 patients with clinical diagnosis of A-T belonging to 14 families and 1 patient with atypical clinical features. ATM function was evaluated in patient lymphoblastoid cell lines by measuring H2AX and KAP1 phosphorylation in response to ionizing radiation, confirming the A-T diagnosis for 16 cases. In accordance with previous studies, we showed that missense mutations associated with A-T often lead to ATM protein underexpression (15 out of 16 cases). In addition, we demonstrated that most missense mutations lead to an abnormal cytoplasmic localization of ATM, correlated with its decreased expression. This new finding highlights ATM mislocalization as a new mechanism of ATM dysfunction, which may lead to therapeutic strategies for missense mutation associated A-T.

Fertility defects revealing germline biallelic nonsense NBN mutations.

Biallelic mutations in the NBN/NBS1 gene are the cause of Nijmegen breakage syndrome (NBS), a severe pediatric disease characterized by dysmorphy with a bird‐like face, microcephaly, growth retardation, immune deficiency, and proneness to cancer. We here report two adult siblings that are compound heterozygotes for two previously unreported NBN nonsense mutations. These patients presented with the unique clinical symptom of fertility defects. Contrasting with the absence of any developmental abnormality, biological analyses revealed defects similar to those observed in NBS patients, including chromosomal instability, cellular hyperradiosensitivity and checkpoint defects as measured by radioresistant DNA synthesis (RDS). NBN mutations should thus be considered a new cause of infertility, and should be searched for if associated with the biological abnormalities of NBS. Hum Mutat 0, 1–7, 2008.

Fanconi anemia and solid malignancies in childhood: A national retrospective study

Fanconi anemia (FA) predisposes to hematologic disorders and myeloid neoplasia in childhood and to solid cancers, mainly oral carcinomas, in early adulthood. Few cases of solid cancers have been reported in childhood.

Biallelic truncating FANCM mutations cause early-onset cancer but not Fanconi anemia

PurposeMutations in genes involved in Fanconi anemia (FA)/BRCA DNA repair pathway cause cancer susceptibility diseases including familial breast cancer and Fanconi anemia (FA). A single FA patient with biallelic FANCM mutations was reported in 2005 but concurrent FANCA pathogenic mutations precluded assignment of FANCM as an FA gene. Here we report three individuals with biallelic FANCM truncating mutations who developed early-onset cancer and toxicity to chemotherapy but did not present congenital malformations or any hematological phenotype suggestive of FA.MethodsChromosomal breakages, interstrand crosslink sensitivity, and FANCD2 monoubiquitination were assessed in primary fibroblasts. Mutation analysis was achieved through Sanger sequencing. Genetic complementation of patient-derived cells was performed by lentiviral mediated transduction of wild-type FANCM complementary DNA followed by functional studies.ResultsPatient-derived cells exhibited chromosomal fragility, hypersensitivity to interstrand crosslinks, and impaired FANCD2 monoubiquitination. We identified two homozygous mutations (c.2586_2589del4; p.Lys863Ilefs*12 and c.1506_1507insTA; p.Ile503*) in FANCM as the cause of the cellular phenotype. Patient-derived cells were genetically complemented upon wild-type FANCM complementary DNA expression.ConclusionLoss-of-function mutations in FANCM cause a cancer predisposition syndrome clinically distinct from bona fide FA. Care should be taken with chemotherapy and radiation treatments in these patients due to expected acute toxicity.

Mutiple DICER1-related lesions associated with a germline deep intronic mutation

Germline DICER1 pathogenic variants predispose to numerous benign and malignant tumors. In this report, we describe DICER1 gene analysis in an adolescent diagnosed with multinodular goiter, ovarian Sertoli–Leydig cell tumor, and lung cyst. DICER1 mutational screening at the DNA level failed to detect any pathogenic variant. Subsequent messenger RNA (mRNA) analysis revealed a 132 nucleotide intronic sequence exonization. This truncating event was caused by a deep intronic mutation generating a de novo acceptor splice site. This study demonstrates that some undetected DICER1 mutations should be investigated at the mRNA level.

Telomere length, ATM mutation status and cancer risk in Ataxia-Telangiectasia families.

Both telomere length (TL) and ATM mutations have been associated with cancer susceptibility and ATM participates in the signaling of telomere erosion. We wondered whether carriage of an ATM mutation influences age-related TL shortening and cancer risk in ataxia-telangiectasia families.

High frequency of exon 15 deletion in the FANCA gene in Tunisian patients affected with Fanconi anemia disease: implication for diagnosis

Tunisian population is characterized by its heterogeneous ethnic background and high rate of consanguinity. In consequence, there is an increase in the frequency of recessive genetic disorders including Fanconi anemia (FA). The aim of this study was to confirm the existence of a founder haplotype among FA Tunisian patients and to identify the associated mutation in order to develop a simple tool for FA diagnosis. Seventy‐four unrelated families with a total of 95 FA patients were investigated. All available family members were genotyped with four microsatellite markers flanking FANCA gene. Haplotype analysis and homozygosity mapping assigned 83 patients belonging to 62 families to the FA‐A group. A common haplotype was shared by 42 patients from 26 families at a homozygous state while five patients from five families were heterozygous. Among them, 85% were from southern Tunisia suggesting a founder effect. Using multiplex ligation‐dependent probe amplification (MLPA) technique, we have also demonstrated that this haplotype is associated with a total deletion of exon 15 in FANCA gene. Identification of a founder mutation allowed genetic counseling in relatives of these families, better bone marrow graft donor selection and prenatal diagnosis. This mutation should be investigated in priority for patients originating from North Africa and Middle East.