Proportion and phenotype of MYH-associated colorectal neoplasia in a population-based series of Finnish colorectal cancer patients

Signaling pathways involved in colorectal cancer: pathogenesis and targeted therapy

Colorectal cancer (CRC) remains one of the leading causes of cancer-related mortality worldwide. Its complexity is influenced by various signal transduction networks that govern cellular proliferation, survival, differentiation, and apoptosis. The pathogenesis of CRC is a testament to the dysregulation of these signaling cascades, which culminates in the malignant transformation of colonic epithelium. This review aims to dissect the foundational signaling mechanisms implicated in CRC, to elucidate the generalized principles underpinning neoplastic evolution and progression. We discuss the molecular hallmarks of CRC, including the genomic, epigenomic and microbial features of CRC to highlight the role of signal transduction in the orchestration of the tumorigenic process. Concurrently, we review the advent of targeted and immune therapies in CRC, assessing their impact on the current clinical landscape. The development of these therapies has been informed by a deepening understanding of oncogenic signaling, leading to the identification of key nodes within these networks that can be exploited pharmacologically. Furthermore, we explore the potential of integrating AI to enhance the precision of therapeutic targeting and patient stratification, emphasizing their role in personalized medicine. In summary, our review captures the dynamic interplay between aberrant signaling in CRC pathogenesis and the concerted efforts to counteract these changes through targeted therapeutic strategies, ultimately aiming to pave the way for improved prognosis and personalized treatment modalities in colorectal cancer.

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.

Monoallelic MUTYH pathogenic variants ascertained via multi-gene hereditary cancer panels are not associated with colorectal, endometrial, or breast cancer

We aimed to determine whether monoallelic MUTYH pathogenic and likely pathogenic variants (PVs) are associated with colorectal, breast, and endometrial cancer. Cases were individuals with colorectal, female breast, or endometrial cancer who reported European ancestry alone and underwent a multi-gene hereditary cancer panel at a large reference laboratory. Controls were individuals of European (non-Finnish) descent from GnomAD with cancer cohorts removed. We performed a Fisher's exact test to generate odds ratios (ORs) with 95% confidence intervals (CI). Prevalence of single MUTYH PVs in cancer cohorts versus controls, respectively, was: colorectal cancer, 2.1% vs. 1.8% (OR 1.2, 95% CI 0.99-1.5, p = 0.064); breast cancer 1.9% vs. 1.7% (OR 1.1, 95% CI 0.96-1.3, p = 0.15); and endometrial cancer, 1.7% vs. 1.7% (OR 0.98; 95% CI 0.70-1.3, p = 0.94). Using the largest colorectal and endometrial cancer cohorts and one of the largest breast cancer cohorts from a single case-control study, we did not observe a significant difference in the prevalence of monoallelic MUTYH PVs in these cohorts compared to controls. Additionally, frequencies among cancer cohorts were consistent with the published MUTYH carrier frequency of 1-2%. These findings suggest there is no association between colorectal, endometrial, or breast cancer and MUTYH heterozygosity in individuals of European ancestry.

MUTYH-associated polyposis - colorectal phenotype and management

AIM

The aim was to determine the presentation, management and outcomes of MUTYH-associated polyposis (MAP).

METHOD

A prospectively maintained database was used to identify patients with MAP. Demographic data and data on germline mutation, surgical management, histopathology of tumours and endoscopic surveillance were collected.

RESULTS

In all, 134 patients with MAP were identified. The majority presented symptomatically (n = 83). Sixty-eight patients developed cancer (seven synchronous, 12 metachronous). The median age at diagnosis of first colorectal cancer was 47 years (range 33-74 years). Cancers occurred in the context of a few adenomas (< 10). The majority of patients (n = 108) had surgery as the first line management. One patient received palliative care. Twenty-five patients had endoscopic surveillance as first line management; no cancers occurred in this group. Patients who had segmental resection and postoperative surveillance still appeared to be at risk of metachronous cancer (5/30, 17%).

CONCLUSIONS

MUTYH testing should be considered even in the context of cancers occurring with fewer than 10 adenomas. In cases of primary colorectal cancers, extended surgery should be considered if patients do not have access to high quality endoscopic surveillance postoperatively. For some patients, endoscopic therapy is an appropriate and safe option in expert hands.

Clinical characterization and mutation spectrum in patients with familial adenomatous polyposis in China

BACKGROUND AND AIM

Familial adenomatous polyposis (FAP) is the most common adenomatous polyposis syndrome. Patients with FAP are screened for germline mutations of two genes, APC and MUTYH. However, limited data exist on the clinical characterization and genotypic spectrum of FAP in China. This study was aimed to determine APC and MUTYH mutational status in a small cohort of FAP probands in China and to characterize the genotype-phenotype correlation in mutated patients.

METHODS

Mutation screening of 46 unrelated probands was performed using multigene panels by next-generation sequencing. Clinical data of the index were used to assess genotype-phenotype correlations.

RESULTS

Overall, 42 out of 46 (91.30%) unrelated probands found mutations, including 35 (76.09%) with APC mutations, 3 (6.52%) with MUTYH mutations, and 4 (8.70%) with both APC and MUTYH mutations. Ten APC genetic alterations variants were novel. The hereditary pattern of the family with both APC and MUTYH mutations was autosomal dominant inheritance. Upper gastrointestinal polyp was the most common extracolonic manifestations. The onset time for patients with both APC and MUTYH mutations was earlier than MUTYH mutation carriers and similar to APC mutation carriers. But the age of carcinogenesis for patients with both APC and MUTYH mutations was later than APC mutation carriers and similar to MUTYH mutation carriers.

CONCLUSION

In this study, we show the importance of using multigene panels that allow for a parallel comprehensive screening. We suggest that genetic testing of patients with suspected adenomatous polyposis syndromes should include APC and MUTYH gene mutation analyses simultaneously.

The role of inherited genetic variants in colorectal polyposis syndromes

Colorectal carcinoma (CRC) is the third most common cancer in men and the second most common cancer in women across the world. Most CRCs occur sporadically, but in 15-35% of cases, hereditary factors are important. Some patients with an inherited predisposition to CRC will be diagnosed with a "genetic polyposis syndrome" such as familial adenomatous polyposis (FAP), MUTYH-associated polyposis (MAP), polymerase proofreading associated polyposis (PPAP), NTHL1-associated polyposis, MSH3-associated polyposis or a hamartomatous polyposis syndrome. Individuals with ≥10 colorectal polyps have traditionally been referred for genetic diagnostic testing to identify APC and MUTYH mutations which cause FAP and MAP respectively. Mutations are found in most patients with >100 adenomas but in only a minority of those with 10-100 adenomas. The reasons that diagnostic laboratories are not identifying pathogenic variants include mutations occurring outside of the open reading frames of genes, individuals exhibiting generalized mosaicism and the involvement of additional genes. It is important to identify patients with an inherited polyposis syndrome, and to define the mutations causing their polyposis, so that the individuals and their relatives can be managed appropriately.

