The complex genotype-phenotype relationship in familial adenomatous polyposis

Novel Mutation in APC Gene Associated with Multiple Osteomas in a Family and Review of Genotype-Phenotype Correlations of Extracolonic Manifestations in Gardner Syndrome

Gardner syndrome is a neoplasic disease that associates intestinal polyposis and colorectal adenocarcinoma with osteomas and soft tissue tumors determined by germline mutations in the APC gene. The early diagnosis and identification of high-risk individuals are important because patients have a 100% risk of colon cancer. We present the case of a family with Gardner syndrome. Cephalometric, panoramic X-rays and CBCT of the proband and her brother showed multiple osteomas affecting the skull bones, mandible and paranasal sinuses. The detailed family history showed an autosomal dominant transmission with the presence of the disease in the mother and maternal grandfather of the proband. Both had the typical signs of disease and died in the fourth decade of life. Based on these aspects the clinical diagnosis was Gardner syndrome. By gene sequencing, a novel pathogenic variant c.4609dup (p.Thr1537Asnfs*7) in heterozygous status was identified in the APC gene in both siblings. We reviewed literature data concerning the correlation between the localization of mutations in the APC gene and the extracolonic manifestations of familial adenomatous polyposis as well as their importance in early diagnosis and adequate oncological survey of patients and families based on abnormal genomic variants.

Novel Pathogenic Germline Variant of the Adenomatous Polyposis Coli (APC) Gene, p.S2627Gfs*12 Identified in a Mild Phenotype of APC-Associated Polyposis: A Case Report

Patient: Male, 80-year-old

Final Diagnosis: Attenuated APC-associated polyposis

Symptoms: Colon polyps • renal carcinoma

Medication: —

Clinical Procedure: —

Specialty: Genetics

Identification a nonsense mutation of APC gene in Chinese patients with familial adenomatous polyposis

Familial adenomatous polyposis (FAP; Mendelian of Inherintance in Man ID, 175100) is a rare autosomal dominant disorder characterized by the development of numerous adenomatous polyps throughout the colon and rectum associated with an increased risk of colorectal cancer. FAP is at time accompanied with certain extraintestinal manifestations such as congenital hypertrophy of the retinal pigment epithelium, dental disorders and desmoid tumors. It is caused by mutations in the adenomatous polyposis coli (APC) gene. The present study reported on a Chinese family with FAP. Polymerase chain reaction and direct sequencing of the full coding sequence of the APC gene were performed to identify the mutation in this family. A nonsense mutation of the APC gene was identified in this pedigree. It is a heterozygous G>T substitution at position 2,971 in exon 15 of the APC gene, which formed a premature stop codon at amino acid residue 991 (p.Glu991*). The resulting truncated protein lacked 1,853 amino acids. The present study expanded the database on APC gene mutations in FAP and enriched the spectrum of known germline mutations of the APC gene. Prophylactic proctocolectomy may be considered as a possible treatment for carriers of the mutation.

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.

Two Chinese pedigrees for adenomatous polyposis coli: new mutations at codon 1309 and predisposition to phenotypic variations

Familial adenomatous polyposis (FAP) is an autosomal dominant inherited disease caused by a mutation in the adenomatous polyposis coli (APC) gene. Some studies have attempted to correlate mutations at codon 1309 with classic FAP (≥100 colorectal polyps). We report two Chinese FAP pedigrees with new frameshift mutations at codon 1309, in which affected individuals manifest phenotypic variations. Comprehensive physical examinations were performed for all living individuals and the medical data of deceased patients were collected. Screening of the APC and human mutY homolog (MUTYH) genes for germline mutations was conducted by direct polymerase chain reaction (PCR) sequencing. In two pedigrees, a heterozygous deletion in exon 16 of the APC gene was present in all FAP patients but absent in the unaffected individuals. There were no changes to the MUTYH gene. The first pedigree, with a new frameshift mutation at c.3926_3930 del AAAAG (p. Glu1309Aspfs X4), exhibited obvious differences in the polyp number such that the proband manifested only three colorectal polyps, whereas another patients showed the symptoms of classic FAP. The second pedigree, also traced a new mutation at c.3922_3925 del AAAG (p. Glu1309Argfs X11). Although all of the patients presented with classic polyposis, one of them exhibited a delayed onset of colorectal cancer in his 50s. Two novel mutations at codon 1309 in two Chinese families suffering from FAP could enrich the germline mutation spectrum of the APC gene. Families of individuals might manifest different phenotypes, even with an identical codon 1309 mutation, unlike in previous studies.

