Localization of the gene for familial adenomatous polyposis on chromosome 5

Impact of a hospital-based register on the management of familial adenomatous polyposis

Colorectal cancer in familial adenomatous polyposis is a preventable disease in at-risk relatives of patients with primary cases. Until the recent establishment of a register in Western Australia, there has been no registration of pedigrees or central organization of surveillance in Australia. In the present study, the experience of 20 such families who were associated with The Royal Melbourne Hospital was documented, with an analysis of the reasons for any failure of management. The impact of a hospital-based register on the management of the disease was studied. In each family, results were categorized according to whether "at-risk" relatives had been diagnosed at surveillance examinations, and whether the Hospital register were involved. Before involvement with the register, 24 family members presented with symptomatic polyposis after the first affected case had been diagnosed. Eighteen of these had colorectal cancer at diagnosis, and 16 subjects now are dead. Identifiable reasons for the failure of surveillance were family communication failure (two cases), family denial (two cases), failure of the hospital clinic (two cases) and a failure to cover extended branches of families who were living locally (nine cases), interstate (four cases) or overseas (three cases). In contrast, only two (6%) of 33 affected cases that were identified at a planned surveillance endoscopy had colorectal cancer at diagnosis. Without the active surveillance of at-risk family members, lethal delays in diagnosis are likely to occur. Most reasons for failure potentially are correctable by a dedicated registry that is responsible for notifying clinicians and patients about the timing of surveillance procedures.

Characteristics of familial colon cancer in a large population data base

Early age onset and proximal colonic location are two specific characteristics of colon cancer which have been used clinically to assess the risk that an individual case is of familial rather than sporadic origin. This practice derives from the observation that these characteristics are typical of the rare, nonpolyposis inherited colorectal cancer syndromes. This study examines these two characteristics in cases of common colon cancer to determine whether they actually distinguish individuals at increased risk for familial colorectal cancer. Familial clusters of colon cancer in the Utah Population Data Base were examined. Common colon cancers were found to cluster excessively in families; however, the measure of familial clustering for distal colonic cases was increased to the same degree as proximal colonic cases. Early age onset was likewise not a distinguishing factor of familial cases. These results suggest that factors other than those that predispose to the rare syndromes are important in determining familial risk for common colon cancers, and that the absence of these two clinical features should not suggest the absence of familial risk of colorectal cancer.

Increased chromosome breakage by N-methyl-N1-nitro-N-nitrosoguanidine in patients with adenomatous polyposis coli

In a search for hypersensitivity to chromosome breaking agents, lymphocytes and fibroblasts from patients with the precancerous condition adenomatous polyposis coli (APC) were treated with N-methyl-N1-nitro-N-nitrosoguanidine (MNNG) and bleomycin. The APC cells showed a significantly increased level of chromatid-type damage following MNNG treatment (5 micrograms/ml for lymphocytes, 1 or 2 micrograms/ml for fibroblasts). No such differential effect was noted for bleomycin, but a threefold increase in "pulverized" cells was seen in APC lymphocyte cultures treated in G0, that is before cells have entered the cell cycle. Increased spontaneous and induced chromosome instability appears to be an important effect of the APC mutant gene as molecular evidence suggests that chromosomal mechanisms are likely to play a major role in tumorigenesis both in this condition and in sporadic colorectal cancer.

Familial adenomatous polyposis in association with thyroiditis. Report of two cases

The authors report two patients with familial adenomatous polyposis and thyroiditis. One patient was discovered at autopsy to have in addition, a follicular carcinoma of the thyroid and focal nodular hyperplasia of the liver. The other patient had a sister with familial adenomatous polyposis and a papillary carcinoma of the thyroid. The association between familial adenomatous polyposis and thyroiditis has not been previously reported.

