Close linkage of a highly polymorphic marker (D5S37) to familial adenomatous polyposis (FAP) and confirmation of FAP localization on chromosome 5q21-q22

Hereditary Gastrointestinal Tumor Syndromes: When Risk Comes with Your Genes

Despite recent campaigns for screening and the latest advances in cancer therapy and molecular biology, gastrointestinal (GI) neoplasms remain among the most frequent and lethal human tumors. Most GI neoplasms are sporadic, but there are some well-known familial syndromes associated with a significant risk of developing both benign and malignant GI tumors. Although some of these entities were described more than a century ago based on clinical grounds, the increasing molecular information obtained with high-throughput techniques has shed light on the pathogenesis of several of them. The vast amount of information gained from next-generation sequencing has led to the identification of some high-risk genetic variants, although others remain to be discovered. The opportunity for genetic assessment and counseling in these families has dramatically changed the management of these syndromes, though it has also resulted in significant psychological distress for the affected patients, especially those with indeterminate variants. Herein, we aim to summarize the most relevant hereditary cancer syndromes involving the stomach and colon, with an emphasis on new molecular findings, novel entities, and recent changes in the management of these patients.

Mouse models in colon cancer, inferences, and implications

Mouse models of colorectal cancer (CRC) have been crucial in the identification of the role of genes responsible for the full range of pathology of the human disease and have proved to be dependable for testing anti-cancer drugs. Recent research points toward the relevance of tumor, angiogenic, and immune microenvironments in CRC progression to late-stage disease, as well as the treatment of it. This study examines important mouse models in CRC, discussing inherent strengths and weaknesses disclosed during their construction. It endeavors to provide both a synopsis of previous work covering how investigators have defined various models and to evaluate critically how researchers are most likely to use them in the future. Accumulated evidence regarding the metastatic process and the hope of using checkpoint inhibitors and immunological inhibitor therapies points to the need for a genetically engineered mouse model that is both immunocompetent and autochthonous.

Hepatoblastoma in patients with molecularly proven familial adenomatous polyposis: Clinical characteristics and rationale for surveillance screening

Familial adenomatous polyposis (FAP) due to APC mutation is associated with an increased risk of hepatoblastoma. All cases of hepatoblastoma in patients with FAP reported in the literature were reviewed. One hundred and nine patients were identified. Thirty-five patients (of 49 with data) were diagnosed with hepatoblastoma prior to a later diagnosis of FAP (often in association with advanced colorectal carcinoma), emphasizing a need to identify patients earlier with germline APC mutations for early colorectal carcinoma screening. Hepatoblastoma may present at birth, and screening for hepatoblastoma in infancy in families with FAP prior to APC mutation testing results may be warranted.

Chromosome rearrangement with no apparent gene mutation in familial adenomatous polyposis and hepatocellular neoplasia

We have identified a constitutional inversion in chromosome 5 associated with familial adenomatous polyposis in three generations of a Mexican family. Two of three siblings developed hepatic neoplasia in infancy. The gene truncation assay failed to demonstrate a truncated protein in the segment harboring the adenomatous polyposis coli (APC) genes. Polymerase chain reaction (PCR) amplification of APC gene coding exons and sequencing of PCR products did not reveal any significant mutation. The data suggest that in this family, the phenotype may be the result of a "position effect."

Familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal dominant condition resulting in the development of more than 100 adenomatous polyps in the large bowel. In addition, a number of extracolonic manifestations of the condition may occur. Recently, increasing knowledge relating to the extracolonic abnormalities, and localization and sequencing of the gene for FAP, have had important implications for screening and long-term follow-up of those affected. In this review the natural history of the disease and the extracolonic manifestations associated with it are considered. Surgical management and advances in understanding at a molecular level are discussed, as well as the problems relating to screening for FAP and the implications of the new knowledge.

