Hereditary Non-polyposis Colon Cancer Families Research Articles

Detection of PMS2 Mutations by Screening Hereditary Nonpolyposis Colon Cancer Families from Denmark and Sweden.

Background and Aims: Hereditary nonpolyposis colon cancer (HNPCC) and Lynch syndrome (LS) are characterized by defects in the mismatch repair (MMR) system, which protects the integrity of the genome. Pathogenic variants in four MMR genes (MLH1, MSH2, MSH6, and PMS2) are responsible for LS, an autosomal, dominant hereditary disease that occurs with a frequency of 2-5% among all colorectal cancer cases. It has been estimated that ∼2-5% of all pathogenic variants found in the four MMR genes in LS cases are detected in the PMS2 gene. An overview of detected variants is presented here. Materials and Methods: Long-range (LR) PMS2 polymerase chain reaction (PCR) and PMS2 multiplex ligation probe amplification (MLPA) assays were used to detect PMS2 variants in ∼1500 probands. In a subset of the probands, pathogenic PMS2 variants were detected by next-generation sequencing, and all detected variants were confirmed by LR-PCR combined with an MLPA assay. Results: A summary of PMS2 mutation analyses performed on colon cancer patients from molecular diagnostic laboratories in Denmark and Sweden is presented. By screening ∼1500 HNPCC probands, a total of 40 different PMS2 variants were detected in 71 probands (5%); 20 variants were classified as pathogenic (C5), 2 variants as likely pathogenic (C4), 15 variants as variants of unknown significance (VUSs) (C3), 1 variant as likely benign (C2), and 2 variants as benign (C1). In total, 22/71 (31%) of the probands carried a pathogenic sequence variant. Among the probands with isolated loss of pPMS2 expression, the fraction of pathogenic variants was 20/35 (55%). Conclusions: Approximately 5% of the probands found in the Danish and Swedish populations presented here carried a PMS2 variant. In this study, six novel pathogenic variants and seven VUSs are reported.

Hereditary nonpolyposis colorectal cancer

Abstract: Hereditary nonpolyposis colon cancer (HNPCC), also known as Lynchsyndrome, is characterized by germline and somatic mutations of DNA mismatch repairgenes with dominant inheritance of site-specific colorectal cancer or colorectal cancerplus cancers of extracolonic sites. We describe two Taiwanese HNPCC families withmembers who had predominantly gynecologic malignancies. In one family, the 53-year-old proband was found to have five synchronous and metachronous tumors ofthe genitourinary system, which included endometrial adenocarcinoma, cervicalsquamous cell carcinoma, ureteral and bladder transitional cell carcinoma, and ovarianteratoma. Fourteen of her first- and second-degree relatives were victims of genitouri-nary and gastrointestinal malignancies. The other family was characterized by four sisterswho developed endometrial adenocarcinomas at young ages (36–42 yr). Their fatherdied of both stomach cancer and colon cancer at age 47. The diagnosis of HNPCCwas confirmed in this family by genetic analysis. A heterozygous germline mutation(G5 to G6 frame-shift at 183–187) of the

Quantitative multiplex PCR analysis for large rearrangements in the MLH1 and MSH2 genes for hereditary non- polyposis colorectal cancer