Upper gastrointestinal cancer in patients with familial adenomatous polyposis

102 patients with familial adenomatous polyposis underwent upper gastrointestinal endoscopy as a screening test for gastroduodenal adenomas. 100 had duodenal abnormalities (dysplasia in 94, and hyperplasia in 6), usually in the second and third parts of the duodenum (91%). The periampullary area was abnormal in 87 of 97 patients who had a biopsy specimen taken from this site (dysplasia 72, hyperplasia 13, and inflammation 2). By contrast, gastric dysplasia was found in only 6 patients. Classification of duodenal polyposis on a 5-grade scale (stages 0-IV), based on polyp number, size, histology, and severity of dysplasia, showed that 11 had stage IV disease: these patients are at greatest risk of malignant change and require close surveillance. The pattern of dysplasia observed in the upper gastrointestinal tract resembled the pattern of mucosal exposure to bile.

Familial bone marrow monosomy 7. Evidence that the predisposing locus is not on the long arm of chromosome 7

Loss of expression of a tumor-suppressing gene is an attractive model to explain the cytogenetic and epidemiologic features of cases of myelodysplasia and acute myelogenous leukemia (AML) associated with bone marrow monosomy 7 or partial deletion of the long arm (7q-). We used probes from within the breakpoint region on 7q-chromosomes (7q22-34) that detect restriction fragment length polymorphisms (RFLPs) to investigate three families in which two siblings developed myelodysplasia with monosomy 7. In the first family, probes from the proximal part of this region identified DNA derived from the same maternal chromosome in both leukemias. The RFLPs in these siblings diverged at the more distal J3.11 marker due to a mitotic recombination in one patient, a result that suggested a critical region on 7q proximal to probe J3.11. Detailed RFLP mapping of the implicated region was then performed in two additional unrelated pairs of affected siblings. In these families, DNA derived from different parental chromosome 7s was retained in the leukemic bone marrows of the siblings. We conclude that the familial predisposition to myelodysplasia is not located within a consistently deleted segment on the long arm of chromosome 7. These data provide evidence implicating multiple genetic events in the pathogenesis of myelodysplasia seen in association with bone marrow monosomy 7 or 7q-.

Association between tumor DNA aneuploidy and in vitro tetraploidy of skin fibroblasts in patients with colorectal neoplasms

In vitro tetraploidy (IVT) in cultures of skin fibroblasts was compared with tumor DNA ploidy, as determined by flow cytometry on paraffin-embedded material, in 99 patients with colorectal neoplasm. In 63 patients with non-heritable carcinoma we found a significant correlation between the number of aneuploid stemlines in the tumor and IVT in the fibroblast culture. Furthermore, tumor aneuploidy was significantly correlated to the size of the tetraploid subpopulation in the fibroblasts. There was no correlation between aneuploidy and Dukes's stage or the degree of differentiation. In 36 patients with adenoma no correlation between tumor aneuploidy and fibroblast IVT was demonstrated, whereas the number of tumor stemlines was significantly correlated to histopathologic stage and grade of dysplasia. IVT in cultured skin fibroblasts, which has been reported to reflect a genetic predisposition to colorectal cancer in heritable colon cancer syndromes, thus seems to be relevant also for the understanding of tumor formation and progression in the 'non-heritable' type of colorectal cancer.

Familial adenomatous polyposis

Familial adenomatous polyposis is an autosomal dominant disease that includes early development of up to thousands of colorectal adenomas and several extracolonic manifestations. All untreated patients will develop colorectal adenocarcinoma. The treatment of choice is colectomy and ileorectal anastomosis, but restorative proctocolectomy may be considered in selected cases. Polyposis patients treated with ileorectal anastomosis should be followed for life, with regular proctosigmoidoscopy and destruction of new adenomas. Furthermore, regular gastroduodenoscopy should be carried out because of frequent occurrence of premalignant duodenal adenomas. The prognosis is good after prophylactic colectomy in patients without carcinoma. All first degree relatives of affected family members should be examined regularly with proctosigmoidoscopy from the age of ten, and prophylaxis should be organised using a national or regional polyposis register. The recent detection of a specific gene for familial adenomatous polyposis is a long step forward, and several problems may be solved by increasing international cooperation.