Congenital hypertrophy of the retinal pigment epithelium and mandibular osteomata as markers in familial colorectal cancer

Congenital hypertrophy of the retinal pigment epithelium (CHRPE) and multiple mandibular osteomata are markers of familial adenomatous polyposis (FAP). We have assessed their prevalence in non-polyposis familial colorectal neoplasia. Multiple mandibular osteomata were present in 1/29 (3%) patients with familial colorectal neoplasia. CHRPE was present in 11/33 (33%) patients with familial colorectal neoplasia compared with 3/36 (8%) with sporadic disease (P = 0.01) and 4/32 (12.5%) control subjects (P = 0.04). Seven patients with familial colorectal neoplasia had multiple areas of CHRPE compared with one with sporadic disease (P = 0.02) and one control subject (P = 0.02). There was no obvious correlation between calculated familial colorectal cancer risk and the presence of multiple areas of CHRPE. A proportion of patients with familial colorectal cancer have a marker found in FAP and may therefore have a constitutional genetic defect, at least in part responsible for their cancer, making them an interesting group for genetic study. Ophthalmoscopy may contribute to risk assessment in familial colorectal cancer.

Non-allelic heterogeneity of familial adenomatous polyposis

Linkage studies on familial adenomatous polyposis (FAP) reported so far suggest that FAP is a genetically homogeneous disease. Recently, we found that the putative gene for Turcot syndrome, an apparently autosomal recessive clinical variant of FAP, is not allelic to FAP. Here we describe another family, segregating for an autosomal dominant disease clinically indistinguishable from FAP but genetically not linked to the APC locus, adding further evidence for the occurrence of non-allelic heterogeneity of FAP. These observations have implications to the linkage-based genetic counselling of persons at risk for FAP especially when they are drawn from small families giving insufficient information.

Tumour suppressor genes and colorectal neoplasia

Two distinct gene classes have been implicated in colorectal carcinogenesis. Tumour promoter genes (oncogenes, dominant oncogenes) produce an excessive positive stimulus to cell proliferation. The ras family of oncogenes are an example. Acquired mutations of the c-k-ras gene are commonly found in colonic adenomas and carcinomas. Tumour suppressor genes (anti-oncogenes, recessive oncogenes) normally constrain or regulate cell proliferation. Loss of this function through gene deletion or mutation is oncogenic. Inherited tumour suppressor gene mutations have now been identified in several of the familial cancer syndromes. Acquired tumour suppressor gene mutations are found in both sporadic and hereditary cancers. Together with the tumour promoter genes they provide the genetic basis for the cellular changes occurring during carcinogenesis. The retinoblastoma gene was the first human tumour suppressor gene to be characterized and exemplifies the class. More recently, linkage studies in the hereditary cancer syndromes and the detection of specific deletions in sporadic tumours have helped to identify several new tumour suppressor genes. At least four of these (MCC, APC, p53 and DCC) apparently contribute to sporadic colorectal carcinogenesis. Germ line APC mutations produce the inherited colorectal cancer syndrome familial adenomatous polyposis (FAP). Detection of these mutations using linked markers has already found clinical application in the screening of families with this disease. In the future, genetic diagnosis of hereditary non-polyposis colorectal cancer (HNPCC) and the recognition of those genetically susceptible to sporadic colorectal cancer may become possible. At the same time, as our understanding of the genes involved improves, new avenues for treatment and prevention of colorectal cancer may emerge.

Heredity, molecular genetics and colorectal cancer: a review

It is estimated that the hereditary polyposis and non-polyposis colorectal cancer (CRC) syndromes, which have an autosomal dominant pattern of inheritance, represent less than 10% of the total CRC burden. Thus, more than 90% of all cases of CRC have previously been considered to arise 'sporadically', with no identifiable genetic link. However, recent clinical evidence now suggests that a significant proportion of CRC seen in the general population may involve an inherited genetic susceptibility. Therefore, constructing an accurate family tree on all patients with a family history of CRC is an essential part of identifying families with an increased risk for CRC who could then be offered screening. Also, molecular genetic study of colorectal adenomas and carcinomas has led to a proposed genetic model of colorectal tumorigenesis which involves interactions between oncogenes and tumour suppressor genes. This information has important potential implications for screening, determining prognosis and for providing multiple targets for altering the sequence of malignant transformation.

