Clinical and screening implications of the I1307K adenomatous polyposis coli gene variant in Israeli Ashkenazi Jews with familial colorectal neoplasia. Evidence for a founder effect

BACKGROUND: The authors previously found the I1307K adenomatous polyposis coli (APC) gene variant in 5% of Ashkenazi control participants, in 15.4% of those who had familial colorectal neoplasia, but also in 1.6% of non-Ashkenazi control participants. In this study, they evaluated its use in a screening program for familial colorectal neoplasia and examined for a founder effect. METHODS: Consecutive Ashkenazim with a personal and/or family history of colorectal neoplasia had the DNA test. Markers flanking the APC gene were examined in Ashkenazi and non-Ashkenazi I1307K carriers and noncarriers. RESULTS: Among 718 persons, I1307K occurred in 6.2% of Ashkenazi participants, in 1.5% of non-Ashkenazi control participants (P = 0.02), and in 10.7% of Ashkenazim with familial neoplasia (relative risk, 1.73 [not significant compared with controls]; 95% confidence interval, 0.7-3.2). Colorectal neoplasia was detected in carriers at a younger age (P < 0.05) without excess risk for multiple colorectal neoplasia or noncolorectal neoplasia. I1307K attributable risk for colorectal neoplasia was 0.5-0.6%. Compared with noncarriers, both Ashkenazi and non-Ashkenazi I1307K carriers had similar flanking polymorphic alleles (P < 0.01). CONCLUSIONS: I1307K is a low-penetrance genetic variant that indicates a 1.7 relative risk for neoplasia in carriers who have familial carcinoma, clinically equivalent to obtaining a family history of sporadic colorectal neoplasia and promoting early screening. I1307K is a founder genetic variant in Jews of different ethnic origin, mainly Ashkenazim, but it explains only partially their higher incidence of colorectal carcinoma.     

The APC p.I1307K polymorphism is a significant risk factor for CRC in average risk Ashkenazi Jews

BackgroundThe p.I1307K adenomatous polyposis coli (APC) gene variant, prevalent among Ashkenazi Jews, may increase the risk for colorectal neoplasia. We studied the clinical importance of screening for this polymorphism in 3305 Israelis undergoing colonoscopy.Patients and methodsClinical data regarding potential risk factors for colorectal cancer (CRC) were collected from individuals undergoing colonoscopic examination at the Tel-Aviv medical center. The APC p.I1307K was detected using real-time PCR (polymerase chain reaction) from DNA extracted from peripheral mononuclear cells.ResultsThe overall prevalence of the p.I1307K polymorphism was 8.0% (10.1% among Ashkenazi and 2.7% among Sephardic Jews, p < 0.001). The overall adjusted odds ratio (OR) for colorectal neoplasia among carriers was 1.51 (95% confidence intervals (CI), 1.16–1.98). Among average risk Ashkenazi Jews, the adjusted OR was 1.75 (95% CI 1.26–2.45). A multiplicative interaction was identified between Ashkenazi ethnicity and APC p.I1307K carrier status (P_INTERACTION = 0.055). The histopathological features of adenomas and carcinomas did not differ between carriers and non-carriers.ConclusionsThe APC p.I1307K gene variant is an important risk factor for colorectal neoplasia in average risk Ashkenazi Jews. Carriers in this group should be considered for screening colonoscopy at the age of 40, to be repeated every 5 years, similar to recommendations in individuals with family history of colorectal cancer.     

Adenomatous polyposis coli I1307K mutation in Jewish patients with different ethnicity: prevalence and phenotype

