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Letters to the Editor
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Figure 3. UBE2T does not have a major role in the repair of non-interstrand crosslink DNA lesions. (A) Cell survival assay after ultraviolet treatment of comple- mented pairs of RA2627 fibroblasts compared to BJ wild-type (WT) fibroblasts depleted of XPF used as a positive control. The immunoblot shows decreased XPF levels after siRNA depletion. (B) Cell survival assay of RA2627 fibroblasts after treatment with irradiation. HA239F fibroblasts with RAD50 mutations are sensi- tive to irradiation and act as a positive control (RAD50mut). (C, D) Cell sensitivity assays comparing RA2627 fibroblasts to RA3331 Fanconi anemia patient-derived fibroblasts with SLX4 mutations (SLX4mut) expressing WT SLX4 or empty vector exposed to camptothecin (C) and the PARP inhibitor, olaparib (D). (E) Cell survival assay after hydroxyurea treatment of RA2627 cells compared to the RA3226 BRCA2 patient cell line (BRCA2mut). Error bars indicate the standard deviation. EV: empty vector; UV: ultraviolet irradiation; IR: irradiation; CPT: camptothecin; PARPi: PARP inhibitor; HU: hydroxyurea.
fibroblasts and the p.P66T UBE2T variant performed here demonstrate that the hypomorphic variant is the likely cause of disease in this patient and can be classified as likely pathogenic following the recommendations of the American College of Medical Genetics and Genomics and the Association for Molecular Pathology.12
The c.196C>A (p.Pro66Thr) UBE2T variant is likely damaging to UBE2T function by conferring both reduced E2 activity and reduced stability as immunoblotting demonstrated decreased protein levels. The p.P66T vari- ant affects a residue highly conserved across various E2 and likely affects the interaction with FANCL due to the amino acid residue substitution being at the hydrophobic E2-E3 interface.10 The patients previously reported by Hira et al. who also had a missense variant, p.Q2E, were likewise demonstrated to be hypomorphic in RA2627 cells,13 but heterozygous and in trans to loss of function variants suggesting the possibility of UBE2T dosage sen- sitivity, as the two patients presented with more severe disease. Disease severity may also be increased in those two patients because of the presence of the ALDH2* vari- ant which is known to interact genetically with the FA pathway.14
We hypothesize that the hypomorphic variant and resulting residual function of the c.196C>A (p.P66T) vari- ant in UBE2T explains our patient’s mild phenotype. This case adds to the limited knowledge regarding this rare FA-T complementation group. It is possible that there are other undiagnosed patients with mild phenotypes, emphasizing the utility of an algorithmic approach utiliz- ing genomic sequencing and functional analysis for patients with non-specific hematologic phenotypes.
Laura Schultz-Rogers,1* Francis P. Lach,2*
Kimberly A. Rickman,2 Alejandro Ferrer,1
Abhishek A. Mangaonkar,3 Tanya L. Schwab,4
Christopher T. Schmitz,4 Karl J. Clark,4 Nikita R. Dsouza,5 Michael T. Zimmermann,5,6 Mark Litzow,3 Nicole Jacobi,7 Eric W. Klee,1,8 Agata Smogorzewska2# and Mrinal M. Patnaik3#
1Center for Individualized Medicine, Mayo Clinic, Rochester, MN; 2Laboratory of Genome Maintenance, The Rockefeller University, New York, NY; 3Department of Hematology, Mayo Clinic, Rochester, MN; 4Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN; 5Bioinformatics Research and Development Laboratory, Genomics Sciences and Precision Medicine Center, Medical College of Wisconsin, Milwaukee, WI; 6Clinical and Translational Sciences Institute, Medical College of Wisconsin, Milwaukee, WI; 7Department of Hematology Oncology, Hennepin County Medical Center, Minneapolis, MN and 8Department of Clinical Genomics, Mayo Clinic, Rochester, MN, USA
*LS-R and FPL contributed equally as co-first authors.
#EWK, AS and MMP contributed equally as co-senior authors.
Correspondence:
MRINAL PATNAIK - patnaik.mrinal@mayo.edu
AGATA SMOGORZEWSKA - asmogorzewska@rockefeller.edu doi:10.3324/haematol.2020.259275
Disclosures: no conflicts of interest to disclose.
Contributions: FPL, KAR, LSR, AF, KJC, EWK and AS designed the study and interpreted the results. FPL, KAR, TLS and CTS per- formed the study. MMP, AM and ML were the treating team at the Mayo Clinic where the patient was seen in the institutional inherited bone marrow failure clinic. NJ oversaw the patient’s care at Hennepin
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