4109 Background: Hereditary non-polyposis colon cancer (HNPCC) is caused by germline mutations in the mismatch repair genes MLH1, MSH2, MSH6 and PMS2. HNPCC patients have ∼80% increased risk of colon cancer, and elevated risk for cancers of the endometrium, ovary, stomach, small intestine and upper urinary tract. Molecular genetic testing in HNPCC families showed that ∼90% of cases are due to MLH1 and MSH2, 7–10% to MSH6, and <5% to PMS2. The majority are point mutations detectable by sequencing; however, about 5% and 20% of mutations in MLH1 and MSH2, respectively, are large rearrangements that require other detection techniques such as Southern blot or multiplex ligation-dependent probe amplification (MLPA). Our laboratory had previously developed and implemented a quantitative multiplex PCR (QMPCR) endpoint assay for clinical testing for large rearrangements in the BRCA1 and BRCA2 genes. We have developed a similar assay for the MLH1 and MSH2 genes in HNPCC which we refer to as CART (Colorectal cancer Rearrangement Test). Methods: CART consists of 9 multiplexes of 8–12 amplicons each, with at least 2 amplicons targeting each coding exon, promoter, and 3’UTR of both genes. Copy numbers are normalized against MLH1, MSH2, and two unlinked control genes. Internally developed software provides automated analysis and statistical confidence levels for the presence or absence of large rearrangements. Results: Initial validation of CART has been performed on 14 MLH1 or MSH2 rearrangement-positive and 30 negative DNA samples. Results were 100% concordant with previous Southern blot data, as well as supplemental MLPA studies. CART has greatly improved turnaround time, accuracy, and consistency compared to Southerns and MLPA. Conclusions: QMPCR is a superior diagnostic tool for detecting large rearrangements in disease genes. Validation of CART for MLH1 and MSH2 rearrangements is underway on a larger set of previously genotyped samples in a blinded manner. In conjunction with sequencing of the MLH1 and MSH2 genes, the CART assay is expected to improve molecular diagnostic testing on individuals at risk for HNPCC. No significant financial relationships to disclose.

Mutations in the DNA mismatch repair gene MLH1 associated with early-onset colon cancer

Hereditary nonpolyposis colon cancer (HNPCC) is an autosomal dominant disorder characterized by the predisposition to develop a number of cancers, especially colorectal cancer (CRC). We present a HNPCC family with CRC at age 12 years. Our observations suggest that the germline mutation of the both copies of the MLH1 gene may play a role in the early onset of CRC.

Expression of the MutL Homologue hMLH3 in Human Cells and its Role in DNA Mismatch Repair

The human mismatch repair (MMR) proteins hMLH1 and hPMS2 function in MMR as a heterodimer. Cells lacking either protein have a strong mutator phenotype and display microsatellite instability, yet mutations in the hMLH1 gene account for approximately 50% of hereditary nonpolyposis colon cancer families, whereas hPMS2 mutations are substantially less frequent and less penetrant. Similarly, in the mouse model, Mlh1-/- animals are highly cancer prone and present with gastrointestinal tumors at an early age, whereas Pms2-/- mice succumb to cancer much later in life and do not present with gastrointestinal tumors. This evidence suggested that MLH1 might functionally interact with another MutL homologue, which compensates, at least in part, for a deficiency in PMS2. Sterility of Mlh1-/-, Pms2-/-, and Mlh3-/- mice implicated the Mlh1/Pms2 and Mlh1/Mlh3 heterodimers in meiotic recombination. We now show that the hMLH1/hMLH3 heterodimer, hMutLgamma, can also assist in the repair of base-base mismatches and single extrahelical nucleotides in vitro. Analysis of hMLH3 expression in colon cancer cell lines indicated that the protein levels vary substantially and independently of hMLH1. If hMLH3 participates in MMR in vivo, its partial redundancy with hPMS2, coupled with the fluctuating expression levels of hMLH3, may help explain the low penetrance of hPMS2 mutations in hereditary nonpolyposis colon cancer families.

Syndrome of Early Onset Colon Cancers, Hematologic Malignancies & Features of Neurofibromatosis in HNPCC Families with Homozygous Mismatch Repair Gene Mutations