CTNNB1 genotyping and APC screening in pediatric desmoid tumors: a proposed algorithm

Desmoid fibromatosis is a rare, locally aggressive fibroblastic/myofibroblastic tumor that occasionally involves children. We examined a series of pediatric desmoids for CTNNB1 mutations, seen in sporadic tumors, and APC germline mutations, associated with familial adenomatous polyposis (FAP). Forty-four desmoids in pediatric patients were identified in the pathology files of 2 large referral centers (1995-2009). Clinical charts were reviewed for history of FAP. Germline APC gene mutations were determined on blood samples from patients presenting with FAP. Immunohistochemistry for beta-catenin was performed. CTNNB1 genotyping was done by Sanger sequencing on formalin-fixed paraffin-embedded tissue. CTNNB1 mutations were observed in 29 of 44 (66%) desmoids, with 3 mutations identified: T41A (64%), S45F (29%), and S45P (7%). Germline APC mutations were present in 7 (16%) desmoid patients. Eight (18%) patients had desmoids that were wild type for CTNNB1 and had no known clinical signs or family history suspicious for FAP at the time of testing or with extended follow up (n  =  6). Beta-catenin nuclear labeling was observed in 38 of 41 (92%) tested cases, 34 (89%) of which showed mutations in either CTNNB1 (n  =  29) or APC (n  =  5). Nuclear localization of beta-catenin was seen in the majority of pediatric desmoids and was most often associated with somatic mutations in CTNNB1. However, a significant proportion of pediatric patients harbored germline mutations in APC. Given the implications, genetic counseling is recommended for children diagnosed with desmoid tumors lacking CTNNB1 mutations because this population is enriched for FAP patients.

A De Novo Germline APC Mutation (3927del5) in a Patient with Familial Adenomatous Polyposis: Case Report and Literature Review

Introduction

Characterized by the development of hundreds to thousands of colonic adenomas, classic familial adenomatous polyposis (FAP) is one of the most common hereditary syndromes associated with an increased risk of colorectal cancer. Several studies have attempted to correlate specific APC mutations with clinical phenotype.6 However, there is considerable variability in the expression of specific phenotypes within families and among individuals with identical mutations.7

Case presentation

A 30 year-old Hispanic female presented to the emergency department with a 2-week history of persistent, worsening, left lower quadrant abdominal pain. She had no family history of malignancy. Sigmoidoscopy revealed innumerable polyps in the rectum and sigmoid colon and a large mass in the sigmoid colon. Biopsy of the mass revealed a moderately differentiated adenocarcinoma invading the subserosa. Endoscopy revealed innumerable polyps. Genetic testing of the patient via southern blot revealed a germline APC mutation 3927del5, resulting in a premature truncation of the APC protein at amino acid position 1312.

Conclusion

Genetic information has only recently started being incorporated into clinical care. More research and randomized clinical trials need to be conducted to definitively characterize random mutations. Once these mutations are further understood, FAP patients may be able to be risk stratified and this may ultimately improve the screening, diagnosis, and treatment of this rare condition.

Association between colorectal cancer and tumor suppressor genes: recent research progress

Colorectal cancer is a common high-risk gastrointestinal cancer, and approximately 1.2 million new cases are diagnosed each year worldwide. In recent years, due to the improvement of people's living standards and changes in dietary habits and structure, the incidence and mortality rate of colorectal cancer increase rapidly in China. Moreover, patients have a significantly earlier age of onset. At present, the median age of colorectal cancer onset in China is 58 years old, 12 to 18 years earlier than other countries in Europe and America. The development of colorectal cancer is a complex multi-stage process involving multiple genetic alterations. Many studies have shown that colorectal carcinogenesis involves activation of oncogenes and inactivation of tumor suppressor genes. Tumor suppressor genes associated with colorectal carcinogenesis include p53, APC, DCC, and MMR, and proto-oncogenes include K-ras and c-myc. In this paper, we discuss the association between tumor suppressor genes and colorectal carcinogenesis.

Extracolonic manifestations of hereditary colorectal cancer syndromes

Familial colorectal adenocarcinoma (CRC) accounts for approximately 15 to 20% of CRC. Of these, hereditary nonpolyposis colorectal cancer (HNPCC) and familial adenomatous polyposis (FAP) represent the most common hereditary syndromes associated with CRC, followed by other less common diseases including juvenile polyposis (JP) and Peutz-Jeghers syndrome (PJS). Extracolonic manifestations are common in each of these syndromes having significant implications for surveillance and management in at-risk individuals. The authors review the most common and clinically relevant extracolonic manifestations for each of these syndromes focusing on incidence, presentation, genotype/phenotype correlations, and management (including surveillance) strategies.

