LAUSR

Background Patients with serrated polyposis syndrome (SPS) have multiple and/or large serrated colonic polyps and higher risk for colorectal cancer. SPS inherited genetic basis is mostly unknown. We aimed to identify new germline predisposition factors for SPS by functionally evaluating a candidate gene and replicating it in additional SPS cohorts. Methods After a previous whole-exome sequencing in 39 SPS patients from 16 families (discovery cohort), we sequenced specific genes in an independent validation cohort of 211 unrelated SPS cases. Additional external replication was also available in 297 SPS cases. The WNK2 gene was disrupted in HT-29 cells by gene editing, and WNK2 variants were transfected using a lentiviral delivery system. Cells were analysed by immunoblots, real-time PCR and functional assays monitoring the mitogen-activated protein kinase (MAPK) pathway, cell cycle progression, survival and adhesion. Results We identified 2 rare germline variants in the WNK2 gene in the discovery cohort, 3 additional variants in the validation cohort and 10 other variants in the external cohorts. Variants c.2105C>T (p.Pro702Leu), c.4820C>T (p.Ala1607Val) and c.6157G>A (p.Val2053Ile) were functionally characterised, displaying higher levels of phospho-PAK1/2, phospho-ERK1/2, CCND1, clonogenic capacity and MMP2. Conclusion After whole-exome sequencing in SPS cases with familial aggregation and replication of results in additional cohorts, we identified rare germline variants in the WNK2 gene. Functional studies suggested germline WNK2 variants affect protein function in the context of the MAPK pathway, a molecular hallmark in this disease.