Hereditary nonpolyposis colon cancer (HNPCC) is the most common hereditary colon cancer syndrome. It is characterized by multiple colon as well as extracolonic cancers such as endometrial, ovarian and urinary tract cancers. In addition, it is well known that some cases of HNPCC can present with unique tumor spectrums such as sebaceous tumors, which is often referred to as the 'Muir-Torre' syndrome. In recent years there have been a few reports of families presenting with early onset of colon tumors along with café-au-lait spots and/or hematologic malignancies often associated with homozygous mutations involving one of the mismatch repair genes. In this article we have performed a comprehensive review of the entire medical literature to identify all cases with similar presentations reported in the literature and have summarized the clinical features and genetic test results of the same. The available data clearly highlight such presentations as a distinct clinical entity characterized by early onset of gastrointestinal tumors, hematologic malignancies as well as features of neurofibromatosis (easily remembered by the acronym ;CoLoN'; Colon tumors or/and Leukemia/Lymphoma or/and Neurofibromatosis features). Furthermore, there has also been some evidence that the neurofibromatosis type-1 gene is a mutational target of the mismatch repair deficiency that is seen in families with HNPCC, and that mlh1 deficiency can accelerate the development of leukemia in neurofibromatosis (Nf1) heterozygous mice. Recognition of this syndrome has significant importance in terms of earlier detection of cancers, cancer screening recommendations as well as genetic counseling offered to such families.

Clinical identification and long-term surveillance of 22 hereditary non-polyposis colon cancer Italian families

To assess the efficacy of a hereditary non-polyposis colon cancer (HNPCC) identification and surveillance policy. Familial clustering of colorectal cancer (CRC) and extracolonic cancers (ECs) was investigated in 1520 consecutive CRC patients and relatives. HNPCC was identified by Amsterdam criteria, and individuals at risk were offered biennial colonoscopy and other examinations, starting from age 25 years. Twenty-two HNPCC families were identified. The CRC prevalence was 27.8% (121/435), decreasing from 59.4% in the first generation to 24.4% and 8% in the second and third generation, respectively. Twenty-nine patients had multiple CRC and 34 patients (in 12 families) had ECs.A total of 199/331 at-risk individuals accepted surveillance. The mean follow-up was 48+/-32 months. CRCs were detected at first surveillance in four out of 199 surveilled individuals (2%); in two surveilled individuals (1%), three CRCs developed during follow-up. The overall CRC incidence was 7/199 (3.5%) in surveilled individuals and 5/132 (3.7%) in unsurveilled individuals. CRCs were less advanced in surveilled than in unsurveilled patients. Eleven individuals had 22 adenomas (one with high-grade dysplasia). Three individuals had adenomas at first surveillance; two of them and eight more individuals during surveillance. Seven surveilled individuals and six unsurveilled individuals, all belonging to families with a history of EC, had EC during the study period. All patients with CRC detected by surveillance are alive. One of the unsurveilled patients who had CRC died 18 months after the diagnosis. Data confirm the importance of the family history collected in each patient with CRC for identification of HNPCC and support the efficacy of repeated colonoscopies for early diagnosis and prevention of CRC in at-risk members. Reasons for surveillance failure could be an accelerated progression of small adenomas and a lesion missing at colonoscopy. Longer follow-up is required to assess the efficacy of surveillance for EC.

Colon cancer screening practices following genetic testing for hereditary nonpolyposis colon cancer (HNPCC) mutations.

Although increased colonoscopic surveillance is recommended for hereditary nonpolyposis colon cancer (HNPCC) mutation carriers, limited information is available on adherence to colorectal cancer screening recommendations. This study investigated colonoscopy practices following genetic testing for HNPCC mutations. This prospective cohort study was conducted between May 22, 1996, and November 13, 1999. Participants were 98 men and women without a personal history of colon cancer or colectomy who were identified from 11 extended HNPCC families. Colonoscopy use was evaluated by telephone before genetic counseling and was reassessed 1, 6, and 12 months following test results disclosure. During the 12 months following genetic counseling and testing, 73% (16/22) of HNPCC mutation carriers, 16% (8/49) of noncarriers, and 22% (6/27) of decliners reported having a colonoscopy (chi(2) = 23.97, P<.001). After controlling for clinical factors and pretest screening practices, HNPCC mutation carriers were significantly more likely than test decliners to have a colonoscopy (odds ratio [OR], 12.12; 95% confidence interval [CI], 3.42-42.96; P<.001). There were no differences in colonoscopy use between noncarriers and decliners (OR, 0.60; 95% CI, 0.28-1.29; P =.19). Perceived control over developing colon cancer also had a significant effect on posttest colonoscopy use (OR, 2.19; 95% CI, 1.22-3.94; P =.01). Genetic testing may motivate increased colonoscopic screening among HNPCC mutation carriers. Increased efforts may be needed to assess patients' family histories of colon cancer and provide appropriate referrals for genetic counseling and testing to target colonoscopic screening to high-risk individuals.

