RESUMEN
Two forms of genetic instability have been described in colorectal cancer: microsatellite instability and chromosomal instability. Microsatellite instability results from mutations in mismatch repair genes; chromosomal instability is the hallmark of many colorectal cancers, although it is not completely understood at the molecular level. As truncations of the Adenomatous Polyposis Coli (APC) gene are found in most colorectal tumours, we thought that mutations in APC might be responsible for chromosomal instability. To test this hypothesis, we examined mouse embryonic stem (ES) cells homozygous for Min (multiple intestinal neoplasia) or Apc1638T alleles. Here we show that Apc mutant ES cells display extensive chromosome and spindle aberrations, providing genetic evidence for a role of APC in chromosome segregation. Consistent with this, APC accumulates at the kinetochore during mitosis. Apc mutant cells form mitotic spindles with an abundance of microtubules that inefficiently connect with kinetochores. This phenotype is recapitulated by the induced expression of a 253-amino-acid carboxy-terminal fragment of APC in microsatellite unstable colorectal cancer cells. We conclude that loss of APC sequences that lie C-terminal to the beta-catenin regulatory domain contributes to chromosomal instability in colorectal cancer.
Asunto(s)
Aberraciones Cromosómicas , Proteínas del Citoesqueleto/fisiología , Genes Supresores de Tumor , Proteína de la Poliposis Adenomatosa del Colon , Animales , Proteínas del Citoesqueleto/genética , Cinetocoros/metabolismo , Ratones , Ratones Endogámicos C57BL , Mutagénesis , Células Tumorales CultivadasRESUMEN
A mouse model with a targeted mutation in the 3' end of the endogenous Brca1 gene, Brca1(1700T), was generated to compare the phenotypic consequences of truncated Brca1 proteins with other mutant Brca1 models reported in the literature to date. Mice heterozygous for the Brca1(1700T) mutation do not show any predisposition to tumorigenesis. Treatment of these mice with ionizing radiation or breeding with Apc, Msh-2 or Tp53 mutant mouse models did not show any change in the tumor phenotype. Like other Brca1 mouse models, the Brca1(1700T) mutation is embryonic lethal in homozygous state. However, homozygous Brca1(1700T) embryos reach the headfold stage but are delayed in their development and fail to turn. Thus, in contrast to Brca1(null) models, the mutant embryos do not undergo growth arrest leading to a developmental block at 6.5 dpc, but continue to proliferate and differentiate until 9.5 dpc. Homozygous embryos die between 9.5-10.5 dpc due to massive apoptosis throughout the embryo. These results indicate that a C-terminal truncating Brca1 mutation removing the last BRCT repeat has a different effect on normal cell function than does the complete absence of Brca1.
Asunto(s)
Apoptosis/genética , Genes BRCA1/genética , Animales , Proteína BRCA1/genética , Proteína BRCA1/fisiología , Femenino , Muerte Fetal/genética , Genes Letales , Genes p53 , Endogamia , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Modelos Animales , Mutagénesis Insercional , Fenotipo , Embarazo , Estructura Terciaria de Proteína , Proteína p53 Supresora de Tumor/genética , Proteína p53 Supresora de Tumor/fisiologíaRESUMEN
Familial adenomatous polyposis (FAP) can be considered as a condition of the whole body as extracolonic features derived from all the three embryonic lineages are recorded with varying frequency in addition to the presence of multiple adenomas in the large intestine. Here, we describe two unrelated cases of FAP with unusual extracolonic phenotypes, namely several abnormalities of mesodermal origin strongly resembling Marfan syndrome (MFS) or a Marfan-like habitus. Conventional cytogenetic and FISH analysis did not reveal any gross chromosomal rearrangement on the long arm of chromosome 5 where the APC and FBN2 genes were located. However, in case 2 the FAP-causing mutation in the APC gene was found in the donor splice site of exon 4 and was shown to result in a frameshift and a premature termination codon. We propose that such connective tissue abnormalities may result from germline APC mutations in combination with specific genetic and/or environmental modifying factors.