Colon cancer genetics

The terms "hereditary," "sporadic," and "familial" colorectal cancer (CRC) suggest a knowledge of causation; however, current understanding of CRC does not permit categorization of differing CRC risks in accord with their cause per se. Despite these serious shortcomings, these terms are defined operationally on the basis of a family history of cancer, and when available, additional phenotypic information. The sporadic type occurs in the absence of a family history of CRC in a first-degree relative. The familial type occurs when at least one first-degree relative has CRC. Both these categories require the exclusion of hereditary CRC. In the case of hereditary CRC, this type is defined as a family history of CRC occurring in a pattern that indicates autosomal-dominant inheritance, which also may involve certain phenotypic signs (depending on the specific disorder, i.e., florid adenomatous polyps, benign and malignant extracolonic lesions, cancer of unusually early onset, and multiple primary cancer, particularly synchronous and metachronous CRC). Although this operational classification does not produce etiologically homogeneous groups, it is believed to have pragmatic utility with respect to planning targeted surveillance and management strategies. Because of the distinctive natural history of CRC in hereditary syndromes, it is of paramount clinical importance to identify hereditary CRC when it does occur. Even in patients with no evidence of hereditary CRC syndrome, their family history may be second only to age in determining the best CRC screening program for those who are asymptomatic. In an attempt to provide a perspective on the clinical evaluation of CRC risk, research was reviewed on pathologic features and biomarkers that may be related to CRC causes, especially the genetic basis of CRC susceptibility. The long-term objective of studies on the genetic epidemiology of CRC is primary and secondary prevention through development of targeted management and surveillance recommendations (based on an understanding of CRC causation) that is relevant to hereditary, familial, and sporadic CRC.

Loss of constitutional heterozygosity in human astrocytomas

Inactivation of tumour suppressor genes or anti-oncogenes as well as activation of dominant acting oncogenes seem to be important mechanisms in the pathogenesis of gliomas. We compared constitutional and tumoural genotypes at different restriction fragment length polymorphism loci (RFLP) on chromosomes 10 and 17 in 15 unrelated individuals. Loss of heterozygosity (LOH) pointing to chromosomal loss or deletions was detected for at least one chromosome 17 marker in 11 gliomas (astrocytomas grades I-III and glioblastoma multiforme), whereas LOH for chromosome 10 loci was only detected in 3 out of 9 cases of glioblastoma multiforme and was not detected in low grade gliomas. Since LOH for chromosome 10 loci seems to be restricted only to glioblastoma multiforme, it is possible that recessive mutations on chromosome 10 are engaged in tumour progression from astrocytomas to glioblastoma multiforme. As LOH of chromosome 17 markers occurs in astrocytomas as in glioblastoma multiforme, chromosome 17 loci probably are involved in early tumour development.

Eight novel inactivating germ line mutations at the APC gene identified by denaturing gradient gel electrophoresis

Familial adenomatous polyposis (FAP) is a dominantly inherited condition predisposing to colorectal cancer. The recent isolation of the responsible gene (adenomatous polyposis coli or APC) has facilitated the search for germ line mutations in affected individuals. Previous authors have used the RNase protection assay and the single-strand conformation polymorphisms procedure to screen for mutations. In this study we used denaturing gradient gel electrophoresis (DGGE). DGGE analysis of 10 APC exons (4, 5, 7, 8, 9, 10, 12, 13, 14, and part of 15) in 33 unrelated Dutch FAP patients has led to the identification of eight novel germ line mutations resulting in stop codons or frameshifts. The results reported here indicate that (1) familial adenomatous polyposis is caused by an extremely heterogeneous spectrum of point mutations; (2) all the mutations found in this study are chain terminating; and (3) DGGE represents a rapid and sensitive technique for the detection of mutations in the unusually large APC gene. An extension of the DGGE analysis to the entire coding region in a sufficient number of clinically well-characterized, unrelated patients will facilitate the establishment of genotype-phenotype correlations. On the other hand, the occurrence of an extremely heterogeneous spectrum of mutations spread throughout the entire length of the large APC gene among the FAP patients indicates that this approach may not be useful as a rapid presymptomatic diagnostic procedure in a routine laboratory. Nevertheless, the above DGGE approach has incidentally led to the identification of a common polymorphism in exon 13. Such intragenic polymorphisms offer a practical approach to a more rapid procedure for presymptomatic diagnosis of FAP by linkage analysis in informative families.

