Tandem duplication and triplication in BRCA1: revisiting the large genomic rearrangements via optical genome mapping

Large genomic rearrangements (LGRs) within the human genome are becoming more recognized by novel genome-wide technologies and may be underreported so far. This class of genomic variation includes copy number variations like duplications or triplications of coding or non-coding genomic regions. Here, we report two LGRs targeting BRCA1, a duplication of exons 18-19 and a triplication of exons 1-2 in two independent families. Utilizing Optical Genome Mapping (OGM), Whole Genome Sequencing (WGS) and cDNA analysis, we characterized the genomic organization and transcriptomic effects of these LGRs regarding its. We show that the tandem duplication ogm[GRCh38]dup(17)(q21.31q21.31)(43057052_43063373), targeting BRCA1 exon 18-19 is predicted to generate a premature termination codon, namely p.(His1732Metfs*10). The triplication of BRCA1 exon 1-2 ogm[GRCh38]trip(17)(q21.31q21.31)(43117155_43124115) is also sequentially arranged. The transcript shows an insertion of a small part of intron 2 (chr17:43,121,558-43,121,676) that theoretically will generate a premature termination codon as well. Collectively, OGM and WGS help elucidating the architecture of these LGRs. However, the final curation depends on how adequate the functional consequences of these LGR can be clarified. Deeper investigation of LGRs on transcript level is important to attain accurate conclusions with respect to therapeutic decisions.