Linkage analysis in a large Swedish family supports the presence of a susceptibility locus for adenoma and colorectal cancer on chromosome 9q22.32-31.1

Dominantly Inherited Hereditary Nonpolyposis Colorectal Cancer Not Caused by MMR Genes

In the past two decades, multiple studies have been undertaken to elucidate the genetic cause of the predisposition to mismatch repair (MMR)-proficient nonpolyposis colorectal cancer (CRC). Here, we present the proposed candidate genes according to their involvement in specific pathways considered relevant in hereditary CRC and/or colorectal carcinogenesis. To date, only pathogenic variants in RPS20 may be convincedly linked to hereditary CRC. Nevertheless, accumulated evidence supports the involvement in the CRC predisposition of other genes, including MRE11, BARD1, POT1, BUB1B, POLE2, BRF1, IL12RB1, PTPN12, or the epigenetic alteration of PTPRJ. The contribution of the identified candidate genes to familial/early onset MMR-proficient nonpolyposis CRC, if any, is extremely small, suggesting that other factors, such as the accumulation of low risk CRC alleles, shared environmental exposures, and/or gene-environmental interactions, may explain the missing heritability in CRC.

Linkage analysis revealed risk loci on 6p21 and 18p11.2-q11.2 in familial colon and rectal cancer, respectively

Colorectal cancer (CRC) is one of the major cancer types in the western world including Sweden. However, known genetic risk factors could only explain a limited part of heritability of the disease. Moreover, colon and rectal cancers are habitually discussed as one entity, colorectal cancer, although different carcinogenesis has been recognized. A genome-wide linkage scan in 32 colon- and 56 rectal cancer families from Sweden was performed based on 475 non-FAP/HNPCC patients genotyped using SNP arrays. A maximum HLOD of 2.50 at locus 6p21.1-p12.1 and a HLOD of 2.56 at 18p11.2 was obtained for colon and rectal cancer families, respectively. Exome sequencing over the regions of interest in 12 patients from six families identified 22 and 25 candidate risk variants for colon and rectal cancer, respectively. Haplotype association analysis in the two regions was carried out between additional 477 familial CRC cases and 4780 controls and suggested candidate haplotypes possibly associated with CRC risk. This study suggested two new linkage regions for colon cancer and rectal cancer with candidate predisposing variants. Further studies are required to elucidate the pathogenic mechanism of these regions and to pinpoint the causative genes.

Update on genetic predisposition to colorectal cancer and polyposis

The present article summarizes recent developments in the characterization of genetic predisposition to colorectal cancer (CRC). The main themes covered include new hereditary CRC and polyposis syndromes, non-CRC hereditary cancer genes found mutated in CRC patients, strategies used to identify novel causal genes, and review of candidate genes that have been proposed to predispose to CRC and/or colonic polyposis. We provide an overview of newly described genes and syndromes associated with predisposition to CRC and polyposis, including: polymerase proofreading-associated polyposis, NTHL1-associated polyposis, mismatch repair gene biallelic inactivation-related adenomatous polyposis (including MSH3- and MLH3-associated polyposes), GREM1-associated mixed polyposis, RNF43-associated serrated polyposis, and RPS20 mutations as a rare cause of hereditary nonpolyposis CRC. The implementation of next generation sequencing approaches for genetic testing has exposed the presence of pathogenic germline variants in genes associated with hereditary cancer syndromes not traditionally linked to CRC, which may have an impact on genetic testing, counseling and surveillance. The identification of new hereditary CRC and polyposis genes has not deemed an easy endeavor, even though known CRC-related genes explain a small proportion of the estimated familial risk. Whole-genome sequencing may offer a technology for increasing this proportion, particularly if applied on pedigree data allowing linkage type of analysis. The final section critically surveys the large number of candidate genes that have been recently proposed for CRC predisposition.

Evidence for GALNT12 as a moderate penetrance gene for colorectal cancer

Characterizing moderate penetrance susceptibility genes is an emerging frontier in colorectal cancer (CRC) research. GALNT12 is a strong candidate CRC-susceptibility gene given previous linkage and association studies, and inactivating somatic and germline alleles in CRC patients. Previously, we found rare segregating germline GALNT12 variants in a clinic-based cohort (N = 118) with predisposition for CRC. Here, we screened a new population-based cohort of incident CRC cases (N = 479) for rare (MAF ≤1%) deleterious germline GALNT12 variants. GALNT12 screening revealed eight rare variants. Two variants were previously described (p.Asp303Asn, p.Arg297Trp), and additionally, we found six other rare variants: five missense (p.His101Gln, p.Ile142Thr, p.Glu239Gln, p.Thr286Met, p.Val290Phe) and one putative splice-altering variant (c.732-8 G>T). Sequencing of population-matched controls (N = 400) revealed higher burden of these variants in CRC cases compared with healthy controls (P = 0.0381). We then functionally characterized the impact of substitutions on GALNT12 enzyme activity using in vitro-derived peptide substrates. Three of the newly identified GALNT12 missense variants (p.His101Gln, p.Ile142Thr, p.Val290Phe) demonstrated a marked loss (>2-fold reduction) of enzymatic activity compared with wild-type (P ≤ 0.05), whereas p.Glu239Gln exhibited a ∼2-fold reduction in activity (P = 0.077). These findings provide strong, independent evidence for the association of GALNT12 defects with CRC-susceptibility; underscoring implications for glycosylation pathway defects in CRC.

WISARD: workbench for integrated superfast association studies for related datasets

BACKGROUND

A Mendelian transmission produces phenotypic and genetic relatedness between family members, giving family-based analytical methods an important role in genetic epidemiological studies-from heritability estimations to genetic association analyses. With the advance in genotyping technologies, whole-genome sequence data can be utilized for genetic epidemiological studies, and family-based samples may become more useful for detecting de novo mutations. However, genetic analyses employing family-based samples usually suffer from the complexity of the computational/statistical algorithms, and certain types of family designs, such as incorporating data from extended families, have rarely been used.

RESULTS

We present a Workbench for Integrated Superfast Association studies for Related Data (WISARD) programmed in C/C++. WISARD enables the fast and a comprehensive analysis of SNP-chip and next-generation sequencing data on extended families, with applications from designing genetic studies to summarizing analysis results. In addition, WISARD can automatically be run in a fully multithreaded manner, and the integration of R software for visualization makes it more accessible to non-experts.

