APC, MYH, and the correlation genotype-phenotype in colorectal polyposis

Phenotype correlations with pathogenic DNA variants in the MUTYH gene

MUTYH -associated polyposis (MAP) is an autosomal recessive disorder where the inheritance of constitutional biallelic pathogenic MUTYH variants predisposes a person to the development of adenomas and colorectal cancer (CRC). It is also associated with extracolonic and extraintestinal manifestations that may overlap with the phenotype of familial adenomatous polyposis (FAP). Currently, there are discrepancies in the literature regarding whether certain phenotypes are truly associated with MAP. This narrative review aims to explore the phenotypic spectrum of MAP to better characterise the MAP phenotype. A literature search was conducted to identify articles reporting on MAP-specific phenotypes. Clinical data from 2109 MAP patients identified from the literature showed that 1123 patients (53.2%) had CRC. Some patients with CRC had no associated adenomas, suggesting that adenomas are not an obligatory component of MAP. Carriers of the two missense founder variants, and possibly truncating variants, had an increased cancer risk when compared to those who carry other pathogenic variants. It has been suggested that somatic G:C>T:A transversions are a mutational signature of MAP, and could be used as a biomarker in screening and identifying patients with atypical MAP, or in associating certain phenotypes with MAP. The extracolonic and extraintestinal manifestations that have been associated with MAP include duodenal adenomas, duodenal cancer, fundic gland polyps, gastric cancer, ovarian cancer, bladder cancer and skin cancer. The association of breast cancer and endometrial cancer with MAP remains disputed. Desmoids and Congenital Hypertrophy of the Retinal Pigment Epithelium (CHRPEs) are rarely reported in MAP, but have long been seen in FAP patients, and thus could act as a distinguishing feature between the two. This collection of MAP phenotypes will assist in the assessment of pathogenic MUTYH variants using the American College of Medical Genetics and the Association for Molecular Pathology (ACMG/AMP) Variant Interpretation Guidelines, and ultimately improve patient care.

Presentation and Follow-up of Familial Adenomatous Polyposis: Differences Between APC and MUTYH Mutations

BACKGROUND

Familial adenomatous polyposis is described as one of the common two types of genetic disorders: APC and MUTYH gene associated polyposis syndrome and the clinical differences between the two can sometimes be unclear.

MATERIALS AND METHODS

A retrospective analysis and comparison was made of clinical, surgical, and histological criteria, mutation types and the long-term results of patients who underwent genetic analysis which resulted in the diagnosis of Familial Adenomatous Polyposis between 1984 and 2018.

RESULTS

Of the total 71 patients included in the study, 14 were identified with the MUTYH gene, and 57 with the APC mutation. In patients with the APC mutation, 63% had duodenal adenoma, 61% gastric polyp and 54% had desmoid tumor. Of the patients with the MUTYH mutation, 21% had duodenal adenoma and 21% were diagnosed with gastric polyps. In 21% of the patients with APC mutation, the polyp count was <100, and 64% of those with the MUTYH mutation had >100 polyps in the colon No statistical difference was determined between the groups in respect of the proportion of patients with >100 polyps.

CONCLUSION

The pre-operative genetic testing of patients with polyposis coli will be useful in determining the future clinical outcome and helpful in guiding an informed decision as to whether to apply surgical treatment. It is useful to determine the colonic and extra-colonic involvement of genetic mutation diseases in patients with Familial adenomatous polyposis.

Colorectal family polyadenomatous diseases. What management in 2020?