Association of monoallelic MUTYH mutation among Egyptian patients with colorectal cancer

Colorectal cancer (CRC) is a heterogeneous triat that involves both environmental and genetic factors. Genetic mutations of MUTYH (p.Y179C and p.G396D) have been reported to be associated with increased risk of CRC among several ethnic populations. The aim of this work is to assess the association of the monoallelic MUTYH mutations (p.Y179C and p.G396D) with increased risk of CRC among Egyptian patients. This study included 120 unrelated CRC Egyptian patients who were compared with 100 healthy controls from the same locality. For all individuals, DNA was genotyped for MUTYH p.Y179C and MUTYH p.G396D mutations using the T-ARMS-PCR technique. The frequencies of monoallelic MUTYH mutations showed a strong association with the increased risk of CRC among Egyptian patients compared with controls (12.5 vs. 4.0 %, OR = 3.49, 95 % CI = 1.12-10.90, P = 0.03). Moreover, the frequency of MUTYH p.Y179C mutation was noted to be significantly higher among CRC patients compared to controls rather than MUTYH p.G396D mutation. Interestingly, CRC patients with tumors in the right side colon showed an evidence for association with the MUTYH p.Y179C mutation compared with tumors in the left side colon (p = 0.01). MUTYH p.Y179C mutation was associated with an increased risk of CRC among Egyptian patients rather than MUTYH p.G396D mutation.

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.

Increased risk for colorectal adenomas and cancer in mono-allelic MUTYH mutation carriers: results from a cohort of North-African Jews

Bi-allelic MUTYH gene mutations are associated with a clinical phenotype of multiple colorectal adenomas and an increased risk for colorectal cancer (CRC). It is unclear whether mono-allelic MUTYH gene carriers (heterozygotes) are also at increased risk for even few adenomas or cancer. In order to clarify an association between MUTYH heterozygotes and adenomas, we evaluated the frequency and types of MUTYH mutations and variants in 72 North-African Jews having few (≥3) colorectal adenomas with or without early onset (<50 years) CRC compared to 29 healthy controls. Germ-line DNA was analyzed for a panel of 6 MUTYH mutations and variants, and Sanger sequencing of the entire MUTYH gene was performed for mono-allelic MUTYH mutation carriers. APC gene mutations and Lynch syndrome were excluded in the relevant cases according to accepted clinical criteria. Twenty-two of the 72 adenoma subjects (30.5%) had MUTYH mutations or variants. Nine were homozygotes or compound heterozygotes: all had >10 adenomas and one had CRC. Thirteen others were mono-allelic carriers (heterozygotes) of a single MUTYH mutation: six had more than ten adenomas and seven had less than ten adenomas; of these 13 mono-allelic carriers, six had a neoplasm: three CRCs and three extra-intestinal tumors. Eleven of the thirteen mono-allelic carriers with adenomas had a family history of cancer in first or second degree relatives. A multivariable model showed positive correlation between G396D, Y179C and 1186 ins GG mutations and number of adenomas (OR 8.6, 10.2 and 14.4, respectively). The Q324H variant was negatively associated with the number of adenomatous polyps (OR -5.23). In conclusion, MUTYH mutations are prevalent among Jews of North-African origin with colorectal adenomas with or without early onset CRC. Mono-allelic MUTYH carriers with a family history of cancer had a clinical phenotype that varied from having only few adenomas to multiple (>10) adenomas. These findings support MUTYH testing in patients with even few adenomas and suggest the consideration of increased surveillance in mono-allelic carriers with a family history of cancer.

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.

The Genetics of Colorectal Cancer

The hereditary colorectal cancer syndromes comprise a heterogeneous group of conditions with varying cancer risks, gastrointestinal polyp types, nonmalignant findings, and inheritance patterns. Although each one is unique in its own right, these syndromes often have overlapping features, making diagnoses difficult in select cases. Obtaining accurate polyp history (histologic type, number, location, and age of onset), cancer history (location, type, and age of onset), and other nonmalignant features is imperative in determining the likely disease diagnosis and thereby the appropriate genetic tests for precise diagnosis in a timely fashion. This process often necessitates collaboration among surgical oncology team members and genetic counselors.

The genetic basis of familial adenomatous polyposis and its implications for clinical practice and risk management

Familial adenomatous polyposis (FAP) is an inherited disorder that represents the most common gastrointestinal polyposis syndrome. Germline mutations in the APC gene were initially identified as responsible for FAP, and later, several studies have also implicated the MUTYH gene as responsible for this disease, usually referred to as MUTYH-associated polyposis (MAP). FAP and MAP are characterized by the early onset of multiple adenomatous colorectal polyps, a high lifetime risk of colorectal cancer (CRC), and in some patients the development of extracolonic manifestations. The goal of colorectal management in these patients is to prevent CRC mortality through endoscopic and surgical approaches. Individuals with FAP and their relatives should receive appropriate genetic counseling and join surveillance programs when indicated. This review is focused on the description of the main clinical and genetic aspects of FAP associated with germline APC mutations and MAP.

ACG clinical guideline: Genetic testing and management of hereditary gastrointestinal cancer syndromes

This guideline presents recommendations for the management of patients with hereditary gastrointestinal cancer syndromes. The initial assessment is the collection of a family history of cancers and premalignant gastrointestinal conditions and should provide enough information to develop a preliminary determination of the risk of a familial predisposition to cancer. Age at diagnosis and lineage (maternal and/or paternal) should be documented for all diagnoses, especially in first- and second-degree relatives. When indicated, genetic testing for a germline mutation should be done on the most informative candidate(s) identified through the family history evaluation and/or tumor analysis to confirm a diagnosis and allow for predictive testing of at-risk relatives. Genetic testing should be conducted in the context of pre- and post-test genetic counseling to ensure the patient's informed decision making. Patients who meet clinical criteria for a syndrome as well as those with identified pathogenic germline mutations should receive appropriate surveillance measures in order to minimize their overall risk of developing syndrome-specific cancers. This guideline specifically discusses genetic testing and management of Lynch syndrome, familial adenomatous polyposis (FAP), attenuated familial adenomatous polyposis (AFAP), MUTYH-associated polyposis (MAP), Peutz-Jeghers syndrome, juvenile polyposis syndrome, Cowden syndrome, serrated (hyperplastic) polyposis syndrome, hereditary pancreatic cancer, and hereditary gastric cancer.

