After obtaining further written informed consent, subsequent genetic testing performed for hereditary colorectal cancer syndromes, including those associated with mismatch repair genes (MLH1, MSH2, PMS2, and MSH6), adenomatous polyposis coli, and mutYH-associated polyposis revealed one homozygous frame shift mutation in MSH6 (NM_000179.2; c.3261del p.Phe1088SerfsTer2), which was reported as pathogenic (ClinVar accession VCV000089363.14, https://www.ncbi.nlm.nih.gov/clinvar/, last accessed May 15, 2021), confirming the diagnosis of CMMRD (Fig. 2 A). The gene discussed is MSH6; the disease is Familial adenomatous polyposis.