Familial Adenomatous Polyposis with Atypical Clinical Morphology and Genetic Variants - Case Report

Sep 24, 2026

Uploaded by kopisore

Familial adenomatous polyposis (FAP) arises from pathogenic APC gene variants on chromosome 5q, with clinical severity often correlating to germline APC findings. Reports exist of attenuated FAP and, conversely, FAP phenotypes lacking APC germline pathogenic variants and showing few typical signs. This case describes a 16-year-old girl whose early, multiple large bowel cancers plus small bowel cancers suggested a carcinogenic tendency exceeding typical FAP.

LanguageEnglish

CategoryHealthcare

FormatPDF

Pages5

Reading Time13 min

AccessFree to download

Introduction

Case Report

doi: 10.2169/internalmedicine.2050-23 Intern Med 63: 1075-1079, 2024 [http://internmed.jp](http://internmed.jp) 【CASE REPORT】 Familial Adenomatous Polyposis with Atypical Clinical Morphology and Genetic Variants Yoriaki Komeda 1, Hideki Ishikawa 2, Teruhiko Yoshida 3,4, Mineko Ushiama 3,4, Saki Yoshida 1, Kenji Nomura 1, Masashi Kono 1, Shunsuke Omoto 1, Mamoru Takenaka 1, Satoru Hagiwara 1, Hiroshi Kashida 1 and Masatoshi Kudo 1 | Abstract:
Familial adenomatous polyposis (FAP) is caused by pathogenic variants of the APC gene on the long arm of chromosome 5 . An analysis showed an association between germline APC gene variants and clinical signs of FAP; however, attenuated FAP has also been reported in cases with pathogenic variants. In contrast, a phenotype of FAP with no APC germline pathogenic variant and with few signs has been reported. We herein report a 16-year-old girl in whom the presence of multiple large bowel cancers from a young age and several small bowel cancers reflected a carcinogenic tendency higher than that typical for FAP.
Key words: familial adenomatous polyposis, duodenal adenoma, duodenal papillary cancer, APC gene, small bowel cancer, large bowel cancer
(Intern Med 63: 1075-1079, 2024)
(DOI: 10.2169/internalmedicine.2050-23) | | | --- | --- | |
Introduction | In the case described in the present report, the risk of carcinogenesis tended to be higher than that for typical FAP; however, the patient did not have a pathogenic variant of the | | Familial adenomatous polyposis (FAP) is a genetic disor- | APC gene based on a routine search, although an additional | | der characterized by multiple adenomatous polyps in the | search revealed a variant of the lesion. Patients previously | | large intestine. Several cases of FAP are caused by patho- | reported to have no pathogenic variant of the APC gene | | genic variants of the APC gene on the long arm of chromo- | were considered to have similar risks, and the present case | | some 5 (1, 2) . There have been reports of a relationship between germline APC gene variants and clinical signs of | is reported with this consideration. | | FAP (3-9) . Attenuated FAP with mild adenomatous polyposis in the presence of a pathogenic variant of the APC |
Case Report | | gene has also been reported (7) . | A 16-year-old girl with mild intellectual disability was | | In contrast, a case of a FAP phenotype with no patho- | found to have anemia on a preoperative examination for | | genic variant of the germline APC gene was reported with a | plastic surgery for a subcutaneous mass (epidermoid cyst) | | few signs, such as fundic gland polyps, duodenal adenoma, | on the right back and buttocks. She was subsequently fol- | | and osteoma (10) . There has been another report of fewer | lowed as an outpatient at the pediatrics department while re- | | than 100 colorectal adenomas with poor prognoses (11) . | ceiving oral iron treatment. She was referred to our depart- | | Furthermore, some studies have found that dense adenoma- | ment because of progressive anemia and a positive fecal oc- | | tous polyposis and duodenal adenoma are infrequent in this | cult blood test result. Regarding her family history, while | | phenotype (8, 12) . | her parents were divorced and her paternal family history | 1 Department of Gastroenterology and Hepatology, Kindai University Faculty of Medicine, Japan, 2 Department of Molecular-Targeting Prevention, Kyoto Prefectural University of Medicine, Japan, 3 Department of Genetic Medicine and Services, National Cancer Center Hospital, Japan and 4 Department of Clinical Genomics, National Cancer Center Research Institute, Japan Received: March 30, 2023; Accepted: July 2, 2023; Advance Publication by J-STAGE: August 9, 2023 Correspondence to Dr. Yoriaki Komeda, [y-komme@mvb.biglobe.ne.jp](y-komme@mvb.biglobe.ne.jp) Figure 1. Diagnostic examinations of the patient. (a) EGD revealed multiple fundic gland polyps. No

FAQs

What genetic mechanism is usually associated with familial adenomatous polyposis (FAP)?

FAP is typically caused by pathogenic variants of the APC gene on the long arm of chromosome 5.

Why is this case considered atypical for FAP?

The patient had multiple large bowel cancers from a young age and several small bowel cancers, suggesting a higher carcinogenic tendency than typical FAP, and routine testing did not show an APC pathogenic variant.

What procedures were used to evaluate and treat lesions in this patient?

Diagnostic examinations included EGD and imaging for polyps and cancer features; CT addressed intussusception, and endoscopic resections and balloon enteroscopy were used for multiple intestinal polyps.

Sep 24, 2026

Uploaded by kopisore