ACMG technical standards and guidelines for genetic testing for inherited colorectal cancer (Lynch syndrome, familial adenomatous polyposis, and MYH-associated polyposis)

Lynch syndrome, familial adenomatous polyposis, and Mut Y homolog (MYH)-associated polyposis are three major known types of inherited colorectal cancer, which accounts for up to 5% of all colon cancer cases. Lynch syndrome is most frequently caused by mutations in the mismatch repair genes MLH1, MSH2, MSH6, and PMS2 and is inherited in an autosomal dominant manner. Familial adenomatous polyposis is manifested as colonic polyposis caused by mutations in the APC gene and is also inherited in an autosomal dominant manner. Finally, MYH-associated polyposis is caused by mutations in the MUTYH gene and is inherited in an autosomal recessive manner but may or may not be associated with polyps. There are variants of both familial adenomatous polyposis (Gardner syndrome--with extracolonic features--and Turcot syndrome, which features medulloblastoma) and Lynch syndrome (Muir-Torre syndrome features sebaceous skin carcinomas, and Turcot syndrome features glioblastomas). Although a clinical diagnosis of familial adenomatous polyposis can be made using colonoscopy, genetic testing is needed to inform at-risk relatives. Because of the overlapping phenotypes between attenuated familial adenomatous polyposis, MYH-associated polyposis, and Lynch syndrome, genetic testing is needed to distinguish among these conditions. This distinction is important, especially for women with Lynch syndrome, who are at increased risk for gynecological cancers. Clinical testing for these genes has progressed rapidly in the past few years with advances in technologies and the lower cost of reagents, especially for sequencing. To assist clinical laboratories in developing and validating testing for this group of inherited colorectal cancers, the American College of Medical Genetics and Genomics has developed the following technical standards and guidelines. An algorithm for testing is also proposed.

MUTYH DNA glycosylase: the rationale for removing undamaged bases from the DNA

Maintenance of genetic stability is crucial for all organisms in order to avoid the onset of deleterious diseases such as cancer. One of the many proveniences of DNA base damage in mammalian cells is oxidative stress, arising from a variety of endogenous and exogenous sources, generating highly mutagenic oxidative DNA lesions. One of the best characterized oxidative DNA lesion is 7,8-dihydro-8-oxoguanine (8-oxo-G), which can give rise to base substitution mutations (also known as point mutations). This mutagenicity is due to the miscoding potential of 8-oxo-G that instructs most DNA polymerases (pols) to preferentially insert an Adenine (A) opposite 8-oxo-G instead of the appropriate Cytosine (C). If left unrepaired, such A:8-oxo-G mispairs can give rise to CG→AT transversion mutations. A:8-oxo-G mispairs are proficiently recognized by the MutY glycosylase homologue (MUTYH). MUTYH can remove the mispaired A from an A:8-oxo-G, giving way to the canonical base-excision repair (BER) that ultimately restores undamaged Guanine (G). The importance of this MUTYH-initiated pathway is illustrated by the fact that biallelic mutations in the MUTYH gene are associated with a hereditary colorectal cancer syndrome termed MUTYH-associated polyposis (MAP). In this review, we will focus on MUTYH, from its discovery to the most recent data regarding its cellular roles and interaction partners. We discuss the involvement of the MUTYH protein in the A:8-oxo-G BER pathway acting together with pol λ, the pol that can faithfully incorporate C opposite 8-oxo-G and thus bypass this lesion in a correct manner. We also outline the current knowledge about the regulation of MUTYH itself and the A:8-oxo-G repair pathway by posttranslational modifications (PTM). Finally, to achieve a clearer overview of the literature, we will briefly touch on the rather confusing MUTYH nomenclature. In short, MUTYH is a unique DNA glycosylase that catalyzes the excision of an undamaged base from DNA.

MUTYH-associated polyposis (MAP): evidence for the origin of the common European mutations p.Tyr179Cys and p.Gly396Asp by founder events

MUTYH-associated polyposis (MAP) is an autosomal recessive adenomatous polyposis caused by biallelic germline mutations of the base-excision-repair gene MUTYH. In MAP patients of European origin, the combined allele frequency of the mutations p.Tyr179Cys and p.Gly396Asp ranges between 50 and 82%, while these mutations have not been identified in Far Eastern Asian populations, supporting the hypothesis that a founder effect has occurred at some point in European history. To investigate the natural history of the two common European MUTYH alleles, we genotyped six gene-flanking microsatellite markers in 80 unrelated Italian and German MAP patients segregating one or both mutations and calculated their age in generations (g) by using DMLE+2.2 software. Three distinct common haplotypes, one for p.Tyr179Cys and two for p.Gly396Asp, were identified. Estimated mutation ages were 305 g (95% CS: 271-418) for p.Tyr179Cys and 350 g (95% CS: 313-435) for p.Gly396Asp. These results provide evidence for strong founder effects and suggest that the p.Tyr179Cys and p.Gly396Asp mutations derive from ancestors who lived between 5-8 thousand years and 6-9 thousand years B.C., respectively.

The first mutations in the MYH gene reported in Moroccan colon cancer patients

BACKGROUND

Biallelic germline mutations in the MYH gene cause MYH-associated polyposis (MAP) disease, an autosomal recessive form of inherited colorectal cancer. People with MAP tend to develop attenuated multiple adenomatous colon polyps during their lifetime and will have an increased risk of colorectal cancer. Contrary to familial adenomatous polyposis, the number of adenomas is often lower in MAP (from 5 to 100), and even some patients have recently been reported with no identified adenomas. There have been many investigations into MAP that have been conducted in many different countries. Currently there is limited data on MAP in Morocco, and it is reasonable to think, that the prevalence of this form of genetic predisposition is as high as other autosomal recessive genetic diseases found in countries with high rates of consanguinity. The aim of this study is to examine the frequency of MYH mutations in colorectal cancer and/or attenuated polyposis in Moroccan patients.

PATIENTS AND METHODS

The study population consisted of 62 patients; 52 with colorectal cancer, three of them had attenuated polyposis (2 to 99 adenomatous polyps). 10 other patients were referred to our department for polyposis without colorectal cancer. We carried out DNA analysis in 62 patients to screen for the three recurrent mutations c.494A>G (p.Tyr165Cys), c.1145G>A (p.Gly382Asp) and c.1185_1186dup, p.Glu396GlyfsX43, whereas 40 subjects were screened for germline MYH mutations in the whole coding sequence of the MYH gene by direct DNA sequencing. All these 40 patients, except two, had colorectal cancer without polyposis.

