Novel mutations of the APC gene and genetic consequences of splicing mutations in the Czech FAP families

Abstract

Familial adenomatous polyposis (FAP) is an autosomal dominant syndrome with almost 100 % risk of colorectal cancer. The typical FAP is characterized by hundreds to thousands of colorectal adenomatous polyps and by extracolonic manifestations, later onset and lower number of polyps in colon is characteristic of an attenuated form (AFAP). We analyzed the APC gene for germline mutations in 90 FAP/AFAP patients. Mutation screening was performed using Denaturing Gradient Gel Electrophoresis. DNA fragments showing an aberrant electrophoretic banding pattern were sequenced. APC-mutation-negative probands were screened for large deletions of the APC gene using multiplex ligation dependent probe amplification. Analysis of mRNA variants followed in probands with possible splicing mutation by PCR amplification of target site flanking exons and sequencing the normal and aberrant products. We identified 30 germline variants among 36 unrelated probands including large deletions. Eleven APC variants detected last two years have not been reported yet. At all, fifteen of them are expected to cause errors in mRNA splicing. Analysis of mRNA in ten of these patients revealed exon skipping in seven cases, exonisation of intron in one of these as well, change of the amount of alternatively spliced product in one case, and no effect was found in three cases. In two of the patients, the biopsy of colon mucosa and polyp enabled us to examine the effect of the mutation on splicing pattern in colon cells directly. The comparison of alternative and standard transcript amount showed similar transcription pattern of exon 14 in control colon mucosa tissue (9 samples) as in 51 blood control samples.

Contribution of APC and MUTYH mutations to familial adenomatous polyposis susceptibility in Hungary

“…There is only limited information of the spectrum of APC and MUTYH mutations in the Central-Eastern-European region [ 20 – 25 ]. In this study the coding region of the APC gene has been screened for mutations in a panel of 87 unrelated probands diagnosed with familial adenomatous polyposis.…”

“…In the present study we examined the first set of (A)FAP patients from Hungary and one of the largest cohort from Central-Eastern Europe [ 20 – 25 ] in order to determine the mutational spectra of the APC and MUTYH genes diagnosed with colorectal polyposis to compare the clinical features of the mutation carriers and also to evaluate the respective roles of these genes in the inherited CRC burden in this Central-Eastern-European population.…”

Cribriform-Morular Variant of Papillary Thyroid Carcinoma With Poorly Differentiated Features: A Case Report With Immunohistochemical and Molecular Genetic Analysis

“…This variant, which affects the canonical 3′ splice-donor region of APC intron 13 has been described as a pathogenic germline variant in a Czech FAP family and was shown to produce exon skipping and protein truncation. 25,26 No additional APC mutation was identified in the nonneoplastic thyroid tissue. With the exception of a missense variant of uncertain clinical significance detected in the EP400 gene (c.6167C>T, p.Thr2056Met, NM_015409.4) in the PDTC area of the specimen, which has not been previously reported in cancer databases (www.…”

“…This pathogenic variant affects the canonical 3′ splice-donor region of APC intron 13 and interferes with mRNA splicing/processing of this gene, resulting in exon-skipping events and protein truncation. 25,26 No additional APC mutation, other than the known constitutional deletion of chromosome 5q15-31, was identified in the nonneoplastic thyroid tissue.…”

How does genome sequencing impact surgery?

“…Independent of mutation type, sur gery is recommended as soon as FAP syndrome is diagnosed because this is associ ated with an almost 100% risk of CRC. 30 However, since cancer is rare before the age of 20, surgery is often deferred to the late teen years or in between major life changes, such as in academ ic transitions or between jobs. 29 The amount of polyps in the rectum are correlated with disease severity and are of crucial importance for deciding on the type of anastomosis.…”