Familial Colorectal Cancer Type X Research Articles

Inherited BRCA1 and RNF43 pathogenic variants in a familial colorectal cancer type X family

AbstractGenetic susceptibility to familial colorectal cancer (CRC), including for individuals classified as Familial Colorectal Cancer Type X (FCCTX), remains poorly understood. We describe a multi-generation CRC-affected family segregating pathogenic variants in both BRCA1, a gene associated with breast and ovarian cancer and RNF43, a gene associated with Serrated Polyposis Syndrome (SPS). A single family out of 105 families meeting the criteria for FCCTX (Amsterdam I family history criteria with mismatch repair (MMR)-proficient CRCs) recruited to the Australasian Colorectal Cancer Family Registry (ACCFR; 1998–2008) that underwent whole exome sequencing (WES), was selected for further testing. CRC and polyp tissue from four carriers were molecularly characterized including a single CRC that underwent WES to determine tumor mutational signatures and loss of heterozygosity (LOH) events. Ten carriers of a germline pathogenic variant BRCA1:c.2681_2682delAA p.Lys894ThrfsTer8 and eight carriers of a germline pathogenic variant RNF43:c.988 C > T p.Arg330Ter were identified in this family. Seven members carried both variants, four of which developed CRC. A single carrier of the RNF43 variant met the 2019 World Health Organization (WHO2019) criteria for SPS, developing a BRAF p.V600 wildtype CRC. Loss of the wildtype allele for both BRCA1 and RNF43 variants was observed in three CRC tumors while a LOH event across chromosome 17q encompassing both genes was observed in a CRC. Tumor mutational signature analysis identified the homologous recombination deficiency (HRD)-associated COSMIC signatures SBS3 and ID6 in a CRC for a carrier of both variants. Our findings show digenic inheritance of pathogenic variants in BRCA1 and RNF43 segregating with CRC in a FCCTX family. LOH and evidence of BRCA1-associated HRD supports the importance of both these tumor suppressor genes in CRC tumorigenesis.

Germline heterozygous exons 8–11 pathogenic BARD1 gene deletion reported for the first time in a family with suspicion of a hereditary colorectal cancer syndrome: more than an incidental finding?

BackgroundColorectal cancer (CRC) is a highly prevalent disease in developed countries. Inherited Mendelian causes account for approximately 5% of CRC cases, with Lynch syndrome and familial adenomatous polyposis being the most prevalent forms. Scientific efforts are focused on the discovery of new candidate genes associated with CRC and new associations of phenotypes with well-established cancer-related genes. BRCA1-associated ring domain (BARD1) gene deleterious germline variants are associated with a moderate increase in the relative risk of breast cancer, but their association with other neoplasms, such as CRC, remains unclear.Case presentationWe present the case of a 49-year-old male diagnosed with rectal adenocarcinoma whose maternal family fulfilled Amsterdam clinical criteria for Lynch syndrome. Genetic test confirmed the presence in heterozygosis of a germline pathogenic deletion of exons 8–11 in BARD1 gene. The predictive genetic study of the family revealed the presence of this pathogenic variant in his deceased cancer affected relatives, confirming co-segregation of the deletion with the disease.ConclusionsTo the best of our knowledge, this is the first published work in which this BARD1 deletion is detected in a family with familial colorectal cancer type X (FCCTX) syndrome, in which the clinical criteria for Lynch syndrome without alteration of the DNA mismatch repair (MMR) system are fulfilled. Whether this incidental germline finding is the cause of familial colorectal aggregation remains to be elucidated in scientific forums. Patients should be carefully assessed in specific cancer genetic counseling units to account for hypothetical casual findings in other genes, in principle unrelated to the initial clinical suspicion, but with potential impact on their health.

New insights on familial colorectal cancer type X syndrome

Familial colorectal cancer type X (FCCTX) is a heterogeneous colorectal cancer predisposition syndrome that, although displays a cancer pattern similar to Lynch syndrome, is mismatch repair proficient and does not exhibit microsatellite instability. Besides, its genetic etiology remains to be elucidated. In this study we performed germline exome sequencing of 39 cancer-affected patients from 34 families at risk for FCCTX. Variant classification followed the American College of Medical Genetics and Genomics (ACMG) guidelines. Pathogenic/likely pathogenic variants were identified in 17.65% of the families. Rare and potentially pathogenic alterations were identified in known hereditary cancer genes (CHEK2), in putative FCCTX candidate genes (OGG1 and FAN1) and in other cancer-related genes such as ATR, ASXL1, PARK2, SLX4 and TREX1. This study provides novel important clues that can contribute to the understanding of FCCTX genetic basis.

