Mutation analysis of the APC gene in unrelated Korean patients with FAP: four novel mutations with unusual phenotype

Looking at Thyroid Cancer from the Tumor-Suppressor Genes Point of View

Thyroid cancer is the most frequent endocrine malignancy and accounts for approximately 1% of all diagnosed cancers. A variety of mechanisms are involved in the transformation of a normal tissue into a malignant one. Loss of tumor-suppressor gene (TSG) function is one of these mechanisms. The normal functions of TSGs include cell proliferation and differentiation control, genomic integrity maintenance, DNA damage repair, and signaling pathway regulation. TSGs are generally classified into three subclasses: (i) gatekeepers that encode proteins involved in cell cycle and apoptosis control; (ii) caretakers that produce proteins implicated in the genomic stability maintenance; and (iii) landscapers that, when mutated, create a suitable environment for malignant cell growth. Several possible mechanisms have been implicated in TSG inactivation. Reviewing the various TSG alteration types detected in thyroid cancers may help researchers to better understand the TSG defects implicated in the development/progression of this cancer type and to find potential targets for prognostic, predictive, diagnostic, and therapeutic purposes. Hence, the main purposes of this review article are to describe the various TSG inactivation mechanisms and alterations in human thyroid cancer, and the current therapeutic options for targeting TSGs in thyroid cancer.

APC Splicing Mutations Leading to In-Frame Exon 12 or Exon 13 Skipping Are Rare Events in FAP Pathogenesis and Define the Clinical Outcome

Familial adenomatous polyposis (FAP) is caused by germline mutations in the tumor suppressor gene APC. To date, nearly 2000 APC mutations have been described in FAP, most of which are predicted to result in truncated protein products. Mutations leading to aberrant APC splicing have rarely been reported. Here, we characterized a novel germline heterozygous splice donor site mutation in APC exon 12 (NM_000038.5: c.1621_1626+7del) leading to exon 12 skipping in an Italian family with the attenuated FAP (AFAP) phenotype. Moreover, we performed a literature meta-analysis of APC splicing mutations. We found that 119 unique APC splicing mutations, including the one described here, have been reported in FAP patients, 69 of which have been characterized at the mRNA level. Among these, only a small proportion (9/69) results in an in-frame protein, with four mutations causing skipping of exon 12 or 13 with loss of armadillo repeat 2 (ARM2) and 3 (ARM3), and five mutations leading to skipping of exon 5, 7, 8, or (partially) 9 with loss of regions not encompassing known functional domains. The APC splicing mutations causing skipping of exon 12 or 13 considered in this study cluster with the AFAP phenotype and reveal a potential molecular mechanism of pathogenesis in FAP disease.

A novel pathogenic germline mutation in the adenomatous polyposis coli gene in a Chinese family with familial adenomatous coli

Familial adenomatous polyposis (FAP) is an autosomal dominant disease manifesting as colorectal cancer in middle-aged patients. Mutations of the adenomatous polyposis coli (APC) gene contribute to both FAP and sporadic or familial colorectal carcinogenesis. Here we describe the identification of the causative APC gene defects associated with FAP in a Chinese pedigree. All patients with FAP were diagnosed by their combination of clinical features, family history, colonoscopy, and pathology examinations. Blood samples were collected and genomic DNA was extracted. Mutation analysis of APC was conducted by targeted next-generation sequencing, long-range PCR and Sanger sequencing. A novel mutation in exon 14–15(c.1936_-2148 del) and intron 14 of the APC gene was demonstrated in all FAP patients and was absent in unaffected family members. This novel deletion causing FAP in Chinese kindred expands the germline mutation spectrum of the APC gene in the Chinese population.

Racial variation in frequency and phenotypes of APC and MUTYH mutations in 6,169 individuals undergoing genetic testing

PURPOSE

The aim of this study was to assess whether differences in frequency and phenotype of APC and MUTYH mutations exist among racially/ethnically diverse populations.

METHODS

We studied 6,169 individuals with a personal and/or family history of colorectal cancer (CRC) and polyps. APC testing involved full sequencing/large rearrangement analysis (FS/LRA); MUTYH involved "panel testing" (for Y165C, G382D mutations) or FS/LRA performed by Myriad Genetics, a commercial laboratory. Subjects were identified as Caucasian, Asian, African American (AA), or other. Statistical tests included χ(2), Fisher's exact test, analysis of variance, and z approximation.

RESULTS

Among participants, 17.5% had pathogenic APC mutations and 4.8% were biallelic MUTYH carriers. With regard to race/ethnicity, 18% were non-Caucasian, with >100 adenomas and younger ages at adenoma or CRC diagnosis (P < 0.0001) than Caucasians. The overall APC mutation rate was higher in Asians, AAs, and others as compared with Caucasians (25.2, 30.9, 24, and 15.5%, respectively; P < 0.0001) but was similar in all groups when adjusted for polyp burden. More MUTYH biallelic carriers were Caucasian or other than Asian or AA (5, 7, 2.7, and 0.3%, respectively; P < 0.0001). Among Caucasians, 5% were biallelic carriers identified by panel testing versus 2% identified by sequencing/large rearrangement analysis (LRA) (P = 0.002). Among non-Caucasians, 3% undergoing panel testing were biallelic carriers versus 10% identified by sequencing/LRA (P < 0.0002).