CONCLUSIONS

Comparison with existing toolsets showed that WISARD is computationally suitable for integrated analysis of related subjects, and demonstrated that WISARD outperforms existing toolsets. WISARD has also been successfully utilized to analyze the large-scale massive sequencing dataset of chronic obstructive pulmonary disease data (COPD), and we identified multiple genes associated with COPD, which demonstrates its practical value.

Two novel colorectal cancer risk loci in the region on chromosome 9q22.32

Highly penetrant cancer syndromes account for less than 5% of all cases with familial colorectal cancer (CRC), and other genetic contribution explains the majority of the genetic contribution to CRC. A CRC susceptibility locus on chromosome 9q has been suggested. In this study, families where risk of CRC was linked to the region, were used to search for predisposing mutations in all genes in the region. No disease-causing mutation was found. Next, haplotype association studies were performed in the region, comparing Swedish CRC cases (2664) and controls (4782). Two overlapping haplotypes were suggested. One 10-SNP haplotype was indicated in familial CRC (OR 1.4, p = 0.00005) and one 25-SNP haplotype was indicated in sporadic CRC (OR 2.2, p = 0.0000012). The allele frequencies of the 10-SNP and the 25-SNP haplotypes were 13.7% and 2.5% respectively and both included one RNA, RP11-332M4.1 and RP11-l80l4.2, in the non-overlapping regions. The sporadic 25-SNP haplotype could not be studied further, but the familial 10-SNP haplotype was analyzed in 61 additional CRC families, and 6 of them were informative for all markers and had the risk haplotype. Targeted sequencing of the 10-SNP region in the linked families identified one variant in RP11-332M4.1, suggestive to confer the increased CRC risk on this haplotype. Our results support the presence of two loci at 9q22.32, each with one RNA as the putative cause of increased CRC risk. These RNAs could exert their effect through the same, or different, genes/pathways, possibly through the regulation of neighboring genes, such as PTCH1, FANCC, DKFZP434H0512, ERCC6L2 or the processed transcript LINC00046.

Familial Colorectal Cancer Type X

The genetic background is unknown for the 50-60% of the HNPCC families, who fulfill the Amsterdam criteria, but do not have a mutation in an MMR gene, and is referred to as FCCTX. This study reviews the clinical, morphological and molecular characteristics of FCCTX, and discusses the molecular genetic methods used to localize new FCCTX genes, along with an overview of the genes and chromosomal areas that possibly relate to FCCTX. FCCTX is a heterogeneous group, mainly comprising cases caused by single high-penetrance genes, or by multiple low-penetrance genes acting together, and sporadic CRC cases. FCCTX differs in clinical, morphological and molecular genetic characteristics compared to LS, including a later age of onset, distal location of tumours in the colon, lower risk of developing extracolonic tumours and a higher adenoma/carcinoma ratio, which indicates a slower progression to CRC. Certain characteristics are shared with sporadic CRC, e.g. similarities in gene expression and a high degree of CIN+, with significanly increased 20q gain in FCCTX. Other molecular characteristics of FCCTX include longer telomere length and hypomethylation of LINE-1, both being a possible explanation for CIN+. Some genes in FCCTX families (RPS20, BMPR1A, SEMA4A) have been identified by using a combination of linkage analysis and sequencing. Sequencing strategies and subsequent bioinformatics are improving fast. Exome sequencing and whole genome sequencing are currently the most promising tools. Finally, the involvement of CNV’s and regulatory sequences are widely unexplored and would be interesting for further investigation in FCCTX.

Recent Discoveries in the Genetics of Familial Colorectal Cancer and Polyposis

The development of genome-wide massively parallel sequencing, ie, whole-genome and whole-exome sequencing, and copy number approaches has raised high expectations for the identification of novel hereditary colorectal cancer genes. Although relatively successful for genes causing adenomatous polyposis syndromes, both autosomal dominant and recessive, the identification of genes associated with hereditary non-polyposis colorectal cancer has proven extremely challenging, mainly because of the absence of major high-penetrance genes and the difficulty in demonstrating the functional impact of the identified variants and their causal association with tumor development. Indeed, most, if not all, novel candidate non-polyposis colorectal cancer genes identified so far lack corroborative data in independent studies. Here we review the novel hereditary colorectal cancer genes and syndromes identified and the candidate genes proposed in recent years as well as discuss the challenges we face.

The analysis of a large Danish family supports the presence of a susceptibility locus for adenoma and colorectal cancer on chromosome 11q24

Hereditary colorectal cancer accounts for approximately 30% of all colorectal cancers, but currently only 5% of these families can be explained by highly penetrant, inherited mutations. In the remaining 25% it is not possible to perform a gene test to identify the family members who would benefit from prophylactic screening. Consequently, all family members are asked to follow a screening program. The purpose of this study was to localize a new gene which causes colorectal cancer. We performed a linkage analysis using data from a SNP6.0 chip in one large family with 12 affected family members. We extended the linkage analysis with microsatellites (STS) and single nucleotide polymorphisms (SNP's) and looked for the loss of heterozygosity in tumour tissue. Furthermore, we performed the exome sequencing of one family member and we sequenced candidate genes by use of direct sequencing. Major rearrangements were excluded after karyotyping. The linkage analysis with SNP6 data revealed three candidate areas, on chromosome 2, 6 and 11 respectively, with a LOD score close to two and no negative LOD scores. After extended linkage analysis, the area on chromosome 6 was excluded, leaving areas on chromosome 2 and chromosome 11 with the highest possible LOD scores of 2.6. Two other studies have identified 11q24 as a candidate area for colorectal cancer susceptibility and this area is supported by our results.