Hereditary Colorectal Cancer and Polyposis Syndromes

The majority of cases of inherited colorectal cancer (CRC) are accounted for by two syndromes: Lynch syndrome and familial adenomatous polyposis (FAP). In the management of FAP, the role of prophylactic surgery is clearly defined, although the optimal procedure for an individual patient depends on a number of factors. In the management of Lynch syndrome, the indications for prophylactic procedures are emerging. The authors address the clinical evaluation, investigation findings, medical and surgical therapy, and extracolonic diseases of FAP, attenuated form of FAP (AFAP), MYH-associated polyposis, Lynch syndrome, familial colorectal cancer type X (FCCTX), hyperplastic polyposis syndrome, Peutz-Jeghers syndrome, and juvenile polyposis syndrome. AFAP has been described that is associated with fewer adenomas and later development of CRC compared with classic FAP. The AFAP phenotype occurs in less than 10% of FAP patients. The clinical criteria for AFAP are no family members with more than 100 adenomas before the age of 30 years and (1) at least two patients with 10 to 99 adenomas at age over 30 years or (2) one patient with 10 to 99 adenomas at age over 30 years and a first-degree relative with CRC with few adenomas. Given that polyposis has a later onset and the risk of CRC is less well established in AFAP, some authors question whether prophylactic colectomy is necessary in all AFAP patients. This review contains 26 tables and 173 references Keywords: Colorectal cancer, Lynch syndrome, hyperplastic polyp, Peutz-Jeghers syndrome, juvenile polyposis syndrome, familial adenomatous polyposis

Hereditary Colorectal Cancer and Polyposis Syndromes

The majority of cases of inherited colorectal cancer (CRC) are accounted for by two syndromes: Lynch syndrome and familial adenomatous polyposis (FAP). In the management of FAP, the role of prophylactic surgery is clearly defined, although the optimal procedure for an individual patient depends on a number of factors. In the management of Lynch syndrome, the indications for prophylactic procedures are emerging. The authors address the clinical evaluation, investigation findings, medical and surgical therapy, and extracolonic diseases of FAP, attenuated form of FAP (AFAP), MYH-associated polyposis, Lynch syndrome, familial colorectal cancer type X (FCCTX), hyperplastic polyposis syndrome, Peutz-Jeghers syndrome, and juvenile polyposis syndrome. AFAP has been described that is associated with fewer adenomas and later development of CRC compared with classic FAP. The AFAP phenotype occurs in less than 10% of FAP patients. The clinical criteria for AFAP are no family members with more than 100 adenomas before the age of 30 years and (1) at least two patients with 10 to 99 adenomas at age over 30 years or (2) one patient with 10 to 99 adenomas at age over 30 years and a first-degree relative with CRC with few adenomas. Given that polyposis has a later onset and the risk of CRC is less well established in AFAP, some authors question whether prophylactic colectomy is necessary in all AFAP patients. This review contains 26 tables and 173 references Keywords: Colorectal cancer, Lynch syndrome, hyperplastic polyp, Peutz-Jeghers syndrome, juvenile polyposis syndrome, familial adenomatous polyposis

Adenoma and colorectal cancer risks in Lynch syndrome, Lynch-like syndrome and familial colorectal cancer type X.