Screening for gynecologic cancers among women in HNPCC families

1023 Background: Hereditary non-polyposis colon cancer (HNPCC) syndrome confers 60% and 12% lifetime risks of endometrial cancer (EC) and ovarian cancer (OC), respectively, and EC is the second most commonly diagnosed cancer in this syndrome. Women at risk for HNPCC-related cancers are advised to begin annual EC and OC screening between ages 25–35 years. We evaluated EC and OC screening behaviors among women from HNPCC families, their attitudes toward screening, and communication with their physicians and family members about EC and OC risk and screening needs. Methods: Women age ≥ 25 years with an HNPCC-predisposing mutation and/or who met Amsterdam I or II criteria completed a study questionnaire. Those with prior hysterectomy and oophorectomy were excluded. Results: Twenty three women (median age=41 years) enrolled, and accrual is ongoing. Seventy four percent had an HNPCC-predisposing mutation, and all but one had received genetic counseling about their risk for HNPCC. Forty five percent or more had never undergone screening by endometrial biopsy, transvaginal ultrasound, or CA-125 serum testing. All respondents generally endorsed the importance and benefits of EC and OC screening; however, 43% were not aware of the recommended age range to begin screening. No participants recalled receiving advice from their gynecologists or other primary care physicians about EC or OC screening. Colonoscopy screening was discussed in all families more frequently compared with EC or OC screening. Although 61% had a family history of EC or OC, only 17% reported that their relatives had ever discussed EC or OC risk with them. Conclusions: HNPCC-affected families and their primary care physicians may lack accurate knowledge of EC and OC risks. Among HNPCC-affected families, there may be greater awareness of the need for screening colonoscopy than the need for gynecologic cancer screening. Nonetheless, women in these families may be receptive to advice and support from their families and physicians for adherence to these screening tests. No significant financial relationships to disclose.

Screening for gynecologic cancers among women in HNPCC families

1023 Background: Hereditary non-polyposis colon cancer (HNPCC) syndrome confers 60% and 12% lifetime risks of endometrial cancer (EC) and ovarian cancer (OC), respectively, and EC is the second mos...

Germline hMLH1 promoter mutation in a Newfoundland HNPCC kindred.

Hereditary non-polyposis colon cancer (HNPCC) is an autosomal dominant form of inherited predisposition to colorectal and other malignancies. It is associated with mutations in DNA mismatch-repair genes, especially hMSH2 and hMLH1. Management of HNPCC families is improved if the underlying mutation in each family can be discovered. We describe a Newfoundland kindred, meeting the Amsterdam Criteria for HNPCC, in which a mutation in the promoter region of the hMLH1 gene co-segregates with the disease phenotype. The -42C > T mutation is within a putative Myb proto-oncogene binding site. Using electrophoretic mobility shift assays, we demonstrated that the mutated Myb binding sequence is less effective in binding nuclear proteins than the wild-type promoter sequence. Using in vivo transfection experiments in HeLa cells, we further demonstrated that the mutated promoter has only 37% of the activity of the wild-type promoter in driving the expression of a reporter gene. The average age of onset in six family members affected with colorectal cancer is 62 years, which is substantially later than the typical age of onset in HNPCC families. This is consistent with a substantial decrease, but not total elimination, of mismatch repair function in affected members of this family. This is the first report of a heritable hMLH1 promoter mutation in any HNPCC family.

Personal theories of inheritance, coping strategies, risk perception and engagement in hereditary non-polyposis colon cancer families offered genetic testing.

