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PubMed2001

Immunoglobulin heavy chain gene analysis of ocular adnexal extranodal marginal zone B-cell lymphoma.

PURPOSE: To clarify the cellular origin of extranodal marginal-zone B-cell lymphoma (EZML) of the mucosa-associated lymphoid tissue (MALT) type in ocular adnexa, the somatic mutation was analyzed in the immunoglobulin heavy-chain variable region (VH) gene. METHODS: Eight cases of EZML in the orbit and four in the conjunctiva were studied. The VH genes were amplified by a seminested PCR and sequenced directly. These were compared with the closest published VH germline segments to determine the somatic mutation frequency. Intraclonal microheterogeneity, which was termed the ongoing mutation frequency in the current study, was estimated by counting the number of single nucleotide substitutions in individual clones and dividing by the total number of nucleotides analyzed. Nine cases of gastrointestinal EMZL were also examined for comparison. RESULTS: The somatic mutation frequency varied between 2.0% and 12.7%, with a mean value of 7.9%. Ten cases with intraclonal microheterogeneity showed between one and six further substitutions. The average of ongoing mutation frequency was 0.11%, with a range of 0% to 0.25%. In the gastrointestinal EMZLs, the average of somatic mutation frequency was 8.5% (1.5%-14.2%) and of ongoing mutation frequency was 0.51% (0.25%-0.75%). CONCLUSIONS: The average of ongoing mutation frequency in ocular adnexal EMZL was lower than that in gastrointestinal EMZL. Both ocular adnexal and gastrointestinal EMZLs are derived from postgerminal center memory B cells, but the low ongoing mutation frequencies of ocular adnexal EMZL may result from less antigen stimulation and follicular colonization in the orbit relative to gastrointestinal EMZL.

Adult↗
PubMed2006

COSMIC 2005.

The Catalogue Of Somatic Mutations In Cancer (COSMIC) database and web site was developed to preserve somatic mutation data and share it with the community. Over the past 25 years, approximately 350 cancer genes have been identified, of which 311 are somatically mutated. COSMIC has been expanded and now holds data previously reported in the scientific literature for 28 known cancer genes. In addition, there is data from the systematic sequencing of 518 protein kinase genes. The total gene count in COSMIC stands at 538; 25 have a mutation frequency above 5% in one or more tumour type, no mutations were found in 333 genes and 180 are rarely mutated with frequencies <5% in any tumour set. The COSMIC web site has been expanded to give more views and summaries of the data and provide faster query routes and downloads. In addition, there is a new section describing mutations found through a screen of known cancer genes in 728 cancer cell lines including the NCI-60 set of cancer cell lines.

Databases, Genetic↗
PubMed2005

Human splenic marginal zone B cells lack expression of activation-induced cytidine deaminase.

It has been speculated that somatic hypermutation of rearranged immunoglobulin variable (V) region genes does not only take place in the germinal center (GC) microenvironment, but also in the marginal zone (MZ) of the spleen, and that human peripheral blood IgM-positive B cells with somatically mutated V region genes may derive from mutating MZ B cells. As somatic hypermutation is strictly dependent on the enzyme activation-induced cytidine deaminase (AID), we used an AID-specific monoclonal antibody that is suitable for immunohistochemical staining to analyze human splenic MZ cells for AID expression. Analysis of tissue sections from 29 spleens revealed only very rare MZ cells (approx. 0.05%) showing AID staining, whereas in 25 of the spleen samples strong AID staining of GC B cells was observed. Thus, there are virtually no AID-expressing MZ B cells, indicating that somatic hypermutation does not take place at a significant level in the MZ. Consequently, it appears unlikely that the somatically mutated IgM B cells are generated in the splenic MZ. Moreover, the lack of AID-positive MZ B cells questions the recent speculation that B cell chronic lymphocytic leukemias with mutated V genes are derived from mutating MZ B cells.

Adolescent↗
PubMed1983

Mutagens: some possible health impacts beyond carcinogenesis.