Association of a let-7 miRNA binding region of TGFBR1 with hereditary mismatch repair proficient colorectal cancer (MSS HNPCC)

The purpose of this study was to identify novel colorectal cancer (CRC)-causing alleles in unexplained familial CRC cases. In order to do so, coding regions in five candidate genes (MGMT, AXIN2, CTNNB1, TGFBR1 and TGFBR2) were sequenced in 11 unrelated microsatellite-stable hereditary non-polyposis CRC (MSS HNPCC) cases. Selected genetic variants were genotyped in a discovery set of 27 MSS HNPCC cases and 85 controls. One genetic variant, rs67687202, in TGFBR1 emerged as significant (P = 0.002), and it was genotyped in a replication set of 87 additional MSS HNPCC-like cases and 338 controls where it was also significantly associated with MSS HNPCC cases (P = 0.041). In the combined genotype data, rs67687202 was associated with a moderate increase in CRC risk (OR = 1.68; 95% CI = 1.13-2.50; P = 0.010). We tested a highly correlated SNP rs868 in 723 non-familial CRC cases compared with 629 controls, and it was not significantly associated with CRC risk (P = 0.370). rs868 is contained in a let-7 miRNA binding site in the 3'UTR of TGFBR1, which might provide a functional basis for the association in MSS HNPCC. In luciferase assays, the risk-associated allele for rs868 was associated with half the luciferase expression in the presence of miRNA let-7b-5p compared with protective allele, suggesting more binding of let-7b-5p and less TGFBR1 expression. Thus, rs868 potentially is a CRC risk-causing allele. Our results support the concept that rs868 is associated with lower TGFBR1 expression thereby increasing CRC risk.

Exome sequencing in one family with gastric- and rectal cancer

Background

Heritable factors are well known to increase the risk of cancer in families. Known susceptibility genes account for a small proportion of all colorectal cancer cases. The aim of this study was to identify the genetic background in a family suggested to segregate a dominant cancer syndrome with a high risk of rectal- and gastric cancer. We performed whole exome sequencing in three family members, 2 with rectal cancer and 1 with gastric cancer and followed it up in additional family members, other patients and controls.

Results

We identified 12 novel non-synonymous single nucleotide variants, which were shared among 5 affected members of this family. The mutations were found in 12 different genes; DZIP1L, PCOLCE2, IGSF10, SUCNR1, OR13C8, EPB41L4B, SEC16A, NOTCH1, TAS2R7, SF3A1, GAL3ST1, and TRIOBP. None of the mutations was suggested as a high penetrant mutation. It was not possible to completely rule out any of the mutations as contributing to disease, although seven were more unlikely than the others. Neither did we rule out the effect of all thousands of intronic, intergenic and synonymous variants shared between the three persons used for exome sequencing.

Conclusions

We propose this family, suggested to segregate dominant disease, could be an example of complex inheritance.

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

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

Our results highlight the heterogeneity of FCCTX tumours and call into question the utility of using only clinical criteria to identify FCCTX cases.

Genetic predisposition to colorectal cancer: Where we stand and future perspectives

The development of colorectal cancer (CRC) can be influenced by genetic factors in both familial cases and sporadic cases. Familial CRC has been associated with genetic changes in high-, moderate- and low-penetrance susceptibility genes. However, despite the availability of current gene-identification techniques, the genetic causes of a considerable proportion of hereditary cases remain unknown. Genome-wide association studies of CRC have identified a number of common low-penetrance alleles associated with a slightly increased or decreased risk of CRC. The accumulation of low-risk variants may partly explain the familial risk of CRC, and some of these variants may modify the risk of cancer in patients with mutations in high-penetrance genes. Understanding the predisposition to develop CRC will require investigators to address the following challenges: the identification of genes that cause uncharacterized hereditary cases of CRC such as familial CRC type X and serrated polyposis; the classification of variants of unknown significance in known CRC-predisposing genes; and the identification of additional cancer risk modifiers that can be used to perform risk assessments for individual mutation carriers. We performed a comprehensive review of the genetically characterized and uncharacterized hereditary CRC syndromes and of low- and moderate-penetrance loci and variants identified through genome-wide association studies and candidate-gene approaches. Current challenges and future perspectives in the field of CRC predisposition are also discussed.

Little evidence for association between the TGFBR1*6A variant and colorectal cancer: a family-based association study on non-syndromic family members from Australia and Spain

Background

Genome-wide linkage studies have identified the 9q22 chromosomal region as linked with colorectal cancer (CRC) predisposition. A candidate gene in this region is transforming growth factor β receptor 1 (TGFBR1). Investigation of TGFBR1 has focused on the common genetic variant rs11466445, a short exonic deletion of nine base pairs which results in truncation of a stretch of nine alanine residues to six alanine residues in the gene product. While the six alanine (*6A) allele has been reported to be associated with increased risk of CRC in some population based study groups this association remains the subject of robust debate. To date, reports have been limited to population-based case–control association studies, or case–control studies of CRC families selecting one affected individual per family. No study has yet taken advantage of all the genetic information provided by multiplex CRC families.

Methods

We have tested for an association between rs11466445 and risk of CRC using several family-based statistical tests in a new study group comprising members of non-syndromic high risk CRC families sourced from three familial cancer centres, two in Australia and one in Spain.

Results

We report a finding of a nominally significant result using the pedigree-based association test approach (PBAT; p = 0.028), while other family-based tests were non-significant, but with a p-value <; 0.10 in each instance. These other tests included the Generalised Disequilibrium Test (GDT; p = 0.085), parent of origin GDT Generalised Disequilibrium Test (GDT-PO; p = 0.081) and empirical Family-Based Association Test (FBAT; p = 0.096, additive model). Related-person case–control testing using the “More Powerful” Quasi-Likelihood Score Test did not provide any evidence for association (M_QLS; p = 0.41).

Conclusions

After conservatively taking into account considerations for multiple hypothesis testing, we find little evidence for an association between the TGFBR1*6A allele and CRC risk in these families. The weak support for an increase in risk in CRC predisposed families is in agreement with recent meta-analyses of case–control studies, which estimate only a modest increase in sporadic CRC risk among 6*A allele carriers.