Hereditary nonpolyposis colorectal carcinoma: cancer family syndrome

During the past 20 years details of hundreds of families with aggregation of nonpolyposis colorectal carcinoma (CRC) have been published. High frequency of CRC and some other adenocarcinomas with early age of onset, with common multiplicity and with dominant mode of genetic transmission are characteristic for this inherited disorder originally called the cancer family syndrome (CFS). It has now been shown that at least 5% of all CRCs can be classified as CFS and it constitutes a potentially important subject for family screening for CRC. About 50 CFS families have been identified in Finland and systematic family screening for CRC has been performed since 1983. Positive screening results in CFS are at least 20 to 30 times higher than in the general population of corresponding age. However, the problem of definite verification of the syndrome in the absence of a specific biomarker and difficulties in establishing continuity of the follow up once started have handicapped arrangements for nation wide screening programmes. Nevertheless, there are good reasons to identify all cases of CFS in clinical practice because this has clear implications for the surgical and follow up strategies in individual patients with CFS.

A genetic linkage study of facioscapulohumeral (Landouzy-Déjérine) disease with 24 polymorphic DNA probes

From analysis of DNA polymorphisms in a panel of 455 subjects from 25 families with facioscapulohumeral (Landouzy-Déjérine) disease, we have found no evidence for close linkage of the disease at 24 different genetic loci, including one from a candidate chromosomal region. Added to previous data, our results provide direction for future collaborative linkage studies.

Loss of allelic heterozygosity at a second locus on chromosome 11 in sporadic Wilms' tumor cells

Children with associated Wilms' tumor, aniridia, genitourinary malformations, and mental retardation (WAGR syndrome) frequently have a cytogenetically visible germ line deletion of chromosomal band 11p13. In accordance with the Knudson hypothesis of two-hit carcinogenesis, the absence of this chromosomal band suggests that loss of both alleles of a gene at 11p13 causes Wilms' tumor. Consistent with this model, chromosomes from sporadically occurring Wilms' tumor cells frequently show loss of allelic heterozygosity at polymorphic 11p15 loci, and therefore it has been assumed that allelic loss extends proximally to include 11p13. We report here that in samples from five sporadic Wilms' tumors, allelic loss occurred distal to the WAGR locus on 11p13. In cells from one tumor, mitotic recombination occurred distal to the gamma-globin gene on 11p15.5. Thus, allelic loss in sporadic Wilms' tumor cells may involve a second locus on 11p.

Familial colorectal cancer and familial adenomatous polyposis

Familial adenomatous polyposis (FAP) affects around 1 in 10,000 individuals; the gene for this condition was recently shown to be located on chromosome 5, and it is only a matter of time before its precise location and function are determined, making prephenotypic, and even prenatal, diagnosis more generally available and reliable. In the mean time, care of FAP families will continue to depend on careful registration of family information, prophylactic bowel surgery and surveillance for other potentially serious manifestations of the disease. Upper gastrointestinal malignancies and desmoid tumours have overtaken colorectal cancer as the leading causes of death in some centres. Other dominantly-inherited colorectal cancer syndromes produce less striking phenotypes, but affect far more individuals than FAP. It appears that there are two patterns of hereditary non-polyposis colorectal cancer (HNPCC) syndromes, one involving cases of bowel cancer alone, the other associated with breast and gynaecological cancers; these may prove to be variable expressions of a common gene abnormality. More effort is required by clinicians managing cases of colorectal cancer to identify affected families in order to offer surveillance and appropriate treatment in the hope that such measures may prevent cancer in family members.

Screening an asymptomatic population for colorectal cancer

The best prospect of realizing a reduction in mortality from colorectal cancer appears to be by presymptomatic detection in a screened population. Presently, the only feasible method of mass population screening is by the detection of faecal occult blood and it is encouraging that all the major trials demonstrate that asymptomatic malignancy may be detected in this way. Furthermore, the screen-detected cancers are generally at an earlier pathological stage than those appearing in control populations. However, a note of caution is required. At the present time it is too early to demonstrate a reduction in mortality from the disease and there is evidence of a length bias, with more of the screen-detected cancers being well differentiated. The results of the large controlled trials will enable the benefits of screening to be viewed objectively and a recommendation for, or against, screening to be made.

