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Henry T Lynch

Publications and source records attributed to Henry T Lynch.

At least 73 records · Page 4Linked to original sources
PubMed2004

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.

Adult↗
PubMed2004

Inflammatory bowel disease in Ashkenazi Jews: implications for familial colorectal cancer.

Inflammatory bowel disease (IBD) has a multifactorial etiology and includes ulcerative colitis (UC) and Crohn's disease (CD). Powerful epidemiologic and genetic studies have provided ample evidence that a subset of both CD and UC are attributable to a likely primary genetic etiology. This is evidenced by the recent identification of the IBD1 gene ( NOD2 ) mutations which show an association with susceptibility to CD. The IBD complex shows a significant increased frequency in Jews when compared to non-Jews. While there is an increased incidence of colorectal cancer (CRC) in patients with IBD, it nevertheless is important to realize that IBD likely accounts for no more than 1-3% of all cases of CRC in Ashkenazi Jews. Importantly, however, awareness of the increased CRC risk in IBD may aid immeasurably in preventive interventions. The molecular pathway leading to CRC in IBD appears to differ from the well-known adenoma-to-CRC sequence, given the fact that these cancers appear to arise from either flat, dysplastic tissue or dysplasia-associated lesions or masses (DALMs). An important model, but by no means an absolute one, for colon carcinogenesis in IBD follows progression from an absence of dysplasia, to indefinite dysplasia, to low-grade dysplasia, on to high-grade dysplasia, and ultimately to invasive CRC. This carcinogenic process relates to the disease duration with respect to the extent of colonic involvement and may also involve primary sclerosing cholangitis. Given this knowledge of an increased risk for CRC in UC and CD, surveillance colonoscopy should initially be performed 8-10 years after onset of symptoms as opposed to diagnosis, and it should be performed 1-2 years after 8 years of disease in patients with pancolitis or after 15 years in those with left-sided colitis. A search for dysplasia of colonic mucosa with biopsies performed in all four quadrants every 10 cm throughout the colon is exceedingly important. Additional biopsies should be taken of any flat lesions, masses, or strictures. Prophylactic colectomy may then be indicated when severe dysplasia is confirmed by knowledgeable pathologists.

Adult↗
PubMed2004

Familial pancreatic carcinoma in Jews.

Pancreatic cancer (PC) is the most fatal of all gastrointestinal cancers, wherein its mortality compares strikingly with its incidence. Unfortunately, 80-90% of PCs are diagnosed in the nonresectable stage. While the lifetime risk of PC in developed countries is approximately 1-3%, it is the fifth most common cause of cancer deaths among both males and females in Western countries. It occurs in excess in Jews. Approximately 5-10% of PC shows familial clustering. Examination of such familial clusters must take into consideration cancers of diverse anatomic sites, such as malignant melanoma in the familial atypical multiple melanoma (FAMMM) syndrome due to the CDKN2A (p16) germline mutation, and combinations of colorectal and endometrial carcinoma, ovarian carcinoma, and several other cancers in hereditary nonpolyposis colorectal cancer (HNPCC), which are due to mismatch repair germline mutations, the most common of which are MSH2 and MLH1 . Other hereditary disorders predisposing to PC include Peutz-Jeghers syndrome, due to the STK11 mutation, familial pancreatitis due to the cationic trypsinogen gene, site-specific familial pancreatic cancer which may be due to the 4q32-34 mutation, hereditary breast-ovarian cancer (HBOC) syndrome that is due to BRCA2 and possibly some families with HBOC that is due to BRCA1 , familial adenomatous polyposis due to the ATP gene, and ataxia telangiectasia due to the ATM germline mutation. This extant heterogeneity mandates that the physician be knowledgeable about these PC-prone syndromes which play such an important role when considering the differential diagnosis of hereditary PC. Unfortunately, there are no PC screening programs with acceptable sensitivity and specificity. However, the gold standard for screening at this time is endoscopic ultrasound. Clearly, there is a great need for the development of novel screening approaches with acceptable sensitivity and specificity. Further research is needed to elucidate those etiologic factors that contribute to the apparent excess of PC in Ashkenazi Jews. Attention should also be given to the search for mutations predisposing to PC in Jews so that opportunities to learn more about the disease's pathogenesis, as well as screening and control, may take place.

