This difficulty arises mainly from the limited inclusion of MCM8/MCM9 genes in current diagnostic gene panels for cancer and polyposis, constraining our case series, and the relative rarity of germline MCM8/MCM9 variants in the general population, as reflected by our investigations in gnomAD version 2.1.1, the 100000 Genomes Project, and the 200,000 exome release of the UK Biobank. Here, MCM9 is linked to polyposis.