The gene for human complement C9 is on chromosome 5

By hybridizing a cloned cDNA coding for human complement factor C9 to hybrid cells containing subsets of human chromosomes on a rodent background, we have determined that the human gene for C9 is localized on chromosome 5.

Tumour suppressor genes: oncogenesis update

Evidence for tumour suppressor genes (anti-oncogenes, hemerogenes, flatogenes) has been obtained from the behaviour of familial childhood tumours in man, tumours in Drosophila caused by recessive mutations, experiments on fusing tumour cells to normal cells in tissue culture and revertants of oncogene-transformed cells. They may comprise more than one class of genes, one of which is likely to consist of genes responsible for normal differentiation. In large long-lived animals like man, which have a large potential somatic mutational load, mutant genes are associated with autosomal dominant behaviour in families. The susceptible individuals inherit heterozygosity of the tumour gene but the emergence of a tumour appears to follow a second somatic mutational event which results in homozygosity or hemizygosity. Hence, in tumour cells the mutations behave in a recessive manner. Success in isolating the normal genes may provide new tools for antenatal diagnosis of carriers and open up the possibility of developing new gene therapy.

Genetic alterations in primary breast cancer

A serious effort has been made to identify and characterize mutations that frequently occur during the evolution of primary human breast cancer. Some of these mutations involve amplification of protooncogenes (c-myc, c-erbB-2, and int-2) that have been shown to contribute to experimentally induced breast cancer in mouse model systems. Tumor development in mice containing the c-myc or c-erbB-2 transgene suggests that the cellular and developmental contexts in which the genes are expressed define their relative contribution to tumorigenesis. Homozygous deletions or loss of heterozygosity (LOH) represent another type of mutation that has been frequently observed on four chromosomes (1q, 3p, 11p, and 13q) in tumor DNA. They are thought to unmask recessive mutations (LOH) that inactivate or remove (homozygous deletion) suppressor genes that regulate normal cell proliferation. Attempts to determine whether specific mutations are associated with certain clinical parameters have led to the controversial hypothesis that some mutations may be useful prognostic indicators of the post-surgical course of the disease. The current results underscore the necessity for much larger, better control studies to unambiguously define the potential of such mutations as clinical markers.

Congenital hypertrophy of the retinal pigment epithelium in familial adenomatous polyposis

One hundred fifty-three members of 56 kindreds with familial adenomatous polyposis (FAP) underwent funduscopic examination for congenital hypertrophy of the retinal pigment epithelium (CHRPE). All patients underwent wide-angle fundus photography to document lesions, proctosigmoidoscopy to document polyps, and examination for extracolonic manifestations. Ninety-seven patients were diagnosed as having FAP and 56 patients were offspring of FAP patients and thus at 50% risk of inheriting the disease. In two thirds of the kindreds, CHRPE could be used as a congenital phenotypic marker to predict the presence or development of polyps. In these kindreds, all patients with diagnosed FAP and 39% of the patients at risk had at least four CHRPE lesions. In one third of the kindreds, CHRPE could not be used as a predictive congenital marker, and in these kindreds all patients had zero to three total lesions of CHRPE. The presence of CHRPE did not correlate with any other extracolonic manifestations. In kindreds without any other extracolonic manifestations, CHRPE can still be present and can be used as a predictive congenital phenotypic marker.