Asunto(s)
Poliposis Adenomatosa del Colon/genética , Síndrome de Marfan/genética , Poliposis Adenomatosa del Colon/complicaciones , Adulto , Secuencia de Aminoácidos , Femenino , Fibrilina-2 , Fibrilinas , Genes APC , Humanos , Hibridación Fluorescente in Situ , Masculino , Síndrome de Marfan/complicaciones , Proteínas de Microfilamentos/genética , Datos de Secuencia Molecular , Mutación , LinajeRESUMEN
Turcot syndrome (TS) is a rare genetic disease in which brain tumors occur in association with colonic polyposis. Since Turcot's original description in 1959, there have been disagreements about the mode of inheritance as well as the clinical expression of this condition. Some investigators maintain that TS is a phenotypic variant of the autosomal dominant familial adenomatous polyposis (FAP), while others observe that there are clinical differences between TS and FAP, and that the pattern of inheritance of TS is autosomal recessive. The distribution of persons with colonic lesions in a family with a patient of colonic polyposis and a brain tumor, described in this report, favored the recessive hypothesis. In this family, the involvement of the FAP gene on chromosome 5q21-q22 could be excluded by a linkage study using a panel of FAP-linked DNA markers. This finding, which indicates the occurrence of another polyposis gene elsewhere in the genome, will have consequences for the presymptomatic diagnosis of FAP by linked DNA markers. We conclude that TS is a distinct clinical-genetical entity with the triad of atypical polyposis coli, CNS tumors, and a recessive mode of inheritance.
Asunto(s)
Poliposis Adenomatosa del Colon/genética , Neoplasias del Sistema Nervioso Central/genética , Poliposis Adenomatosa del Colon/clasificación , Adolescente , Adulto , Alelos , Niño , Femenino , Genes Recesivos/genética , Ligamiento Genético/genética , Humanos , Masculino , Persona de Mediana Edad , Sistema de Registros , SíndromeAsunto(s)
Adenosina Desaminasa/genética , Genes , Nucleósido Desaminasas/genética , Adenosina Desaminasa/biosíntesis , Secuencia de Aminoácidos , Secuencia de Bases , Línea Celular , Clonación Molecular , ADN/metabolismo , Enzimas de Restricción del ADN , Inducción Enzimática , Humanos , Leucemia Mieloide Aguda , ARN Mensajero/genéticaRESUMEN
Germ-line mutations in the adenomatous polyposis coli (APC) gene are responsible for familial adenomatous polyposis (FAP). Genotype-phenotype correlation studies in patients with FAP have demonstrated associations of certain variants of the disease with mutations at specific sites within the APC gene. In a large FAP family, we identified a frameshift mutation located in the alternatively spliced region of exon 9. Phenotypic studies of affected family members showed that the clinical course of FAP was delayed, with gastrointestinal symptoms and death from colorectal carcinoma occurring on average 25 and 20 years later than usual, respectively. The numbers of colorectal adenomas differed markedly among affected individuals and the location of colorectal cancer lay frequently in the proximal colon. Our findings suggest that the exon 9 mutation identified in the pedigree is associated with late onset of FAP. The atypical phenotype may be explained by the site of the mutation in the APC gene. Analysis of the APC protein product indicated that the exon 9 mutation did not result in a detectable truncated APC protein. Given the location of the mutation within an alternatively spliced exon of APC, it is conceivable that normal APC proteins are produced from the mutant allele by alternative splicing.
Asunto(s)
Poliposis Adenomatosa del Colon/genética , Empalme Alternativo , Proteínas del Citoesqueleto/genética , Exones , Genes APC , Adenoma/genética , Poliposis Adenomatosa del Colon/fisiopatología , Proteína de la Poliposis Adenomatosa del Colon , Adolescente , Adulto , Edad de Inicio , Anciano , Western Blotting , Colon/patología , Neoplasias Colorrectales/genética , Neoplasias Colorrectales/mortalidad , Proteínas del Citoesqueleto/biosíntesis , Femenino , Estudios de Seguimiento , Mutación del Sistema de Lectura , Tamización de Portadores Genéticos , Humanos , Masculino , Persona de Mediana Edad , Linaje , Fenotipo , Factores de TiempoRESUMEN
The gene for human adenosine deaminase (ADA), an enzyme constitutively expressed in all tissues investigated so far and deficient in some cases of severe combined immune deficiency, was previously assigned to chromosome 20 by syntenic analysis, using somatic cell hybrids and quantitative enzyme studies on patients with chromosome abnormalities. Attempts at regional localization of ADA through indirect approaches have so far resulted in uncertainties, as well as apparent inconsistencies. In situ hybridization of high-resolution somatic and pachytene chromosomes using a 3H-labeled cDNA probe of the ADA gene localized the gene to 20q12----q13.11. Rearrangements involving this region have been reported in various human hematological malignancies; in this regard, possible implications of the physical proximity of the ADA gene locus to that of SRC, an oncogene previously localized to the same region of chromosome 20, are briefly discussed.