Lynch syndrome (LS), Lynch-like syndrome (LLS) and familial colorectal cancer type X (FCCX) are different entities of familial cancer predisposition leading to an increased risk of colorectal cancer (CRC). The aim of this prospective study was to characterise and to compare the risks for adenoma and CRC in these three risk groups. Data was taken from the registry of the German Consortium for Familial Intestinal Cancer. Patients were prospectively followed up in an intensified colonoscopic surveillance programme that included annual examinations. Cumulative risks for adenoma and CRC were calculated separately for LS, LLS and FCCX, and then for males and females. Multivariate Cox regression was used to analyse the independent contributions of risk group, mismatch repair gene (within LS), sex and previous adenoma. The study population comprised 1448 individuals (103 FCCX, 481 LLS and 864 LS). The risks were similar for colorectal adenomas, but different for first and metachronous CRC between the three risk groups. CRC risk was highest in LS, followed by LLS and lowest in FCCX. Male sex and a prevalent adenoma in the index colonoscopy were associated with a higher risk for incident adenoma and CRC. In patients with LS, CRC risks were particularly higher in female MSH2 than MLH1 carriers. Our study may support the development of risk-adapted surveillance policies in LS, LLS and FCCX.

A practical screening strategy for Lynch syndrome and Lynch syndrome mimics in colorectal cancer.

The objective of the study is to provide an efficient and practical screening strategy to distinguish a broader spectrum of Lynch syndrome (LS) and LS mimics-associated colorectal cancer (CRC), including Lynch-like syndrome (LLS), constitutional mismatch repair-deficiency, familial CRC type X (FCCTX), and polymerase proofreading-associated polyposis syndrome. 1294 cases of CRC samples were detected mismatch repair (MMR) status using immunohistochemistry (IHC) staining, in which the cases with MLH1-deficient CRC underwent BRAF mutation analysis by IHC. Following the personal and/or family history survey, next-generation sequencing (NGS) was used to detect gene variants. 1294 CRC patients were dichotomized into tumors caused by a deficient MMR (dMMR) system and a proficient MMR (pMMR) system after MMR status analysis. 45 patients with suspected sporadic dMMR CRC were then separated from MLH1-deficient CRC though BRAF mutation status analysis by IHC. Following the personal and/or family history survey for 1294 patients, as well as germline genetic testing by NGS, 34 patients were diagnosed as LS (8 cases), SLS (13 cases), LLS ( 6 cases), FCCTX (3 cases), and sporadic CRC (4 cases). Our screening strategy, which consists of clinical and molecular analyses, is expected to improve the screening efficiency and management for the LS and LS mimics.

Comparison Between Familial Colorectal Cancer Type X and Lynch Syndrome: Molecular, Clinical, and Pathological Characteristics and Pedigrees.

ObjectiveThis study aimed to compare the molecular, clinical, and pathological characteristics and pedigrees of familial colorectal cancer type X (FCCTX) with those of Lynch syndrome (LS) to provide a theoretical basis for the management of FCCTX.MethodsOverall, 46 cases of FCCTX and 47 LS probands and affected families were enrolled between June 2008 and September 2018 for this study. Multigene cancer panel tests that included 139 genes were performed for all patients, and variants in each group were described. The clinical, pathological, and pedigree characteristics were also compared between the two groups.ResultsIn total, 42 variants were detected in 27 (58.7%) cases in the FCCTX group, with BRCA1, BRCA2, POLE, POLD1, ATR, and ATM being the most frequently mutated genes. The mean onset age of colorectal cancer (CRC) was significantly older in the FCCTX group than in the LS group (53.57 ± 12.88 years vs. 44.36 ± 11.26 years, t = −9.204, p < 0.001). The proportion of patients with rectal cancer was also higher in the FCCTX group than in the LS group [43.5% (20/46) vs. 10.6% (5/47), χ2 = 12.823, p = 0.005]. Within a median follow-up time of 53.9 ± 37.0 months, the proportion of patients who developed metachronous CRC was significantly higher in the LS group than in the FCCTX group [34.0% (16/47) vs. 13.0% (6/46), χ2 = 5.676, p = 0.017]. When comparing pedigrees, older age at cancer onset and rectal cancer clustering were observed in the FCCTX families. A higher prevalence in male patients was also observed in the FCCTX families.ConclusionFCCTX is an entity distinct from LS, but its genetic etiology remains unknown. A larger multigene panel would be recommended for determining the underlying pathogenic variants. Considering the pathology and moderate penetrance of the CRC link to FCCTX, less stringent surgical treatments and colonoscopy surveillance would be preferable. Rectum preference is a typical feature of FCCTX. Colonoscopy surveillance in FCCTX families could be less intensive, and more attention should be given to male members.