BACKGROUND: A new mutation, I1307K, recently was reported in the adenomatous polyposis coli (APC) gene. This mutation was found to be predominant in Ashkenazi Jews, creating a hypermutable area and predisposing the development of carcinoma. The objective of the current study was to estimate the prevalence of this mutation in several of the ethnic groups that comprise the Israeli population and to elucidate the clinical features of the mutation carriers with colorectal carcinoma (CRC). METHODS: A total of 111 consecutive CRC patients were evaluated and their medical history and clinical data recorded. The general population (298 Ashkenazim and 189 Yemenites) also was tested for the presence of this mutation. Mutation screening was performed using both the polymerase chain reaction-based amplification refractory mutation system and a commercial APC kit. RESULTS: Of the total of 111 CRC patients, 15 (13.5%) carried the I1307K mutation and 26 of 487 subjects from the general population (5.3%) carried the I1307K mutation (P = 0.004). Among the 71 Ashkenazi CRC patients there were 12 carriers (16.9%) whereas 17 of the 298 Ashkenazi Jewish general population (5.7%) carried the mutation (P = 0.004). Of the 4 CRC patients of Yemenite origin, 3 carried the mutation and 9 carriers were found among 189 subjects in the general Yemenite population (4.7%) (P = 0.0007). None of the 34 Sepharadic or 2 Arab CRC patients carried the APC I1307K allele. Late age at diagnosis (64.6 years +/- 10.0, which is similar to that of the noncarriers), mostly right-sided tumors, and moderate to good differentiation constituted the phenotype of the mutation carriers. CONCLUSIONS: The authors believe the findings of the current study broaden the known spectrum of ethnic groups in which the APC I1307K mutation is prevalent. The phenotype of the mutation carrier CRC patients does not conform to the expected familial pattern of germline mutations. The phenotype and the differential incidence rate of CRC among APC I1307K carriers of various ethnic groups suggest low penetrance.     

Genetic factors and colorectal cancer in Ashkenazi Jews

The observed increased incidence of colorectal cancer in Ashkenazi Jews compared to other populations is unexplained but likely has a genetic component. The I1307K APC polymorphism/mutation is carried by 6--8% of Ashkenazim and increases the risk of colorectal cancer 1.5–2 fold. There are few differences between the phenotype of colorectal cancer in I1307K carriers and sporadic cases. It is estimated that the mutation accounts for 6% of cases of colorectal cancer in Jews of Eastern European heritage. It should not be the subject of mass screening in Ashkenazi Jews, although it may be important in cases of familial colorectal cancer. Even rarer is the 1906G→C MSH2 mutation carried by less than 1% of Ashkenazim, but as with other HNPCC mutations likely associated with a high risk of malignancy. Mutations at 15q13–14 are associated with the colorectal adenoma and carcinoma syndrome (CRAC) described in Ashkenazi families. The prevalence of the mutation is not known, nor its significance as a cause of colorectal cancer. Despite the paucity of genetic explanations for the high risk of colorectal cancer in Ashkenazim, that risk warrants aggressive colorectal cancer screening and particular attention to family history of malignancy in all Jews of Ashkenazi descent.     

Genetic factors and colorectal cancer in Ashkenazi Jews

The observed increased incidence of colorectal cancer in Ashkenazi Jews compared to other populations is unexplained but likely has a genetic component. The I1307K APC polymorphism/mutation is carried by 6--8% of Ashkenazim and increases the risk of colorectal cancer 1.5–2 fold. There are few differences between the phenotype of colorectal cancer in I1307K carriers and sporadic cases. It is estimated that the mutation accounts for 6% of cases of colorectal cancer in Jews of Eastern European heritage. It should not be the subject of mass screening in Ashkenazi Jews, although it may be important in cases of familial colorectal cancer. Even rarer is the 1906GC MSH2 mutation carried by less than 1% of Ashkenazim, but as with other HNPCC mutations likely associated with a high risk of malignancy. Mutations at 15q13–14 are associated with the colorectal adenoma and carcinoma syndrome (CRAC) described in Ashkenazi families. The prevalence of the mutation is not known, nor its significance as a cause of colorectal cancer. Despite the paucity of genetic explanations for the high risk of colorectal cancer in Ashkenazim, that risk warrants aggressive colorectal cancer screening and particular attention to family history of malignancy in all Jews of Ashkenazi descent.     

The effect of the I1307K APC polymorphism on the clinicopathological features and natural history of breast cancer.

