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RAD51C loss-of-function variants are associated with an increased risk of breast and ovarian cancers. Likewise, splicing disruptions are a frequent mechanism of gene inactivation. Taking advantage of a previous splicing-reporter minigene with exons 2-8 (mgR51C_ex2-8), we proceeded to check its impact on the splicing of candidate ClinVar variants. A total of 141 RAD51C variants at the intron/exon boundaries were analyzed with MaxEntScan. Twenty variants were selected and genetically engineered into the wild-type minigene. All the variants disrupted splicing, and 18 induced major splicing anomalies without any trace or minimal amounts (, The EAV lab is supported by grants from the Spanish Ministry of Science and Innovation, Plan Nacional de I+D+I 2013–2016, ISCIII (PI17/00227 and PI20/00225), co-funded by FEDER (the European Regional Development Fund, European Union) and the Consejería de Educación, Junta de Castilla y León, ref. CSI242P18 (actuación cofinanciada P.O. FEDER 2014–2020 de Castilla y León) and Programa Estratégico Instituto de Biología y Genética Molecular (IBGM), Escalera de Excelencia, Junta de Castilla y León (Ref. CLU-2019-02). The MdlH lab is supported by a grant from the Spanish Ministry of Science and Innovation, Plan Nacional de I+D+I 2013–2016, ISCIII (PI20/00110), cofunded by FEDER. LS-M is supported by a predoctoral fellowship from the AECC Scientific Foundation, Sede Provincial de Valladolid (2019–2023). EB-M is a postdoctoral researcher funded by the University of Valladolid (POSTDOC-UVA05, 2022–2025). IL-B is supported by a predoctoral fellowship from the Consejería de Educación, Junta de Castilla y León (2018–2022). AE-S is supported through the Operational Program for Youth Employment and the Youth Employment Initiative (YEI), set up by the Community of Madrid in 2020 and co-financed by the European Social Fund.

PALB2 loss-of-function variants are associated with significant increased risk of breast cancer as well as other types of tumors. Likewise, splicing disruptions are a common mechanism of disease susceptibility. Indeed, we previously showed, by minigene assays, that 35 out of 42 PALB2 variants impaired splicing. Taking advantage of one of these constructs (mgPALB2_ex1-3), we proceeded to analyze other variants at exons 1 to 3 reported at the ClinVar database. Thirty-one variants were bioinformatically analyzed with MaxEntScan and SpliceAI. Then, 16 variants were selected for subsequent RNA assays. We identified a total of 12 spliceogenic variants, 11 of which did not produce any trace of the expected minigene full-length transcript. Interestingly, variant c.49-1G > A mimicked previous outcomes in patient RNA (transcript ∆(E2p6)), supporting the reproducibility of the minigene approach. A total of eight variant-induced transcripts were characterized, three of which (∆(E1q17), ∆(E3p11), and ∆(E3)) were predicted to introduce a premature termination codon and to undergo nonsense-mediated decay, and five (▼(E1q9), ∆(E2p6), ∆(E2), ▼(E3q48)-a, and ▼(E3q48)-b) maintained the reading frame. According to an ACMG/AMP (American College of Medical Genetics and Genomics/Association for Molecular Pathology)-based classification scheme, which integrates mgPALB2 data, six PALB2 variants were classified as pathogenic/likely pathogenic, five as VUS, and five as likely benign. Furthermore, five ±1,2 variants were catalogued as VUS because they produced significant proportions of in-frame transcripts of unknown impact on protein function., The EAV lab is supported by grants from the Spanish Ministry of Science and Innovation, Plan Nacional de I+D+I 2013–2016, ISCIII (PI20/00225), co‐funded by FEDER (the European Regional Development Fund, European Union) and the Consejería de Educación, Junta de Castilla Cancers 2022, 14, 4541 16 of 18 y León, ref. CSI242P18 (actuación cofinanciada P.O. FEDER 2014–2020 de Castilla y León) and Pro‐ grama Estratégico Instituto de Biología y Genética Molecular (IBGM), Escalera de Excelencia, Junta de Castilla y León (Ref. CLU‐2019‐02). The MdlH lab is supported by a grant from the Spanish Ministry of Science and Innovation, Plan Nacional de I+D+I 2013–2016, ISCIII (PI20/00110), co‐funded by FEDER. L.S.‐M. is supported by a predoctoral fellowship from the AECC Scientific Foundation, Sede Provincial de Valladolid (2019–2023). E.B.‐M. is a postdoctoral researcher funded by the University of Valladolid (POSTDOC‐UVA05, 2022–2025). I.L.‐B. is supported by a predoctoral fellowship from the Consejería de Educación, Junta de Castilla y León (2022–2025). A.E.‐S. is supported through the Operational Program for Youth Employment and the Youth Employment Initiative (YEI), set up by the Community of Madrid in 2020 and co‐financed by the European Social Fund.