Risks of Colorectal Cancer and Cancer-Related Mortality in Familial Colorectal Cancer Type X and Lynch Syndrome Families.

The risk of cancers is well characterized in Lynch syndrome (LS) families but has been less studied in familial colorectal cancer type X (FCCTX) families. In this article, we compare the risk estimates of first and second colorectal cancers (CRCs) in 168 FCTTX and 780 LS families recruited through the Colon Cancer Family Registry as well as the risk of cancer-related deaths and disease-free survival (DFS) after a first CRC. Our methodology is based on a survival analysis approach, developed specifically to model the occurrence of successive cancers (ie, first and second CRCs) in the presence of competing risk events (ie, death from any causes). We found an excess risk of first and second CRC in individuals with LS compared to FCCTX family members. However, for an average age at first CRC of 60 years in FCCTX families and 50 years in LS families, the DFS rates were comparable in men but lower in women from FCCTX vs LS families, eg , 75.1% (95% confidence interval [CI] = 69.0% to 80.9%) vs 78.9% (95% CI = 76.3% to 81.3%) for the 10-year DFS. The 10-year risk of cancer-related death was higher in FCCTX families vs LS families, eg, 15.4% in men (95% CI = 10.9% to 19.8%) and 19.3% in women (95% CI = 13.6% to 24.7%) vs 8.9% (95% CI = 7.5% to 11.4%) and 8.7% (95% CI = 7.1% to 10.8%), respectively. Individuals with CRCs arising in the context of FCCTX do not experience the same improved DFS and overall survival of those with LS, and that difference may be relevant in management decisions.

Impact of colonoscopic screening in Familial Colorectal Cancer Type X.

BackgroundHereditary Non‐Polyposis Colorectal cancer is caused by Lynch Syndrome (LS; an autosomal dominant condition) or by Familial Colorectal Cancer Type‐X (FCCTX; a condition of high family risk that fulfills Amsterdam criteria). The lifetime risk of developing colorectal cancer (CRC) in FCCTX family members is high and CRC occurs later than in LS.MethodsTo determine the impact of primary prevention colonoscopic screening in asymptomatic first‐degree relatives of incident CRC cases in 20 families with FCCTX, we compared cancer incidence and survival in 79 males and 83 females, assumed to be at 50% risk of inheriting a genetic CRC susceptibility factor, who entered screening to an unscreened control group from the families, matched for age at entry into screening and for sex.ResultsIn males, median age at entry into screening was 44.8 years, median follow‐up 12.4 years, 12% developed CRC, and 46% died after 30 years of follow‐up. Compared to the unscreened group, relative risk of CRC was 0.27 (95% confidence intervals (CI) 0.10–0.71). In screened females, comparable results were 44.5 years at entry, 11.2 years of follow‐up, 7.1% developed CRC, and 7.2% died after 30 years of follow‐up. The relative risk of CRC compared to the unscreened group was 0.19 (95% CI 0.07–0.48).ConclusionPrimary prevention screening colonoscopy in asymptomatic family members significantly decreased the risk of CRC in FCCTX.

Differential expression of CK20, \u03b2-catenin, and MUC2/5AC/6 in Lynch syndrome and familial colorectal cancer type X

BackgroundHereditary non-polyposis colorectal cancer comprises Lynch syndrome and familial colorectal cancer type X (FCCTX). Differences in genetics, demographics and histopathology have been extensively studied. The purpose of this study is to characterize their immunoprofile of markers other than MMR proteins.MethodsWe compared the expression patterns of cytokeratins (CK7 and CK20), mucins (MUC2/5 AC/6), CDX2 and β-catenin in Lynch syndrome and FCCTX.ResultsDifferences were identified for CK20 and nuclear β-catenin, which were significantly more often expressed in FCCTX than in Lynch syndrome (p < 0.001), whereas MUC2, MUC5AC and MUC6 were overexpressed in Lynch syndrome tumors compared with FCCTX tumors (p = 0.001, < 0.01, and < 0.001, respectively). We observed no differences in the expression patterns of CK7 and CDX2.ConclusionsIn summary, we identified significant differences in the immunoprofiles of colorectal cancers linked to FCCTX and Lynch syndrome with a more sporadic-like profile in the former group and a more distinct profile with frequent MUC6 positivity in the latter group.