The I1307K polymorphism in APC has been found to predispose to colorectal cancer in Ashkenazi Jews, and has recently been associated with an increased risk for breast cancer in the same population. In that study, we genotyped 205 paraffin-embedded breast cancers from Ashkenazi Jewish women diagnosed below the age of 65. We now present an extended analysis, with clinicopathological correlations between carriers of I1307K and non-carriers. Twenty-four of 209 cases (11.5%, 95% confidence interval 7.5-16.6) were found to carry the I1307K polymorphism. When stratifying the data by other relevant clinicopathological variables, we observed no association between the presence of this polymorphism and age at diagnosis (P = 0.52), grade (P = 0.074), tumour size (P = 0.99), lymph node status (P = 0.82), oestrogen receptor status (P = 0.23) or P53 immunoreactivity (P = 0.80). The breast-cancer specific 5-year survival for women with I1307 K polymorphism was 88.9% compared with 81.6% in women without I1307K (P = 0.34). Using microdissected samples and direct sequencing, no somatic mutations were observed in any of the 24 I1307K-positive cases. Single-strand conformation analysis of 158 of the I1307K-negative breast cancers that were available for study revealed no mobility shifts. We conclude that the presence of the I1307K polymorphism does not appear to be associated with any particular clinicopathological feature of breast cancer and importantly, does not affect the prognosis.     

Low prevalence of the APC I1307K sequence in Jewish and non-Jewish patients with inflammatory bowel disease.

A germline sequence alteration at codon 1307 of the APC gene (I1307K) has been reported in 6-7% of the Ashkenazi Jewish population in the United States. This alteration is believed to predispose the APC gene to a secondary mutation at the same locus, resulting in an increased risk of colorectal carcinoma. There is an increased risk of colorectal carcinoma in patients with inflammatory bowel disease (IBD), a relatively large proportion of whom are Ashkenazi Jews. We therefore sought to determine whether the I1307K sequence variant occurred in the germline DNA of IBD patients. To our surprise, we found this sequence in only two of 267 patients with IBD (0.7%), occurring in only 1.5% of Jewish IBD patients. The I1307K sequence variant was not found in 67 patients with esophageal cancer, 53 patients with gastric carcinoma (13 MSI-H and 44 MSI-negative), or ten patients with sporadic MSI-H colon cancer. These findings suggest that the I1307K sequence is relatively rare in the germline of Jewish as well as non-Jewish IBD patients. It does not appear to contribute to the increased colorectal cancer risk present in these patients.     

The APC I1307K allele conveys a significant increased risk for cancer

This study is the first attempt to evaluate the association between the APC I1307K variant and overall cancer risk. It is unique in both its large sample size and in the reliability of data in the control group. The findings described in this article have major implications in terms of identifying asymptomatic individuals who are at increased risk to harbor cancer and therefore targeted to be enrolled in specific early detection and prevention programs. The prevalence of the APC I1307K missense mutation among Ashkenazi Jews is ～6%. Carriers are at an increased risk for colorectal neoplasia. In this study, we examined the association of this variant with non‐colorectal cancers. Consecutive 13,013 healthy subjects who underwent screening at the Integrated Cancer Prevention Center between 2006 and 2014 were enrolled. This population was supplemented with 1,611 cancer patients from the same institution. Demographics, medical history, and pathological data were recorded. Mortality data were obtained from the Ministry of Health's registry. The prevalence of APC I1307K in cancer patients and healthy subjects was compared. The APC I1307K variant was detected in 189 (11.8%) cancer patients compared to 614 (4.7%) healthy subjects, reflecting an adjusted age and sex odds ratio (OR) of 2.53 (p < 0.0001). History of two or more cancer types was associated with a positive carrier prevalence (OR = 4.38 p < 0.0001). Males had significantly increased carrier prevalence in lung, urologic, pancreatic, and skin cancers. The carrier prevalence among females was significantly higher only in breast and skin cancers. Female carriers developed cancer at a significantly older age compared to non‐carriers (average 62.7 years vs. 57.8, respectively, p = 0.027), had better survival rates (HR = 0.58, p = 0.022) and overall increased longevity (average age of death 78.8 vs. 70.4 years, respectively, p = 0.003). In conclusion, the APC I1307K variant is a reliable marker for overall cancer risk (OR 2.53). Further studies are needed to evaluate its use for specific cancer types—particularly in males. Female carriers have better prognosis and increased lifespan.     