Considerable attention is currently being given to the roles of environmental and endogenous mutagens in tumor induction and in tumor progression through the abilities of mutagens to induce one or another kind of somatic mutation. It is proposed here that mutagens, also through induction of somatic mutations, initiate a spectrum of additional, much more common, focal lesions that are important to the human condition. While individually they are of relative insignificance and thus neglected by many clinicians, the functional attributes of these focal lesions have important impacts on human physiology and thus contribute substantially to the process of aging. Additionally, one individual focus may progress to an extent that it produces clinically recognizable symptoms and may even jeopardize the carrier's life. The ultimate and developed expression of these lesions is heterogeneous, is far removed in time from initial induction, and relies on additional host and environmental factors for expression; therefore, the possible role of somatic mutation is readily overlooked. The focal lesions reviewed are fibrous atherosclerotic plaques, senile cataracts, and metaplasias. Literature that implicates metaplasias as precursor or as predisposing lesions in the ultimate formation of gallstones, duodenal ulcers, and adenocarcinomas is summarized.

Arteriosclerosis↗
PubMed2003

Autosomal mutation in somatic cells of the mouse.

Tumor suppressor genes are located on autosomal chromosomes. Therefore, an understanding of how cancer-related mutations occur in somatic cells requires a detailed understanding of spontaneous and induced autosomal mutagenesis. This review will present recent advances in the study of how autosomal mutations form in somatic cells by focusing on the mouse Aprt and Tk model systems that have been developed to examine the formation of autosomal mutations in vivo. These loci can detect the entire spectrum of mutations known to inactivate tumor suppressor genes. Studies with these models have provided novel information on the frequencies and types of spontaneous autosomal mutations that occur in different cell types. They also show great promise for the screening of genotoxic effects resulting from environmental exposures and for the study of mutation when DNA repair pathways are compromised. Continued use of the mouse Aprt and Tk models will have a significant impact on our understanding of some of the earliest steps in the conversion of normal cells to those with malignant phenotypes.

Adaptor Proteins, Signal Transducing↗
PubMed2005

The evolution of human anti-double-stranded DNA autoantibodies.

It has been proposed that the anti-double-stranded DNA (dsDNA) response in patients with systemic lupus erythematosus (SLE) is antigen driven and that DNA or nucleosomes select anti-DNA reactive, somatically mutated B cells. We have used site-directed mutagenesis to systematically revert the somatic mutations of two human anti-dsDNA antibodies from SLE patients to analyze the resulting changes in DNA binding as well as binding to other autoantigens. Our data demonstrate that high-affinity binding to dsDNA and nucleosomes is acquired by somatic replacement mutations in a stepwise manner. Reactivity to surface structures of apoptotic cells is acquired by the same somatic mutations that generate high-affinity dsDNA binding. Importantly, revertant antibodies with germ-line V regions did not show any measurable DNA reactivity. We propose that anti-DNA autoantibodies are generated from nonautoreactive B cells during a normal immune response. B cells may acquire autoreactivity de novo during the process of somatic hypermutation. Nucleosomes, if available in lupus patients because of defects in clearing of apoptotic debris, might subsequently positively select high affinity anti-DNA B cells.

Amino Acid Sequence↗
PubMed2001

Analysis of BCL-6 mutations in classic Hodgkin disease of the B- and T-cell type.

BCL-6 is essential for germinal center formation and thus for affinity maturation of immunoglobulin (Ig) genes by somatic mutations. The 5'-noncoding region of the BCL-6 gene is even a target for the mutation machinery. Translocations of the BCL-6 gene to heterologous promoters and mutations of its 5'-noncoding regulatory region were reported to be potential mechanisms for deregulating BCL-6 expression and for playing a role in the genesis of non-Hodgkin lymphoma. In line with this hypothesis is the observation that B-cell lymphoma with somatic mutations, such as diffuse large B-cell lymphoma and follicular lymphoma, also carry BCL-6 mutations, some of which are recurrently detectable. Classic Hodgkin disease (cHD) is also derived from B cells with high loads of somatic mutations and thus a further candidate for BCL-6 mutations. To determine the presence and potential role of BCL-6 mutations in cHD, the 5'-noncoding BCL-6 proportion of single Hodgkin and Reed-Sternberg (HRS) cells from 6 cases of cHD and 6 cases of HD-derived cell lines was analyzed. All B-cell-derived HD cases and cell lines harbored BCL-6 mutations. In contrast, both T-cell-derived HD cases and cell lines were devoid of BCL-6 mutations. With only one exception, there were no lymphoma-specific recurrent BCL-6 mutations detected, and BCL-6 protein was absent from the HRS cells of most cases. In conclusion, (1) somatic BCL-6 mutations are restricted to cHD cases of B-cell origin, and (2) the BCL-6 mutations represent mostly irrelevant somatic base substitutions without consequences for BCL-6 protein expression and the pathogenesis of cHD.