Adult↗
PubMed2004

Challenging pedigrees seen in a hereditary cancer consultation center.

The clinical translation of the significance of cancer "running in families" has become a source of major contention as a result of the explosion of knowledge about cancer causality at the molecular level. At the clinical level, the increasing awareness of the familial and hereditary burden of cancer has contributed heavily to both physician and lay concern about cancer risk. Problems in interpretation of the significance of a cancer family history may arise due to a variety of factors, and even if the physician correctly diagnoses a hereditary cancer-predisposing syndrome there may still be barriers to patient compliance with surveillance and management recommendations. Our purpose is to discuss a variety of potential barriers in the diagnosis and management of patients at increased hereditary cancer risk, drawing on examples from a cohort of approximately 300 families evaluated at Creighton University's Hereditary Cancer Consultation Center over 8 years. Each case was selected because of the presence of one or more clinical, pathologic, molecular genetic, psychosocial, economic, confidentiality, or insurance or employment discrimination factors that had the potential to pose an obstacle in diagnosis or in patient compliance with screening and management recommendations.

Aged↗
PubMed2004

Identification of high-risk pancreatic cancer-prone families.

Pancreatic cancer-prone families provide a unique resource for studying the etiology, natural history, genetics, and treatment of pancreatic cancer. The only effective way of identifying these families is by obtaining a complete family history, since it is not possible to differentiate sporadic pancreatic cancer cases from hereditary cases based on either clinical presentation or features. These families also would benefit greatly from early detection or prevention strategies. Ultimately, this knowledge could be applied to the more common sporadic form of pancreatic cancer, where diagnosis is almost always late, and prognosis remains quite grim.

Genes, BRCA2↗
PubMed2004

Immunoassay for wild-type protein in lymphocytes predicts germline mutations in patients at risk for hereditary colorectal cancer.

Using colorectal cancer (CRC) as an example, we present the hypothesis that quantitative immunoassays for wild-type (full-length) proteins can be used to identify carriers of traits for hereditary diseases. In the case of hereditary CRC, this involves identifying individuals with germline mutations in a mismatch-repair (MMR) gene (mainly hMSH2 or hMLH1) or in the adenomatous polyposis coli (APC) gene. Because expression of wild-type protein should reflect wild-type gene dosage, we predicted that individuals harboring a germline mutation will have a reduction of approximately 50% in expression in lymphocytes of the corresponding full-length protein. In this pilot study, we tested lymphoblastoid cell lines that had been established from controls and individuals with, or at high risk for, hereditary CRC: 9 lines from healthy, unaffected individuals; 4 from affected members in familial adenomatous polyposis families (with known germ-line APC mutation); 42 from CRC patients in our Familial CRC Registry (increased risk of hereditary nonpolyposis colon cancer as assessed by family history, age at adenoma or carcinoma diagnosis, and other clinical criteria). For MSH2 and MLH1 we used western blots; for APC we used immunoprecipitation. All familial adenomatous polyposis lines had about 50% less immunoprecipitable full-length APC protein. Some cell lines (7 of 42) from Familial CRC Registry patients showed on western blots a reduction (mean 46%) in either MSH2 or MLH1 (relative to the other protein). All 7 subsequently were proved to contain a germline MMR mutation. We conclude that (1) because most of the expected CRC-causing germ line mutations are truncation-causing, immunoassays for wild-type protein should be able to identify most individuals with hereditary CRC-causing traits; (2) these assays, which are more practical and inexpensive than current mutation-detecting tests for hereditary CRC traits, have the potential for commercial development into broad-based population screens of high-risk patients and their families and the potential to save both lives and health-care dollars; (3) this strategy may be useful for other hereditary cancers and even other hereditary diseases; (4) our approach has the potential to greatly benefit public-health programs for cancer control.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Analysis of CHEK2 gene for ovarian cancer susceptibility.