Screening of BMPR1a for pathogenic mutations in familial colorectal cancer type X families from Newfoundland.

The Canadian province of Newfoundland and Labrador (NL) reports one of the highest incidence rates of familial colorectal cancer (CRC) worldwide. The NL population is an invaluable resource for studying genetic disorders because of a unique ancestry, and a willingness to participate in research studies. Familial colorectal cancer type X (FCCTX) describes a cluster of families with strong predisposition for CRC, of unknown etiology. A putative link between FCCTX and BMPR1a mutations has been identified in the Finnish population; however these findings have not been independently replicated. To investigate a potential connection between BMPR1a and FCCTX, we screened a cohort of 22 probands from unrelated NL FCCTX families using Sanger sequencing. This analysis did not independently replicate findings seen in Finland; as no candidate pathogenic BMPR1a mutations were uncovered. Our findings highlight that BMPR1a mutations are not a major contributor of FCCTX incidence in NL. Further investigation of additional FCCTX populations may assist in delineating a role for BMPR1a, if any, in FCCTX globally.

Germline INDELs and CNVs in a cohort of colorectal cancer patients: their characteristics, associations with relapse-free survival time, and potential time-varying effects on the risk of relapse.

INDELs and CNVs are structural variations that may play roles in cancer susceptibility and patient outcomes. Our objectives were a) to computationally detect and examine the genome‐wide INDEL/CNV profiles in a cohort of colorectal cancer patients, and b) to examine the associations of frequent INDELs/CNVs with relapse‐free survival time. We also identified unique variants in 13 Familial Colorectal Cancer Type X (FCCX) cases. The study cohort consisted of 495 colorectal cancer patients. QuantiSNP and PennCNV algorithms were utilized to predict the INDELs/CNVs using genome‐wide signal intensity data. Duplex PCR was used to validate predictions for 10 variants. Multivariable Cox regression models were used to test the associations of 106 common variants with relapse‐free survival time. Score test and the multivariable Cox proportional hazards models with time‐varying coefficients were applied to identify the variants with time‐varying effects on the relapse‐free survival time. A total of 3486 distinct INDELs/CNVs were identified in the patient cohort. The majority of these variants were rare (83%) and deletion variants (81%). The results of the computational predictions and duplex PCR results were highly concordant (93–100%). We identified four promising variants significantly associated with relapse‐free survival time (P < 0.05) in the multivariable Cox proportional hazards regression models after adjustment for clinical factors. More importantly, two additional variants were identified to have time‐varying effects on the risk of relapse. Finally, 58 rare variants were identified unique to the FCCX cases; none of them were detected in more than one patient. This is one of the first genome‐wide analyses that identified the germline INDEL/CNV profiles in colorectal cancer patients. Our analyses identified novel variants and genes that can biologically affect the risk of relapse in colorectal cancer patients. Additionally, for the first time, we identified germline variants that can potentially be early‐relapse markers in colorectal cancer.

Outcome of 24 years national surveillance in different hereditary colorectal cancer subgroups leading to more individualised surveillance

BackgroundIndividuals with hereditary non-polyposis colorectal cancer (HNPCC) have a high risk of colorectal cancer (CRC). The benefits of colonic surveillance in Lynch syndrome and Amsterdam-positive (familial CRC type X familial...

Clinicopathological differences between familial colorectal cancer type X and sporadic cancer in an isolated area of spain.

