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A novel ribosomal protein S20 variant in a family with unexplained colorectal cancer and polyposis

Colorectal cancer (CRC) has a large hereditary component, which is only partially explained by known genetic causes. Recently, variants in ribosomal protein S20 (RPS20, [OMIM: 603682]) were identified in a family with familial CRC type X and in a CRC cancer case-control screen. This study describes a novel splice donor variant in RPS20, NM_001023.3:c.177+1G>A. It segregates with CRC [OMIM: 114500] and polyposis [HP: 0200063] within the proband’s family. Reverse transcription-polymerase chain reaction (RT-PCR) confirms the variant results in two aberrantly-spliced transcripts that are absent in controls. The location of the novel RPS20 variant is near two previously-reported truncating RPS20 variants associated with CRC. DNA from colon adenocarcinoma showed no evidence of loss-of-heterozygosity, supporting a haploinsufficiency or dominant negative disease mechanism. These findings support designation of RPS20 as a CRC predisposition gene, and expand the phenotypic spectrum of RPS20 truncating variants to include polyposis.