Linkage analysis in familial non-Lynch syndrome colorectal cancer families from Sweden

Family history is a major risk factor for colorectal cancer and many families segregate the disease as a seemingly monogenic trait. A minority of familial colorectal cancer could be explained by known monogenic genes and genetic loci. Familial polyposis and Lynch syndrome are two syndromes where the predisposing genes are known but numerous families have been tested without finding the predisposing gene. We performed a genome wide linkage analysis in 121 colorectal families with an increased risk of colorectal cancer. The families were ascertained from the department of clinical genetics at the Karolinska University Hospital in Stockholm, Sweden and were considered negative for Familial Polyposis and Lynch syndrome. In total 600 subjects were genotyped using single nucleotide polymorphism array chips. Parametric- and non-parametric linkage analyses were computed using MERLIN in all and subsets of families. No statistically significant result was seen, however, there were suggestive positive HLODs above two in parametric linkage analysis. This was observed in a recessive model for high-risk families, at locus 9q31.1 (HLOD=2.2, rs1338121) and for moderate-risk families, at locus Xp22.33 (LOD=2.2 and HLOD=2.5, rs2306737). Using families with early-onset, recessive analysis suggested one locus on 4p16.3 (LOD=2.2, rs920683) and one on 17p13.2 (LOD/HLOD=2.0, rs884250). No NPL score above two was seen for any of the families. Our linkage study provided additional support for the previously suggested region on chromosome 9 and suggested additional loci to be involved in colorectal cancer risk. Sequencing of genes in the regions will be done in future studies.

GALNT12 is not a major contributor of familial colorectal cancer type X

Previous evidence indicates that mutations in the GALNT12 gene might cause a fraction of the unexplained familial colorectal cancer (CRC) cases: GALNT12 is located in 9q22-33, in close proximity to a CRC linkage peak; and germline missense variants that reduce the enzymatic activity of the protein have been identified in CRC patients, some of them with familial CRC history. We hypothesized that mutations in GALNT12 might explain part of the high-risk families grouped as familial CRC type X (fCRC-X), that is, Amsterdam-positive families with mismatch repair proficient tumors. We sequenced the coding regions of the gene in 103 probands of fCRC-X families, finding no functionally relevant mutations. Our results rule out GALNT12 as a major high CRC susceptibility gene. Additional studies are required to provide further evidence about its role as a moderate/low susceptibility gene in familial aggregation of cancer.

Identification of novel variants in colorectal cancer families by high-throughput exome sequencing

BACKGROUND

Colorectal cancer (CRC) in densely affected families without Lynch Syndrome may be due to mutations in undiscovered genetic loci. Familial linkage analyses have yielded disparate results; the use of exome sequencing in coding regions may identify novel segregating variants.

METHODS

We completed exome sequencing on 40 affected cases from 16 multicase pedigrees to identify novel loci. Variants shared among all sequenced cases within each family were identified and filtered to exclude common variants and single-nucleotide variants (SNV) predicted to be benign.

RESULTS

We identified 32 nonsense or splice-site SNVs, 375 missense SNVs, 1,394 synonymous or noncoding SNVs, and 50 indels in the 16 families. Of particular interest are two validated and replicated missense variants in CENPE and KIF23, which are both located within previously reported CRC linkage regions, on chromosomes 1 and 15, respectively.

CONCLUSIONS

Whole-exome sequencing identified DNA variants in multiple genes. Additional sequencing of these genes in additional samples will further elucidate the role of variants in these regions in CRC susceptibility.

IMPACT

Exome sequencing of familial CRC cases can identify novel rare variants that may influence disease risk.

Colorectal cancer linkage on chromosomes 4q21, 8q13, 12q24, and 15q22

A substantial proportion of familial colorectal cancer (CRC) is not a consequence of known susceptibility loci, such as mismatch repair (MMR) genes, supporting the existence of additional loci. To identify novel CRC loci, we conducted a genome-wide linkage scan in 356 white families with no evidence of defective MMR (i.e., no loss of tumor expression of MMR proteins, no microsatellite instability (MSI)-high tumors, or no evidence of linkage to MMR genes). Families were ascertained via the Colon Cancer Family Registry multi-site NCI-supported consortium (Colon CFR), the City of Hope Comprehensive Cancer Center, and Memorial University of Newfoundland. A total of 1,612 individuals (average 5.0 per family including 2.2 affected) were genotyped using genome-wide single nucleotide polymorphism linkage arrays; parametric and non-parametric linkage analysis used MERLIN in a priori-defined family groups. Five lod scores greater than 3.0 were observed assuming heterogeneity. The greatest were among families with mean age of diagnosis less than 50 years at 4q21.1 (dominant HLOD = 4.51, α = 0.84, 145.40 cM, rs10518142) and among all families at 12q24.32 (dominant HLOD = 3.60, α = 0.48, 285.15 cM, rs952093). Among families with four or more affected individuals and among clinic-based families, a common peak was observed at 15q22.31 (101.40 cM, rs1477798; dominant HLOD = 3.07, α = 0.29; dominant HLOD = 3.03, α = 0.32, respectively). Analysis of families with only two affected individuals yielded a peak at 8q13.2 (recessive HLOD = 3.02, α = 0.51, 132.52 cM, rs1319036). These previously unreported linkage peaks demonstrate the continued utility of family-based data in complex traits and suggest that new CRC risk alleles remain to be elucidated.

A review of the genetic background and tumour profiling in familial colorectal cancer

Inherited predisposition plays a role in 10-30% of colorectal cancer (CRC) cases. Of the large families with a clearly positive family history of CRC, ∼40% is not affected by known CRC syndromes. The existence of families with unexplained forms of inherited CRC--familial CRC--suggests the presence of still unknown high- or moderate-risk CRC predisposing factors. While the genomic profiles of sporadic CRCs have been studied extensively, few studies have analysed the tumour profiles of hereditary or familial CRC. Here, we review recent advances in genomic tumour profiling in familial CRC in comparison with sporadic CRC. In addition, we discuss the role of known CRC risk factors in familial CRC.