From the geneticist's (or 'genetic counsellor's') perspective, lay models of inheritance can be perceived as problematic because they might interfere with understanding and acceptance of the explanation of inheritance provided in genetic counselling. The work presented here forms part of a larger qualitative grounded-theory study where the aim was to develop theory that could explain variations in adjustment to genetic testing for hereditary non-polyposis colon cancer (HNPCC). Ten of the 29 individuals interviewed who were at 50% or 25% risk used a 'personal theory of inheritance' to justify or explain a belief that they did, or did not, carry the family mutation. Two others indicated that, as a coping strategy, they chose to believe themselves to be carriers. This article presents part of the theory of engagement that was constructed using this data, relating to the process of development of risk perception. The theory suggests that for some individuals, these beliefs can form part of a process of coping and coming to terms with risk. An exploration of these processes may help practitioners to better understand the complexity of risk perception in individuals at genetic risk for cancer, particularly those preparing for predictive test results. Further development and testing of the theory is discussed.

Functional analysis of MLH1 mutations linked to hereditary nonpolyposis colon cancer

Hereditary nonpolyposis colon cancer (HNPCC) is associated with malfunction of postreplicative mismatch repair (MMR). While a majority of HNPCC-associated mutations in the MMR genes MLH1, MSH2, or MSH6 genes cause truncations—and thus loss of function—of the respective polypeptides, little is currently known about the biochemical defects associated with nontruncating mutations. We studied the interactions of six MLH1 variants, carrying either missense mutations or in-frame deletions, with normal PMS2 and tested the functionality of these heterodimers of MLH1 and PMS2 (MutLα) in an in vitro MMR assay. Three MLH1 carboxy-terminal mutations, consisting of internal deletions of exon 16 (amino acids 578–632) or exon 17 (amino acids 633–663), or a missense R659P mutation in exon 17, affected the formation of a functional MutLα. Interestingly, mutations C77R and I107R in the amino-terminal part of MLH1 did not affect its heterodimerization with PMS2. The complexes MLH1(C77R)/PMS2 and MLH1(I107R)/PMS2, however, failed to complement a MMR-deficient extract lacking a functional MutLα. As all these five mutations were identified in typical HNPCC families and produce nonfunctional proteins, they can be considered disease-causing. In contrast, the third amino-terminal mutation S93G did not affect the heterodimerization, and the MLH1(S93G)/PMS2 variant was functional in the in vitro MMR assay, given thus the nature of the HNPCC family in question. Although the missense mutation segregates with the disease, the mean age of onset in the family is unusually high (∼65 years). © 2002 Wiley-Liss, Inc.

Functional analysis of MLH1 mutations linked to hereditary nonpolyposis colon cancer

Hereditary nonpolyposis colon cancer (HNPCC) is associated with malfunction of postreplicative mismatch repair (MMR). While a majority of HNPCC-associated mutations in the MMR genes MLH1, MSH2, or MSH6 genes cause truncations-and thus loss of function--of the respective polypeptides, little is currently known about the biochemical defects associated with nontruncating mutations. We studied the interactions of six MLH1 variants, carrying either missense mutations or in-frame deletions, with normal PMS2 and tested the functionality of these heterodimers of MLH1 and PMS2 (MutL(alpha)) in an in vitro MMR assay. Three MLH1 carboxy-terminal mutations, consisting of internal deletions of exon 16 (amino acids 578-632) or exon 17 (amino acids 633-663), or a missense R659P mutation in exon 17, affected the formation of a functional MutL(alpha). Interestingly, mutations C77R and I107R in the amino-terminal part of MLH1 did not affect its heterodimerization with PMS2. The complexes MLH1(C77R)/PMS2 and MLH1(I107R)/PMS2, however, failed to complement a MMR-deficient extract lacking a functional MutL(alpha). As all these five mutations were identified in typical HNPCC families and produce nonfunctional proteins, they can be considered disease-causing. In contrast, the third amino-terminal mutation S93G did not affect the heterodimerization, and the MLH1(S93G)/PMS2 variant was functional in the in vitro MMR assay, given thus the nature of the HNPCC family in question. Although the missense mutation segregates with the disease, the mean age of onset in the family is unusually high (approximately 65 years).