Loss of alleles from the distal short arm of chromosome 1 occurs late in melanoma tumor progression

The gene for familial malignant melanoma and its precursor lesion, the dysplastic nevus, has been assigned to a region of the distal short arm of chromosome 1, which is frequently involved in karyotypic abnormalities in melanoma cells. We have examined loci on chromosome 1p for loss-of-constitutional heterozygosity in 35 melanomas and 21 melanoma cell lines to analyze the role of these abnormalities in melanocyte transformation. Loss-of-heterozygosity at loci on chromosome 1p was identified in 15/35 (43%) melanomas and 11/21 (52%) melanoma cell lines. Analysis of multiple metastases derived from the same patient and of melanoma and lymphoblastoid samples from a family with hereditary melanoma showed that the loss-of-heterozygosity at loci on distal 1p is a late event in tumor progression, rather than the second mutation that would occur if melanoma were due to a cellular recessive mechanism. Comparisons with neuroblastoma and multiple endocrine neoplasia (MEN2) suggest that the frequent 1p loss-of-heterozygosity in these malignancies is a common late event of neuroectodermal tumor progression.

pp60c-src activation in human colon carcinoma

We measured the in vitro protein-tyrosine kinase activity of pp60c-src from human colon carcinoma cell lines and tumors. The activity of pp60c-src from six of nine carcinoma cell lines was higher (on average, fivefold as measured by enolase phosphorylation, or eightfold as measured by autophosphorylation) than that of pp60c-src from normal colonic mucosal cells, or human or rodent fibroblasts. Similarly, the activity of pp60c-src from 13 of 21 primary colon carcinomas was five- or sevenfold higher than that of pp60c-src from normal colonic mucosa adjacent to the tumor. The increased pp60c-src activity did not result solely from an increase in the level of pp60c-src protein, suggesting the specific activity of the pp60c-src kinase is elevated in the tumor cells. pp60c-src from colon carcinoma cells and normal colonic mucosal cells was phosphorylated at similar sites. We used immunoblotting with antibodies to phosphotyrosine to identify substrates of protein-tyrosine kinases in colonic cells. Three phosphotyrosine-containing proteins were detected at significantly higher levels in most colon carcinoma cell lines than in normal colonic mucosal cells or human or rat fibroblasts. All colon carcinoma cell lines with elevated pp60c-src in vitro kinase activity, showed increased phosphorylation of proteins on tyrosine in vivo, suggesting the presence of an activated protein-tyrosine kinase(s).

Evidence that the familial adenomatous polyposis gene is involved in a subset of colon cancers with a complementable defect in c-myc regulation

Human colorectal carcinomas frequently express elevated levels of c-myc mRNA in the absence of a gross genetic change at the c-myc locus. To test the hypothesis that these tumors are defective in a gene function necessary for the regulation of c-myc expression, we fused an osteosarcoma cell line that exhibits normal c-myc regulation with two colon carcinoma cell lines that express deregulated levels of c-myc mRNA. The levels of c-myc transcripts in all of the hybrid clones examined were normal and were induced normally by a mitogenic stimulus. Since rates of c-myc mRNA turnover in the colon carcinoma cells were found to be comparable to those in normal cells, increased message stability cannot account for the increased steady-state levels of transcripts. Our findings suggest that loss of function of a trans-acting regulator is responsible for the deregulation of c-myc expression in a major fraction of colorectal carcinomas. Analysis of restriction fragment length polymorphisms in tumor/normal tissue pairs from patients with primary colorectal lesions indicated that deregulation of c-myc expression in the tumors is correlated with frequent loss of alleles of syntenic markers on chromosome 5q; allele loss on 5q could be detected in 9 of 19 tumors expressing deregulated levels of c-myc mRNA, but not in any of 8 tumors expressing normal levels of c-myc RNA. Chromosome 5q is the region known to contain the gene for familial adenomatous polyposis, an inherited predisposition to colon cancer. These findings, together with the earlier finding that the colonic distribution of tumors exhibiting deregulated c-myc expression is similar to that reported for familial polyposis, provide evidence that loss of function of the familial adenomatous polyposis gene is involved in a subset of colorectal cancers in which c-myc expression is deregulated.