Seeking genetic susceptibility variants for colorectal cancer: the EPICOLON consortium experience

The EPICOLON consortium was initiated in 1999 by the Gastrointestinal Oncology Group of the Spanish Gastroenterology Association. It recruited consecutive, unselected, population-based colorectal cancer (CRC) cases and control subjects matched by age and gender without personal or familial history of cancer all over Spain with the main goal of gaining knowledge in Lynch syndrome and familial CRC. This epidemiological, prospective and multicentre study collected extensive clinical data and biological samples from ∼2000 CRC cases and 2000 controls in Phases 1 and 2 involving 25 and 14 participating hospitals, respectively. Genetic susceptibility projects in EPICOLON have included candidate-gene approaches evaluating single-nucleotide polymorphisms/genes from the historical category (linked to CRC risk by previous studies), from human syntenic CRC susceptibility regions identified in mouse, from the CRC carcinogenesis-related pathways Wnt and BMP, from regions 9q22 and 3q22 with positive linkage in CRC families, and from the mucin gene family. This consortium has also participated actively in the identification 5 of the 16 common, low-penetrance CRC genetic variants identified so far by genome-wide association studies. Finishing their own pangenomic study and performing whole-exome sequencing in selected CRC samples are among EPICOLON future research prospects.

Inherited deleterious variants in GALNT12 are associated with CRC susceptibility

A recent report detailed the occurrence of both somatic and constitutional variants in the GALNT12 gene, located at 9q22.33, in some colorectal cancer (CRC) patients. In this study, we investigate the occurrence of inherited deleterious variants in GALNT12 in 118 families referred to a cancer genetics clinic. We discovered two deleterious variants (c.907G>A (p.Asp303Asn); c.1187A>G (p.Tyr396Cys)) in 4/118 probands. The variants, which were not found in 149 control individuals (P = 0.0376), cosegregate with CRC and/or adenomatous polyps in other family members. The probability by chance that cosegregation of c.907G>A with CRC and/or adenomatous polyps occurred, in the two pedigrees combined, was 1.56%. Although this study does not provide irrefutable evidence that GALNT12 variants are highly penetrant alleles that predispose to CRC in the majority of unexplained hereditary CRC families, it does provide additional evidence to support an important role of these variants in a proportion of this considerable high-risk group.

Debate about TGFBR1 and the susceptibility to colorectal cancer

Recent years have witnessed enormous progress in our understanding of the genetic predisposition to colorectal cancer (CRC). Estimates suggest that all or most genetic susceptibility mechanisms proposed so far, ranging from high-penetrance genes to low-risk alleles, account for about 60% of the population-attributable fraction of CRC predisposition. In this context, there is increasing interest in the gene encoding the transforming growth factor β receptor 1 (TGFBR1); first when over a decade ago a common polymorphism in exon 1 (rs11466445, TGFBR1*6A/9A) was suggested to be a risk allele for CRC, then when linkage studies identified the chromosomal region where the gene is located as susceptibility locus for familial CRC, and more recently when the allele-specific expression (ASE) of the gene was proposed as a risk factor for CRC. Published data on the association of TGFBR1 with CRC, regarding polymorphisms and ASE and including sporadic and familial forms of the disease, are often contradictory. This review gives a general overview of the most relevant studies in order to clarify the role of TGFBR1 in the field of CRC genetic susceptibility.

Linkage to chromosome 2q32.2-q33.3 in familial serrated neoplasia (Jass syndrome)

Causative genetic variants have to date been identified for only a small proportion of familial colorectal cancer (CRC). While conditions such as Familial Adenomatous Polyposis and Lynch syndrome have well defined genetic causes, the search for variants underlying the remainder of familial CRC is plagued by genetic heterogeneity. The recent identification of families with a heritable predisposition to malignancies arising through the serrated pathway (familial serrated neoplasia or Jass syndrome) provides an opportunity to study a subset of familial CRC in which heterogeneity may be greatly reduced. A genome-wide linkage screen was performed on a large family displaying a dominantly-inherited predisposition to serrated neoplasia genotyped using the Affymetrix GeneChip Human Mapping 10 K SNP Array. Parametric and nonparametric analyses were performed and resulting regions of interest, as well as previously reported CRC susceptibility loci at 3q22, 7q31 and 9q22, were followed up by finemapping in 10 serrated neoplasia families. Genome-wide linkage analysis revealed regions of interest at 2p25.2-p25.1, 2q24.3-q37.1 and 8p21.2-q12.1. Finemapping linkage and haplotype analyses identified 2q32.2-q33.3 as the region most likely to harbour linkage, with heterogeneity logarithm of the odds (HLOD) 2.09 and nonparametric linkage (NPL) score 2.36 (P = 0.004). Five primary candidate genes (CFLAR, CASP10, CASP8, FZD7 and BMPR2) were sequenced and no segregating variants identified. There was no evidence of linkage to previously reported loci on chromosomes 3, 7 and 9.

A two-phase case-control study for colorectal cancer genetic susceptibility: candidate genes from chromosomal regions 9q22 and 3q22

Background:

Colorectal cancer (CRC) is the second cause of cancer-related death in the Western world. Much of the CRC genetic risk remains unidentified and may be attributable to a large number of common, low-penetrance genetic variants. Genetic linkage studies in CRC families have reported additional association with regions 9q22–31, 3q21–24, 7q31, 11q, 14q and 22q. There are several plausible candidate genes for CRC susceptibility within the aforementioned linkage regions including PTCH1, XPA and TGFBR1 in 9q22–31, and EPHB1 and MRAS in 3q21–q24.

Methods:

CRC cases and matched controls were from EPICOLON, a prospective, multicentre, nationwide Spanish initiative, composed of two independent phases. Phase 1 corresponded to 515 CRC cases and 515 controls, whereas phase 2 consisted of 901 CRC cases and 909 controls. Genotyping was performed for 172 single-nucleotide polymorphisms (SNPs) in 84 genes located within regions 9q22–31 and 3q21–q24.

Results:

None of the 172 SNPs analysed in our study could be formally associated with CRC risk. However, rs1444601 (TOPBP1) and rs13088006 (CDV3) in region 3q22 showed interesting results and may have an effect on CRC risk.

Conclusions:

TOPBP1 and CDV3 genetic variants on region 3q22 may modulate CRC risk. Further validation and meta-analysis should be undertaken in larger CRC cohorts.