Loss of normal allele of the APC gene in an adrenocortical carcinoma from a patient with familial adenomatous polyposis

Endocrine neoplasms have been reported occasionally in patients with familial adenomatous polyposis (FAP). An adrenocorotical carcinoma was studied in a patient with a family history of FAP. Loss of heterozygosity (LOH) in the region close to the adenomatous polyposis coli (APC) gene was detected in this carcinoma, and evidence was obtained that there was a loss of the normal allele of the APC gene. This is the first demonstration of LOH at the APC locus in adrenocortical tumors. The present results and our previous data on LOH in a recurring desmoid tumor suggest that the heterozygous mutant/wild-type condition of the APC gene may give rise to benign tumors, and that functional loss of this gene leads to development of tumors not only in the colon but also in other various parts of the body in FAP patients.

Genetic evidence that Turcot syndrome is not allelic to familial adenomatous polyposis

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.

Multiple intestinal neoplasia caused by a mutation in the murine homolog of the APC gene

Germ-line mutations of the APC gene are responsible for familial adenomatous polyposis (FAP), an autosomal dominantly inherited disease in humans. Patients with FAP develop multiple benign colorectal tumors. Recently, a mouse lineage that exhibits an autosomal dominantly inherited predisposition to multiple intestinal neoplasia (Min) was described. Linkage analysis showed that the murine homolog of the APC gene (mApc) was tightly linked to the Min locus. Sequence comparison of mApc between normal and Min-affected mice identified a nonsense mutation, which cosegregated with the Min phenotype. This mutation is analogous to those found in FAP kindreds and in sporadic colorectal cancers.

Predictive diagnosis of familial adenomatous polyposis with linked DNA markers: population based study

OBJECTIVES

To evaluate the use of polymorphic DNA probes linked to the APC gene in the presymptomatic diagnosis of familial adenomatous polyposis.

DESIGN

Four DNA probes were tested on an unselected population of patients at risk of familial adenomatous polyposis.

SUBJECTS

The first 47 families notified to the West Midlands familial adenomatous polyposis register. Plus five families sent to our hospital as part of the West of Britain DNA consortium.

MAIN OUTCOME MEASURES

The proportion of families and family members in whom DNA testing could be used to adjust the estimate of risk.

RESULTS

Only 17 families on the register (containing 46% (74/162) of the population at risk) had a suitable pedigree structure for DNA analysis. DNA was analysed in 12 of these families plus the five families from the West of Britain consortium. At least one probe was informative in 27 of the 33 subjects born with 50% risk, but the most informative probe (pi 227) was the one with the highest recombination rate (10%). Flanking markers were informative in only four of the 33 subjects.

CONCLUSIONS

These findings confirm the potential for accurate predictive diagnosis of familial adenomatous polyposis with polymorphic DNA probes, but such an approach is currently limited to about one third of affected families. A combined approach to presymptomatic diagnosis, which includes DNA testing and indirect ophthalmoscopy, is advocated.

Risk estimation in familial adenomatous polyposis using DNA probes linked to the familial adenomatous polyposis gene

The familial adenomatous polyposis gene has recently been assigned to the long arm of chromosome five through linkage to several 5q DNA probes. These probes can now be used to trace inheritance of the disease gene in affected families. In this study, DNA samples from 152 members of 10 Australian familial adenomatous polyposis families have been examined for restriction fragment length polymorphisms detected by DNA probes C11P11, ECB27, and YN5.48. Linkage analysis confirmed linkage between the familial adenomatous polyposis gene and each probe with a maximum combined LOD score of 2.82 for C11P11, 2.90 for ECB27 and 5.49 for YN5.48 all at a recombination fraction of zero. Risk estimates were determined for the 51 at risk individuals in these families based on their restriction fragment length polymorphism data alone or in addition by including the effect of age dependent penetrance. Thirty two of those at risk (63%) could be assigned specific high (greater than or equal to 95%) or low (less than or equal to 5%) risks of developing familial adenomatous polyposis on the basis of their probe results. When the effect of age dependent penetrance was included, 26 (51%) fell at the extremes of risk (greater than or equal to 99% or less than or equal to 1%). Such estimates provide a sound basis for planning sigmoidoscopic screening of at risk family members and will thus facilitate surveillance in familial adenomatous polyposis families.