OBJECTIVES: A deletion variant in the CHEK2 gene (del1100C) has been implicated as a low-penetrance risk factor for breast cancer. We sought to determine contribution of CHEK2 mutations to the etiology of ovarian cancer (OvCa). METHODS: We used cases ascertained from the United States through Gynecologic Oncology Group (GOG) protocols 172, 182, and 144, the University of Hawaii Cancer Research Center, and Creighton University. Control women were recruited from Pittsburgh and Hawaii. Denaturing high-performance liquid chromatography, sequence analysis, and single nucleotide polymorphism genotyping by Pyrosequencing were employed to analyze the CHEK2 gene. RESULTS: Mutation screening of the CHEK2 gene in 48 cases who had a first-degree relative with OvCa uncovered only del1100C and A252G variants. Altogether, the del1100C variant was detected in none of 751 unselected cases, in 1 of 52 (1.9%) cases who had a first-degree relative with OvCa, and in 3 of 521 (0.6%) unselected controls. The frequencies of del1100C and A252G variants did not show statistically significant differences between the cases and the controls. CONCLUSIONS: These results suggest that variations in CHEK2 do not make a significant contribution to the pathogenesis of OvCa in the U.S. population.

Adult↗
PubMed2004

Cancer variation associated with the position of the mutation in the BRCA2 gene.

Inherited mutations of the BRCA2 gene give rise to a multi-site cancer phenotype which includes breast cancer (in female and males), ovarian, pancreatic and prostate cancer, ocular and other melanomas, laryngeal, colon and stomach cancers. Interpretation of test results and risk assessment is therefore complex. It has been proposed that families with mutations in the ovarian cancer cluster region (OCCR) of exon 11 (nucleotides 3035-6629) express a higher ratio of ovarian to breast cancer, than families with mutations elsewhere in the BRCA2 gene. In this study we have investigated the presence of 7 types of cancer (ovary, male breast, pancreas, prostate, colon, stomach and melanoma) in first- and second-degree relatives of mutation-positive individuals in 440 families with a BRCA2 mutation. We reviewed histories of cancer in relatives among families with mutations distributed throughout the gene. Families with ovarian cancer were more likely to harbour mutations in the OCCR (nucleotides 3035-6629) than elsewhere in the gene (OR = 2.21; P = 0.0002). We also compared cancer risks according to ethnic group. Ashkenazi Jewish families with the 6174delT founder mutation were more likely to have a family member with ovarian cancer (OR = 1.58; P = 0.002) and less likely to have a family member with prostate cancer (OR = 0.62; P = 0.04) than were non-Jewish families. In contrast, a reduced presence of ovarian cancer was found in families of French-Canadian ancestry, compared to other ancestries (OR = 0.37; P = 0.0026). A high risk of male breast cancer was observed with the 6503delTT mutation (OR = 15.7; P = 0.023). Families of Polish ancestry had a reduced frequency of pancreatic cancer (OR = 0.0; P = 0.03) compared to families of other ethnic origins. In conclusion, both the position of mutation and the ethnic background of the family appear to contribute to the phenotypic variation observed in families with BRCA2 mutations.

BRCA2 Protein↗
PubMed2003

Loss of surface and cyst epithelial basement membranes and preneoplastic morphologic changes in prophylactic oophorectomies.

BACKGROUND: The authors suggested that the loss of collagen IV and laminin-containing basement membrane and the loss of Disabled-2 (Dab2) expression were two critical events associated with morphologic dysplastic changes of the ovarian surface epithelium as a step in tumorigenicity. Both the basement membrane and Dab2, a candidate tumor suppressor of ovarian carcinoma, were involved in epithelial cell surface positioning and organization. The authors speculated that the purging of the basement membrane may be similar to the proteolysis during gonadotropin-stimulated ovulation, a cyclooxygenase 2 (Cox-2)-mediated process. METHODS: Prophylactic oophorectomy is used to prevent breast and ovarian carcinoma in high-risk populations. These ovarian tissue specimens often contain an increased presence of morphologically abnormal lesions that are believed to be preneoplastic. The authors evaluated archived prophylactic oophorectomy specimens to verify whether the loss of Dab2 expression and the removal of the basement membrane that occur at the ovarian surface and inclusion cyst epithelia are molecular markers of preneoplastic lesions. Of the 36 samples containing identifiable ovarian surface epithelial components on slides, immunostaining was employed to evaluate the intactness of the basement membrane (periodic acid-Schiff [PAS], collagen IV, and laminin) and the expression of Dab2 and Cox-2. Expression of Cox-1 and Cox-2 also were evaluated in cultured ovarian surface epithelial cells prepared from ovarian tissue specimens removed from patients who underwent prophylactic surgery. RESULTS: The morphologically normal ovarian surface epithelium typically contained a collagen IV- and laminin-positive basement membrane, which also was detected by PAS staining. Many morphologically altered areas, such as papillomatosis, invaginations, inclusion cysts, stratification, adenomas, and microscopic adenocarcinomas, were found in these specimens. Both the morphologically altered and adjacent morphologically normal epithelia consistently exhibited loss of basement membrane and/or Dab2 expression and an increase in Cox-2 staining. Frequently, an increase in Cox-2 staining was correlated with the loss of epithelial basement membrane in morphologically normal areas. CONCLUSIONS: The loss of Dab2 and basement membrane and the overexpression of Cox-2 were observed in presumptive neoplastic precursor areas of oophorectomy specimens obtained from a population at high risk for ovarian carcinoma. Transient loss of collagen IV and laminin in the basement membrane of the preneoplastic epithelium and the loss of Dab2 expression are common early events associated with morphologic alteration and tumorigenicity of the ovarian surface epithelium. The authors concluded that Cox-2 overexpression may play a role in the purging of basement membrane of the ovarian surface epithelium, mimicking the process of ovulation. Further experiments may be able to test the hypothetical model derived from these histologic observations.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Familial sarcoma: challenging pedigrees.