Asunto(s)
Adenosina Desaminasa/genética , Cromosomas Humanos Par 20/ultraestructura , Nucleósido Desaminasas/genética , Mapeo Cromosómico , Humanos , Hibridación de Ácido NucleicoRESUMEN
Germ-line mutations in the human adenomatous polyposis coli (APC) gene result in familial adenomatous polyposis, an autosomal dominant disorder characterized by the early onset of multiple adenomatous polyps in the large bowel with a high likelihood of developing colorectal carcinomas. To understand the role of APC in intestinal tumor formation, we have introduced a chain-termination mutation in the 15th exon of the mouse Apc gene and employed it to modify the endogenous gene by homologous recombination in embryonic stem cells. Mice which are heterozygous for the Apc gene modification progressively develop intestinal tumors in a manner that is similar to that observed in patients with familial adenomatous polyposis and in mice which carry a mutation called multiple intestinal neoplasia (Min). Our results indicate that the Apc gene modification is a critical event in the initiation of intestinal tumor formation and results in an autosomal dominant predisposition toward development of spontaneous colonic and intestinal tumors in mice.
Asunto(s)
Poliposis Adenomatosa del Colon/genética , Neoplasias Intestinales/genética , Animales , Secuencia de Bases , Cartilla de ADN/química , Genes Letales , Neoplasias Intestinales/patología , Ratones , Ratones Transgénicos , Datos de Secuencia Molecular , MutaciónRESUMEN
The APC gene, originally identified as the gene for familial adenomatous polyposis (FAP), is now considered as the true "gatekeeper" of colonic epithelial proliferation. Its main tumor suppressing activity seems to reside in the capacity to properly regulate intracellular beta-catenin signaling. Most somatic APC mutations are detected between codons 1286 and 1513, the mutation cluster region (MCR). This clustering can be explained either by the presence of mutation-prone sequences within the MCR, or by the selective advantage provided by the resulting truncated polypeptides. Here, a Msh2-deficient mouse model (Msh2(delta 7N) ) was generated and bred with Apc(1638N) and Apc(Min) that allowed the comparison of the somatic mutation spectra along the Apc gene in the different allelic combinations. Mutations identified in Msh2(delta 7N/delta 7N) tumors are predominantly dinucleotide deletions at simple sequence repeats leading to truncated Apc polypeptides that partially retain the 20 a.a. beta-catenin downregulating motifs. In contrast, the somatic mutations identified in the wild type Apc allele of Msh2(delta 7N/delta 7N) /Apc(+/1638N) and Msh2(delta 7N/delta 7N) /Apc(+/Min) tumors are clustered more to the 5' end, thereby completely inactivating the beta-catenin downregulating activity of APC. These results indicate that somatic Apc mutations are selected during intestinal tumorigenesis and that inactivation of the beta-catenin downregulating function of APC is likely to represent the main selective factor.
Asunto(s)
Poliposis Adenomatosa del Colon/genética , Proteínas del Citoesqueleto/genética , Proteínas de Unión al ADN , Regulación hacia Abajo/genética , Genes APC/genética , Mutación/genética , Transactivadores , Animales , Modelos Animales de Enfermedad , Femenino , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , Proteína 2 Homóloga a MutS , Proteínas Proto-Oncogénicas/deficiencia , Proteínas Proto-Oncogénicas/genética , beta CateninaRESUMEN
BACKGROUND & AIMS: Inactivation of the adenomatous polyposis coli (APC) gene is observed at early stages of intestinal tumor formation, whereas loss of E-cadherin is usually associated with tumor progression. Because both proteins compete for the binding to beta-catenin, an essential component of the Wnt signaling pathway, reduction of E-cadherin levels in an Apc mouse model could influence both tumor initiation and progression. In addition, loss or haploinsufficiency of E-cadherin may affect tumorigenesis by altering its cell-adhesive and associated functions. METHODS: Apc1638N mice were bred with animals carrying a targeted E-cadherin knockout mutation. RESULTS: Double heterozygous animals showed a significant 9-fold and 5-fold increase of intestinal and gastric tumor numbers, respectively, compared with Apc1638N animals. The intestinal tumors of both groups showed no significant differences in grading and staging. Loss of heterozygosity analysis at the Apc and E-cadherin loci in both intestinal and gastric Apc(+/1638N)/E-cad(+/-) tumors revealed loss of the wild-type Apc allele in most cases, whereas the wild-type E-cadherin allele was always retained. This was supported by a positive, although reduced, staining for E-cadherin of intestinal tumor sections. CONCLUSIONS: Introduction of the E-cadherin mutation in Apc1638N animals enhances Apc-driven tumor initiation without clearly affecting tumor progression.