RESULTS

Three patients with colorectal cancer and attenuated polyposis carried biallelic mutations in the MUTYH gene one with the c.494 A>G mutation, one with the c.1105delC mutation, one with the c.1145G>A mutation. One patient with 25 adenomas without colorectal cancer carried the c.1145G>A mutation at a homozygote state and one patient with 3 polyps was heterozygote for the mutation c.1145G>A. No biallelic mutations of MYH gene were detected in colorectal cancer patients and in patients with small number (<5) of polyps without colorectal cancer.

CONCLUSION

We report the first biallelic MYH mutations in four Moroccan patients with clinical criteria of MAP; three of them had colorectal cancer with attenuated polyposis. No MYH mutations were found in colorectal patients without polyposis. Despite the relatively small sample size of the current study, our findings suggest that the MAP is not a frequent cause of colon cancer in Morocco as we had expected, and the molecular analysis of MYH gene should be restricted to patients displaying the classical phenotype of MAP.

Hereditary colon cancer syndromes

Colon cancer is associated with a family history in up to 25% of cases. As many as 5% are associated with an established hereditary syndrome, demonstrating the profound influence of inheritable genetic mechanisms in the development of this disease. These syndromes confer a diverse spectrum of risk, age of presentation, endoscopic and histological findings, extracolonic manifestations, and modes of inheritance. As the molecular characteristics of these disorders become better described, enhanced genotype-phenotype correlations may offer a more targeted approach to diagnosis, screening, and surveillance. While the strategies for diagnosis and management of familial adenomatous polyposis (FAP) and Lynch syndrome are more established, the approach to newly recognized syndromes such as MUTYH-associated polyposis (MAP) and hyperplastic polyposis syndromes continues to evolve. Effective cancer prevention in affected individuals and at-risk family members first requires timely recognition of these hereditary colon cancer syndromes followed by integration of genetic testing and clinical examinations.

MUTYH Associated Polyposis (MAP)

MUTYH Associated Polyposis (MAP), a Polyposis predisposition caused by biallelic mutations in the Base Excision Repair (BER) gene MUTYH, confers a marked risk of colorectal cancer (CRC). The MAP phenotype is difficult to distinguish from other hereditary CRC syndromes. Especially from Familial Adenomatous Polyposis (FAP) and to a lesser extend Lynch Syndrome, which are caused by germline mutations in the APC and Mismatch Repair (MMR) genes, respectively.

Here we review research findings regarding MUTYH interactions, genotypic and phenotypic characteristics of MAP, as well as surveillance and treatment of the disease. The applied papers, published between 1/1 2002- 1/2 2008, were found through PubMed.

The exact role of MUTYH in CRC tumorgenesis is still uncertain, although MAP tumors show distinct molecular features, including somatic G:C>T:A transversions in the APC gene. Furthermore, cooperation between the BER and the MMR systems exists, as MUTYH interacts with MMR gene-products. Possibly, monoallelic defects in both pathways are of significance to CRC development.

Specific MUTYH variants are found to be characteristic in distinct ethnic populations, which could facilitate future genetic screening. Knowledge concerning functional consequences of many MUTYH germline mutations remains sparse. Most thoroughly investigated are the two most common MUTYH variants, Y179C and G396D, both generating dysfunctional gene products.

Phenotypic features of MAP include: development of 10-100 colorectal adenomas, debuting at 46-47 years, often CRC at time of clinical diagnosis, and in some, development of extracolonic manifestations.

Association between monoallelic MUTYH mutation and colorectal cancer risk: a meta-regression analysis

Whether people who inherit a mutation in MUTYH from only one parent (monoallelic mutation) are at increased risk of colorectal cancer (CRC) remains controversial. Most previous studies and meta-analyses have not found statistically significant associations but, given carriers are relatively rare, may be underpowered to detect small increased risks. We have conducted a systematic review and meta-regression analysis of previously published case-control studies to estimate the strength of association for monoallelic MUTYH mutation and CRC risk. Potential sources of heterogeneity were evaluated. We have compared the carrier frequency in cases with a family history of CRC to that of controls, as a novel and powerful design, to measure statistical evidence of an association but not the strength of association. The magnitude of the genotype-disease association, estimated from a pooled odds ratio comparing cases unselected for family history with controls, was 1.15 (95% CI = 0.98-1.36) and not substantially altered by adjustment for potential sources of heterogeneity. Monoallelic mutation carrier frequency was greater for cases ascertained due to a family history (3.3%; SE 0.9%) than for controls (1.4%; SE 0.3%) (P = 0.02). Monoallelic MUTYH mutation carriers are at increased risk of CRC but the average increase is small.

MUTYH-associated polyposis - variability of the clinical phenotype in patients with biallelic and monoallelic MUTYH mutations and report on novel mutations

To further characterize 215 APC mutation-negative patients with colorectal neoplasias classified in classical, attenuated, or atypical familial adenomatous polyposis (FAP) coli we performed mutation screening in the Mut Y homologue (MUTYH) gene. The incidence was 15% for biallelic and 3.7% for monoallelic MUTYH mutations. We describe six novel MUTYH mutations in biallelic constellation and two novel monoallelic missense mutations. Of 33 MUTYH-associated polyposis coli (MAP) patients 57% were attenuated familial adenomatous polyposis (AFAP) patients, 10% display early-onset classical FAP and 18% had only few adenomas at higher age. Biallelic cases had a high incidence of extracolonic polyposis in 32% and colorectal cancer (CRC) in 33% of the cases. The clinical picture of MAP ranged from classical FAP or synchronous CRC at age 30 years to few adenomas at age 54 years without evidence of CRC, initially suspected for hereditary non-polyposis colorectal cancer (HNPCC). The mean age of onset was 43 years, with 11 (33%) patients being younger than 40 years of age, indicating that the clinical manifestation can be earlier than so far reported. Monoallelic MUTYH mutation carriers had a positive family history in seven of eight cases allowing the hypothesis of a disease-causing synergism of MUTYH mutations with other genes.

A large-scale meta-analysis to refine colorectal cancer risk estimates associated with MUTYH variants

Background:

Defective DNA repair has a causal role in hereditary colorectal cancer (CRC). Defects in the base excision repair gene MUTYH are responsible for MUTYH-associated polyposis and CRC predisposition as an autosomal recessive trait. Numerous reports have suggested MUTYH mono-allelic variants to be low penetrance risk alleles. We report a large collaborative meta-analysis to assess and refine CRC risk estimates associated with bi-allelic and mono-allelic MUTYH variants and investigate age and sex influence on risk.

Methods:

MUTYH genotype data were included from 20 565 cases and 15 524 controls. Three logistic regression models were tested: a crude model; adjusted for age and sex; adjusted for age, sex and study.

