Variants in the netrin-1 receptor UNC5C prevent apoptosis and increase risk of familial colorectal cancer.

BACKGROUND & AIMS: Expression of the netrin-1 dependence receptor UNC5C is reduced in many colorectal tumors; mice with the UNC5C mutations have increased progression of intestinal tumors. We investigated whether specific variants in UNC5C increase risk of colorectal cancer (CRC). METHODS: We analyzed the sequence of UNC5C in blood samples from 1801 patients with CRC and 4152 controls from 3 cohorts (France, United States, and Finland). Almost all cases from France and the United States had familial CRC; of the Finnish cases, 92 of 984 were familial. We analyzed whether CRC segregates with the UNC5C variant A628K in 3 families with histories of CRC. We also performed haplotype analysis to determine the origin of this variant. RESULTS: Of 817 patients with familial CRC, 14 had 1 of 4 different, unreported missense variants in UNC5C. The variants p.Asp353Asn (encodes D353N), p.Arg603Cys (encodes R603C), and p.Gln630Glu (encodes Q630E) did not occur significantly more often in cases than controls. The variant p.Ala628Lys (A628K) was detected in 3 families in the French cohort (odds ratio, 8.8; Wald's 95% confidence interval, 1.47-52.93; P = .03) and in 2 families in the US cohort (odds ratio, 1.9; P = .6) but was not detected in the Finnish cohort; UNC5C A628K segregated with CRC in families. Three families with A628K had a 109-kilobase identical haplotype that spanned most of UNC5C, indicating recent origin of this variant in white subjects (14 generations; 95% confidence interval, 6-36 generations). Transfection of HEK293T cells with UNC5C-A628K significantly reduced apoptosis compared with wild-type UNC5C, measured in an assay of active caspase-3. CONCLUSIONS: Inherited mutations in UNC5C prevent apoptosis and increase risk of CRC.

Screening for the Lynch syndrome (hereditary nonpolyposis colorectal cancer).

BACKGROUND: Germ-line mutations in the mismatch-repair genes MLH1, MSH2, MSH6, and PMS2 lead to the development of the Lynch syndrome (hereditary nonpolyposis colorectal cancer), conferring a strong susceptibility to cancer. We assessed the frequency of such mutations in patients with colorectal cancer and examined strategies for molecular screening to identify patients with the syndrome. METHODS: Patients with a new diagnosis of colorectal adenocarcinoma at the major hospitals in metropolitan Columbus, Ohio, were eligible for the study. Genotyping of the tumor for microsatellite instability was the primary screening method. Among patients whose screening results were positive for microsatellite instability, we searched for germ-line mutations in the MLH1, MSH2, MSH6, and PMS2 genes with the use of immunohistochemical staining for mismatch-repair proteins, genomic sequencing, and deletion studies. Family members of carriers of the mutations were counseled, and those found to be at risk were offered mutation testing. RESULTS: Of 1066 patients enrolled in the study, 208 (19.5 percent) had microsatellite instability, and 23 of these patients had a mutation causing the Lynch syndrome (2.2 percent). Among the 23 probands with the Lynch syndrome, 10 were more than 50 years of age and 5 did not meet the Amsterdam criteria or the Bethesda guidelines for the diagnosis of hereditary nonpolyposis colorectal cancer (including the use of age and family history to identify patients at high risk for the Lynch syndrome). Genotyping for microsatellite instability alone and immunohistochemical analysis alone each failed to identify two probands. In the families of 21 of the probands, 117 persons at risk were tested, and of these, 52 had Lynch syndrome mutations and 65 did not. CONCLUSIONS: Routine molecular screening of patients with colorectal adenocarcinoma for the Lynch syndrome identified mutations in patients and their family members that otherwise would not have been detected. These data suggest that the effectiveness of screening with immunohistochemical analysis of the mismatch-repair proteins would be similar to that of the more complex strategy of genotyping for microsatellite instability.

Screening for Lynch syndrome (hereditary nonpolyposis colorectal cancer) among endometrial cancer patients.

Endometrial cancer is the most common cancer in women with Lynch syndrome. The identification of individuals with Lynch syndrome is desirable because they can benefit from increased cancer surveillance. The purpose of this study was to determine the feasibility and desirability of molecular screening for Lynch syndrome in all endometrial cancer patients. Unselected endometrial cancer patients (N = 543) were studied. All tumors underwent microsatellite instability (MSI) testing. Patients with MSI-positive tumors underwent testing for germ line mutations in MLH1, MSH2, MSH6, and PMS2. Of 543 tumors studied, 118 (21.7%) were MSI positive (98 of 118 MSI high and 20 of 118 MSI low). All 118 patients with MSI-positive tumors had mutation testing, and nine of them had deleterious germ line mutations (one MLH1, three MSH2, and five MSH6). In addition, one case with an MSI-negative tumor had abnormal MSH6 immunohistochemical staining and was subsequently found to have a mutation in MSH6. Immunohistochemical staining was consistent with the mutation result in all seven truncating mutation-positive cases but was not consistent in two of the three missense mutation cases. We conclude that in central Ohio, at least 1.8% (95% confidence interval, 0.9-3.5%) of newly diagnosed endometrial cancer patients had Lynch syndrome. Seven of the 10 Lynch syndrome patients did not meet any published criteria for hereditary nonpolyposis colorectal cancer, and six of them were diagnosed at age >50. Studying all endometrial cancer patients for Lynch syndrome using a combination of MSI and immunohistochemistry for molecular prescreening followed by gene sequencing and deletion analysis is feasible and may be desirable.

Frequency of germline PTEN mutations in differentiated thyroid cancer.