Asunto(s)
Cadherinas/genética , Proteínas del Citoesqueleto/genética , Mucosa Gástrica/patología , Genes APC , Mucosa Intestinal/patología , Neoplasias Intestinales/genética , Pérdida de Heterocigocidad , Neoplasias Gástricas/genética , Proteína de la Poliposis Adenomatosa del Colon , Alelos , Animales , Cadherinas/análisis , Cadherinas/fisiología , Mapeo Cromosómico , Proteínas del Citoesqueleto/deficiencia , Proteínas del Citoesqueleto/fisiología , Modelos Animales de Enfermedad , Femenino , Heterocigoto , Neoplasias Intestinales/patología , Masculino , Ratones , Ratones Endogámicos C57BL , Ratones Endogámicos , Ratones Noqueados , Neoplasias Gástricas/patologíaRESUMEN
BACKGROUND & AIMS: Germline mutations in the adenomatous polyposis coli (APC) gene are responsible for familial adenomatous polyposis (FAP), an autosomal dominant predisposition to the formation of multiple colorectal adenomas. Moreover, patients with FAP are at high risk of developing several extracolonic manifestations, including desmoids, cutaneous cysts, and tumors of the upper gastrointestinal tract. Although by definition desmoids are nonmalignant, because of their aggressive invasion of local structures, they represent one of the major causes of morbidity and mortality among patients with FAP. METHODS: This study describes the histopathologic and molecular characterization of Apc1638N, a mouse model for the broad spectrum of extracolonic manifestations characteristic of FAP. RESULTS: Heterozygous Apc+/Apc1638N animals develop fully penetrant and multifocal cutaneous follicular cysts and desmoid tumors in addition to attenuated polyposis of the upper gastrointestinal tract. Moreover, breeding of Apc+/Apc1638N mice in a p53-deficient background results in a dramatic seven-fold increase of the desmoid multiplicity. CONCLUSIONS: Because of the attenuated nature of their intestinal phenotype, these mice survive longer than other murine models for Apc-driven tumorigenesis. Therefore, Apc1638N represents an ideal laboratory tool to test various therapeutic intervention strategies for the management of intestinal as well as extraintestinal tumors.
Asunto(s)
Poliposis Adenomatosa del Colon/complicaciones , Quistes/etiología , Modelos Animales de Enfermedad , Fibromatosis Agresiva/etiología , Enfermedades de la Piel/etiología , Poliposis Adenomatosa del Colon/genética , Edad de Inicio , Animales , Quistes/patología , Femenino , Fibromatosis Agresiva/patología , Genes APC/genética , Genes p53/genética , Pérdida de Heterocigocidad , Masculino , Ratones , Ratones Endogámicos A , Ratones Endogámicos C3H , Ratones Endogámicos C57BL , Mutación/fisiología , Neoplasias Primarias Múltiples/complicaciones , Fenotipo , Distribución por Sexo , Enfermedades de la Piel/patologíaRESUMEN
Familial adenomatous polyposis (FAP) is an inherited predisposition to colorectal cancer characterized by the development of numerous adenomatous polyps predominantly in the colorectal region. Germline mutations in the adenomatous polyposis coli (APC) gene are responsible for most cases of FAP. Mutations at the 5' end of APC are known to be associated with a relatively mild form of the disease, called attenuated adenomatous polyposis coli (AAPC). We identified a frameshift mutation in the 3' part of exon 15, resulting in a stop codon at 1862, in a large Dutch kindred with AAPC. Western blot analysis of lymphoblastoid cell lines derived from affected family members from this kindred, as well as from a previously reported Swiss family carrying a frameshift mutation at codon 1987 and displaying a similar attenuated phenotype, showed only the wild-type APC protein. Our study indicates that chain-terminating mutations located in the 3' part of APC do not result in detectable truncated polypeptides and we hypothesize that this is likely to be the basis for the observed AAPC phenotype.