Risk of colorectal neoplasia associated with the adenomatous polyposis coli E1317Q variant

BackgroundReports of the risk of colorectal neoplasia associated with a variant of the adenomatous polyposis coli (APC E1317Q) gene are conflicting. Using a case–control design, we investigated this relationship within a clinic-based cohort followed through the Integrated Cancer Prevention Center and the Tel-Aviv Sourasky Medical Center.Materials and MethodsAll study subjects were tested for the APC E1317Q variant at enrollment. Subjects underwent colonoscopic evaluation (±biopsy and/or polypectomy) and had cancer history and colorectal neoplasia risk factors assessed. The crude and adjusted risks of neoplasia associated with the E1317Q variant were calculated.ResultsThe prevalence of the E1317Q variant was 1.4% in the entire study sample and 3.2% in Sephardic Jews. E1317Q was more prevalent among cases: 15 of 458 (3.3%) cases were carriers compared with 11 of 1431 (0.8%) controls [odds ratio (OR) 4.4, 95% CI 2.0–9.6]. When stratified by neoplasia type, adenoma risk was significantly elevated in carriers (OR 4.1, 95% CI 1.8–9.4) but colorectal cancer risk was not (OR 2.1, 95% CI 0.8–5.3). After adjustment, the E1317Q variant remained a significant predictor of colorectal adenoma (OR 4.6, 95% CI 2.0–10.8).ConclusionsThe APC E1317Q variant is associated with colorectal neoplasia, particularly colorectal adenomas, but further studies are still needed. Variant prevalence is elevated in Sephardic Jews.     

Common MUTYH mutations and colorectal cancer risk in multiethnic populations

MUTYH is associated with colorectal cancer (CRC) risk. We studied the frequency of MUTYH and risk of CRC in Arabs, North African and European Jews. Participants were all 593 Sephardi Moroccan Jews (232 cases, 361 controls) and all 631 Arabs (327 cases, 304 controls) recruited into a population-based study of colorectal cancer in Israel, as well as a random sample of 189 Ashkenazi Jewish cases. Two MUTYH mutations, G396D and Y179C, were studied in 1,413 individuals, with MUTYH sequence analysis in 46 cases with CRC in a sibling or adenoma. No carriers of mutations in MUTYH were identified in Ashkenazi Jews and only one in Arabs. In Sephardi Jews, 28 carriers of G396D, 25 (4.2%) heterozygotes and 3 (0.5%) homozygotes were identified. Four (0.7%) were heterozygote carriers of the Y179C mutation. Two compound heterozygous carriers of Y179C and G396D were identified. Homozygote carriers of G396D had nonsignificantly elevated risk of CRC (OR?=?11.0, 95% CI: 0.91–213.9, p?=?0.06), and combined bi-allelic carriers of G396D and Y179C had increased risk, OR?=?17.4, 95% CI?=?(1.9–316.7, p?=?0.009). Four of five bi-allelic carriers reported a family history of CRC. Sequencing of 46 colorectal cancer cases with family history and additional adenomas, did not identify any other non-founder mutations. MUTYH carriers of the two common founder mutations are profoundly under-represented among both Ashkenazi Jews and Arabs. The prevalence of MUTYH carriers of the common mutations is much higher in Sephardi Jews. Bi-allelic carriers of mutations in MUTYH, are associated with highly risk of colorectal cancer.     

Single nucleotide polymorphisms and colorectal neoplasia risk: Updates and impact

Polymorphisms in genes related to various endogenous pathways (eg, metabolic, detoxification, and DNA repair) have been linked to colorectal cancer risk. To date, much of the literature has focused on the study of single nucleotide polymorphisms (SNPs) in DNA repair pathways (eg, base excision repair and nucleotide excision repair). Over the past years, SNPs within known cancer risk loci and in pathways related to one-carbon metabolism, inflammation or inflammatory mediators, and leptin signaling (among others) have expanded our understanding of how polymorphic variation across several genes and pathways influences disease risk. Work from our group explores how variants of the adenomatous polyposis coli (APC) gene and the CD24 gene impact colorectal neoplasia risk. Despite brisk research in this area, clinical applicability remains limited. This article includes an up-to-date review (2007-present) of several studies examining polymorphisms and colorectal neoplasia risk, a discussion of recent findings in the assessment of colorectal neoplasia risk associated with the APC I1307K and E1317Q variants from our group, and finally a brief assessment of the impact of polymorphism research on clinical practice to date.     