CLC and IFNAR1 are differentially expressed and a global immunity score is distinct between early- and late-onset colorectal cancer

Colorectal cancer (CRC) incidence increases with age, and early onset of the disease is an indication of genetic predisposition, estimated to cause up to 30% of all cases. To identify genes associated with early-onset CRC, we investigated gene expression levels within a series of young patients with CRCs who are not known to carry any hereditary syndromes (n=24; mean 43 years at diagnosis), and compared this with a series of CRCs from patients diagnosed at an older age (n=17; mean 79 years). Two individual genes were found to be differentially expressed between the two groups, with statistical significance; CLC was higher and IFNAR1 was less expressed in early-onset CRCs. Furthermore, genes located at chromosome band 19q13 were found to be enriched significantly among the genes with higher expression in the early-onset samples, including CLC. An elevated immune content within the early-onset group was observed from the differentially expressed genes. By application of outlier statistics, H3F3A was identified as a top candidate gene for a subset of the early-onset CRCs. In conclusion, CLC and IFNAR1 were identified to be overall differentially expressed between early- and late-onset CRC, and are important in the development of early-onset CRC.

No association between germline allele-specific expression of TGFBR1 and colorectal cancer risk in Caucasian and Ashkenazi populations

Background:

Germline allele-specific expression (ASE) of the TGFBR1 gene has been reported as a strong risk factor for colorectal cancer (CRC) with an odds ratio close to 9. Considering the potential implications of the finding, we undertook the task of validating the initial results in this study.

Methods:

Allele-specific expression was measured using the highly quantitative and robust technique of pyrosequencing. Individuals from two different populations were studied, one Caucasian-dominated and the other of Ashkenazi Jewish descent, with different sources of non-tumoral genetic material in each.

Results:

Our results showed no statistically significant differences in the degree of ASE between CRC patients and controls, considering ASE as either a quantitative or a binary trait. Using defined cutoff values to categorise ASE, 1.0% of blood lymphocytes from informative Israeli cases (total n=96) were ASE positive (median 1.00; range 0.76–1.31) and 2.2% of informative matched controls (total n=90) were ASE positive (median 1.00; range 0.76–1.87). Likewise, normal mucosae from Spanish patients (median 1.03; range: 0.68–1.43; n=75) did not show significant differences in the degree of ASE when compared with the Israeli patients or controls.

Conclusions:

Taken together, these results suggest that ASE of TGFBR1 does not confer an increased risk of CRC.

Comprehensive genetic analysis of seven large families with mismatch repair proficient colorectal cancer

Approximately 40% of colorectal cancer (CRC) families with a diagnosis of hereditary nonpolyposis CRC on the basis of clinical criteria are not a consequence of mismatch repair (MMR) deficiency. Such families provide supporting evidence for the existence of a hitherto unidentified highly penetrant gene mutation. To gain further understanding of MMR-competent familial colorectal cancer (FCC), we studied seven large families with an unexplained predisposition for CRC to identify genetic regions that could harbor CRC risk factors. First, we conducted a genome-wide linkage scan using 10K single-nucleotide polymorphism (SNP) arrays to search for disease loci. Second, we studied the genomic profiles of the tumors of affected family members to identify commonly altered genomic regions likely to harbor tumor suppressor genes. Finally, we studied the possible role of recently identified low-risk variants in the familial aggregation of CRC in these families. Linkage analysis did not reveal clear regions of linkage to CRC. However, our results provide support linkage to 3q, a region that has previously been linked to CRC susceptibility. Tumor profiling did not reveal any genomic regions commonly targeted in the tumors studied here. Overall, the genomic profiles of the tumors show some resemblance to sporadic CRC, but additional aberrations were also present. Furthermore, the FCC families did not appear to have an enrichment of low-risk CRC susceptibility loci. These data suggest that factors other than a highly penetrant risk factor, such as low or moderate-penetrance risk factors, may explain the increased cancer risk in a subset of familial CRCs.

Confirmation of linkage to and localization of familial colon cancer risk haplotype on chromosome 9q22

Genetic risk factors are important contributors to the development of colorectal cancer. Following the definition of a linkage signal at 9q22-31, we fine mapped this region in an independent collection of colon cancer families. We used a custom array of single-nucleotide polymorphisms (SNP) densely spaced across the candidate region, performing both single-SNP and moving-window association analyses to identify a colon neoplasia risk haplotype. Through this approach, we isolated the association effect to a five-SNP haplotype centered at 98.15 Mb on chromosome 9q. This haplotype is in strong linkage disequilibrium with the haplotype block containing HABP4 and may be a surrogate for the effect of this CD30 Ki-1 antigen. It is also in close proximity to GALNT12, also recently shown to be altered in colon tumors. We used a predictive modeling algorithm to show the contribution of this risk haplotype and surrounding candidate genes in distinguishing between colon cancer cases and healthy controls. The ability to replicate this finding, the strength of the haplotype association (odds ratio, 3.68), and the accuracy of our prediction model (approximately 60%) all strongly support the presence of a locus for familial colon cancer on chromosome 9q.

Distinct high resolution genome profiles of early onset and late onset colorectal cancer integrated with gene expression data identify candidate susceptibility loci

Background

Estimates suggest that up to 30% of colorectal cancers (CRC) may develop due to an increased genetic risk. The mean age at diagnosis for CRC is about 70 years. Time of disease onset 20 years younger than the mean age is assumed to be indicative of genetic susceptibility. We have compared high resolution tumor genome copy number variation (CNV) (Roche NimbleGen, 385 000 oligo CGH array) in microsatellite stable (MSS) tumors from two age groups, including 23 young at onset patients without known hereditary syndromes and with a median age of 44 years (range: 28-53) and 17 elderly patients with median age 79 years (range: 69-87). Our aim was to identify differences in the tumor genomes between these groups and pinpoint potential susceptibility loci. Integration analysis of CNV and genome wide mRNA expression data, available for the same tumors, was performed to identify a restricted candidate gene list.

Results

The total fraction of the genome with aberrant copy number, the overall genomic profile and the TP53 mutation spectrum were similar between the two age groups. However, both the number of chromosomal aberrations and the number of breakpoints differed significantly between the groups. Gains of 2q35, 10q21.3-22.1, 10q22.3 and 19q13.2-13.31 and losses from 1p31.3, 1q21.1, 2q21.2, 4p16.1-q28.3, 10p11.1 and 19p12, positions that in total contain more than 500 genes, were found significantly more often in the early onset group as compared to the late onset group. Integration analysis revealed a covariation of DNA copy number at these sites and mRNA expression for 107 of the genes. Seven of these genes, CLC, EIF4E, LTBP4, PLA2G12A, PPAT, RG9MTD2, and ZNF574, had significantly different mRNA expression comparing median expression levels across the transcriptome between the two groups.