Phenotypic analysis of hMSH2 mutations in mouse cells carrying human chromosomes.

Conversion of diploidy to haploidy is a method that allows the generation of stable murine/human hybrid cell lines carrying selected human chromosomes in only a single copy. In this setting, it is possible to detect genetic mutations with greater sensitivity and reliability than in diploid cells. Using this method, we were able to identify mutations in the human mismatch repair (MMR) gene hMSH2 in hereditary nonpolyposis colon cancer families, which have escaped detection by the conventional methods. In this report, we show that such hybrid cell lines can also be a valuable tool in the study of the mutated MMR proteins, in particular the variants found in hereditary nonpolyposis colon cancer families that carry missense mutations and where it is unclear whether they predispose to colon cancer. This analysis is made possible by the fact that the human hMSH2 protein is able to complement the MMR defect in the host murine cell line.

Tolerance of human MSH2+/- lymphoblastoid cells to the methylating agent temozolomide.

Members of hereditary nonpolyposis colon cancer (HNPCC) families harboring heterozygous germline mutations in the DNA mismatch repair genes hMSH2 or hMLH1 present with tumors generally two to three decades earlier than individuals with nonfamilial sporadic colon cancer. We searched for phenotypic features that might predispose heterozygous cells from HNPCC kindreds to malignant transformation. hMSH2(+/-) lymphoblastoid cell lines were found to be on average about 4-fold more tolerant than wild-type cells to killing by the methylating agent temozolomide, a phenotype that is invariably linked with impairment of the mismatch repair system. This finding was associated with an average 2-fold decrease of the steady-state level of hMSH2 protein in hMSH2(+/-) cell lines. In contrast, hMLH1(+/-) heterozygous cells were indistinguishable from normal controls in these assays. Thus, despite the fact that HNPCC families harboring mutations in hMSH2 or hMLH1 cannot be distinguished clinically, the early stages of the carcinogenic process in hMSH2 and hMLH1 mutation carriers may be different. Should hMSH2(+/-) colonocytes and lymphoblasts harbor a similar phenotype, the increased tolerance of the former to DNA-damaging agents present in the human colon may play a key role in the initiation of the carcinogenic process.

Novel dominant mutations in Saccharomyces cerevisiae MSH6.

Inherited mutations in the mismatch repair (MMR) genes MSH2 and MLH1 are found in most hereditary nonpolyposis colon cancer (HNPCC) patients studied. Eukaryotic MMR uses two partially redundant mispair-recognition complexes, Msh2p-Msh6p and Msh2p-Msh3p (ref.2) Inactivation of MSH2 causes high rates of accumulation of both base-substitution and frameshift mutations. Mutations in MSH6 or MSH3 cause partial defects in MMR, with inactivation of MSH6 resulting in high rates of base-substitution mutations and low rates of frameshift mutations; inactivation of MSH3 results in low rates of frameshift mutations. These different mutator phenotypes provide an explanation for the observation that MSH2 mutations are common in HNPCC families, whereas mutations in MSH3 and MSH6 are rare. We have identified novel missense mutations in Saccharomyces cerevisiae MSH6 that appear to inactivate both Msh2p-Msh6p- and Msh2p-Msh3p-dependent MMR. Our work suggests that such mutations may underlie some cases of inherited cancer susceptibility similar to those caused by MSH2 mutations.

MLH3: a DNA mismatch repair gene associated with mammalian microsatellite instability

DNA mismatch repair is important because of its role in maintaining genomic integrity and its association with hereditary non-polyposis colon cancer (HNPCC). To identify new human mismatch repair proteins, we probed nuclear extracts with the conserved carboxy-terminal MLH1 interaction domain. Here we describe the cloning and complete genomic sequence of MLH3, which encodes a new DNA mismatch repair protein that interacts with MLH1. MLH3 is more similar to mismatch repair proteins from yeast, plants, worms and bacteria than to any known mammalian protein, suggesting that its conserved sequence may confer unique functions in mice and humans. Cells in culture stably expressing a dominant-negative MLH3 protein exhibit microsatellite instability. Mlh3 is highly expressed in gastrointestinal epithelium and physically maps to the mouse complex trait locus colon cancer susceptibility I (Ccs1). Although we were unable to identify a mutation in the protein-coding region of Mlh3 in the susceptible mouse strain, colon tumours from congenic Ccs1 mice exhibit microsatellite instability. Functional redundancy among Mlh3, Pms1 and Pms2 may explain why neither Pms1 nor Pms2 mutant mice develop colon cancer, and why PMS1 and PMS2 mutations are only rarely found in HNPCC families.