Results:

All three models produced very similar results. MUTYH bi-allelic carriers demonstrated a 28-fold increase in risk (95% confidence interval (CI): 6.95–115). Significant bi-allelic effects were also observed for G396D and Y179C/G396D compound heterozygotes and a marginal mono-allelic effect for variant Y179C (odds ratio (OR)=1.34; 95% CI: 1.00–1.80). A pooled meta-analysis of all published and unpublished datasets submitted showed bi-allelic effects for MUTYH, G396D and Y179C (OR=10.8, 95% CI: 5.02–23.2; OR=6.47, 95% CI: 2.33–18.0; OR=3.35, 95% CI: 1.14–9.89) and marginal mono-allelic effect for variants MUTYH (OR=1.16, 95% CI: 1.00–1.34) and Y179C alone (OR=1.34, 95% CI: 1.01–1.77).

Conclusions:

Overall, this large study refines estimates of disease risk associated with mono-allelic and bi-allelic MUTYH carriers.

Prevalence of MYH-associated polyposis related to three recurrent mutations in Morocco

BACKGROUND

MYH-associated polyposis (MAP) is an autosomal recessive inherited disease. People with MAP tend to develop multiple adenomatous colon polyps during their lifetime and have an increased risk of colorectal cancer. MAP has only recently been described and there is much to be learned about the condition. Recessively inherited mutations in the base excision repair gene MYH have recently been associated with predisposition to colorectal adenomas and cancer. The epidemiology of MYH-associated polyposis (MAP) is poorly known in populations with high levels of consanguinity like North African populations, in particular in Morocco, and the MAP carrier frequency in the general Moroccan population has never been evaluated. The present study was carried out among the Moroccan population, using molecular epidemiology methods, to estimate the prevalence of homozygote or compound heterozygote genotype conferring MAP due to three mutations reported as recurrent in MAP: c.494A>G (Y165C), c.1145G>A (G382D) and c.1186_1187insGG (p.Glu396fsX42).

METHODS

To estimate the prevalence of MYH mutations in Morocco, DNA extracted from blood samples of 400 healthy Moroccans was tested for recurrent MYH mutations using real-time PCR or DNA fragment analysis. Heterozygotes profiles were confirmed by direct sequencing. We searched for the mutations c.494A>G and c.1145G>A in 400 subjects, and the mutation c.1186_1187insGG in 250 subjects.

RESULTS

One subject was heterozygous for c.494A>G (1/400 or 0.25%), three others for c.1145G>A (3/400 or 0.75%) and one was heterozygous for p.Glu396fsX42 (1/250 or 0.4%). The carrier frequency of one of these three mutations in the Moroccan population was calculated to be 1.4% and the frequency of homozygous or compound heterozygote for these three recurrent mutations is 1/10 000.These figures allowed one to estimate at 3500 the number of Moroccans with high risk of developing colon cancer due only to these three recurrent mutations.

CONCLUSION

This preliminary study shows that the Moroccan population is at risk for MAP. This could help to define diagnosis strategies and patient care and may also have implications for genetic counselling.

Tgf-beta signaling alterations and colon cancer

Colorectal cancer is the second most common cause of cancer-related death in the United States. Twin studies suggest that 35% of all colorectal cancer cases are inherited. High-penetrance tumor susceptibility genes account for at most 3-6% of all colorectal cancer cases and the remainder of the unexplained risk is likely due to a combination of low to moderate penetrance genes. Recent genome-wide association studies have identified several SNPs near genes belonging to the transforming growth factor beta (TGF-beta) superfamily such as GREM1 and SMAD7. Together with the recent discovery that constitutively decreased TGFBR1 expression is a potent modifier of colorectal cancer risk, these findings strongly suggest that germline variants of the TGF-beta superfamily may account for a sizeable proportion of colorectal cancer cases. The TGF-beta superfamily signaling pathways mediate many different biological processes during embryonic development, and in adult organisms they play a role in tissue homeostasis. TGF-beta has a central role in inhibiting cell proliferation and also modulates processes such as cell invasion, immune regulation, and microenvironment modification. Mutations in the TGF-beta type II receptor (TGFBR2) are estimated to occur in approximately 30% of colorectal carcinomas. Mutations in SMAD4 and BMPR1A are found in patients with familial juvenile polyposis, an autosomal dominant condition associated with an increased risk of colorectal cancer. This chapter provides an overview of the genetic basis of colorectal cancer and discusses recent discoveries related to alterations in the TGF-beta pathways and their role in the development of colorectal cancer.

Frequent mutation in North African patients with MUTYH-associated polyposis

MUTYH-associated polyposis (MAP) has been characterized as an autosomal recessive disease predisposing to a variable number of colorectal adenomas with a high risk of cancer. Numerous studies have indicated that two missense mutations (Y179C and G396D) account for about 80% of MUTYH allelic variants in Europeans. Ethnic and geographic differences in the mutation spectrum have been observed. The aim of this study was to report mutations in patients from North Africa, determine the incidence of the c.1227_1228dup mutation in our cohort of MUTYH patients and to evaluate the existence of a founder effect. Within a group of 36 families with MAP, 11 were shown to have a homozygous c.1227_1228dup mutation. These families came from Algeria (n = 5), Tunisia (n = 4), Morocco (n = 1) and Portugal (n = 1). Probands belonging to families of North African origin showed a significantly higher frequency of c.1227_1228dup (78.6% vs 4.5%, p < 0.0001). Haplotype analyses were performed using 10 microsatellite markers surrounding the MUTYH gene spanning a region of 4.4 cM. We identified a common haplotype of at least 1.3 cM in all families suggesting a founder effect for this mutation.

MUTYH-associated polyposis (MAP)

The human mutY homologue (MUTYH) gene is responsible for inheritable polyposis and colorectal cancer. This review discusses the molecular genetic aspects of the MUTYH gene and protein, the clinical impact of mono- and biallelic MUTYH mutations and histological aspects of the MUTYH tumors. Furthermore, the relationship between MUTYH and the mismatch repair genes in colorectal cancer (CRC) families is examined. Finally, the role of other base excision repair genes in polyposis and CRC patients is discussed.

MUTYH-associated polyposis and colorectal cancer

This article reviews the role of defective base excision repair, and MUTYH specifically, in colorectal cancer etiology and discusses the consequences of MUTYH gene defects, with particular emphasis on clinical relevance to colorectal polyposis, colorectal cancer risk, and appraising the risk of extra-colonic malignancy. Evidence guiding clinical practice, in terms of surveillance recommendations and options for surgical and other prophylactic interventions, is reviewed.