Conclusions

Ten genomic loci, containing more than 500 protein coding genes, are identified as more often altered in tumors from early onset versus late onset CRC. Integration of genome and transcriptome data identifies seven novel candidate genes with the potential to identify an increased risk for CRC.

Beyond genome-wide association studies: genetic heterogeneity and individual predisposition to cancer

Genome-wide association studies (GWAS) using population-based designs have identified many genetic loci associated with risk of a range of complex diseases including cancer; however, each locus exerts a very small effect and most heritability remains unexplained. Family-based pedigree studies have also suggested tentative loci linked to increased cancer risk, often characterized by pedigree-specificity. However, comparison between the results of population- and family-based studies shows little concordance. Explanations for this unidentified genetic 'dark matter' of cancer include phenotype ascertainment issues, limited power, gene-gene and gene-environment interactions, population heterogeneity, parent-of-origin-specific effects, and rare and unexplored variants. Many of these reasons converge towards the concept of genetic heterogeneity that might implicate hundreds of genetic variants in regulating cancer risk. Dissecting the dark matter is a challenging task. Further insights can be gained from both population association and pedigree studies.

TGFBR1 variants TGFBR1(*)6A and Int7G24A are not associated with an increased familial colorectal cancer risk

Variants of the transforming growth factor-beta receptor type 1 (TGFBR1) gene, TGFBR1*6A and Int7G24A, have been suggested to act as low-penetrance tumour susceptibility alleles with TGFBR1*6A being causally responsible for some cases of familial colorectal cancer (CRC). We performed a case–control study of 262 unrelated familial CRC cases; 83 hereditary non-polyposis colorectal cancer (HNPCC) and 179 non-HNPCC. Patients were genotyped for TGFBR1*6A and Int7G24A and compared with 856 controls. Further, we screened the coding region of TGFBR1 in affected members of a large family with CRC linked to 9q22.32-31.1. TGFBR1*6A allelic frequency was not significantly different in all of the familial cases compared with controls (0.107 and 0.106, respectively; P=0.915). In a subgroup analysis allele frequencies were, however, different between HNPCC and non-HNPCC familial cases (0.157 and 0.084, respectively; P=0.013). TGFBR1*6A genotype did not influence age of onset. Int7G24A allele frequencies were similar in cases and controls. No germ-line mutation was identified in the family with CRC linked to this chromosomal region. Our study provides no substantial support for the hypothesis that the polymorphic variants TGFBR1*6A or Int7G24A contribute to familial CRC risk. We cannot, however, exclude the possibility that TGFBR1 variants have a modifying effect on inherited risk per se.

Analysis of families with Lynch syndrome complicated by advanced serrated neoplasia: the importance of pathology review and pedigree analysis

The identification of Lynch syndrome has been greatly assisted by the advent of tumour immunohistochemistry (IHC) for mismatch repair (MMR) proteins, and by the recognition of the role of acquired somatic BRAF mutation in sporadic MMR-deficient colorectal cancer (CRC). However, somatic BRAF mutation may also be present in the tumours in families with a predisposition to develop serrated polyps in the colorectum. In a subgroup of affected members in these families, CRCs emerge which demonstrate clear evidence of MMR deficiency with absent MLH1 staining and high-level microsatellite instability (MSI). This may result in these families being erroneously classified as Lynch syndrome, or conversely, an individual is considered "sporadic" due to the presence of a somatic BRAF mutation in a tumour. In this report, we describe two Lynch syndrome families who demonstrated several such inconsistencies. In one family, IHC deficiency of both MSH2 and MLH1 was demonstrated in tumours from different affected family members, presenting a confusing diagnostic picture. In the second family, MLH1 loss was observed in the lesions of both MLH1 mutation carriers and those who showed normal MLH1 germline sequence. Both families had Lynch syndrome complicated by an independently segregating serrated neoplasia phenotype, suggesting that in families such as these, tumour and germline studies of several key members, rather than of a single proband, are indicated to clarify the spectrum of risk.

Germline allele-specific expression of TGFBR1 confers an increased risk of colorectal cancer

Much of the genetic predisposition to colorectal cancer (CRC) in humans is unexplained. Studying a Caucasian-dominated population in the United States, we showed that germline allele-specific expression (ASE) of the gene encoding transforming growth factor-beta (TGF-beta) type I receptor, TGFBR1, is a quantitative trait that occurs in 10 to 20% of CRC patients and 1 to 3% of controls. ASE results in reduced expression of the gene, is dominantly inherited, segregates in families, and occurs in sporadic CRC cases. Although subtle, the reduction in constitutive TGFBR1 expression alters SMAD-mediated TGF-beta signaling. Two major TGFBR1 haplotypes are predominant among ASE cases, which suggests ancestral mutations, but causative germline changes have not been identified. Conservative estimates suggest that ASE confers a substantially increased risk of CRC (odds ratio, 8.7; 95% confidence interval, 2.6 to 29.1), but these estimates require confirmation and will probably show ethnic differences.

Deciphering the genetics of hereditary non-syndromic colorectal cancer

Previously we have localized to chromosome 3q21-q24, a predisposition locus for colorectal cancer (CRC), through a genome-wide linkage screen (GWLS) of 69 families without familial adenomatous polyposis or hereditary non-polyposis CRC. To further investigate Mendelian susceptibility to CRC, we extended our screen to include a further GWLS of an additional 34 CRC families. We also searched for a disease gene at 3q21-q24 by linkage disequilibrium mapping in 620 familial CRC cases and 960 controls by genotyping 1676 tagging SNPs and sequencing 30 candidate genes from the region. Linkage analysis was conducted using the Affymetrix 10K SNP array. Data from both GWLSs were pooled and multipoint linkage statistics computed. The maximum NPL score (3.01; P=0.0013) across all families was at 3q22, maximal evidence for linkage coming from families segregating rectal CRC. The same genomic position also yielded the highest multipoint heterogeneity LOD (HLOD) score under a dominant model (HLOD=2.79; P=0.00034), with an estimated 43% of families linked. In the case-control analysis, the strongest association was obtained at rs698675 (P=0.0029), but this was not significant after adjusting for multiple testing. Analysis of candidate gene mapping to the region of maximal linkage on 3q22 failed to identify a causal mutation. There was no evidence for linkage to the previously reported 9q CRC locus (NPL=0.95, P=0.23; HLOD(dominant)=0.40, HLOD(recessive)=0.20). Our findings are consistent with the hypothesis that variation at 3q22 contributes to the risk of CRC, but this is unlikely to be mediated through a restricted set of alleles.