Epidermal growth factor receptors and epidermal growth factor-like activity in colorectal mucosa, adenomas and carcinomas

The epidermal growth factor (EGF) and alpha-tumor growth factor are mitogenic proteins which bind to the EGF-receptor and may play a role in carcinogenesis or tumor progression. Our study investigated whether colorectal carcinomas and adenomas express altered levels of EGF-receptors or overproduce EGF-like activity by comparing histologically normal mucosa to carcinomas resected from the same patients. EGF-receptors were characterized by radioligand binding studies. Carcinomas contained unchanged or decreased levels of EGF-receptors in 13/16 and moderately increased levels in 3/16 patients as compared to normal mucosa. Adenomas obtained from 2 patients with familial polyposis coli and from a third patient with a coincident carcinoma had similar numbers of EGF-receptors as normal mucosa. EGF-like growth factors, in contrast, were significantly elevated in carcinoma extracts as compared to extracts from normal mucosa of the same patients. Adenomas did not contain elevated levels of EGF-like activity. We conclude that increased expression of EGF-receptors is infrequent in colonic adenocarcinomas. Increased production of EGF-like growth factors may frequently occur but seems to be associated with tumor progression rather than with premalignant lesions as represented by adenomas.

The ninth Gordon Hamilton-Fairley memorial lecture. Hereditary cancers: clues to mechanisms of carcinogenesis

The study of hereditary cancer in humans, notably retinoblastoma, has identified a category of cancer genes that is different from that of the oncogenes. Whereas the latter group of genes exerts its effect through expression, the former does so as a result of failure of normal expression. Primary oncogene abnormality seems to play a crucial initiating role in certain neoplasms, particularly leukaemias, lymphomas and some sarcomas. In contrast, anti-oncogenes (tumour suppressor genes) appear to be important in the initiation of several solid tumours of children, as well as some common carcinomas of adults. Both classes are apparently involved in tumour progression and metastasis. Virtually every kind of cancer can occur in hereditary form, so the role of anti-oncogenes in the origin of human cancers may be considerable. The prototypic anti-oncogene has been that for retinoblastoma. For this tumour the recessive mechanism has been demonstrated by molecular means, and the gene has been cloned. The possibility has been suggested that gene (or gene product) replacement therapy could be accomplished.

Applications of molecular genetics to gastrointestinal and liver diseases. II. Clinical relevance

The use of DNA probes within or near disease genes is becoming increasingly important in clinical medicine. Probes are available for prenatal and carrier diagnosis for several of the more than 100 genetic diseases of the gastrointestinal tract and liver. These include familial adenomatous polyposis, haemochromatosis, cystic fibrosis, alpha 1-antitrypsin deficiency and the hereditary porphyrias. This review uses examples drawn from such diseases to show the relevance of these approaches to the clinician.

Strategies for linkage studies in schizophrenia

Significant advances in linkage studies have occurred the past decade based on the use of polymorphic DNA markers known as restriction fragment length polymorphisms (RFLPs). This approach has led to the chromosomal localization of a number of important genetic diseases, and is being increasingly applied to schizophrenia. We discuss two strategies for performing linkage studies in schizophrenia, one based on methodical testing of the human genome, and the other based on selective use of markers. The selective approach uses data from the mode of transmission, previous linkage studies, cytogenetic studies, association studies, case reports, and candidate genes to identify markers that may have an increased likelihood for linkage.

Multistage models for carcinogenesis

The multistage model is tested on several human and animal data sets. It fits in some cases but not in others. With human lung cancer data, there is a drop in risk for ex-smokers quite different from the predictions of the model. The results are not conclusive but are compatible with the view that the multistage model provides a family of curves that often fit cancer incidence data, but may not capture the underlying biological reality.

Clonal allele loss in gastrointestinal cancers

Using a panel of DNA probes for hypervariable DNA regions we screened 52 gastrointestinal carcinomas for clonal allele losses on chromosomes 1, 5, 7, 12, 16 and 17. A total of 24/35 informative cases of colorectal cancers showed loss of constitutional heterozygosity at a locus on chromosome 17p, while 9/31 cases informative for a locus on 5q showed allele loss. Loss of sequences at 5q was linked to allele loss at 17p with a single exception. In gastric cancers loss of heterozygosity most frequently occurred at 1q (5/10 tumours) and at 12q (6/11 tumours). Gastrointestinal tumours show consistent chromosomal losses and the loci involved are different in gastric and colorectal cancers.