An intrachromosomal insertion causing 5q22 deletion and familial adenomatous polyposis coli in two generations

We report familial adenomatous polyposis coli (FAPC) with epidermoid cysts, osteomata, and areas of congenital hypertrophy of the retinal pigment epithelium (CHRPEs) in a male patient and his maternal aunt, both of whom suffered a mild to moderate degree of mental handicap. Both had an interstitial deletion of the long arm of chromosome 5 (del(5)(q22q23.2)). Two other normal family members had the underlying direct insertion of chromosome 5(dir ins(5)(q31.3q22q23.2)). Molecular genetic and fluorescent hybridisation studies have shown that loci D5S37 and D5S98 are outside the deletion whereas loci detected by probes EF5.44 and YN5.48 are lost. As expected, the molecular analyses indicate loss of one allele at the MCC and APC loci. The APC gene is located within band 5q22. Familial direct insertions should be considered as a cause of recurrent microdeletion syndromes.

Gene mapping of ocular diseases

Increasing awareness of the role of genetic factors in the causation of many human eye diseases has made ocular genetics one of the fastest growing areas of ophthalmology. The objective of this paper is to present the basic principles of gene mapping and their application to ophthalmology. The techniques used to map the genome are reviewed with emphasis placed on molecular genetics. The advances in this area have already provided the major impetus to the areas of diagnosis and prevention of some genetic eye disorders. Tables are presented that list the autosomal, X-linked and mitochondrial assignment of eye genes and disorders with ocular involvement.

Gardner syndrome in a boy with interstitial deletion of the long arm of chromosome 5

We described a 15-year-old boy with Gardner syndrome (GS), mental retardation, and craniofacial abnormalities. High-resolution banding analysis showed an interstitial deletion of the long arm of chromosome 5 (q22.1----q31.1). The breakpoints in the present case and in 3 previously reported 5q- patients with adenomatous polyposis coli suggest that the gene responsible for GS/or familial polyposis coli (FPC) is in the 5q22 region, a result consistent with the findings of linkage studies.

Linkage analysis in adenomatous polyposis coli: the use of four closely linked DNA probes in 20 UK families

Linkage analysis was carried out on 20 unselected UK families segregating for adenomatous polyposis coli (APC) using four closely linked DNA probes. Significant lod scores were obtained between APC and three markers: pi 227 (D5S37) theta = 0.16; C11p11 (D5S71) theta = 0.10; and YN5.48 (D5S81) theta = 0.00. The fourth, ECB27 (D5S98), gave low lod scores. The APC gene showed linkage with at least one of the probes used in all families, which is in agreement with previous publications. Combined lod scores are now sufficiently high to allow the use of these probes in presymptomatic diagnosis. Despite the fact that 61% of persons at risk were informative for at least one DNA marker, only 15% were informative with flanking probes. One prenatal diagnosis was performed where the initial request had been for sterilisation.

Value of combined phenotypic markers in identifying inheritance of familial adenomatous polyposis