Definition of candidate low risk APC alleles in a Swedish population

Many families experience an apparently inherited increased risk of colorectal cancer (CRC) similar to the known syndromes familial adenomatous polyposis (FAP) and hereditary nonpolyposis colorectal cancer (HNPCC). Besides these high-risk syndromes, approximately 10% of all CRC cases come from families with 2 affected 1st-degree relatives, and even 1st-degree relatives to a single case of CRC are at increased risk. Risk subjects from these families frequently show polyps at colonoscopy, which suggests the APC gene as a good candidate susceptibility gene for these attenuated polypotic syndromes. We used the sensitive DHPLC technique to search for possible predisposing germline mutations in the entire APC gene in 91 risk subjects from these high- and low-risk syndromes with unknown predisposing genes. Most exons were also screened for mutations in 96 normal controls and 96 colorectal cancer cases. In our study we probably have identified the most common APC variants in a Swedish population. Among 30 germline variants identified, 1 clearly pathogenic nonsense mutation and 11 putative pathogenic variants (10 missense and one 3' UTR) were found in 20 index patients (22%). Twelve silent as well as 5 intronic variants were considered nonpathogenic. Two of the missense variants found here, E1317Q and D1822V, have previously been related to a difference in risk of colorectal cancer. One variant, 8636C>A, located within the 3' UTR region of the APC gene, was suggested to constitute an additional low risk allele with a similar relative risk as the Jewish I1307K mutation (OR = 1.8; 95% CI, 0.96-3.40). The question of whether all the other variants confer an increased colorectal cancer risk warrants future large association studies.     

Interaction between interleukin-10 (IL-10) polymorphisms and dietary fibre in relation to risk of colorectal cancer in a Danish case-cohort study

ABSTRACT: BACKGROUND: More than 50% of the colorectal cancer (CRC) etiology has been attributed to diet. Established or suspected dietary factors modifying risk of CRC are red meat, cereals, fish, and fibre. Diet and lifestyle may be linked to cancer through inflammation. Interleukin-10 (IL-10) is an anti-inflammatory cytokine. We wanted to test if dietary factors and IL10 polymorphisms interact in relation to colorectal carcinogenesis. METHODS: The functional IL10 polymorphism C-592A (rs1800872) and the marker rs3024505 were assessed in relation to diet and lifestyle in a nested case-cohort study of 378 CRC cases and 775 randomly selected participants from a prospective study of 57,053 persons. Genotyping data on the IL10 polymorphism C-592A, smoking and non-steroidal anti-inflammatory drugs (NSAID) was retrieved from Vogel et al (Mutat Res, 2007; 624:88). Incidence rate ratios (IRR) and 95% Confidence Interval (95% CI) were calculated. RESULTS: No associations were found between the IL10 rs3024505 polymorphism and risk of CRC. There was interaction between rs3024505 and dietary fibre (P-value for interaction=0.01). IL10 rs3024505 homozygous wildtype carriers were at 27% reduced risk of CRC per 10 g fibre per day (95% CI: 0.60-0.88) whereas variant carriers had no risk reduction by fibre intake. Also, interaction between IL10 C-592A and intake of fibre was found (P-value for interaction=0.02). Among those eating <17.0 grams of fibre per day, carriers of an C-592A variant allele had a statistically significantly higher risk of colorectal cancer compared to homozygous wildtypes. No significant differences in colorectal cancer risk were observed between the reference group (CC and <17.0 g/day) and carriers of one C-592A variant allele eating 17.0 or more grams of dietary fibre per day. This suggests that the increased risk due to carrying the variant allele can be overcome by higher fibre intake. No interactions between IL10 polymorphisms and dietary meat, cereal, or fish intake, or between IL10 rs3024505 and smoking or NSAID use were found. CONCLUSIONS: In this northern Caucasian cohort we found interaction between IL10 and dietary fibre in CRC carcinogenesis. High intake of fibre seems to protect against CRC among individuals with IL10 related genetic susceptibility to CRC. This finding should be evaluated in other prospective and population-based cohorts with different ethnic groups.     

The APC E1317Q variant in adenomatous polyps and colorectal cancers.

