AluY-mediated germline deletion, duplication and somatic stem cell reversion inUBE2Tdefines a new subtype of Fanconi anemia

Abstract

Fanconi anemia (FA) is a rare inherited disorder clinically characterized by congenital malformations, progressive bone marrow failure and cancer susceptibility. At the cellular level, FA is associated with hypersensitivity to DNA-crosslinking genotoxins. Eight of 17 known FA genes assemble the FA E3 ligase complex, which catalyzes monoubiquitination of FANCD2 and is essential for replicative DNA crosslink repair. Here, we identify the first FA patient with biallelic germline mutations in the ubiquitin E2 conjugase UBE2T. Both mutations were aluY-mediated: a paternal deletion and maternal duplication of exons 2–6. These loss-of-function mutations in UBE2T induced a cellular phenotype similar to biallelic defects in early FA genes with the absence of FANCD2 monoubiquitination. The maternal duplication produced a mutant mRNA that could encode a functional protein but was degraded by nonsense-mediated mRNA decay. In the patient's hematopoietic stem cells, the maternal allele with the duplication of exons 2–6 spontaneously reverted to a wild-type allele by monoallelic recombination at the duplicated aluY repeat, thereby preventing bone marrow failure. Analysis of germline DNA of 814 normal individuals and 850 breast cancer patients for deletion or duplication of UBE2T exons 2–6 identified the deletion in only two controls, suggesting aluY-mediated recombinations within the UBE2T locus are rare and not associated with an increased breast cancer risk. Finally, a loss-of-function germline mutation in UBE2T was detected in a high-risk breast cancer patient with wild-type BRCA1/2. Cumulatively, we identified UBE2T as a bona fide FA gene (FANCT) that also may be a rare cancer susceptibility gene.

Somatic, hematologic phenotype, long‐term outcome, and effect of hematopoietic stem cell transplantation. An analysis of 97 Fanconi anemia patients from the Italian national database on behalf of the Marrow Failure Study Group of the AIEOP (Italian Association of Pediatric Hematology–Oncology)

“…Details are in Supporting Information Tables I and II. The grade of cytopenia was defined according to an adjusted classification based on that of the FA Guidelines for Diagnosis and Management, 3rd edition 2008 [6], published by Fanconi anemia Research Fund. The adjustment was made following local and national guidelines to define cytopenia, specifically [1] mild cytopenia was defined as at least one of the following: Hb >10 g/dL but lower than the inferior limit according to age, polymorphonuclear cells (PMN) 1.0 < 1.5 3 10 9 /L, platelets 50 < 150 3 10 9 /L; [2] moderate cytopenia was defined as at least one of the following: Hb 8 < 10 g/dL, PMN 0.5 < 1.0 3 10 9 /L, platelets 20 < 50 3 10 9 /L, and [3] severe cytopenia was defined as at least one of the following: Hb < 8 g/dL, PMN < 0.5 3 10 9 /L, platelets <20 3 10 9 /L. The lowest value of the three cell lineages defined the level, meaning for example that a patient with Hb 9 g/dL, PMN 0.7 3 10 9 /L, and platelets 10 3 10 9 /L was regarded as having severe cytopenia.…”

“…Fanconi anemia (FA) is a rare genetic disease due to a recessive or X-linked defect in one of 17 genes (FANCA, B, C, D1 (BRCA2), D2, E, F, G, I, J, L, M, N, RAD51C, P, Q, UBE2T) [1,2]. The cellular defect common to all patients is DNA crosslink sensitivity with formation of double strand breaks after exposure to mitomycin C (MMC) or diepoxybutane (DEB) representing the basis of the diagnostic test for FA.…”

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

“…Recent studies indicate that ubiquitinlike with PHD and RING finger domain 1 (UHRF1) protein functions as an ICL recognition factor and may participate in these steps (Liang et al 2015. Recently, we and two different groups identified UBE2T, which encodes an E2 ubiquitin-conjugating enzyme, as a causative gene for FA (Hira et al 2015, Rickman et al 2015, Virts et al 2015. UBE2T/FANCT is essential for this monoubiquitination event to proceed.…”

Silencing of FANCD2 enhances the radiosensitivity of metastatic cervical lymph node-derived head and neck squamous cell carcinoma HSC-4 cells

“…Patients with FA show high sensitivity to ionizing radiation and to mitomycin C, cisplatin and other DNA cross-linking agents. To date, 18 FA-associated genes have been found (7,8). Proteins encoded by these genes compose an FA signaling pathway that is involved in the repair of DNA crosslink damage.…”