Asunto(s)
Poliposis Adenomatosa del Colon/genética , Mutación de Línea Germinal/genética , Adulto , Anciano , Anciano de 80 o más Años , Análisis Mutacional de ADN , Exones , Femenino , Humanos , Masculino , Persona de Mediana Edad , Linaje , FenotipoRESUMEN
The adenomatous polyposis coli (APC) gene is considered as the true gatekeeper of colonic epithelial proliferation: It is mutated in the majority of colorectal tumors, and mutations occur at early stages of tumor development in mouse and man. These mutant proteins lack most of the seven 20-amino-acid repeats and all SAMP motifs that have been associated with down-regulation of intracellular beta-catenin levels. In addition, they lack the carboxy-terminal domains that bind to DLG, EB1, and microtubulin. APC also appears to be essential in development because homozygosity for mouse Apc mutations invariably results in early embryonic lethality. Here, we describe the generation of a mouse model carrying a targeted mutation at codon 1638 of the mouse Apc gene, Apc1638T, resulting in a truncated Apc protein encompassing three of the seven 20 amino acid repeats and one SAMP motif, but missing all of the carboxy-terminal domains thought to be associated with tumorigenesis. Surprisingly, homozygosity for the Apc1638T mutation is compatible with postnatal life. However, homozygous mutant animals are characterized by growth retardation, a reduced postnatal viability on the B6 genetic background, the absence of preputial glands, and the formation of nipple-associated cysts. Most importantly, Apc1638T/1638T animals that survive to adulthood are tumor free. Although the full complement of Apc1638T is sufficient for proper beta-catenin signaling, dosage reductions of the truncated protein result in increasingly severe defects in beta-catenin regulation. The SAMP motif retained in Apc1638T also appears to be important for this function as shown by analysis of the Apc1572T protein in which its targeted deletion results in a further reduction in the ability of properly controlling beta-catenin/Tcf signaling. These results indicate that the association with DLG, EB1, and microtubulin is less critical for the maintenance of homeostasis by APC than has been suggested previously, and that proper beta-catenin regulation by APC appears to be required for normal embryonic development and tumor suppression.
Asunto(s)
Proteínas del Citoesqueleto/fisiología , Proteínas de Drosophila , Neoplasias Experimentales/etiología , Transactivadores , Proteínas Supresoras de Tumor , Proteína de la Poliposis Adenomatosa del Colon , Factores de Edad , Animales , Peso Corporal , Quistes/genética , Proteínas del Citoesqueleto/análisis , Proteínas del Citoesqueleto/química , Embrión de Mamíferos/metabolismo , Femenino , Fibroblastos/metabolismo , Regulación Neoplásica de la Expresión Génica , Genes Reporteros , Genitales Masculinos/anatomía & histología , Genitales Masculinos/embriología , Proteínas de Insectos/análisis , Masculino , Ratones , Ratones Endogámicos C57BL , Modelos Genéticos , Mutagénesis Insercional , Fenotipo , Glándulas Sebáceas/fisiología , Enfermedades de la Piel/genética , Células Madre/metabolismo , Tubulina (Proteína)/análisis , beta CateninaRESUMEN
Two independent study-groups, one in Britain and the other in the United States, were the first to report linkage between APC and a TaqI restriction fragment length polymorphism (RFLP) at D5S71 (probe C11p11) on chromosome 5q. They found no recombinants in about 50 informative meioses. The same TaqI RFLP was found to be uninformative for linkage in 15 Dutch polyposis families. The recently reported four base-pair deletion polymorphism (DEL1) at D5S71 has raised the polymorphism information content of this marker from 0.17 to 0.40 in the Dutch population. Seven of 20 polyposis families screened for the DEL1 as well as the TaqI polymorphism gave a combined peak lod score of 5.68 with no recombinants in 37 informative meioses. These data, together with those so far reported in the literature, raise the peak lod score to 17.09 at a recombination fraction of 0.05, the 95% upper confidence limit being 0.09. In combination with the use of another informative marker, D5S81 (probe YN5.48) closely mapping on the other side of APC, the presymptomatic diagnosis of the disease can be made with more than 99.9% certainty. It has to be stressed, however, that the the possible existence of more than one polyposis locus cannot, as yet, be excluded.