Familial adenomatous polyposis is an autosomal dominant disease characterised by the development of hundreds of colorectal adenomas in young adults. Occult radio-opaque jaw lesions and pigmented ocular fundus lesions (formerly called congenital hypertrophy of the retinal pigment epithelium) are extraintestinal phenotypic markers for this disorder. We evaluated the usefulness of the combination of these markers for identifying patients who have inherited familial adenomatous polyposis. Forty three affected patients and 12 unaffected first degree relatives from 24 families with familial adenomatous polyposis, including four families without extraintestinal manifestations, were examined for both phenotypic markers. Thirty three of the 43 patients (77%) with familial adenomatous polyposis were positive for both markers, including patients from two families without extraintestinal manifestations. By contrast, only one of 12 (8%) unaffected first degree relatives over 35 years of age had both markers. The sensitivity of the combination of these markers in identifying patients who inherited familial adenomatous polyposis was 77%, the specificity 92%, the predictive value of a positive test 97%, the predictive value of a negative test 52%, and the efficacy 80%. The combined markers had improved efficacy over either marker alone (70% for occult radio-opaque jaw lesions and 67% for pigmented ocular fundus lesions). We conclude that the presence of both occult radio-opaque jaw lesions and pigmented ocular fundus lesions in a person at risk indicates a high probability of inheritance and expression of familial adenomatous polyposis.

Fine mapping of probes in the adenomatous polyposis coli region of chromosome 5 by in situ hybridization

The gene for adenomatous polyposis coli has been localized to 5q21-22. We have mapped six probes from this region using isotopic or nonisotopic in situ hybridization. Using tritium-labeled probes we localized II227 (D5S37) to 5q14-15 and ECB27 (D5S98) to 5q21. Following hybridization with biotin-labeled probes, the positions of signals along the chromosomes were measured as fractional length relative to the length of the chromosome arm from centromere to qter (FLcen-qter). Ninety-five percent confidence limits, compared with standard karyotypes, provided the corresponding band localization. By this method we localized Cllpll (D5S71) to FLcen-qter 0.407-0.452 (5q21.1-21.3), ECB27 to FLcen-qter 0.426-0.473 (5q21.3), YN5.48 (D5S81) to FLcen-qter 0.459-0.496 (5q21.3-22.2), and ECB134 (D5S97) to FLcen-qter 0.509-0.533 (5q22.3-23.1). ECB220 had three sites of hybridization, a major site at FLcen-qter 0.460-0.492 (5q21.3-22.1) and minor sites at FLcen-qter 0.299-0.339 (5q14.3-15) and FLcen-qter 0.629-0.691 (5q23.3-31.2). We have shown that the chromosome 5 breakpoint in a t(5;15) translocation from a patient with Gardner's syndrome (GM03314) is between Cllpll and ECB27. Linkage data are presented suggesting that ECB27 is located on the same side of the APC locus as II227. These and published results including data on several constitutional deletions (M, SD, and brothers PW and ND) give a probable order of [cen] - [II227, proximal SD breakpoint] - [Cllpll] - [proximal PW/ND, M breakpoint(s), GM03314 breakpoint] - [ECB27] - [APC] - [YN5.48] - [distal PW/ND breakpoint] - [ECB134] - [distal M breakpoint] - [qter]. The major site of ECB220 appears to be between ECB27 and the distal PW/ND breakpoint; the distal SD breakpoint is distal to YN5.48.

Mutations of chromosome 5q21 genes in FAP and colorectal cancer patients

Previous studies suggested that one or more genes on chromosome 5q21 are responsible for the inheritance of familial adenomatous polyposis (FAP) and Gardner's syndrome (GS), and contribute to tumor development in patients with noninherited forms of colorectal cancer. Two genes on 5q21 that are tightly linked to FAP (MCC and APC) were found to be somatically altered in tumors from sporadic colorectal cancer patients. One of the genes (APC) was also found to be altered by point mutation in the germ line of FAP and GS patients. These data suggest that more than one gene on chromosome 5q21 may contribute to colorectal neoplasia, and that mutations of the APC gene can cause both FAP and GS. The identification of these genes should aid in understanding the pathogenesis of colorectal neoplasia and in the diagnosis and counseling of patients with inherited predispositions to colorectal cancer.

Genetic characterization of the APC locus involved in familial adenomatous polyposis

Familial adenomatous polyposis is a rare disease inherited in a Mendelian dominant fashion. It is characterized by the occurrence of more than 100 adenomatous polyps in the large bowels of affected individuals. The genetic defect responsible for adenomatous polyposis resides at a locus called APC which has been localized to the long arm of human chromosome 5. In this study, the APC locus was mapped with respect to 11 markers known to map to this chromosomal segment. Linkage of APC to four of these markers had been previously reported. Three additional markers are shown here to be linked to APC. By multipoint analysis, the APC locus maps to an interval bounded by D5S49 and D5S58. The refined map of the APC locus and the new markers described here improve the informativeness and accuracy of the presymptomatic diagnosis of familial adenomatous polyposis.