Genetic susceptibility may play a role in many colorectal cancers (CRCs). Known syndromes such as familial adenomatous polyposis and hereditary nonpolyposis CRC account for <5% of CRCs. The germ-line missense variant of the APC gene, E1317Q, has been proposed to confer a risk for colonic adenomatous polyps (adenomas), but not for CRCs in the general population. These findings are contradictory and controversial. In the present study, 608 cases (377 patients with CRC, 145 patients with 4-100 lifetime adenomas, and 86 with < or =3 lifetime adenomas), and 679 controls (362 spouses and 317 patients with normal colonoscopy) were screened for the APC E1317Q variant. The frequency of heterozygotes for E1317Q among patients with CRC (2.4%), patients with 4-100 adenomas (1.4%), and < or =3 adenomas (3.5%) did not differ from spouse controls (2.8%). When CRC patients were examined by DNA mismatch repair status, age at onset (< or =age 50 versus >50), or family history of CRC, no differences in the frequency of E1317Q were found. The APC variant E1317Q does not appear to be associated with increased risk for colorectal neoplasia in the general population. However, when we used normal colonoscopy controls (E1317Q carrier frequency = 0.3%), the prevalence of E1317Q was significantly increased in CRC patients, in patients with < or =3 adenomas, and in CRC patients with intact mismatch repair status, suggesting a possible role for E1317Q in colorectal tumorigenesis. These results underscore the importance of carefully defining the controls to be used in comparisons of allele frequencies.     

Clinical and genetic findings in an Ashkenazi Jewish population with colorectal neoplasms

BACKGROUND: The authors evaluated the frequency of the carrier status of three ancestral colorectal neoplasm-associated mutations (APC:I1307K, BLM(Ash), and MSH2*1906G>C) found in the Jewish population among a case series with documented colorectal neoplasms. They further compared family and personal histories plus environmental exposures of the carriers and noncarriers of the I1307K mutation and examined clinical differences with regard to the colorectal neoplasms and the specific molecular genetic changes in these lesions. METHODS: Analyses were performed on tissue from stored paraffin-embedded blocks for the three germline mutations plus the KRAS mutation and APC loss of heterozygosity (LOH) and APC gene sequencing. RESULTS: Fifty-four of the 429 individuals (12.6%) were found to carry the APC:I1307K mutation, whereas 4 (0.9%) were found to be heterozygous for the BLM(Ash) mutation and 3 (0.7%) were carriers of the MSH21906G>C* mutation. Carriers of the I1307K mutation did not appear to differ from noncarriers with regard to the number of neoplasms, patient age at detection, or tumor location within the colon. There was no significant difference noted between I1307K carriers and noncarriers with regard to the percentage of patients with first-degree relatives with colorectal carcinoma. A significant risk for APC LOH was found in lesions from carriers who smoked cigarettes compared with nonsmokers. The I1307K mutation was found to be clearly associated with a somatic additional adenine insertion in the region of codons 1306-1309, but other mutations in the region of codons 1277-1348 were found to be no more prevalent in carriers than in noncarriers. CONCLUSIONS: In Jewish individuals previously diagnosed with a colorectal neoplasm, MSH2*1906G>C is uncommon but has been associated with carcinoma occurring at a young age. The BLM(Ash) mutation is uncommon and appears to be of little effect. The I1307K mutation is common among Jews who have had colorectal neoplasms, but overall it was found to have little effect clinically in the current study group. There may be a gene-environment interaction between the I1307K mutation and cigarette use.     

Prevalence of the APC E1317Q variant in colorectal cancer patients

The notion that some common variants of APC might confer an increased colorectal tumour risk is supported by studies of the I1307K polymorphism. Recently it has been proposed that the E1317Q variant is also associated with an increased risk. We have studied the prevalence of E1317Q in 364 colorectal cancer patients and in 290 controls. Two patients were shown to possess E1317Q. Neither had a family history of colorectal cancer or co-existent adenomatous polyps. Two controls also carried E1317Q. This finding suggests that E1317Q is unlikely to be associated with anything more than a moderate increase in risk of colorectal cancer.     

Update on Hereditary Colorectal Cancer: Improving the Clinical Utility of Multigene Panel Testing