5' Untranslated Regions↗
PubMed1996

Hb Costa Rica or alpha 2 beta 2 77(EF1)His --> Arg: the first example of a somatic cell mutation in a globin gene.

We have identified a minor hemoglobin component (approximately 5%) in the blood of a healthy Costa Rican female, but not in her mother and two brothers (father not studied), that has an His --> Arg replacement at position beta 77 (Hb Costa Rica). No other amino acid replacements were observed and no beta- or gamma-chain-like peptides were present. Hb Costa Rica has abnormal stability. Sequence analyses of numerous polymerase chain reaction (PCR)-amplified segments of DNA that contain exon 2 of the beta gene failed to identify a CAC --> CGC (His --> Arg) mutation. The same was the case when cDNA was sequenced, indicating that a beta-Costa Rica-mRNA could not be detected with this procedure. Gene mapping of genomic DNA with Bg/II, BamHI, and HindIII gave normal fragments only and with the same intensity as observed for the fragments of a normal control. The quantities of the beta chain variants Hb J-Iran and Hb Fukuyama with related mutations at beta 77 vary between 30% and 45% in heterozygotes, whereas that of Hb F-Kennestone with the same His --> Arg mutation but in the G gamma-globin gene, is a high 40%-45% (as percentage of total G gamma) in a heterozygous newborn. These different observations exclude a heterozygosity of the A --> G mutation at codon beta 77, as well as a deletion comparable to that of Hbs Lepore or Kenya, or a beta-globin gene duplication, and point to a nontraditional inheritance of Hb Costa Rica. Allele-specific amplification of cDNA with appropriate primers identified the presence of a low level of mutated mRNA in the reticulocytes of the patient, which was confirmed by dotblot analysis of the same material with 32P-labeled probes. Comparable amplification products were not observed in genomic DNA. The A --> G mutation apparently occurred in a somatic cell at a relatively early stage in the development of the hematopoietic cell system, and Hb Costa Rica accumulated through rapid cell divisions in patchy areas in the bone marrow (somatic mosaicism). An unequal distribution of Hb Costa Rica over the red cells supports this possibility.

Adult↗
PubMed1999

New genetic hypothesis of schizophrenia.

Lack of complete concordance for schizophrenia in monozygotic twins has been interpreted as indicative of non-genetic cofactors in transmission of the illness. We present an alternative hypothesis that can parsimoniously explain, using known genetic mechanisms, the heredity pattern, the phenotypic spectrum and the biological abnormalities found in schizophrenia. The inheritance of a single recessive mutated allele of a gene crucial in brain development if followed by a somatic mutation in the normal allele during critical periods of brain development could result in developmental abnormalities that are expressed behaviorally as schizophrenic illness. Acquisition of this somatic mutation is likely enhanced during periods of intense cell division; therefore, the window of opportunity would be restricted to key periods in neurodevelopment. The somatic mutation may not always occur, thus explaining the variability of expression seen in the clinical population. Because the single allele mutation is still transmissible, the equal incidence of schizophrenia in the offspring of monozygotic twins discordant for the disease could also be explained. This possibility has implications for the development of genetic models and the source of genetic material for studies isolating the gene(s) of schizophrenia.

Brain↗
PubMed2005

ERBB2 kinase domain mutation in the lung squamous cell carcinoma.

Mounting evidence exists that the activation of proto-oncogene by somatic mutation plays an important roles in the development of human cancers. Recent reports revealed that the kinase domain of ERBB2 gene, a proto-oncogene, is somatically mutated in the lung adenocarcinomas, suggesting the mutated ERBB2 gene may act as an oncogene in human cancers. The purpose of this was to see whether the ERBB2 kinase domain is mutated in other lung cancer types besides the adenocarcinoma. Here, we performed mutational analysis of the ERBB2 kinase domain by polymerase chain reaction-single strand conformation polymorphism assay in 114 non-adenocarcinoma type non-small cell lung cancers (NSCLCs) tissue samples, including 100 squamous cell carcinomas, three adenosquamous carcinomas and 11 large cell carcinomas. We detected the ERBB2 kinase domain mutation in one squamous cell carcinoma (1.0%). The detected ERBB2 mutation showed G to C transversion at bp 2305 (2305G>C), which would result in the substitution of Asp to His at codon 769 (D769H). The amino acid D769 is located in the alpha-helix within the kinase domain, which is important in the binding of ATP with ERBB2. We simultaneously analyzed the somatic mutations of EGFR, K-RAS, PIK3CA and BRAF genes in the squamous cell carcinoma with the ERBB2 mutation, and found that the tumor did not harbor any EGFR or ERBB2 or K-RAS or PIK3CA or BRAF gene mutation, either. This study demonstrated that in addition to lung adenocarcinoma ERBB2 kinase domain mutation could occur in lung squamous cell carcinomas, and suggested that alterations of ERBB2-mediated signaling pathway by ERBB2 mutations may occasionally contribute to the development of lung squamous cell carcinomas.