HNPCC-like cancer predisposition in mice through simultaneous loss of Msh3 and Msh6 mismatch-repair protein functions.

Cancer predisposition in hereditary non-polyposis colon cancer (HNPCC) is caused by defects in DNA mismatch repair (MMR). Mismatch recognition is attributed to two heterodimeric protein complexes: MutSalpha (refs 2, 3, 4, 5), a dimer of MutS homologues MSH2 and MSH6; and MutSbeta (refs 2,7), a dimer of MSH2 and MSH3. These complexes have specific and redundant mismatch recognition capacity. Whereas MSH2 deficiency ablates the activity of both dimers, causing strong cancer predisposition in mice and men, loss of MSH3 or MSH6 (also known as GTBP) function causes a partial MMR defect. This may explain the rarity of MSH6 and absence of MSH3 germline mutations in HNPCC families. To test this, we have inactivated the mouse genes Msh3 (formerly Rep3 ) and Msh6 (formerly Gtmbp). Msh6-deficient mice were prone to cancer; most animals developed lymphomas or epithelial tumours originating from the skin and uterus but only rarely from the intestine. Msh3 deficiency did not cause cancer predisposition, but in an Msh6 -deficient background, loss of Msh3 accelerated intestinal tumorigenesis. Lymphomagenesis was not affected. Furthermore, mismatch-directed anti-recombination and sensitivity to methylating agents required Msh2 and Msh6, but not Msh3. Thus, loss of MMR functions specific to Msh2/Msh6 is sufficient for lymphoma development in mice, whereas predisposition to intestinal cancer requires loss of function of both Msh2/Msh6 and Msh2/Msh3.

Genetic testing in families with hereditary nonpolyposis colon cancer.

Genetic testing for hereditary nonpolyposis colon cancer (HNPCC) is available, but the rates of acceptance of testing or barriers to participation are not known. To investigate rates and predictors of utilization of genetic testing for HNPCC. Cohort study conducted between July 1996 and July 1998. Hereditary nonpolyposis colon cancer family registry. Adult male and female members (n = 208) of 4 extended HNPCC families contacted for a baseline telephone interview. Family education and individual genetic counseling. Participant acceptance of HNPCC test results. Of the 208 family members, 90 (43%) received test results and 118 (57%) declined. Of 139 subjects (67%) who completed a baseline telephone interview, 84 (60%) received test results and 55 (40%) declined. Of the 84 subjects who received test results, 35 (42%) received information indicating that they had HNPCC-associated mutations and 49 (58%) that they did not. Test acceptors had higher education levels (odds ratio [OR], 3.74; 95% confidence interval [CI], 2.49-5.61) and were more likely to have participated in a previous genetic linkage study (OR, 4.30; 95% CI, 1.84-10.10). The presence of depression symptoms significantly reduced rates of HNPCC test use (OR, 0.34; 95% CI, 0.17-0.66). Although rates of test use were identical among men and women, the presence of depression symptoms resulted in a 4-fold decrease in test use among women (OR, 0.25; 95% CI, 0.08-0.80) and a smaller, nonsignificant reduction among men (OR, 0.49; 95% CI, 0.19-1.27). Despite having significantly elevated risks of developing colon cancer, a relatively small proportion of HNPCC family members are likely to use genetic testing. Barriers to test acceptance may include less formal education and the presence of depression symptoms, especially among women. Additional research is needed to generalize these findings to different clinical settings and racially diverse populations.