Alu-Mediated Duplication and Deletion of Exon 11 Are a Frequent Mechanism of PALB2 Inactivation Predisposing to Hereditary Breast-Ovarian Cancer Syndrome

Large genomic rearrangements of PALB2 gene, particularly deletions and duplications, have been linked to hereditary breast-ovarian cancer. Our research specifically focuses on delineating the intronic breakpoints associated with rearrangements of PALB2 exon 11, which is crucial for understanding the mechanisms underlying these genomic changes in patients with hereditary breast and ovarian syndrome. By next-generation sequencing, we identified one duplication and three deletions of PALB2 exon 11, confirmed by Multiplex Ligation-Dependent Probe Amplification analysis. To assess the impact on transcription and potential splicing issues, Reverse-Transcription PCR was performed on patients' RNA. For detailed characterization of intronic breakpoints, primer walking approach and long-range PCR were implemented, followed by Sanger sequencing. Our analysis revealed a tandem duplication of 5134 base pairs (bp) mediated by AluY repeats located in introns 10 and 11, respectively. Moreover, identical deletions were identified in three unrelated patients, encompassing an approximate 8050 bp region mediated by AluSx elements. Both genomic alterations resulted in a truncated PALB2 protein due to introduction of a premature stop codon. This study underscores the remarkable instability of intronic regions flanking exon 11 of PALB2 and identifies a previously unreported hotspot involving Alu repeats with very high sequence homology in introns 10 and 11 of the gene. Our findings suggest avenues for further research, such as investigating the prevalence of similar genomic rearrangements in larger cohorts and exploring functional studies to understand how these alterations contribute to hereditary breast cancer pathogenesis.