Very few studies have compared the epidemiological characteristics of patients with familial colorectal cancer Type X (FCCTX) with those of sporadic colorectal cancer (S-CRC). The aim of this study was to compare clinicopathological characteristics and survival between FCCTX and S-CRC in patients from a historically isolated geographical region. A retrospective study was carried out of patients with S-CRC and FCCTX treated in the Canary Islands. Family and personal history of colorectal cancer (CRC) were recorded, together with genetic (microsatellite instability), immunohistochemical and clinical variables. Forty-eight (10.6%) of 451 patients were classified as FCCTX and the remaining 403 (89.4%) as S-CRC. Age at the diagnosis of tumour was significantly lower in FCCTX than in S-CRC (64.06±12.65years vs 69.13±10.80 years; P=0.01; Z=-2.48). Patients with FCCTX had a larger number of synchronous tumours (P=0.09). Recurrence was significantly higher in FCCTX than in S-CRC (18.7% vs 8.6%; P=0.01). Survival correlated significantly with the number of first-degree and second-degree relatives with CRC (P=0.04; OR:1.368, 95% CI: 1.01-1.84, and P=0.04; OR:1.363, 95% CI: 1.08-1.65) and with the total number of cases of CRC in the immediate family (P<0.01; OR:1.377, 95% CI: 1.17-1.61). Recurrence-free time was significantly lower in patients with FCCTX (log-rank=0.01). Significant differences were found in several demographic and clinicopathological variables between patients with FCCTX and patients with S-CRC. These included increased tumour presentation under the age of 50years and a higher recurrence rate in patients with FCCTX, suggesting an increased risk of CRC in this group.

Abstract 2745: Exome sequencing analysis of 41 patients with Familial Colorectal Cancer Type X (FCCTX)

Abstract Colorectal cancer (CRC) is the second most common cancer. About 10% of CRC are hereditary including familial adenomatous polyposis (FAP), hereditary non-polyposis colorectal cancer (HNPCC), and rare syndromes. While genetics of FAP and rare syndromes is well studied (APC, STK11, AXIN2), only ∼40-50% of HNPCC have identifiable DNA mismatch-repair gene defects. CRC cases fulfilling Amsterdam Criteria I for HNPCC with normal DNA mismatch repair and elevated risk of microsatellite-stable CRC are called Familial Colorectal Cancer Type X (FCCTX). Compared to HNPCC, FCCTX patients are older, with left-sided CRC, and frequent polyps. We hypothesize that FCCTX is a dominant Mendelian cancer syndrome with incomplete penetrance caused by rare, family-specific mutations in oncogenes and tumor suppressors. To identify novel mutations and genes involved in FCCTX, we performed germline exome sequencing of microsatellite-stable familial CRC from Molecular Epidemiology of Colorectal Cancer (MECC) study, a population-based, case-control CRC study in Northern Israel. We selected 41 patients from 38 FCCTX families with extensive family history of microsatellite stable (MSS) or microsatellite instable low (MSI-Low) CRC. Patients were Ashkenazi Jewish, Sephardi Jewish, Europeans, Druze, and Arabs. Similar to previous studies, stomach cancer was second most common in the families, and left-sided CRC was more prevalent. Exome sequencing of all patients generated 52,722 variants. Stepwise filtering analysis was applied to identify candidate variants and genes. We selected all novel and rare (minor allele frequency &amp;lt;0.001) functional variants in cancer-related genes from literature and cancer databases (COSMIC and TCGA). In line with dominant inheritance, only heterozygous variants predicted to be deleterious by multiple bioinformatic tools were selected. We identified 627 variants in 387 genes. Gene enrichment analysis showed regulation of apoptosis and cell cycle, DNA repair, cell adhesion, and cell surface receptor linked signal transduction. As expected, we found APC*I1307K founder mutation in three Ashkenazi Jewish patients, one novel APC mutation (p.1289_1291del) in a non-Jewish European patient, and found a mutation in MSH6. We identified three promising candidate genes and performed segregation analysis in families. Our preliminary data suggest several novel candidate genes for FCCTX, although older age at onset and incomplete penetrance complicate the interpretation of the results. Further population-based and family-based studies are being conducted to confirm our findings. Citation Format: Marilena Melas, Hung N. Luu, Gad Rennert, Flavio Lejbkowicz, Stephen B. Gruber, Georgia L. Wiesner, Leon Raskin. Exome sequencing analysis of 41 patients with Familial Colorectal Cancer Type X (FCCTX). [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2745. doi:10.1158/1538-7445.AM2015-2745

Genome-wide linkage analysis and tumoral characterization reveal heterogeneity in familial colorectal cancer type X.