BACKGROUND: Partially due to the rare occurrence of soft tissue and osteogenic sarcomas in the general population, scant attention has been given to their hereditary etiology. Their overall poor prognosis might be ameliorated through an understanding of their environmental and hereditary causal factors, and/or their interactions, thereby contributing to earlier diagnosis and even the development of molecularly based targeted therapy. METHODS: The authors selected 10 sarcoma-prone families from their extensive hereditary cancer-prone family resource and focused on their challenging diagnostic, surveillance, and management features. The family study protocol included the compilation of a detailed family history of malignant disease of all anatomic sites and the collection of all available primary medical and pathology documents for verification. Genetic counseling was provided before DNA collection and at disclosure of results. RESULTS: These families displayed marked phenotypic and genotypic heterogeneity. In one of these families, 16 relatives had sarcomas, with 2 of the 16 each having 2 metachronous sarcomas; to our knowledge, this represents the greatest number of sarcomas reported in any family described to date. Two familial atypical multiple-mole melanoma syndrome kindreds with the CDKN2A mutation showed the association of sarcoma with malignant melanoma, whereas one family had several pancreatic carcinomas. Other families with sarcoma had hereditary nonpolyposis colorectal carcinoma with MSH2 mutation, hereditary breast carcinoma with BRCA1 mutation, and p53 mutation in a Li-Fraumeni syndrome. CONCLUSIONS: Sarcoma-prone families reported in the current study were selected carefully to depict clinicopathology and compliance features, the understanding of which could elucidate the etiologic role of genetic factors in concert with the phenotypic and genotypic heterogeneity encountered in such families. The lack of a population-based data set for these families posed a limitation.

Adult↗
PubMed2003

Disruption of the expected positive correlation between breast tumor size and lymph node status in BRCA1-related breast carcinoma.

BACKGROUND: A positive correlation between breast tumor size and the number of axillary lymph nodes containing tumor is well established. It has been reported that patients with BRCA1-related breast carcinoma are more likely than patients with nonhereditary breast carcinoma to have negative lymph node status. Therefore, the authors questioned whether the known positive correlation between tumor size and lymph node status also was present in women with BRCA1-related breast carcinomas. METHODS: The relation between the greatest dimension of the resected breast tumor (size) and the presence of positive axillary lymph nodes (expressed as a percentage of all lymph nodes examined) was evaluated in 1555 women with invasive breast carcinoma who were ascertained at 10 centers in North America between 1975 and 1997. There were 276 BRCA1 mutation carriers, 136 BRCA2 carriers, and 1143 women without a known mutation (208 BRCA1/BRCA2 noncarriers and 935 untested women). Patients were stratified according to tumor size, and odds ratios were estimated for the presence of positive lymph nodes with increasing tumor size. RESULTS: A highly significant positive correlation between tumor size and the frequency of positive axillary lymph nodes was seen for BRCA1/BRCA2 noncarriers, for BRCA2 carriers, and for untested women (overall P < 0.0001 for each). In contrast, there was no clear correlation between tumor size and positive lymph node status in BRCA1 carriers (overall P = 0.20). CONCLUSIONS: The relation between tumor size and lymph node status in patients with breast carcinoma appears to be different in BRCA1 carriers compared with BRCA2 carriers and noncarriers. These findings have important implications for estimating the route of metastatic spread and for evaluating the effectiveness of early diagnosis in patients with BRCA1-related breast carcinoma.