Genetic testing for hereditary colorectal cancer

This article focuses on genetic testing for hereditary colorectal cancer syndromes. Genetic testing is now available in North America for all of the known hereditary colorectal cancer genes. In addition, most of these tests have improved significantly in the past few years with the inclusion of techniques to detect large rearrangements. As a result, clinicians are in a better position than ever to help families with these syndromes to identify the underlying genetic cause. This identification will ensure that they receive appropriate management, and will enable their relatives to determine their precise risks and to tailor their cancer surveillance.

Clinical implications of the colorectal cancer risk associated with MUTYH mutation

PURPOSE

Biallelic mutations in the base excision DNA repair gene MUTYH predispose to colorectal cancer (CRC). Evidence that monoallelic mutations also confer an elevated CRC risk is controversial. Precise quantification of the CRC risk and the phenotype associated with MUTYH mutations is relevant to the counseling, surveillance, and clinical management of at-risk individuals.

METHODS

We analyzed a population-based series of 9,268 patients with CRC and 5,064 controls for the Y179C and G396D MUTYH mutations. We related genotypes to phenotype and calculated genotype-specific CRC risks.

RESULTS

Overall, biallelic mutation status conferred a 28-fold increase in CRC risk (95% CI,17.66 to 44.06); this accounted for 0.3% of CRCs in the cohort. Genotype relative risks of CRC were strongly age dependent, but penetrance was incomplete at age 60 years. CRC that developed in the context of biallelic mutations were microsatellite stable. Biallelic mutation carriers were more likely to have proximal CRC (P = 4.0 x 10(-4)) and synchronous polyps (P = 5.7 x 10(-9)) than noncarriers. The performance characteristics of clinicopathologic criteria for the identification of biallelic mutations are poor. Monoallelic mutation was not associated with an increased CRC risk (odds ratio, 1.07; 95% CI, 0.87 to 1.31).

CONCLUSION

The high risk and the propensity for proximal disease associated with biallielic MUTYH mutation justify colonoscopic surveillance. Although mutation screening should be directed to patients with APC-negative polyposis and early-onset proximal MSS CRC in whom detection rates will be highest, the expanded phenotype associated with MUTYH mutation needs to be recognized. There is no evidence than monoallelic mutation status per se is clinically important.

Introduction to molecular and clinical genetics of colorectal cancer syndromes

The understanding of molecular genetics in the field of gastroenterology has rapidly grown over the last two decades. In recent years many genes involved in the disorders of the gastrointestinal (GI) tract such as colorectal cancer (CRC) and inflammatory bowel disease have been identified. The elucidation of the molecular genetics of these diseases made it possible to study the high-penetrance susceptibility genes for disease-causing mutations with direct implications for relatives of affected individuals. The most immediate application of these advances is the opportunity of pre-symptomatic diagnosis in relatives of affected individuals by molecular genetic testing. In this article, the most commonly employed mutation detection procedures; the outcome and use of these tests in clinical practice are discussed. We focus on the three most common hereditary colorectal cancer syndromes (CCS): Lynch syndrome, familial adenomatous polyposis and MUTYH-associated polyposis.

Germline MutY human homologue mutations and colorectal cancer: a multisite case-control study

BACKGROUND & AIMS

The MutY human homologue (MYH) gene is a member of the base-excision repair pathway involved in the repair of oxidative DNA damage. The objective of this study was to determine colorectal cancer (CRC) risk associated with mutations in the MYH gene.

METHODS

A total of 3811 CRC cases and 2802 controls collected from a multisite CRC registry were screened for 9 germline MYH mutations; subjects with any mutation underwent screening of the entire MYH gene. Logistic regression was used to estimate age- and sex-adjusted odds ratios (AOR). Clinicopathologic and epidemiologic data were reviewed to describe the phenotype associated with MYH mutation status and assess for potential confounding and effect modification.

RESULTS

Twenty-seven cases and 1 control subject carried homozygous or compound heterozygous MYH mutations (AOR, 18.1; 95% confidence interval, 2.5-132.7). CRC cases with homozygous/compound heterozygous mutations were younger at diagnosis (P=.01), had a higher proportion of right-sided (P=.01), synchronous cancers (P<.01), and personal history of adenomatous polyps (P=.003). Heterozygous MYH mutations were identified in 87 CRC cases and 43 controls; carriers were at increased risk of CRC (AOR, 1.48; 95% confidence interval, 1.02-2.16). There was a higher prevalence of low-frequency microsatellite instability (MSI) in tumors from heterozygous and homozygous/compound heterozygous MYH mutation carriers (P=.02); MSI status modified the CRC risk associated with heterozygous MYH mutations (P interaction<.001).

CONCLUSIONS

Homozygous/compound heterozygous MYH mutations account for less than 1% of CRC cases. Heterozygous carriers are at increased risk of CRC. Further studies are needed to understand the possible interaction between the base excision repair and low-frequency MSI pathways.

MUTYH-associated polyposis

MUTYH-associated polyposis (MAP) is an autosomal recessive disorder characterised by adenomatous polyps of the colorectum and a very high risk of colorectal cancer. It appears to be at least as prevalent as autosomal dominant familial adenomatous polyposis (that is caused by truncating mutations in the APC gene) with which it shares important gastroenterological features. It was first recognised as recently as 2002 and its full phenotype and natural history are still being characterised. Key extracolonic manifestations include a predisposition to duodenal adenomas and cancer and a modest increase in risk for several extraintestinal tumours. Testing for mutations in the MUTYH gene is indicated in patients who have multiple colorectal adenomas or a family history suggestive of autosomal recessive colorectal cancer and for the siblings and spouses of patients with MAP in order to inform surveillance and treatment for patients and their families.

Pathological features of colorectal carcinomas in MYH-associated polyposis

AIMS

MYH is a DNA glycosylase in the base excision repair pathway. Germ-line biallelic mutations in the MYH gene are associated with the development of multiple colorectal adenomas and colorectal carcinoma (CRC). A slightly increased risk of CRC is suggested in monoallelic MYH mutation carriers. The aim was to characterize the histopathological features of carcinomas from biallelics and monoallelics.

METHODS AND RESULTS

Clinicopathological features of 57 colorectal carcinomas from 50 patients identified in familial CRC registries were recorded. These included 16 cancers from 14 MYH biallelics; 25 cancers from 22 MYH monoallelics; and 16 cancers from 14 controls. Carcinomas in biallelics demonstrated tubular, papillary or cribriform patterns as the predominant histological subtype, and main histological groups differed according to mutation status (P = 0.0053). All biallelic cancers were low grade, with high-grade tumours more common in monoallelics and controls (P = 0.002). Synchronous polyps were observed in 75% of biallelics, 33% of monoallelics and 43% of controls (P = 0.035). Serrated carcinoma was the predominant type in 12% (3/25) of the monoallelics but in none of the biallelics or controls. MYH immunohistochemistry failed to distinguish between groups.