Nearly 5% of colorectal cancers are hereditary colorectal cancers, including adenomatous polyposis. The aim of this review was to highlight the current management of adenomatous polyposis. The two main genetic conditions responsible for adenomatous polyposis are familial adenomatous polyposis (FAP) (caused by an autosomal dominant mutation of the APC gene) and MUTYH-associated polyposis (MAP) (caused by bi-allelic recessive mutations of the MUTYH (MutY human homolog) gene). FAP is characterized by the presence of >1000 polyps and a young age at diagnosis (mean age of 10). In the absence of screening, the risk of colorectal cancer at age 40 is 100%. It is recommended to start screening at the age of 10-12 years. For patients with FAP and MAP, it is also recommended to screen the upper gastrointestinal tract (stomach and duodenum). In FAP, prophylactic surgery aims to reduce the risk of death without impairment of patient quality of life. The best age for prophylactic surgery is not well-defined; in Europe, prophylactic surgery is usually performed at age 20 as the risk of cancer increases sharply during the third decade. There are three main surgical procedures employed: total colectomy with an ileorectal anastomosis, restorative coloproctectomy with a J pouch anastomosis and coloproctectomy with a stoma. Restorative coloproctectomy with J pouch anastomosis is the reference procedure; however, disease can vary in severity from one patient to another and this must be taken into account to decide which procedure should be performed. In conclusion, the management of adenomatous polyposis is complex but is well-defined by guidelines, particularly in France.

Duodenal Adenomas in Patients With Multiple Colorectal Adenomas Without Germline APC or MUTYH Mutations

BACKGROUND

Patients with genetic adenomatous polyposis syndromes have an increased risk for duodenal cancer, and clear surveillance recommendations exist for this group. However, limited data are available on the duodenal phenotype of patients with multiple colorectal adenomas (10-99) without a germline APC or MUTYH mutation.

OBJECTIVE

We aimed to assess the frequency, extent, and progression of duodenal adenomas in patients with multiple colorectal adenomas without a germline APC or MUTYH mutation.

DESIGN

This was an historical cohort study.

SETTINGS

This study was undertaken at 2 polyposis registries: the Academic Medical Center in the Netherlands, and St. Mark's Hospital in the United Kingdom.

PATIENTS

We collected data on all patients with 10 to 99 colorectal adenomas and absent APC and MUTYH mutations, who underwent ≥1 esophagogastroduodenoscopy.

MAIN OUTCOME MEASURES

The frequency, extent, and progression of duodenal adenomas were measured. Demographic and endoscopic data were collected, described, and compared between patients with and without duodenal adenomas.

RESULTS

Eighty-three patients were identified, of which 8 (9.6%) had duodenal adenomas, detected at a median of 58 years (range, 45-75 y). Duodenal adenomas were detected in 6 of 8 patients at first esophagogastroduodenoscopy. At diagnosis, all 8 patients had Spigelman stage I or II disease. Two of 5 patients with duodenal adenomas who underwent follow-up esophagogastroduodenoscopies increased to stage III disease. The other 3 remained stable. No one developed duodenal cancer. No differences in demographic and endoscopic data were found between patients with and without duodenal adenomas.

LIMITATIONS

This study was limited by its retrospective design, selection bias, and small sample size.

CONCLUSIONS

Duodenal adenomas are found in a minority of patients with multiple colorectal adenomas without a germline APC or MUTYH mutation, at an average age of 58 years, and, at diagnosis, disease severity is mild. These results are a first step in unraveling the duodenal phenotype of these patients, which is needed to provide appropriate upper GI screening and surveillance recommendations. See Video Abstract at http://links.lww.com/DCR/A357.

Gastrointestinal tract cancers: Genetics, heritability and germ line mutations

Gastrointestinal (GI) tract cancers that arise due to genetic mutations affect a large number of individuals worldwide. Even though many of the GI tract cancers arise sporadically, few of these GI tract cancers harboring a hereditary predisposition are now recognized and well characterized. These include Cowden syndrome, MUTYH-associated polyposis, hereditary pancreatic cancer, Lynch syndrome, Peutz-Jeghers syndrome, familial adenomatous polyposis (FAP), attenuated FAP, serrated polyposis syndrome, and hereditary gastric cancer. Molecular characterization of the genes that are involved in these syndromes was useful in the development of genetic testing for diagnosis and also facilitated understanding of the genetic basis of GI cancers. Current knowledge on the genetics of GI cancers with emphasis on heritability and germ line mutations forms the basis of the present review.

Early-onset colorectal cancer: A sporadic or inherited disease?