CONCLUSION

Non-Caucasians undergo genetic testing at more advanced stages of polyposis and/or are younger at CRC/polyp diagnosis. Restricted MUTYH analysis may miss significant numbers of biallelic carriers, particularly in non-Caucasians.

Missense mutations in MLH1, MSH2, KRAS, and APC genes in colorectal cancer patients in Malaysia

BACKGROUND

Colorectal cancer (CRC) is the third most common cancer worldwide with approximately 1 million cases diagnosed annually. In Malaysia, CRC is the second most common cancer in women and ranked first in men. The underlying cause of CRC remains unknown.

AIMS

The aim of this study was to analyze the mutations in genes involved in CRC including MLH1, MSH2, KRAS, and APC genes.

METHODS

A total of 76 patients were recruited. We used the polymerase chain reaction-denaturing high-performance liquid chromatography for the detection of mutations in the mismatch repair (MMR) and APC genes and the PCR single-strand conformation polymorphism for screening of the KRAS gene mutations.

RESULTS

We identified 17 types of missense mutations in 38 out of 76 patients in our patients. Nine mutations were identified in the APC gene, five mutations were detected in the KRAS gene, and two mutations were identified in the MSH2 gene. Only one mutation was identified in MLH1. Out of these 17 mutations, eight mutations (47 %) were predicted to be pathogenic. Seven patients were identified with multiple mutations (3: MSH2 and KRAS, 1: KRAS and APC, 1: MLH1 and APC, 2: APC and APC).

CONCLUSIONS

We have established the PCR-DHPLC and PCR-SSCP for screening of mutations in CRC patients. This study has given a snapshot of the spectrum of mutations in the four genes that were analyzed. Mutation screening in patients and their family members will help in the early detection of CRC and hence will reduce mortality due to CRC.

An AT-rich region in the APC gene may cause misinterpretation of familial adenomatous polyposis molecular screening

Familial adenomatous polyposis (FAP) is an autosomal-dominant condition mainly due to a mutation of the adenomatous polyposis coli (APC) gene. The present study reports evidence of a technical issue occurring during the mutational analysis of APC exon 4. Genetic conventional direct sequence analysis of a repetitive AT-rich region in the splice acceptor site of APC intron 3 could be misinterpreted as a pathogenetic frameshift result. However, this potential bias may be bypassed adopting a method for random mutagenesis of DNA based on the use of a triphosphate nucleoside analogues mixture. Using this method as a second-level analysis, we also demonstrated the nonpathogenic nature of the variant in the poly A trait in APC exon 4 region (c.423-4delA) that do not result in aberrant splicing of APC exons 3-4; conversely, we did not find a previously reported T deletion/insertion polymorphism.

A novel pathogenic germline mutation in the adenomatous polyposis coli gene in a Tunisian family with FAP

Familial adenomatous polyposis (FAP) is an autosomal dominant disorder which typically presents with colorectal cancer in early adult life, secondary to extensive adenomatous polyps of the colon. In addition to the colonic manifestations, the syndrome presents several extracolonic features including, congenital hypertrophy of the retinal pigment, osteomata and desmoid tumors. In this study, we aimed to investigate the clinical and genetic features in a Tunisian family with FAP. Sequence of the APC gene (Adenomatous Polyposis Coli) revealed a novel mutation (c.2016-2017 del TA) in exon 15, present in all affected individuals in an heterozygous state. The frameshift mutation generates a premature stop codon at amino acid 677 of the APC protein (p. H672Qfs X5). The unaffected family members did not harbor this mutation, however, a first degree relative of the patient aged of 32-year-old was phenotypically normal but carries the c.2016-2017 del TA mutation. This discrepancy can be explained by the effect of modifier gene which can affect the expressivity of the disease.

Mutation Analysis of the APC Gene in a Chinese FAP Pedigree with Unusual Phenotype

Background and Aim. Germline mutations of the adenomatous polyposis coli (APC) gene cause familial adenomatous polyposis (FAP), an autosomal dominant inherited disease mainly characterized by colorectal adenomatous polyposis. Genetic studies of FAP have shown that somatic APC mutations are dependent on the position of the germline APC mutation. However, the molecular mechanism underlying these genotype-phenotype associations for APC in Chinese remain largely unknown. Patients and Methods. In this study, we investigated the APC gene mutation in a Chinese FAP family by systematic screening with multiplex ligation-dependent probe amplification (MLPA), denaturing high-performance liquid chromatography (dHPLC), and DNA sequencing. Promoter methylation was detected by methylation-specific PCR. Results. The identical germline mutation c.1999 C>T (Q667X) of APC was identified in 5 affected members, among which 2 members carried somatic mutations of APC, one with promoter hypermethylation and the other with loss of wild-type allele in their adenomas. The somatic mutations were shown connected with the disease severity, demonstrating a unique genotype-phenotype association in this FAP pedigree. Conclusion. The study revealed the existence of novel pathogenic mutations in Chinese patients with FAP. Somatic mutations are of particular interest because of the unusual phenotypic features shown by patients.