RNA-seq Splicing Profile of the CDH1 Gene and Its Impact on the Clinical Pathogenicity Classification of CDH1 Variants: A Description of Alternative and Pathogenic Splicing Patterns

<b>Background/Objectives:</b><i>CDH1</i> gene is widely studied, as pathogenic variants are involved in diffuse gastric cancers and lobular breast cancers. <i>CDH1</i> genotype contributes to the management of clinical practice recommendations for cancer prevention. We proposed a qualitative and quantitative description of <i>CDH1</i> alternative splicing profile on lymphoblastoid cell lines (LCLs). The aim of this description was to allow a comprehensive interpretation of the effect of variants of uncertain significance (VUS) on <i>CDH1</i> splicing. <b>Methods:</b> We studied, using RNAseq, the splicing profile of 22 LCLs (untreated and treated with puromycin) with no pathogenic variant on <i>CDH1</i> and evaluated the effect on <i>CDH1</i> splicing of four VUS. <b>Results:</b> We highlighted a total of eleven alternative splicing events including four junctions starting from intron 2, defining novel isoforms of <i>CDH1</i>. We also identified an isoform causing the skip of exon 11 and leading to a disruption of the reading frame with high levels of expression on negative <i>CDH1</i> control LCLs, confirmed by ddPCR. Splicing RNAseq results for <i>CDH1</i> VUS: c.1008+1G>A and c.1936+5G>A showed complex splicing patterns but allowed their classification as pathogenic. We studied <i>CDH1</i> VUS exon 4 to exon 11 duplication with RNA analysis combined with Bionano optical genome mapping. Depending on alternative splicing of proximal and distal exons 11 within the duplication, we identified four distinct transcripts, leading to truncated proteins, classifying the duplication as pathogenic. <b>Conclusions:</b><i>CDH1</i> has a complex alternative splicing profile characterized by a dynamic splicing of intron 2 making <i>CDH1</i> a good candidate for a study using long-read RNAseq.