Breast Neoplasms↗
PubMed2003

Characterization of the neoplastic phenotype in the familial atypical multiple-mole melanoma-pancreatic carcinoma syndrome.

BACKGROUND: Previous studies suggest that the familial atypical multiple-mole melanoma (FAMMM) syndrome may predispose affected families to nonmelanoma carcinomas, including adenocarcinoma of the pancreas. It has been found that many of these families harbor mutations in the CDKN2A gene on chromosome 9p21. The phenotypic expression of CDKN2A mutations in these families has not been characterized fully. METHODS: The authors studied eight families that appeared to inherit multiple nevi, cutaneous melanomas, and pancreatic carcinomas in association with a CDKN2A germline mutation. The expression of disease within these families was examined, and segregation ratios were estimated to assess the patterns of inheritance according to various definitions of phenotype. RESULTS: Either multiple nevi or pancreatic carcinoma was diagnosed in 53% of first-degree relatives of the probands. The offspring of parents affected with multiple nevi, melanoma, or pancreatic carcinoma were significantly more likely to be affected themselves compared with the offspring of unaffected parents (48.9% vs. 16.7%; P = 0.004). CONCLUSIONS: The current results provide additional evidence that multiple nevi, melanoma, or pancreatic carcinoma may be inherited as autosomal-dominant traits in families known to harbor CDKN2A mutations. Other malignancies may be a part of the phenotype in these families, although this hypothesis requires additional study.

Adult↗
PubMed2003

Three new mutations in hereditary nonpolyposis colorectal cancer (Lynch syndrome II) in Uruguay.

Hereditary nonpolyposis colorectal cancer (HNPCC) is the most common hereditary form of colorectal cancer (CRC). Our purpose is to describe three extended HNPCC families, each of which manifests novel germline mutations in Uruguay, a small country that is a study model for cancer investigation given its high cancer incidence and mortality rate. This is a study of three extended HNPCC families in which extensive genealogic information, medical history, and pathology findings are critically reviewed. DNA testing was performed for evidence of HNPCC mutations. The findings reveal three novel germline mutations, namely MLH1, with a deletion resulting in a frameshift and a premature stop codon (codon 228) in one of the families; in the second family, MSH2 exon 1, codon 61 at nucleotide 181, which results in immediate stop of translation; and in the third family, a mutation in MSH2 at exon 3: the amino acid at nucleotide 530, codon 117, causing a frameshift and a premature stop codon eight base pairs later. We conclude that it is important to study HNPCC mismatch repair genes because of emerging evidence for genotypic and phenotypic heterogeneity, which will harbor the potential to eventually translate this knowledge into specific screening and management protocols. Future projections for such mutations could even contribute to the emergence of molecular-based designer drugs developed through advances in genomics, proteomics, high-throughput screening, and bioinformatics, which would be effective therapeutically for these high-cancer risk patients.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Molecular analysis of hereditary nonpolyposis colorectal cancer in the United States: high mutation detection rate among clinically selected families and characterization of an American founder genomic deletion of the MSH2 gene.