Adult↗
PubMed1999

Lack of c-kit mutation in familial urticaria pigmentosa.

Somatic mutations within c-kit have been reported in individuals with mastocytoses, including urticaria pigmentosa (UP). We have identified three siblings with UP. We aimed to determine whether the c-kit proto-oncogene was playing a part in the aetiology of UP in these three siblings. Using seven microsatellite repeat markers spanning an 8-cM interval encompassing the c-kit gene we followed the transmission of the c-kit gene in this family. Furthermore, single-strand conformation polymorphism analysis was used to scan exon 17 of the c-kit gene for mutations in genomic DNA of all family members and somatic DNA extracted from skin of the eldest affected sibling, the proband. No mutations were found in exon 17 in either genomic DNA of all family members or somatic DNA of the proband. Patients with UP have been shown to possess somatic mutations of the c-kit gene. However, this locus has been excluded as playing a part in the three siblings examined here in whom a second gene locus must be determining their UP. Therefore, this study emphasizes genetic heterogeneity in UP. Future study to identify primary molecular determinants of UP should include affected sib-pair studies.

Child, Preschool↗
PubMed2000

Hormone status selects for spontaneous somatic androgen receptor variants that demonstrate specific ligand and cofactor dependent activities in autochthonous prostate cancer.

We have used the autochthonous transgenic adenocarcinoma of mouse prostate (TRAMP) model to investigate the relationship between somatic mutation in the androgen receptor (AR) and the emergence of androgen-independent prostate cancer. Here we report the identification, isolation, and characterization of distinct classes of AR variants from spontaneous prostate tumors in the TRAMP model. Using cDNA cloning, single stranded conformation polymorphism and sequencing strategies, 15 unique somatic mutations in the AR were identified in prostate tumors obtained from eight TRAMP mice between 24 and 29 weeks of age. At least one mutation was isolated from each mouse. All mutations were single base substitutions, 10 were missense and 5 were silent. Nine mutations in the AR were identified in tumors of four mice that were castrated at 12 weeks of age. Interestingly, the majority of mutations (seven out of nine, 78%) identified in the androgen-independent tumors colocalized in the AR transactivation domain. The remaining mutations colocalized in the AR ligand binding domain. In general, the AR variants demonstrated promoter-, cell-, and cofactor-specific activities in response to various hormones. All AR variants isolated in this study maintained strong sensitivity for androgens, and four AR variants isolated from castrated mice demonstrated increased activities in the absence of ligand. The K638M and F677S variants demonstrated increased activities in response to androgen, and K638M also demonstrated increased response to estradiol. In the presence of AR coactivator ARA70 the E231G variant demonstrated increased activity in response to both androgen and estradiol. However, in the presence of AR coactivator ARA160 the E231G variant was selectively responsive to androgen. Collectively these analyses not only indicate that somatic mutations in the AR gene occur spontaneously in TRAMP tumors but also how changes in the hormonal environment may drive the selection of spontaneous somatic mutations that provide a growth advantage.

Animals↗
PubMed1991

Clonal characterization of the human IgG antibody repertoire to Haemophilus influenzae type b polysaccharide. IV. The less frequently expressed VL are heterogeneous.