Asunto(s)
Poliposis Adenomatosa del Colon/genética , Deleción Cromosómica , Cromosomas Humanos Par 5 , Ligamiento Genético , Polimorfismo de Longitud del Fragmento de Restricción , Poliposis Adenomatosa del Colon/diagnóstico , Adulto , Anciano , Secuencia de Bases , Mapeo Cromosómico , Desoxirribonucleasas de Localización Especificada Tipo II , Femenino , Humanos , Masculino , Persona de Mediana Edad , Datos de Secuencia Molecular , Sondas de Oligonucleótidos , Linaje , Recombinación GenéticaRESUMEN
Familial adenomatous polyposis (FAP) is a disorder with autosomal dominant inheritance, which predisposes to colorectal adenocarcinoma. The gene causing the disorder has been assigned to chromosome 5 by means of a polymorphic DNA marker called C11p11. An informative Dutch pedigree showed that two other linked polymorphic DNA markers, Pi227 and YN5.48, closely flank the FAP locus, one on either side. This finding will allow prenatal and presymptomatic diagnosis of FAP, with more than 99.9% reliability in the majority of families, by means of already available markers.
Asunto(s)
Poliposis Adenomatosa del Colon/diagnóstico , Marcadores Genéticos , Poliposis Adenomatosa del Colon/genética , Adulto , Mapeo Cromosómico , Cromosomas Humanos Par 5 , Humanos , Escala de Lod , Linaje , Polimorfismo de Longitud del Fragmento de Restricción , Recombinación GenéticaRESUMEN
Fifteen apparently unrelated Dutch families with familial adenomatous polyposis (FAP) also known as familial polyposis coli (FPC; McKusick No. 17510) were screened for linkage with the DNA probe C11p11 localized on chromosome 5q21-22 and previously reported to be closely linked to FAP (Bodmer et al. 1987; Leppert et al. 1987). In our study C11p11 was minimally informative, which is ascribable to its low heterozygosity in the North European populations. Of the above families, 12 were investigated also for linkage with D5S37 (DNA probe Pi227). Data from 11 of them were found to be informative and showed that FAP is closely linked to D5S37 previously localized on chromosome 5q21 (peak lod score 7.85 at a recombination fraction of 0.048 with 95% probability limits 0.005-0.145). Results discussed below indicate for the first time that the most likely location of the FAP gene is in the band 5q22 very close to 5q21, if not in the transitional zone between these two bands. The probe Pi227 recognizes 4 restriction fragment length polymorphism (RFLP) sites, exhibiting a total of 9 alleles with 24 theoretically possible haplotypes in the Dutch population. Therefore, this probe appears to have potential as a generally useful predictive marker for FAP until much closer and similarly useful markers become available.
Asunto(s)
Poliposis Adenomatosa del Colon/genética , Cromosomas Humanos Par 5 , Ligamiento Genético , Marcadores Genéticos , Polimorfismo Genético , Mapeo Cromosómico , Femenino , Humanos , Masculino , LinajeRESUMEN
We have investigated the structural gene for adenosine deaminase (ADA) in a female infant with ADA deficiency associated severe combined immune deficiency (ADA-SCID) disease and her family by DNA restriction-fragment-length analysis. In this family a new ADA-specific restriction-fragment-length variant was detected, which involves a 3.2-kb deletion spanning the ADA promoter as well as the first exon. It was found that the patient, who was born to a consanguineous couple, was homozygous and both her parents and her brother were heterozygous for the deletion. No ADA-specific mRNA could be detected by hybridization in fibroblasts derived from this patient. Thus the patient was established to be homozygous for a true null ADA allele. In the light of the apparently normal development of most tissues except the lymphoid tissue the above finding directly questions the classification of ADA as a 'housekeeping' enzyme.