Colorectal polyposes: from phenotype to diagnosis

The colorectal polyposes are uncommon and frequently present diagnostic difficulties. Although the final diagnostic arbiter is the demonstration of a germline mutation, this may not always be demonstrable, and some forms of colorectal polyposis have no known genetic basis. Therefore, an accurate description of the phenotype by the pathologist is central to the establishment of a working diagnosis. This can direct the search for the underlying genetic cause (if any) and is also essential for establishing the magnitude of risk of colorectal malignancy for the patient and the patient's relatives. The pathologist may be provided with only a small and selected sample of endoscopically resected polyps or with prodigious numbers of polyps (too many to sample) when receiving a surgical specimen. Each type of polyposis presents its own particular diagnostic problems that may relate to polyp numbers, gross recognition of small or flat polyps, incomplete development of the full phenotype at the stage of investigation, and the histological classification of unusual or mixed polyps. The aim of this review is to highlight the principles and pitfalls in achieving a comprehensive description of the various types of colorectal polyposis, including classical FAP, attenuated FAP, MUTYH- (formerly MYH-) associated polyposis (MAP), other presentations of multiple adenomas, Peutz-Jeghers syndrome (P-JS), juvenile polyposis syndrome (JPS), Cowden syndrome (CS), hereditary mixed polyposis syndrome (HMPS), and hyperplastic polyposis syndrome (HPS).

Genome-wide linkage scan for colorectal cancer susceptibility genes supports linkage to chromosome 3q

Background

Colorectal cancer is one of the most common causes of cancer-related mortality. The disease is clinically and genetically heterogeneous though a strong hereditary component has been identified. However, only a small proportion of the inherited susceptibility can be ascribed to dominant syndromes, such as Hereditary Non-Polyposis Colorectal Cancer (HNPCC) or Familial Adenomatous Polyposis (FAP). In an attempt to identify novel colorectal cancer predisposing genes, we have performed a genome-wide linkage analysis in 30 Swedish non-FAP/non-HNPCC families with a strong family history of colorectal cancer.

Methods

Statistical analysis was performed using multipoint parametric and nonparametric linkage.

Results

Parametric analysis under the assumption of locus homogeneity excluded any common susceptibility regions harbouring a predisposing gene for colorectal cancer. However, several loci on chromosomes 2q, 3q, 6q, and 7q with suggestive linkage were detected in the parametric analysis under the assumption of locus heterogeneity as well as in the nonparametric analysis. Among these loci, the locus on chromosome 3q21.1-q26.2 was the most consistent finding providing positive results in both parametric and nonparametric analyses Heterogeneity LOD score (HLOD) = 1.90, alpha = 0.45, Non-Parametric LOD score (NPL) = 2.1).

Conclusion

The strongest evidence of linkage was seen for the region on chromosome 3. Interestingly, the same region has recently been reported as the most significant finding in a genome-wide analysis performed with SNP arrays; thus our results independently support the finding on chromosome 3q.

Identification of susceptibility genes for cancer in a genome-wide scan: results from the colon neoplasia sibling study

Colorectal cancer (CRC) is the third most commonly diagnosed cancer in Americans and is the second leading cause of cancer mortality. Only a minority ( approximately 5%) of familial CRC can be explained by known genetic variants. To identify susceptibility genes for familial colorectal neoplasia, the colon neoplasia sibling study conducted a comprehensive, genome-wide linkage scan of 194 kindreds. Clinical information (histopathology, size and number of polyps, and other primary cancers) was used in conjunction with age at onset and family history for classification of the families into five phenotypic subgroups (severe histopathology, oligopolyposis, young, colon/breast, and multiple cancer) prior to analysis. By expanding the traditional affected-sib-pair design to include unaffected and discordant sib pairs, analytical power and robustness to type I error were increased. Sib-pair linkage statistics and Haseman-Elston regression identified 19 linkage peaks, with interesting results for chromosomes 1p31.1, 15q14-q22, 17p13.3, and 21. At marker D1S1665 (1p31.1), there was strong evidence for linkage in the multiple-cancer subgroup (p = 0.00007). For chromosome 15q14-q22, a linkage peak was identified in the full-sample (p = 0.018), oligopolyposis (p = 0.003), and young (p = 0.0009) phenotypes. This region includes the HMPS/CRAC1 locus associated with hereditary mixed polyposis syndrome (HMPS) in families of Ashkenazi descent. We provide compelling evidence linking this region in families of European descent with oligopolyposis and/or young age at onset (<or=51) phenotypes. We found linkage to BRCA2 in the colon/breast phenotypic subgroup and identified a second locus in the region of D21S1437 segregating with, but distinct from, BRCA2. Linkage to 17p13.3 at marker D17S1308 in the breast/colon subgroup identified HIC1 as a candidate gene. We demonstrated that using clinical information, unaffected siblings, and family history can increase the analytical power of a linkage study.

Gastrointestinal polyposes: clinical, pathological and molecular features

This article focuses mainly on noninflammatory epithelial polyposes, particularly the diagnostically important morphological and molecular features of the more recently recognized and/or more poorly understood conditions. One of the most important, but often neglected, of these is hyperplastic polyposis.

Is TGFBR1*6A a susceptibility allele for nonsyndromic familial colorectal neoplasia?

Our analysis definitely excludes the possibility of the TGFBR1*6A allele increasing the risk of colorectal neoplasia in our sample population. A recent study validating linkage of colorectal cancer to chromosome 9q also excluded the TGFBR1*6A allele as a disease-causing variant in that sample. We conclude that there remains an unidentified susceptibility locus in the region 9q22.2-31.2.