CONCLUSIONS

Neither pathological features nor immunohistochemistry could predict the MYH mutation status of CRCs in this study.

Association between genetic polymorphisms of the base excision repair gene MUTYH and increased colorectal cancer risk in a Japanese population

The MUTYH gene encodes a DNA glycosylase that can initiate the base excision repair pathway and prevent G:C > T:A transversion by excising adenine mispaired with 8-hydroxyguanine. Biallelic germline mutations of MUTYH have been shown to predict familial and sporadic multiple colorectal adenomas and carcinomas, however, whether there is an association between single nucleotide polymorphisms (SNPs) of MUTYH and sporadic colorectal cancer (CRC) risk has remained unclear. In this study we investigated four MUTYH SNPs, IVS1+11C > T, IVS6+35G > A, IVS10-2A > G, and 972G > C (Gln324His), for an association with increased CRC risk in a population-based series of 685 CRC patients and 778 control subjects from Kyushu, Japan. A statistically significant association was demonstrated between IVS1+11T and increased CRC risk (odds ratio [OR]: 1.43; 95% confidence interval [CI]: 1.012-2.030; P = 0.042) and one of the five haplotypes based on the four SNPs, the IVS1+11T - IVS6+35G - IVS10-2A - 972C (TGAC) haplotype containing IVS1+11T, was demonstrated to be associated with increased CRC risk (OR, 1.43; 95% CI, 1.005-2.029; P = 0.046). Subsite-specific analysis showed that the TGAC haplotype was statistically significantly (P = 0.013) associated with an increased risk of distal colon, but not proximal colon or rectal cancer. Furthermore, IVS1+11C > T was found to be in complete linkage disequilibrium with -280G > A and 1389G > C (Thr463Thr). The results indicated that Japanese individuals with - 280A/IVS1+11T/1389C genotypes or the TGAC haplotype are susceptible to CRC.

Recently identified colon cancer predispositions: MYH and MSH6 mutations

Single-gene germline mutations conferring a high lifetime risk of colorectal cancer (CRC) account for up to 6% of all CRC cases. The most widely studied monogenic colorectal cancer syndromes include familial adenomatous polyposis (FAP) and Lynch syndrome. However, additional syndromes continue to be defined and new predisposition genes are continuing to be identified. Most recently, MYH-associated polyposis (MAP) and an "atypical Lynch syndrome" related to the presence of MSH6 mutations have been linked to an increased risk of CRC. In this review, we summarize basic information related to these newly recognized gene mutations, including the accumulating data on the prevalence and penetrance of deleterious mutations, as well as the management options for identified carriers and their families. Recognizing these heritable syndromes is essential and predictive genetic testing will continue to transform the field of cancer risk assessment by offering the opportunity to focus on more precise risk management and cancer prevention.

Colorectal adenomatous polyposis Associated with MYH mutations: genotype and phenotype characteristics

PURPOSE

Recent literature reports that several digestive diseases are associated with mutations in the base excision repair gene MYH. This study was designed to establish the prevalence of germ-line MYH mutations in a series of 56 consecutive patients with no detectable APC mutation and describe the phenotype of those with MYH mutations.

METHODS

MYH mutations were screened by DNA sequencing after polymerase chain reaction amplification of each exon. Clinical, endoscopic, and surgical data were collected for the tested patients.

RESULTS

MYH mutations were identified only in the group of patients with attenuated adenomatous polyposis with ten or more adenomatous polyps. The prevalence of MYH mutations was 34.4 percent (11 cases) in this subgroup of 30 patients. There were two homozygotes and eight compound heterozygotes. Only one patient had a monoallelic mutation. At least one of two mutational hot spots was identified in ten patients. Three patients presented with a family history of adenomatous polyposis in siblings, without vertical transmission. The median number of colorectal adenomatous polyps was 53 without preferential localization. Colorectal cancer was associated with polyposis in seven patients. Gastric and duodenal adenomas were diagnosed in one case. Ten of 11 patients underwent colectomy.

CONCLUSIONS

MYH mutations have been observed in one-third of patients with attenuated polyposis. The phenotype of the disease is similar to attenuated familial adenomatous polyposis. Upper gastrointestinal endoscopy also should be recommended. However, its transmission shows evidence of a recessive pattern.

Serrated pathway colorectal cancer in the population: genetic consideration

A significant proportion of colorectal cancer (CRC) develops through the serrated neoplasia pathway. Such tumours show a distinctive molecular phenotype of somatic BRAF mutations and widespread concordant methylation events in CpG islands (CIMP). These features are also observed in the polyps developing in individuals with hyperplastic polyposis syndrome (HPS). In HPS, multiple serrated polyps develop in the colorectum, and approximately 50% of cases present with at least one CRC. Observations of rare affected sibships including identical twins, suggest a recessive or co‐dominant mode of inheritance. In addition, up to 50% of individuals with HPS report a family history of CRC. At a population level, recent work has demonstrated that patients with serrated pathway cancers characterised by BRAF mutation are four times more likely to have a family history of CRC than patients with common CRC. These findings suggest an increased genetic predisposition for serrated pathway CRC in the wider population. We propose that HPS results from the inheritance of two putative co‐dominant alleles in approximately 1 in 2000 individuals. Therefore carriers of one co‐dominant allele may number up to 1 in 25, and it is likely that these carriers are at increased risk of CRC, accounting for, at least in part, the burden of serrated pathway CRC in the population. This proposition may have important implications for screening and prevention of CRC in individuals who have an increased risk for development of serrated pathway cancers, namely those with multiple, proximal, large or advanced serrated polyps, and their relatives.

Computational identification of candidate loci for recessively inherited mutation using high-throughput SNP arrays

MOTIVATION

Single nucleic polymorphisms (SNPs) are one of the most abundant genetic variations in the human genome. Recently, several platforms for high-throughput SNP analysis have become available, capable of measuring thousands of SNPs across the genome. Tools for analysing and visualizing these large genetic data sets in biologically relevant manner are rare. This hinders effective use of the SNP-array data in research on complex diseases, such as cancer.

RESULTS

We describe a computational framework to analyse and visualize SNP-array data, and link the results in relevant databases. Our major objective is to develop methods for identifying DNA regions that likely harbour recessive mutations. Thus, the algorithms are designed to have high sensitivity and the identified regions are ranked using a scoring algorithm. We have also developed annotation tools that automatically query gene IDs, exon counts, microarray probe IDs, etc. In our case study, we apply the methods for identifying candidate regions for recessively inherited colorectal cancer predisposition and suggest directions for wet-lab experiments.