Chromosome 17 deletions and p53 gene mutations in colorectal carcinomas

Previous studies have demonstrated that allelic deletions of the short arm of chromosome 17 occur in over 75% of colorectal carcinomas. Twenty chromosome 17p markers were used to localize the common region of deletion in these tumors to a region contained within bands 17p12 to 17p13.3. This region contains the gene for the transformation-associated protein p53. Southern and Northern blot hybridization experiments provided no evidence for gross alterations of the p53 gene or surrounding sequences. As a more rigorous test of the possibility that p53 was a target of the deletions, the p53 coding regions from two tumors were analyzed; these two tumors, like most colorectal carcinomas, had allelic deletions of chromosome 17p and expressed considerable amounts of p53 messenger RNA from the remaining allele. The remaining p53 allele was mutated in both tumors, with an alanine substituted for valine at codon 143 of one tumor and a histidine substituted for arginine at codon 175 of the second tumor. Both mutations occurred in a highly conserved region of the p53 gene that was previously found to be mutated in murine p53 oncogenes. The data suggest that p53 gene mutations may be involved in colorectal neoplasia, perhaps through inactivation of a tumor suppressor function of the wild-type p53 gene.

Cytogenetic characterization of a colon adenocarcinoma from a familial polyposis coli patient

We report on the cytogenetic findings in a fresh biopsy of a colorectal adenocarcinoma in a patient with familial polyposis coli (FAP). The stemline had 45 chromosomes with several clonal chromosome aberrations including a der(17)t(17;?), and -18, which are the two most recurrent aberrations in sporadic colorectal carcinomas. This finding is discussed in relation to the chromosomal changes described in sporadic colorectal carcinomas and in FAP cell lines.

Loss of allelic heterozygosity at a second locus on chromosome 11 in sporadic Wilms' tumor cells

Children with associated Wilms' tumor, aniridia, genitourinary malformations, and mental retardation (WAGR syndrome) frequently have a cytogenetically visible germ line deletion of chromosomal band 11p13. In accordance with the Knudson hypothesis of two-hit carcinogenesis, the absence of this chromosomal band suggests that loss of both alleles of a gene at 11p13 causes Wilms' tumor. Consistent with this model, chromosomes from sporadically occurring Wilms' tumor cells frequently show loss of allelic heterozygosity at polymorphic 11p15 loci, and therefore it has been assumed that allelic loss extends proximally to include 11p13. We report here that in samples from five sporadic Wilms' tumors, allelic loss occurred distal to the WAGR locus on 11p13. In cells from one tumor, mitotic recombination occurred distal to the gamma-globin gene on 11p15.5. Thus, allelic loss in sporadic Wilms' tumor cells may involve a second locus on 11p.

Recessive mutations and chromosome deletions leading to cancer

This review examines the effect that a small chromosome deletion affecting a specific DNA sequence may have in producing a state of 'hemizygosity' for a gene or genes, and so triggering malignancy of the cells concerned. The association between such deletions and a variety of cancers will be considered and the implications for clinical practice will be outlined.

Increased level of mitochondrial gene expression in polyps of familial polyposis coli patients

To elucidate the mechanism of polyp formation in familial polyposis coli patients, cDNA clones, expressed differently between normal colonic mucosae and polyps, were screened. Three polyp-derived cDNA clones showed increased levels of transcription under neoplastic conditions. Among them, clone P6 was determined to be derived from the mtDNA encoding parts of subunit 1 of NADH dehydrogenase and 16S rRNA. The number of copies and restriction enzyme patterns of the mtDNA did not vary in either normal or neoplastic tissues, and a level of different mitochondrial mRNA was increased in the same proportion, suggesting a change in the rate of synthesis and/or degradation of the mtRNA. No cDNA clone which was expressed higher in normal colonic mucosae than in polyps was isolated from the cDNA library derived from normal mucosae.

