According to a study from Western countries [9], pathogenic germline variants of the APC gene are identified by usual testing methods in approximately 60% of patients with classical (typical) FAP, and pathogenic APC germline variants and biallelic mutations of the MUTYH gene are identified in 10 and 7% of patients with 20–99 colorectal adenomas, respectively, and 5 and 4% of patients with 10–19 colorectal adenomas, respectively [20]. The gene discussed is APC; the disease is Familial adenomatous polyposis.