Clinical characterization and the mutation spectrum in Swedish adenomatous polyposis families

BACKGROUND

The dominantly inherited condition familial adenomatous polyposis (FAP) is caused by germline mutations in the APC gene. Finding the causative mutations has great implications for the families. Correlating the genotypes to the phenotypes could help to improve the diagnosis and follow-up of patients.

METHODS

Mutation screening of APC and the clinical characterization of 96 unrelated FAP patients from the Swedish Polyposis Registry was performed. In addition to generally used mutation screening methods, analyses of splicing-affecting mutations and investigations of the presence of low-frequency mutation alleles, indicating mosaics, have been performed, as well as quantitative real-time polymerase chain reaction to detect lowered expression of APC.

RESULTS

Sixty-one different APC mutations in 81 of the 96 families were identified and 27 of those are novel. We have previously shown that 6 of the 96 patients carried biallelic MUTYH mutations. The 9 mutation-negative cases all display an attenuated or atypical phenotype. Probands with a genotype (codon 1250-1464) predicting a severe phenotype had a median age at diagnosis of 21.8 (range, 11-49) years compared with 34.4 (range, 14-57) years among those with mutations outside this region (P < 0.017). Dense polyposis (> 1000) occurred in 75% of the probands with a severe phenotype compared with 30% in those with mutations outside this region. The morbidity in colorectal cancer among probands was 25% at a mean age of 37.5 years and 29% at a mean age of 46.6 years.

CONCLUSION

Using a variety of mutation-detection techniques, we have achieved a 100% detection frequency in classical FAP. Probands with APC mutations outside codon 1250-1464, although exhibiting a less-severe phenotype, are at high risk of having a colorectal cancer at diagnosis indicating that age at diagnosis is as important as the severity of the disease for colorectal cancer morbidity.

Rare coincidence of familial adenomatous polyposis and a retroperitoneal fibromyxoid sarcoma: report of a case

PURPOSE

Familial adenomatous polyposis is an autosomal-dominant inherited disease with development of as many as thousands of adenomas within colon and rectum. All untreated patients will develop colorectal adenocarcinoma. A variety of extracolonic manifestations can occur, although malignant tumors are rare. An association of familial adenomatous polyposis and sarcomas was reported in a few cases only.

METHODS

We present the exceptional case of a 24-year-old male with genetically verified familial adenomatous polyposis (deletion of 10 base pairs at position 228-237 of exon 15A). The patient underwent prophylactic subtotal proctocolectomy and ileal-pouch rectal anastomosis in 2003. Two years later, an obstruction of the left ureter caused by a retroperitoneal mass was diagnosed.

RESULTS

Histopathologic findings after complete tumor resection showed a low-grade fibromyxoid sarcoma. CT scan and clinical follow-up through 15 months postoperatively revealed no recurrent tumor growth.

CONCLUSIONS

To our knowledge, this is the first reported case of familial adenomatous polyposis with metachronous retroperitoneal fibromyxoid sarcoma. Proctocolectomy or total colectomy and complete tumor resection is the treatment of choice in this case. In addition to more common semimalignant retroperitoneal desmoid tumors in familial adenomatous polyposis patients, a malignant soft-tissue tumor also has to be considered for differential diagnosis.

3' Mutation of the APC gene and family history of FAP in a patient with apparently sporadic desmoid tumors

Desmoid tumors may occur sporadically or as part of the extraintestinal manifestations of familial adenomatous polyposis. Different phenotypes have been described and some genotype-phenotype correlations have been raised, associated with different sites of germline mutations in the adenomatous polyposis coli (APC) gene. We report on a 42-year-old woman ascertained for a large desmoid tumor of the anterior chest wall with pleural involvement, which persistently recurred despite a decade of treatment including hormone therapy, chemotherapy, and surgery. Spontaneous disappearance of the tumor was later noted after 1 year without any treatment and confirmed after 4 years of regular follow-up. Repeated colonoscopies were normal in the proband and DNA sequencing showed a frameshift mutation due to a single adenosine deletion at position 5772 (codon 1924). This mutation, located in the exon 15 at the 3' end of the APC gene, leads to an unusual and late onset phenotype. The pedigree revealed other isolated or familial adenomatous polyposis-associated cases of desmoid tumors. This family report shows that a molecular analysis of the APC gene should be performed in familial desmoid tumors for accurate genetic counseling and follow-up.