Skin fibroblasts from individuals hemizygous for the familial adenopolyposis susceptibility gene show delayed crisis in vitro

Normal human fibroblast cells have not been reported to escape crisis--that is, they die after about 24 doublings in culture. We have been studying the growth properties of skin fibroblast cells from persons in families with familial adenopolyposis of the colon (FAP). An individual hemizygous at the FAP locus will develop hyperplasia of the colonic epithelium followed by colonic polyps, both at an early age. Polyps themselves still retain a single functional FAP allele. A mutation or deletion in this allele in a polyp is hypothesized to lead to further loss of growth control; thus, a tumor is formed. We found that the in vitro life-span of skin fibroblast cells from FAP individuals and from some asymptomatic children were markedly extended when compared with normal individuals.

Applications of molecular genetics to gastrointestinal and liver diseases. I. Technical approaches

Recent developments in recombinant DNA techniques have allowed an understanding of the molecular genetics of many diseases, some affecting the gastrointestinal tract and liver. DNA probes which detect sequences within or near disease genes can be selected by direct approaches, if the gene product or primary gene function is known, or by indirect methods when the chromosomal location is known. Such probes have resulted in extensive family studies which can now define risks to family members of developing a genetic disease. The development of the polymerase chain reaction will also be of considerable use in clinical genetics and in the diagnosis of some infectious diseases. The techniques are summarized and examples of their use are given. A glossary of terms is also provided.

Expression of the nuclear oncogene p53 in colon tumours

The nuclear tumour antigen p53 is expressed by a gene localized on the p-arm of human chromosome 17, a region frequently deleted in colon carcinomas. Using a monoclonal antibody to p53 antigen, immunohistochemical analysis of carcinomas and dysplastic tubular adenomas of the colon has been performed to study the relation between p53 expression and dysplasia or malignancy. With this methods p53 was detectable in 55 per cent of colon carcinomas (n = 29). In 8 per cent of adenomas (n = 74), focal nuclear p53 expression was found in dysplastic epithelial cells. In general, these p53-positive regions of the polyps were histologically indistinguishable from the neighbouring tubuli. Sometimes the p53-positive nuclei were found in a focus of more highly dysplastic epithelium. The results suggest that expression of the p53 gene may be part of the process of malignant transformation of dysplastic colon polyps.

The possible presence of a separate disease entity in nonfamilial polyposis of the large intestine

Familial adenomatosis coli (FAC) traditionally has been diagnosed as the presence of more than 100 colonic adenomas, even if no familial occurrence is present. In the present communication, clinical features of FAC have been compared in detail to detect differences between familial and nonfamilial cases with regard to colonic and extracolonic lesions and to discover whether they constitute the same disease entities. No significant difference was found in the incidence of extracolonic lesions. The average number of colonic polyps in the nonfamilial cases of patients over 30 years old was 1128, the number of polyps was significantly higher in the familial cases (3154). When three patients with approximately 100 polyps were excluded, the mean number of colonic polyps in nonfamilial cases became 2608. This was similar to that of familial cases. Furthermore, the occurrence of approximately 100 polyps was extremely rare in familial patients who were over 30 years old. Therefore, most of the nonfamilial cases can be considered to be familial probands of FAC, but some, such as the three cases in the present study, may be a different disease entity, such as recessive adenomatous polyposis or multiple colonic adenomas.

Congenital hypertrophy of retinal pigment epithelium: a sign of familial adenomatous polyposis

Families of people known to have familial adenomatous polyposis are screened for signs of the disease by yearly examination of the bowel. Multiple areas of congenital hypertrophy of the retinal pigment epithelium have been described in patients with familial adenomatous polyposis. To assess the reliability of this marker 40 patients with familial adenomatous polyposis, representing all 25 pedigrees with living affected members in the Northern region's polyposis registry, were examined for hypertrophy of the retinal pigment epithelium. All had multiple lesions, ranging in number from two to over 40. None of the 35 controls had more than two lesions. Ocular examination is valuable for detecting carriers of the gene for familial adenomatous polyposis before their symptoms develop.