AVAILABILITY

R-package implementation is available at http://www.ltdk.helsinki.fi/sysbio/csb/downloads/CohortComparator/

BRAF Mutations in Multiple Sebaceous Hyperplasias of Patients Belonging to MYH-Associated Polyposis Pedigrees

The characteristics of sebaceous gland hyperplasia (SGH) consist of yellowish or skin-colored papules and nodules. Chronic sun exposure and immunosuppressed conditions are the main environmental risk factors, whereas chronological aging regulated by hormones and molecular changes are the intrinsic risk factors. We have evaluated the contribution of BRAF, K-Ras, and N-Ras mutations to the pathogenesis of SGHs in four patients belonging to three MYH-associated polyposis (MAP) pedigrees. MAP is an autosomal-recessive disease characterized by multiple colorectal adenomas and cancer. Immunohistochemistry of mismatch repair and APC proteins was performed. DNA isolated from blood lymphocytes and formalin-fixed or paraffin-embedded SGHs was PCR amplified and sequenced. In the SGH patients, we detected T1796A heterozygous substitution (V600E) in the BRAF gene. Compound biallelic germline MYH mutations (Y165C/G382D, R168H/379delC, and Y90X/delGGA464) were detected in the MAP patients. In contrast to the majority of melanocytic lesions, activating hotspot mutations in BRAF have not been involved so far in the pathogenesis of SGH. BRAF mutation is not a specific marker of melanocytic cancerogenesis, and it can also be involved in SGHs. In both melanocytic and non-melanocytic skin tumors, BRAF mutation is linked to early tumorigenesis events.

Germline MYH mutations in a clinic-based series of Canadian multiple colorectal adenoma patients

OBJECTIVES

MYH is a member of the DNA base excision repair (BER) pathway and mutations of this gene predispose to the development of colorectal neoplasia in an autosomal recessive transmission pattern. Our objective was to determine the significance of MYH mutations in a series of Canadian patients with multiple adenomas.

METHODS

We screened for germline MYH mutations (by dHPLCO) in 20 clinic-based multiple adenoma patients who were adenomatous polyposis coli (APC) mutation-negative. Suspected mutations were confirmed by sequence analysis.

RESULTS

Six of 20 (30%) patients carried pathogenic biallelic MYH mutations, 1 Y165C homozygote and 5 compound heterozygotes of other sequence variants. We identified three novel variants, Q377X, 1314delA, and P281L, which are likely pathogenic. Twenty-nine relatives of the Y90X/1103delC compound heterozygous carrier were also screened for germline MYH mutations, and 1 homozygous and 14 heterozygous carriers were identified.

CONCLUSIONS

Among patients with multiple adenomas, biallelic MYH mutations account for approximately 30% of APC mutation negative cases and two thirds of these carry mutations other than the "common" Y165C and G382D variants. Clinical screening algorithms which focus only on the Y165C and G382D alleles are inadequate since additional pathogenic mutations may be identified by screening the entire gene.

Explaining the familial colorectal cancer risk associated with mismatch repair (MMR)-deficient and MMR-stable tumors

PURPOSE

There is a paucity of data quantifying the familial risk of colorectal cancer associated with mismatch repair (MMR)-deficient and MMR-stable tumors. To address this, we analyzed a population-based series of 1,042 colorectal cancer probands with verified family histories.

EXPERIMENTAL DESIGN

Constitutional DNA from probands was systematically screened for MYH variants and those with cancers displaying microsatellite instability (MSI) for germ-line MMR mutations; diagnoses of familial adenomatous polyposis and juvenile polyposis were established based on clinical phenotype and mutational analysis. Familial colorectal cancer risks were enumerated from age-, sex-, and calendar-specific population incidence rates. Segregation analysis was conducted to derive a model of the residual familial aggregation of colorectal cancer.

RESULTS

Germ-line predisposition to colorectal cancer was identified in 37 probands [3.4%; 95% confidence interval (95% CI), 2.4-4.6]: 29 with MLH1/MSH2 mutations, 2 with familial adenomatous polyposis, 1 with juvenile polyposis, and 5 with biallelic MYH variants. The risk of colorectal cancer in first-degree relatives of probands with MSI and MMR-stable cancers was increased 5.01-fold (95% CI, 3.73-6.59) and 1.31-fold (95% CI, 1.07-1.59), respectively. MSH2/MLH1 mutations were responsible for 50% of the overall excess familial risk and 80% of the risk associated with MSI cancers but 32% of the familial risk was unaccounted for by known loci. Genetic models based on major gene loci did not provide a better explanation of the residual familial aggregation than a simple polygenic model.

CONCLUSIONS

The information from our analyses should be useful in quantifying familial risks in clinical practice and in the design of studies to identify novel disease alleles.

Identification of MYH mutation carriers in colorectal cancer: a multicenter, case-control, population-based study

BACKGROUND & AIMS

Whereas it has conclusively been demonstrated that biallelic MutY human homolog (MYH) mutations confer a significant risk for colorectal cancer (CRC), the influence of monoallelic mutations remains controversial. Characterization of MYH-associated CRC is critical to identify individuals who might benefit from preventive strategies. This prospective, multicenter, case-control, population-based study was aimed at (1) establishing the CRC risk associated with specific germline MYH mutations and (2) devising a set of clinical criteria to identify MYH carriers among newly diagnosed CRC.

METHODS

Genotyping for Y165C and G382D was performed by TaqMan technology. Single-stranded conformation polymorphism analysis was performed in heterozygotes to screen for mutations in the entire gene. All individuals were re-screened for any additional pathogenic variant.

RESULTS

Biallelic and monoallelic MYH mutations were found in 8 (0.7%) and 19 (1.7%) of 1116 CRC patients, respectively. None of the 934 control subjects carried biallelic mutations, whereas 22 (2.3%) of them were monoallelic carriers. In a meta-analysis including all previous case-control studies, monoallelic MYH carriers were not at increased risk for CRC (odds ratio, 1.11; 95% confidence interval, 0.90-1.37), although a significant association was found with the Y165C mutation in either homozygotes or heterozygotes (odds ratio, 1.67; 95% confidence interval, 1.17-2.40). Furthermore, presence of more than 15 synchronous colorectal adenomas or CRC diagnosed before the age of 50 years was the most effective set of criteria for the identification of biallelic MYH mutation carriers.

CONCLUSIONS

This study proposes the first set of clinical criteria designed to identify CRC patients with biallelic MYH mutations, and it argues against an increased risk for monoallelic carriers.