Colorectal cancer (CRC), one of the most common cancers, is a major public health issue globally, especially in Westernized countries. Up to 35% of CRCs are thought to be due to heritable factors, but currently only 5% to 10% of CRCs are attributable to high-risk mutations in known CRC susceptibility genes, predominantly the mismatch repair genes (Lynch syndrome) and adenomatous polyposis coli gene (APC; familial adenomatous polyposis). In this era of precision medicine, high-risk mutation carriers, when identified, can be offered various risk management options that prevent cancers and improve survival, including risk-reducing medication, screening for early detection, and surgery. The practice of clinical genetics is currently transitioning from phenotype-directed single gene testing to multigene panels, now offered by numerous providers. For CRC, the genes included across these panels vary, ranging from well established, clinically actionable susceptibility genes with quantified magnitude of risk, to genes that lack extensive validation or have less evidence of association with CRC and, therefore, have minimal clinical utility. The current lack of consensus regarding inclusion of genes in CRC panels presents challenges in patient counseling and management, particularly when a variant in a less validated gene is identified. Furthermore, there remain considerable challenges regarding variant interpretation even for the well established CRC susceptibility genes. Ironically though, only through more widespread testing and the accumulation of large international data sets will sufficient information be generated to (i) enable well powered studies to determine if a gene is associated with CRC susceptibility, (ii) to develop better models for variant interpretation and (iii) to facilitate clinical translation.     

Modification of the associations between lifestyle, dietary factors and colorectal cancer risk by APC variants

In a large Scottish case-control study, we investigated the effects of adenomatous polyposis coli (APC) Asp1822Val (rs459552) and APC Glu1317Gln substitutions on colorectal cancer (CRC) risk and whether these associations were influenced by lifestyle and dietary factors. We did not observe any associations between the variants and CRC risk in the whole population. Post-menopausal women taking hormone replacement therapy (HRT) and participants who consumed a diet low in total fat, saturated fatty acids, monounsaturated fatty acids (MUFAs) and trans fatty acids had a lower risk of CRC [odds ratio (95% confidence interval): 0.53 (0.41, 0.68); 0.84 (0.72, 0.98); 0.72 (0.62, 0.85); 0.85 (0.73, 1.00) and 0.78 (0.67, 0.92), respectively]. This risk reduction was stronger in those homozygous for the variant APC 1822 allele with significant interaction relationships for HRT, red meat and MUFA intakes (P for interaction case-only design: 0.02, 0.002 and 0.02, respectively). Low n3 polyunsaturated fatty acids intake was associated with an increased CRC risk for the wild-type and heterozygous APC 1822 individuals but with a decreased CRC risk in those homozygous for the variant allele (P for interaction case-only design: 0.09). The interaction relationships with the APC 1317 variant were of the same direction though not significant, possibly due to the low frequency of the variant allele. Our results confirm the findings of three recent case-control studies suggesting a number of possible biological mechanisms. However, further large-scale studies are necessary in order to replicate these findings and confirm the role of these APC gene variants and their interaction with dietary and lifestyle exposures in colorectal carcinogenesis.     

Association of the I1307K APC mutation with hereditary and sporadic breast/ovarian cancer: more questions than answers

The frequency of the APC I1307K mutation and its association with disease pattern was examined in 996 Ashkenazi women consisting of individuals with either sporadic (n = 382) or hereditary (n = 143) breast and/or ovarian cancer; asymptomatic BRCA1/2 mutation carriers (185delAG, 5382insC and 6174delT) (n= 53) and healthy controls (n= 418). The I1307K allele was equally distributed among women with sporadic (17/382; 4.6%) and inherited (10/143; 7%) breast and/or ovarian cancer irrespective of their being diagnosed before or after 42 years of age and among asymptomatic (7/53; 13.2%) and cancer manifesting BRCA1/2 carriers (10/143; 7%). Taken together, the prevalence of the I1307K allele was significantly higher in BRCA1/2 carriers compared to non-BRCA1/2 carriers (17/196; 8.7% and 40/800, 5%; respectively). The high prevalence of the I1307K allele among BRCA1/2 carriers is not associated with increased cancer risk but seems to be genetically connected because of Jewish ancestry.     

The frequency of the predominant Jewish mutations in BRCA1 and BRCA2 in unselected Ashkenazi colorectal cancer patients

It is presently unclear whether carriers of BRCA1 mutations have an increased risk for colorectal cancer (CRC). To gain insight into this issue, 225 unselected Ashkenazi Jewish CRC patients were tested for the presence of the three common Jewish BRCA1/2 germline mutations: 185delAG and 5382insC (BRCA1) and 6174delT (BRCA2). A total of four carriers was found (4/225, 1.78%). This frequency is similar to the estimated normal Ashkenazi population frequency, thus suggesting that these specific mutations do not contribute to CRC predisposition.