Aggressive mutation in a familial adenomatous polyposis syndrome family: when phenotype guides clinical surveillance

A novel large deletion in the APC gene associated with Gardner syndrome in a Chinese family

INTRODUCTION

Gardner syndrome is a hereditary disease characterized by familial adenomatous polyposis (FAP), accompanied by soft tissue tumors.

MATERIAL AND METHODS

a Chinese FAP family was enrolled and followed-up for three years.

RESULTS

a novel large germline fragment deletion (EX10_16DEL) of the adenomatous polyposis coli (APC) gene was identified by multiplex ligation-dependent probe amplification (MLPA). An unexpected abdominal tumor grew two years after a subtotal colectomy of the proband. The immunohistochemistry study of the abdominal tumor showed SMA(focal+), calponin(+), β-catenin(nucleus+) and CD34(focal+), CD117(-), which was consistent with a desmoid tumor.

CONCLUSION

when a FAP related desmoid tumor appears, the possibility of Gardner syndrome should be considered. This is the first largest deletion of the APC gene in the Chinese population associated with Gardner syndrome.

The Somatic Mutation Hit on Top of Genetic APC mutations Cause Skin Tumor

Inactivation of the adenomatous polyposis coli (APC) gene is the initiating event in familial adenomatous polyposis (FAP) patients. Up to 90% of FAP patients show intestinal tumors and other extracolonic malignancies including hepatoblastomas, desmoid tumors, and brain cancer. APC mutation mice (Apc^Min/+ mice) develop benign polyps in the intestinal tract. It has been reported that small numbers of Apc^Min/+ mice develop breast carcinomas. Here, we found that approximately 1.6% of Apc^Min/+ mice suffered skin neoplasm. The results demonstrated that these skin tumors are not derived from intestinal adenomas. Sequencing of skin tumors of Apc^Min/+ mice and Apc^Min/+ mice skin. The data showed that somatic mutations and gene expression levels changed greatly in skin tumors compared to control. Similarly, APC mutation accounts for 27% in the patients of nonmelanoma skin carcinomas in cancer database, and two above genes mutation coexist was observed in all patients. Furthermore, using gene mutation reagent (DMBA)-treated Apc^Min/+ mice skin, the skin epithelium and glandular begin hyperplasia in Apc^Min/+ mice. These findings revealed that the somatic mutation hit on the germline mutation increase the tumor incidence, suggesting that the somatic mutation should be avoided if the germline mutation exists in one body.