Familial colorectal cancer type X (FCCTX) fulfils clinical criteria defining Lynch syndrome (LS), but is not related to germline mutations in DNA mismatch-repair genes. Its aetiology remains unexplained and there is little evidence of involvement of the common colorectal carcinogenetic pathways. We aimed to identify susceptibility loci and gain insights into carcinogenic pathways involved FCCTX tumour development. We performed a linkage analysis in 22 FCCTX families. We also constructed a tissue microarray in order to define an immunohistochemical (IHC) profile for FCCTX tumours (N = 27) by comparing them to three other types of colorectal tumors: LS (N = 18), stable early-onset (N = 31) and other sporadic disease (N = 80). Additionally, we screened for BRAF/KRAS mutations and determined CpG island methylator phenotype (CIMP) status for all FCCTX tumours. We found suggestive evidence of linkage at four chromosomal regions; 2p24.3, 4q13.1, 4q31.21 and 12q21.2-q21.31. We screened genes in 12q21 and ruled out the implication of RASSF9 and NTS, good candidates due to their potential involvement in carcinogenesis and colorectal epithelium development. Based on IHC profiles FCCTX tumours did not form a single, exclusive cluster. They were clearly different from LS, but very similar to stable early onset tumours. The CIMP and chromosomal instability pathways were implicated in one-third and one-quarter of FCCTX cases, respectively. The remaining cases did not have alterations in any known carcinogenic pathways. Our results highlight the heterogeneity of FCCTX tumours and call into question the utility of using only clinical criteria to identify FCCTX cases.

Germline variants in the SEMA4A gene predispose to familial colorectal cancer type X.

Familial colorectal cancer type X (FCCTX) is characterized by clinical features of hereditary non-polyposis colorectal cancer with a yet undefined genetic background. Here we identify the SEMA4A p.Val78Met germline mutation in an Austrian kindred with FCCTX, using an integrative genomics strategy. Compared with wild-type protein, SEMA4AV78M demonstrates significantly increased MAPK/Erk and PI3K/Akt signalling as well as cell cycle progression of SEMA4A-deficient HCT-116 colorectal cancer cells. In a cohort of 53 patients with FCCTX, we depict two further SEMA4A mutations, p.Gly484Ala and p.Ser326Phe and the single-nucleotide polymorphism (SNP) p.Pro682Ser. This SNP is highly associated with the FCCTX phenotype exhibiting increased risk for colorectal cancer (OR 6.79, 95% CI 2.63 to 17.52). Our study shows previously unidentified germline variants in SEMA4A predisposing to FCCTX, which has implications for surveillance strategies of patients and their families.

BRCA2 gene: a candidate for clinical testing in familial colorectal cancer type X.

Familial colorectal cancer type X (FCCX) encompasses a group of families with dominant inheritance pattern of colorectal cancer (CRC) but no alteration in any known CRC susceptibility gene. Therefore, the explanation of their susceptibility is a priority to offer an accurate genetic counseling. We screened the 27 coding exons and exon-intron boundaries of BRCA2 in 48 FCCX probands. We identified 29 variants including a frameshift mutation. Deleterious variant c.3847_3848delGT p.(Val1283Lysfs*2) showed cosegregation with disease as well as loss of heterozygosity (LOH) in CRC tumor DNA. This is the first evidence of germline BRCA2 pathogenic mutation associated with CRC risk. Furthermore, missense variants c.502C>A p.(Pro168Thr), c.5744C>T p.(Thr1915Met) and c.7759C>T p.(Leu2587Phe) were proposed as candidate risk alleles based on cosegregation, LOH tumor analysis and in silico testing.

Germline Mutation of RPS20, Encoding a Ribosomal Protein, Causes Predisposition to Hereditary Nonpolyposis Colorectal Carcinoma Without DNA Mismatch Repair Deficiency

Little is known about the genetic factors that contribute to familial colorectal cancer type X (FCCX), characterized by hereditary nonpolyposis colorectal carcinoma with no mismatch repair defects. Genetic linkage analysis, exome sequencing, tumor studies, and functional investigations of 4 generations of a FCCX family led to the identification of a truncating germline mutation in RPS20, which encodes a component (S20) of the small ribosomal subunit and is a new colon cancer predisposition gene. The mutation was associated with a defect in pre–ribosomal RNA maturation. Our findings show that mutations in a gene encoding a ribosomal protein can predispose individuals to microsatellite-stable colon cancer. Evaluation of additional FCCX families for mutations in RPS20 and other ribosome-associated genes is warranted.