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Phenotypic differences in familial adenomatous polyposis based on APC gene mutation status.

ABSTRACT: BACKGROUND: Familial adenomatous polyposis (FAP) is a clinically well defined hereditary disease caused by germline mutations within the adenomatous polyposis coli (APC) gene. Although several techniques are applied in the mutation analysis of FAP kindreds about 20-50% of cases remain unclear, with no APC mutation identified (APC negative). AIMS: To delineate phenotypic differences between APC positive and APC negative patients with respect to colonic and extracolonic disease in order to determine whether additional mechanisms are involved in the pathogenesis of FAP. METHODS: The entire coding region of the APC gene was analysed using single stranded conformation polymorphism and protein truncation tests in 50 Swiss FAP families with a total of 161 affected individuals. Differences in phenotypic manifestation were statistically evaluated by Student's t test, Fisher's exact test, and chi2 test. RESULTS: Thirty six families (72%) were APC positive. Statistically significant differences between APC positive and APC negative groups were found for the mean age at diagnosis of colonic polyposis (35.2 versus 45.3 years, respectively) and for the occurrence of stomach polyps (14 patients, all APC positive). Additionally, APC negative patients displayed lower polyp numbers at diagnosis and less extracolonic manifestations. CONCLUSIONS: FAP kindreds without detected APC gene mutations present with a notably milder disease phenotype compared with APC positive families, suggesting that different genetic factors might be involved.

SUBMITTER: Heinimann K

PROVIDER: S-EPMC1727303 | biostudies-other | 1998 Nov

REPOSITORIES: biostudies-other

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Project description:Familial adenomatous polyposis (FAP) is an inherited condition arising from genetic defects in the Adenomatous polyposis coli (APC) gene. Carriers with mutations in the APC gene develop polyps in the colon and rectum which if not managed, transition into colon cancer. In this study, we identified a novel germline mutation in the APC gene in members of an FAP-affected (Familial adenomatous polyposis) family. This unique heterozygous variant (c.735_736insT; p.Ser246PhefsTer6) was identified in ten out of twenty six family members, ranging in age from 6 to 60 years. Polyps were detected in six of the ten individuals (35-60 years) carrying this mutation. The remaining four members (6-23 years) remain polyp free. A significant fraction of FAP affected individuals eventually develop colon cancer and therapeutic interventions to prevent cancer progression remain elusive. To address this issue, we sought to determine if peptides derived from the novel APC mutation could induce a cytotoxic T cell response, thereby qualifying them as vaccine candidates. Peptides harboring the variant amino acids were first interrogated in silico for their immunogenicity using a proprietary neoepitope prioritization pipeline, OncoPeptVAC. A single 9-mer peptide was predicted to be immunogenic. Remarkably, CD8+ T cells isolated from either an FAP+/ APCmut individual, or from a FAP-/ APCmut individual, failed to respond to the peptide, whereas those from either an unaffected family member (FAP-/ APCwt) or from healthy unrelated donors, showed a robust response, suggesting that CD8+ T cells from individuals carrying this germline APC mutation have been tolerized to the mutation. Furthermore, experimental testing of six additional reported APC gene mutation-derived peptides revealed one of the six to be immunogenic. While not all APC mutant peptides are inmmunogenic, a few qualify as vaccine candidates offering novel treatment opportunities to patients with somatic APC gene mutations to delay/treat colorectal cancer.

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Phenotypic differences in familial adenomatous polyposis based on APC gene mutation status.

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