BACKGROUND: Differentiated thyroid cancer (DTC) is seen in 3%-10% of individuals carrying a germline PTEN mutation. Patients with PTEN mutations are at risk for additional neoplasms as are their affected offspring. However, the frequency of PTEN mutations among DTC cases has not been systematically analyzed. The objective of this study was to determine the frequency of PTEN mutations in an unselected group of patients with DTC and to identify whether additional clinical features might indicate the need for referral for genetic counseling and possible testing. METHODS: We collected personal medical and family history information, head circumference data, and blood from 259 consecutively identified clinic-based patients with DTC, unselected for personal or family history. Individuals were categorized for diagnostic criteria for Cowden syndrome (CS) using the 2009 National Comprehensive Cancer Network (NCCN) guidelines and underwent germline PTEN mutation analysis. RESULTS: Two of the 259 patients (0.8%), with both follicular thyroid carcinoma and macrocephaly, were found to carry a germline mutation in the PTEN gene. The PTEN mutation frequency in unselected cases of follicular thyroid carcinoma was 4.8%. CONCLUSION: The frequency of germline pathogenic PTEN mutations in an unselected series of patients with DTC is relatively low, but it is enriched by considering follicular histology and macrocephaly. These results suggest that by adding head circumference to the clinical assessment, thyroid cancer specialists can more effectively identify patients needing referral for cancer genetic services.

The frequency of Muir-Torre syndrome among Lynch syndrome families.

Lynch syndrome is the predisposition to visceral malignancies that are associated with deleterious germline mutations in DNA mismatch repair genes, including MLH1, MSH2, MSH6, and PMS2. Muir-Torre syndrome is a variant of Lynch syndrome that includes a predisposition to certain skin tumors. We determined the frequency of Muir-Torre syndrome among 50 Lynch syndrome families that were ascertained from a population-based series of cancer patients who were newly diagnosed with colorectal or endometrial carcinoma. Histories of Muir-Torre syndrome-associated skin tumors were documented during counseling of family members. Muir-Torre syndrome was observed in 14 (28%) of 50 families and in 14 (9.2%) of 152 individuals with Lynch syndrome. Four (44%) of nine families with MLH1 mutations had a member with Muir-Torre syndrome compared with 10 (42%) of 24 families with MSH2 mutations (P = .302). Families who carried the c.942+3A>T MSH2 gene mutation had a higher frequency of Muir-Torre syndrome than families who carried other mutations in the MSH2 gene (75% vs 25%; P = .026). Muir-Torre syndrome was not found in families with mutations in the MSH6 or PMS2 genes. Our results suggest that Muir-Torre syndrome is simply a variant of Lynch syndrome. Screening for Muir-Torre syndrome-associated skin lesions among patients with Lynch syndrome is recommended.

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.

Origins and prevalence of the American Founder Mutation of MSH2.

Large germline deletions within the mismatch repair gene MSH2 account for a significant proportion (up to 20%) of all deleterious mutations of this gene which are associated with Lynch syndrome. An exons 1 to 6 deletion of MSH2, originally reported in nine families, has been associated with a founding event within the United States, which genealogic studies had previously dated to 1727, and the number of present day carriers was estimated to be 18,981. Here, we report the development of a robust multiplex PCR which has assisted in the detection of 32 new families who carry the MSH2 American Founder Mutation (AFM). By offering testing to family members, 126 carriers of the AFM have been identified. Extensive genealogic studies have connected 27 of the 41 AFM families into seven extended pedigrees. These extended families have been traced back to around the 18th century without any evidence of further convergence between them. Characterization of the genomic sequence flanking the deletion and the identification of a common disease haplotype of between 0.6 and 2.3 Mb in all probands provides evidence for a common ancestor between these extended families. The DMLE+2.2 software predicts an age of approximately 500 years (95% confidence interval, 425-625) for this mutation. Taken together, these data are suggestive of an earlier founding event than was first thought, which likely occurred in a European or a Native American population. The consequences of this finding would be that the AFM is significantly more frequent in the United States than was previously predicted.

Feasibility of screening for Lynch syndrome among patients with colorectal cancer.

PURPOSE: Identifying individuals with Lynch syndrome (LS) is highly beneficial. However, it is unclear whether microsatellite instability (MSI) or immunohistochemistry (IHC) should be used as the screening test and whether screening should target all patients with colorectal cancer (CRC) or those in high-risk subgroups. PATIENTS AND METHODS: MSI testing and IHC for the four mismatch repair proteins was performed on 500 tumors from unselected patients with CRC. If either MSI or IHC was abnormal, complete mutation analysis for the mismatch repair genes was performed. RESULTS: Among the 500 patients, 18 patients (3.6%) had LS. All 18 patients detected with LS (100%) had MSI-high tumors; 17 (94%) of 18 patients with LS were correctly predicted by IHC. Of the 18 probands, only eight patients (44%) were diagnosed at age younger than 50 years, and only 13 patients (72%) met the revised Bethesda guidelines. When these results were added to data on 1,066 previously studied patients, the entire study cohort (N = 1,566) showed an overall prevalence of 44 of 1,566 patients (2.8%; 95% CI, 2.1% to 3.8%) for LS. For each proband, on average, three additional family members carried MMR mutations. CONCLUSION: One of every 35 patients with CRC has LS, and each has at least three relatives with LS; all of whom can benefit from increased cancer surveillance. For screening, IHC is almost equally sensitive as MSI, but IHC is more readily available and helps to direct gene testing. Limiting tumor analysis to patients who fulfill Bethesda criteria would fail to identify 28% (or one in four) cases of LS.