Asunto(s)
Adenosina Desaminasa/deficiencia , Deleción Cromosómica , Exones , Genes , Homocigoto , Síndromes de Inmunodeficiencia/genética , Nucleósido Desaminasas/deficiencia , Regiones Promotoras Genéticas , Adenosina Desaminasa/sangre , Eritrocitos/enzimología , Femenino , Humanos , Síndromes de Inmunodeficiencia/enzimología , Lactante , Leucocitos/enzimología , Masculino , ARN Mensajero/genética , Valores de Referencia , Transcripción GenéticaRESUMEN
Familial adenomatous polyposis (FAP) is an inherited predisposition to colorectal cancer caused by germline mutations in the adenomatous polyposis coli (APC) gene located on chromosome segment 5q21-q22. We detected a germline rearrangement of the APC gene in a Dutch FAP family by screening genomic DNA samples with APC cDNA probes. Subsequent molecular and cytogenetic studies revealed a constitutional reciprocal translocation t(5;10)(q22;q25) that resulted in the disruption of the APC gene. Southern blot and polymorphic marker analysis indicated that part of the APC gene had been deleted. Analysis of the APC protein product indicated that the translocation breakpoint did not lead to the formation of a detectable truncated APC protein but apparently resulted in a null allele. Evaluation of the clinical phenotypes in the patients suggested that they exhibited features of an unusual form of FAP characterized by a slightly delayed age of onset of colorectal cancer and a reduced number of colorectal polyps. The latter were mainly sessile and were located predominantly in the proximal colon. To our knowledge, this is the first description of FAP caused by a reciprocal translocation disrupting the APC gene.
Asunto(s)
Poliposis Adenomatosa del Colon/genética , Cromosomas Humanos Par 10 , Cromosomas Humanos Par 5 , Translocación Genética , Proteína de la Poliposis Adenomatosa del Colon , Adulto , Secuencia de Bases , Mapeo Cromosómico , Proteínas del Citoesqueleto/genética , Femenino , Reordenamiento Génico/genética , Ligamiento Genético , Humanos , Hibridación Fluorescente in Situ , Persona de Mediana Edad , Datos de Secuencia Molecular , Linaje , FenotipoRESUMEN
Familial adenomatous polyposis (FAP) is characterised by hundreds of colorectal adenomas. Endocrine neoplasms have occasionally been reported, as have gastric polyps, which are usually hamartomatous in the fundus of the stomach and adenomatous in the antrum. A 57 year old man with colorectal, gastric, and periampullary adenomatous polyposis, in association with three bilateral adrenocortical adenomas, is presented. Mutation screening showed a 5960delA germline mutation in the adenomatous polyposis coli (APC) gene predicted to lead to a premature stop codon. This mutation was found in three of the four children of the patient. Western blot analysis of a lymphoblastoid cell line derived from the patient failed to detect any truncated APC polypeptide. This rare 3' mutation is responsible for an unusually complex and late onset phenotype of FAP.
Asunto(s)
Poliposis Adenomatosa del Colon/genética , Adenoma Corticosuprarrenal/genética , Genes APC , Mutación de Línea Germinal , Poliposis Adenomatosa del Colon/patología , Adenoma Corticosuprarrenal/patología , Análisis Heterodúplex , Humanos , Masculino , Persona de Mediana Edad , Linaje , Fenotipo , Análisis de Secuencia de ADNRESUMEN
The Apc1638N mouse carries a targeted mutant allele at the endogenous adenomatous polyposis coli (Apc) gene and represents a unique in vivo model to study intestinal tumor formation and progression. Heterozygous Apc+/Apc1638N mice progressively develop 5-6 adenomas and adenocarcinomas of the small intestine within the first 6 months of life following a histologic sequence similar to that observed in human intestinal tumors. Here, we present the somatic mutation analysis of a total of 57 tumors. The results indicate that in > or = 75% of the lesions tested the wild type copy of the Apc gene is lost and that this LOH event extends to the entire mouse chromosome 18. Unexpectedly, mutations at the K-, N- and H-ras genes have not been found in these tumors. Immunohistochemical analysis of the Apc1638N tumors failed to detect accumulation of the Tp53 protein. Also, no mutations have been found in exons 7 and 8 of the Tp53 gene. These results indicate that, although the genetic inactivation of Apc is involved in the initiating event of the human as well as murine intestinal tumorigenesis, tumor growth and progression follow different mutational pathways in these two species.