We previously demonstrated that the human anti-Haemophilus influenzae type b polysaccharide (Hib-PS) VL repertoire is dominated by a product of the V kappa II gene, A2, and that V kappa II-A2 anti-Hib-PS antibodies have little or no somatic mutation in VL. To further study this VL repertoire, we studied non-A2 anti-Hib-PS antibodies that were identified either serologically or by amino-terminal amino acid sequence analysis. Of 15 non-A2 anti-Hib-PS antibodies from 12 vaccinated adults, we found four V lambda, five V kappa I, one non-A2 V kappa II, four V kappa III, and one V kappa IV antibodies. As expected, all but two of these subjects also produced V kappa II-A2 antibodies. Interestingly, one of these subjects lacks the A2 gene in the germ line. However, both subjects who did not produce detectable V kappa II antibody did produce normal amounts of total anti-Hib-PS antibody after vaccination. Candidate V kappa genes for the non-A2 antibodies were identified by comparison of up to 60 VL amino acid residues, including CDR1 and CDR2, with all sequenced V kappa genes. V kappa I antibodies appear to be products of three newly sequenced V kappa I genes, O8, O18, and L11, that are reported here. The O8 and O18 genes encode identical amino acid sequences. The non-A2 V kappa II antibody is a likely product of the A1 or A17 genes, the V kappa III antibodies are likely products of the A27 gene, and the V kappa IV antibody is a product of the single V kappa IV gene, B3. Unlike V kappa II-A2 antibodies, the V kappa I, V kappa III, and V kappa IV antibodies differed by one to five CDR residues from the germ line product of the candidate genes, suggesting the presence of somatic mutations. Thus, anti-Hib-PS antibodies can be divided into two types, the most frequently observed A2 antibodies with little or no somatic mutation and non-A2 antibodies that likely contain somatic mutations.

Amino Acid Sequence↗
PubMed1998

Anti-CD34+ Fabs generated against hematopoietic stem cells in HIV-derived combinatorial immunoglobulin library suggest antigen-selected autoantibodies.

Bone marrow suppression associated with HIV infection does not appear to be solely due to direct viral cytopathic effects. Autoantibodies may play a role in myelosuppression, however it is unclear whether autoantibodies produced in HIV infection represent a primary pathogenic process or merely reflect polyclonal B cell activation. To address these questions, we generated combinatorial immunoglobulin libraries using the pComb3 phagemid from an HIV+ individual with evidence of circulating autoantibodies. From one library, three anti-CD34 Fabs were identified using fresh CD34+ cells as antigenic targets by a method of phage subtraction. The anti-CD34 Fabs are specific by immunoblotting and Elisa and are of high affinity, with calculated Kds in the range of 10(-7) -10(-8) M. Nucleic acid sequencing revealed all three to be of the VH3 family and to have lambda light chains with some gene segments expressing little somatic mutation, while other segments were somatically mutated in patterns suggestive of antigen selection. These findings indicate that (1) A subset of HIV-associated anti-CD34 autoantibodies are monospecific and antigen-selected and are not merely a consequence of polyclonal B cell activation and elevated Ig levels in HIV. Autoreactivity in HIV therefore includes both polyspecific, low affinity antibodies as well as monospecific antigen-selected high affinity antibodies. (2) Although bone marrow suppression in HIV is likely to be multifactorial, autoantibodies to hematopoietic stem cells may contribute to its pathogenesis. (3) Library sampling of VH gene family rearrangements shows no evidence for under-representation of the VH3 family in the immune dysregulation of HIV infection. Phage subtraction is corroborated to be an effective means of identifying, cloning, and characterizing antibodies to hematopoietic differentiation antigens.

Antibody Affinity↗
PubMed2004

Detection of mitochondrial DNA alterations in plasma of malignant melanoma patients.

Genetic changes in mitochondrial DNA (mtDNA) have been detected in a variety of pathologic conditions including cancer. We hypothesized that malignant melanoma has genetic alterations in the displacement loop (D-loop) region and that these mtDNA alterations can be detected in blood as a circulating DNA melanoma marker. D-loop region from 20 melanoma cell lines, 12 metastatic melanoma specimens, and corresponding lymphocytes and plasma samples were sequenced using the CEQ 8000 XL Genetic Analysis System (Beckman Coulter). Nine of 20 (45%) melanoma cell lines and 5 of 12 (42%) melanoma specimens contained somatic mutations in the D-loop region of mtDNA. DNA alterations in the polycytosine tract (C-tract) of D-loop were detected in 6 of 20 (30%) cell lines and 2 of 12 (17%) specimens. Two of five paired plasma samples (40%) contained the same mutations as did melanoma specimens. In a comparison of lymphocytes and plasma of melanoma patients, 9 of 44 paired plasma samples (20%) contained at least one mutation compared to corresponding lymphocytes. Somatic mutations in the D-loop region of tumor and paired plasma did not correlate with the clinicopathological characteristics. However, circulating mtDNA alterations were more frequent in advanced disease. Studies indicate that circulating mtDNA mutations in the plasma of melanoma patients can be detected.