The identification of germline mutations in families with HNPCC is hampered by genetic heterogeneity and clinical variability. In previous studies, MSH2 and MLH1 mutations were found in approximately two-thirds of the Amsterdam-criteria-positive families and in much lower percentages of the Amsterdam-criteria-negative families. Therefore, a considerable proportion of HNPCC seems not to be accounted for by the major mismatch repair (MMR) genes. Does the latter result from a lack of sensitivity of mutation detection techniques, or do additional genes underlie the remaining cases? In this study we address these questions by thoroughly investigating a cohort of clinically selected North American families with HNPCC. We analyzed 59 clinically well-defined U.S. families with HNPCC for MSH2, MLH1, and MSH6 mutations. To maximize mutation detection, different techniques were employed, including denaturing gradient gel electrophoresis, Southern analysis, microsatellite instability, immunohistochemistry, and monoallelic expression analysis. In 45 (92%) of the 49 Amsterdam-criteria-positive families and in 7 (70%) of the 10 Amsterdam-criteria-negative families, a mutation was detected in one of the three analyzed MMR genes. Forty-nine mutations were in MSH2 or MLH1, and only three were in MSH6. A considerable proportion (27%) of the mutations were genomic rearrangements (12 in MSH2 and 2 in MLH1). Notably, a deletion encompassing exons 1-6 of MSH2 was detected in seven apparently unrelated families (12% of the total cohort) and was subsequently proven to be a founder. Screening of a second U.S. cohort with HNPCC from Ohio allowed the identification of two additional kindreds with the identical founder deletion. In the present study, we show that optimal mutation detection in HNPCC is achieved by combining accurate and expert clinical selection with an extensive mutation detection strategy. Notably, we identified a common North American deletion in MSH2, accounting for approximately 10% of our cohort. Genealogical, molecular, and haplotype studies showed that this deletion represents a North American founder mutation that could be traced back to the 19th century.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Hereditary breast-ovarian cancer at the bedside: role of the medical oncologist.

PURPOSE: To provide practical considerations for diagnosing, counseling, and managing patients at high risk for hereditary breast cancer. DESIGN: We have studied 98 extended hereditary breast cancer (HBC)/hereditary breast-ovarian cancer (HBOC) families with BRCA1/2 germline mutations. From these families, 1,315 individuals were counseled and sampled for DNA testing. Herein, 716 of these individuals received their DNA test results in concert with genetic counseling. Several challenging pedigrees were selected from Creighton University's hereditary cancer family registry, as well as one family from Evanston/Northwestern Healthcare, to be discussed in this present report. RESULTS: Many obstacles were identified in diagnosis, counseling, and managing patients at high risk for HBC/HBOC. These obstacles were early noncancer death of key relatives, perception of insurance or employment discrimination, fear, anxiety, apprehension, reduced gene penetrance, and poor compliance. Other important issues such as physician culpability and malpractice implications for failure to collect or act on the cancer family history were identified. CONCLUSION: When clinical gene testing emerged for BRCA1 and BRCA2, little was known about the efficacy of medical interventions. Potential barriers to uptake of testing were largely unexplored. Identification and referral of high-risk patients and families to genetic counseling can greatly enhance the care of the population at the highest risk for cancer. However, because premonitory physical stigmata are absent in most of these syndromes, an HBOC diagnosis may be missed unless a careful family history of cancer of the breast, ovary, or several integrally associated cancers is obtained.

Adult↗
PubMed2003

Pathogenicity of the hereditary colorectal cancer mutation hMLH1 del616 linked to shortage of the functional protein.

BACKGROUND & AIMS: Hereditary nonpolyposis colorectal cancer is associated with mismatch repair deficiency. Most predisposing mutations prevent the production of functional mismatch repair protein. Thus, when the wild-type copy is also inactivated, the cell becomes mismatch repair deficient, and this leads to a high degree of microsatellite instability in tumors. However, tumors linked to nontruncating mutations may display positive or partly positive immunohistochemical staining of the mutated protein and low or atypical microsatellite instability status, which suggests impaired functional activity but not a total lack of mismatch repair. We found human mutL homology (hMLH) 1 del616, one of the most widespread recurring mutations in hereditary nonpolyposis colorectal cancer, segregating in a large hereditary nonpolyposis colorectal cancer family. Because the predicted coding change is a deletion of only 1 amino acid, the pathogenicity of the mutation was evaluated. METHODS: Many analyses were performed to assess the pathogenicity of hMLH1 del616 and to study the expression and function of the mutated messenger RNA and protein. RESULTS: Genetic and immunohistochemical evidence supported hMLH1-linked cancer predisposition in this family. Microsatellite instability varied from low to high, and the hMLH1 protein was lost in 2 tumors but was partly detectable in 1 tumor. Whereas similar optimal amounts of mutated hMLH1 del616 and wild-type hMLH1 proteins were equally functional in an in vitro mismatch repair assay, the amount of in vivo-expressed hMLH1 del616 was much lower than the amount of wild-type protein; this suggests that the deletion imparts instability to the mutant protein. CONCLUSIONS: Our results suggest that the pathogenicity of hMLH1 del616 is not linked to nonfunctionality, but to shortage of the functional protein.

Adaptor Proteins, Signal Transducing↗