Colorectal cancer is the third most common cancer diagnosed worldwide. Although epidemiology data show a marked variability around the world, its overall incidence rate shows a slow but steady decrease, mainly in developed countries. Conversely, early-onset colorectal cancer appears to display an opposite trend with an overall prevalence in United States and European Union ranging from 3.0% and 8.6%. Colorectal cancer has a substantial proportion of familial cases. In particular, early age at onset is especially suggestive of hereditary predisposition. The clinicopathological and molecular features of colorectal cancer cases show a marked heterogeneity not only between early- and late-onset cases but also within the early-onset group. Two distinct subtypes of early-onset colorectal cancers can be identified: a “sporadic” subtype, usually without family history, and an inherited subtype arising in the context of well defined hereditary syndromes. The pathogenesis of the early-onset disease is substantially well characterized in the inherited subtype, which is mainly associated to the Lynch syndrome and occasionally to other rare mendelian diseases, whereas in the “sporadic” subtype the origin of the disease may be attributed to the presence of various common/rare genetic variants, so far largely unidentified, displaying variable penetrance. These variants are thought to act cumulatively to increase the risk of colorectal cancer, and presumably to also anticipate its onset. Efforts are ongoing in the attempt to unravel the intricate genetic basis of this “sporadic” early-onset disease. A better knowledge of molecular entities and pathways may impact on family-tailored prevention and clinical management strategies.

Identification of patients at risk for hereditary colorectal cancer

Diagnosis of hereditary colorectal cancer syndromes requires clinical suspicion and knowledge of such syndromes. Lynch syndrome is the most common cause of hereditary colorectal cancer. Other less common causes include familial adenomatous polyposis (FAP), Peutz-Jeghers syndrome (PJS), juvenile polyposis syndrome, and others. There have been a growing number of clinical and molecular tools used to screen and test at risk individuals. Screening tools include diagnostic clinical criteria, family history, genetic prediction models, and tumor testing. Patients who are high risk based on screening should be referred for genetic testing.

Key genetic considerations in the management of suspected hereditary colorectal cancer

SUMMARY Hereditary bowel cancer syndromes account for up to 5% of colorectal cancer (CRC) incidence. Presentation of CRC under the age of 50 years should alert clinicians to a possible underlying genetic predisposition. This article focuses on Lynch syndrome (hereditary nonpolyposis CRC). Regular bowel screening is effective in reducing the risk of CRC and improving overall survival in Lynch syndrome families. The issues surrounding the clinical diagnostic criteria and the shortcomings of the referral process are described, and it is questioned whether a universal strategy for diagnosis should be employed. This article summarizes the evidence for the benefit of bowel screening and suggests practical steps to help ensure compliance with screening recommendations. Finally, it is discussed how collaboration between geneticists, gastroenterologists and surgeons can inform surgical decision-making for the benefit of the patient.

Unexplained polyposis: a challenge for geneticists, pathologists and gastroenterologists

Two main colorectal polyposis syndromes have been described, familial adenomatous polyposis and MUTYH-associated polyposis syndromes. Some polyposis remains unexplained: 20% of adenomatous polyposis and serrated polyposis. The aim of this study was to evaluate in a cohort of patients with unexplained polyposis whether a genetic defect could be detected. Individuals presenting polyposis with more than 40 adenomas or more than 20 serrated polyps (hyperplastic, sessile serrated and mixed), without causative mutation identified, were included. Complementary explorations on APC or MUTYH were performed: search for APC mosaicism, splicing-affecting mutations, large genomic rearrangement of MUTYH. Four genes of Wnt pathway (AXIN2, PPP2R1B, WIF1, SFRP1) and two genes of transforming growth factor-β (TGF-β) pathway (SMAD4, BMPR1A) were screened for germline mutation. Twenty-five patients had an unexplained adenomatous polyposis (familial or sporadic). Five pathogenic mutations were found: four in APC gene (with one case of mosaicism) and one in BMPR1A gene. The exploration of APC mosaicism was better performed from adenoma DNA with high-resolution melting. The screening of the candidate genes did not find any causative mutation. Thirteen individuals had an unexplained serrated polyposis and a frameshift on SMAD4 gene was identified. All mutations were identified in familial cases of polyposis. After new pathological examination, both BMPR1A and SMAD4 cases were found to be associated with a juvenile polyposis while the polyposis was initially described as adenomatous or undetermined. In 17% (6/38) of the patients the causative mutation of the polyposis was identified. Genetic causes were heterogeneous. Sporadic polyposis patients must be considered as potential APC mosaicism. The histological classification of polyposis is strongly important in direct genetic exploration.