Base Pair Mismatch↗
PubMed1989

Unique V gene usage by B-Ly1 cell lines, and a discordance between isotype switch commitment and variable region hypermutation.

We have previously described a series of Ly-1+ B cell lines obtained as spontaneous outgrowth cultures from mouse spleen cells (B-Ly1 cells). In this study, we report the variable region sequences utilized by independent cell lines derived from three mouse strains. Remarkably, V region utilization and junctional diversification were essentially identical in all three cell lines. These included: lambda 1 light chain; JH1; DSP2-7,8; and, a novel VH gene segement. The VH was highly homologous to CP4, a rare VH family previously found in a group of Ly-1 B cell-derived autoantibodies to bromelain-treated mouse red blood cells. The selective expression of this unusual lg species implies the action of distinctive molecular or immunophysiological processes in the outgrowth of B-Ly1 cell lines. Clarification of these factors may be relevant to understanding the peculiar biology of Ly-1 B cells in vivo. We have also evaluated switch-committed B-Ly1 clones to determine whether this phenotype is accompanied by variable region somatic mutation. However, no evidence for somatic mutation was observed in these induced clones. This may indicate that these two processes are independently regulated, despite their common concordance in vivo.

Amino Acid Sequence↗
PubMed1996

The B cell response to autologous type II collagen: biased V gene repertoire with V gene sharing and epitope shift.

Collagen-induced arthritis is an autoimmune model disease induced in the DBA/1 mouse immunized with type II collagen (CII). Both T and B cells play a critical role for the induction of arthritis. Draining lymph nodes from CII-immunized mice contain high numbers of CII-specific B cells, which are isotype switched and V gene selected. In the present study we analyze the V region gene usage and epitope specificity of CII-reactive B cell hybridomas, randomly isolated from the primary and the secondary response in mice immunized with rat CII we make the following conclusions. 1) There are major epitopes in the native CII molecule to which the B cells preferentially respond. 2) B cells specific for the same epitope show a preferential pairing of certain VH/VK genes or a biased usage of individual VH (VHJ558 and VHX24) or VK genes (VK21). 3) The V genes are germ line encoded in the primary response and somatically mutated in the secondary response. Somatic mutations give the Abs cross-reactivity between CII epitopes, and epitope shift, i.e., another epitope within the CII molecule is recognized. 4) There is a sharing of certain V genes in B cell clones specific for different epitopes, indicating structural similarities of the different CII epitopes.

Amino Acid Sequence↗
PubMed1998

Somatic instability of the APC I1307K allele in colorectal neoplasia.

The adenomatous polyposis coli (APC) gene is proposed to function as a gatekeeper of colorectal neoplasia. A germ-line variant of this gene, the APC I1307K allele, is present in approximately 6% of the Ashkenazi Jewish population. To assess the role in tumorigenesis of the variant (A)8 tract produced by this allele, we undertook a somatic mutation analysis of the region surrounding codon 1307 in colorectal tumors from APC I1307K carriers. Somatic mutations involving the variant (A)8 tract were identified in 53 of 127 (42%) tumors from APC I1307K carriers compared with 5 of 127 (4%) mutations involving the wild-type allele of these tumors (P < 0.0001). Loss of heterozygosity of the wild-type allele was significantly more common in tumors with APC I1307K allele mutations (25 of 41, 61%) compared with APC I1307K carrier tumors without mutation of the variant (A)8 tract (12 of 53, 23%; P < 0.0005). This somatic biallelic APC inactivation further confirms the biological importance of the I1307K germ-line variant. The vast majority of APC I1307K somatic mutations consisted of a single adenine insertion (insA) involving the variant (A)8 tract. This insA mutation was mutually exclusive of the presence of microsatellite instability with 0 of 49 tumors with insA displaying BAT-26 instability compared with 9 of 78 tumors without insA (P=0.01). These findings support a model where somatic instability of the (A)8 tract produced by the APC I1307K allele leads to increased APC gene inactivation and directly accounts for 42% of the colorectal neoplasms occurring in APC I1307K carriers.

Adenomatous Polyposis Coli↗