Lower gastrointestinal tract cancer predisposition syndromes

Although inherited predisposition to colorectal cancer (CRC) has been suspected for more than 100 years, definitive proof of Mendelian syndromes had to await maturation of molecular genetic technologies. Since the l980s, the genetics of several clinically distinct entities has been revealed. Five disorders that share a hereditary predisposition to CRC are reviewed in this article.

Clinical and genetic characterization of classical forms of familial adenomatous polyposis: a Spanish population study

BACKGROUND

Classical familial adenomatous polyposis (FAP) is characterized by the appearance of >100 colorectal adenomas.

PATIENTS AND METHODS

We screened the APC and MUTYH genes for mutations and evaluated the genotype-phenotype correlation in 136 Spanish classical FAP families.

RESULTS

APC/MUTYH mutations were detected in 107 families. Sixty-four distinct APC point mutations were detected in 95 families of which all were truncating mutations. A significant proportion (39.6%) had not been previously reported. Mutations were spread over the entire coding region and great rearrangements were identified in six families. Another six families exhibited biallelic MUTYH mutations. No APC or MUTYH mutations were detected in 29 families. These APC/MUTYH-negative families showed clinical differences with the APC-positive families. A poor correlation between phenotype and mutation site was observed.

CONCLUSIONS

Our results highlight that a broad approach in the genetic study must be considered for classical FAP due to involvement of both APC and MUTYH and the heterogeneous spectrum of APC mutations observed in this Spanish population. The scarcely consistent genotype-phenotype correlation does not allow making specific recommendations regarding screening and management. Differences observed in APC/MUTYH-negative families may reflect a genetic basis other than mutations in APC and MUTYH genes for FAP predisposition.

Risk factors for secondary proctectomy in patients with familial adenomatous polyposis

Background

Colectomy and ileorectal anastomosis (IRA) or restorative proctocolectomy are performed for prophylaxis in familial adenomatous polyposis (FAP). After IRA patients may require secondary proctectomy for worsening polyposis or rectal cancer. Outcomes after IRA were evaluated and risk factors predictive of progressive rectal disease identified.

Methods

Parametric survival analysis was used to identify predictors of progressive rectal disease in all patients undergoing an IRA for FAP at a single centre. Hazard ratios (HRs) were calculated for phenotype, genotype, sex, age at surgery and presence of colonic cancer.

Results

Of 427 patients who underwent IRA, 48 (11·2 per cent) developed rectal cancer and 77 (18·0 per cent) required proctectomy for worsening polyposis over a median follow-up of 15 (range 7–25) years. By the age of 60 years half of the patients retained their rectum. Rectal polyp count exceeding 20 (HR 30·99, 95 per cent confidence interval 9·57 to 100·32; P &lt; 0·001), APC mutation codon 1250–1450 (HR 3·91, 1·45 to 10·51; P = 0·007), colonic polyp count 500 or more (HR 2·18, 1·24 to 3·82; P = 0·006) and age less than 25 years at the time of surgery (HR 1·99, 1·17 to 3·37; P = 0·011) were independent predictors of progressive rectal disease.

Conclusion

The risk of proctectomy after IRA for FAP is based on patient genotype, phenotype and age at surgery.

Familial adenomatous polyposis

Patients with FAP are guaranteed to have one major abdominal surgery in their life. They are also subject to cancers and benign disorders in other organ systems, some of which can be life threatening. Steering a course through life while avoiding preventable disease and complications of treatment, and maintaining good quality of life is a challenge for health care givers, patients, and their families. A successful voyage calls for clinical cooperation between providers and patients, education and understanding, and expertise and experience. FAP patients and families should be involved in a registry or genetic center, not to the exclusion of local practitioners but to their benefit. In this way the best of care is given and the best of outcomes ensured.