Hereditary nonpolyposis colorectal cancer (Lynch syndromes I & II). Genetics, pathology, natural history, and cancer control, Part I

Hereditary nonpolyposis colorectal cancer (HNPCC) is common, accounting for about 4-6% of the total colorectal cancer burden. It is heterogeneous and appears to be delineated into two clinical subsets, Lynch syndromes I and II. Lynch syndrome I is characterized by an autosomal dominantly inherited proclivity to early onset colonic cancer with proximal predominance and an excess of multiple primary colonic cancer. Lynch syndrome II has all of these features plus extracolonic cancer sites, the most common of which is endometrial carcinoma. The lack of premonitory physical signs or biomarkers of HNPCC makes diagnosis difficult. A careful family history, tempered by an understanding of the clinical and pathologic features of HNPCC, is the key to its assessment. This paper reviews HNPCC's natural history, its integral extracolonic cancer associations, its differential diagnosis, surveillance, and management strategies. Attention is focused upon the need for biomarker research in the interest of improving control of HNPCC.

Screening guidelines and premorbid diagnosis of familial adenomatous polyposis using linkage

Restriction fragment-length polymorphisms in the chromosome 5q21-22 region can now be used clinically for premorbid diagnosis and counseling in familial adenomatous polyposis. Two families are presented in which DNA diagnosis for familial adenomatous polyposis was performed using linked restriction fragment-length polymorphisms. Screening guidelines are improved using data from the polyposis registers at St. Mark's Hospital (London) and Western Australia (Perth) on at-risk family members who subsequently developed familial adenomatous polyposis. In these registers, 103 of 137 relatives tested positive on initial screening; of the remaining 34, the average interval between initial negative screening and development of familial adenomatous polyposis was 7.5 years. All those who had inherited the familial adenomatous polyposis gene manifested the polyps by age 34 years. Combined with linkage marker data, the a priori 50% risk for relatives can now be reduced to less than 0.5% by age 30 years if there is an initial negative result on sigmoidoscopy and a negative diagnosis by linkage analysis. The screening management for those found by linkage to have inherited familial adenomatous polyposis remains unchanged from established recommendations; however, for individuals who most likely have not inherited familial adenomatous polyposis, the clinician can emphasize the positive aspects of screening management, including longer screening intervals.

The UK Northern region genetic register for familial adenomatous polyposis coli: use of age of onset, congenital hypertrophy of the retinal pigment epithelium, and DNA markers in risk calculations

A polyposis register has been established in the Northern Region of England. A total of 48 families with 71 living affected subjects has been identified during the first three years of operation, a prevalence of 2.29 x 10(-5). Indirect ophthalmoscopy identifies the majority of gene carriers by showing multiple areas of congenital hypertrophy of the retinal pigment epithelium (CHRPE). The absence of this sign in families limits its value where a relative with CHRPE has not been identified. Combining eye examination with data on age of onset and linked DNA markers is highly effective in carrier exclusion; 38% of 528 first, second, and third degree relatives had their carrier risk reduced to less than 1 in 1000. Even with such assurance many subjects will request continued bowel screening at a reduced frequency. Little interest has been shown in prenatal diagnosis. The principal value of a genetic register with domiciliary nurse visiting is the reduction in early mortality among unrecognised gene carriers.

Linked DNA markers for presymptomatic diagnosis of familial adenomatous polyposis

41 symptom-free individuals aged 0-39 years who were at risk of familial adenomatous polyposis (FAP) were genotyped with six linked DNA probes. 28 individuals were informative for probes flanking the gene and 14 people assigned a probe-derived risk of over 0.93 were subsequently shown to be affected by clinical screening. 4 individuals who had been discharged from follow-up were designated high risk by this method. In those screened negative, risk was calculated from genotypic, colonic, and CHRPE findings and 89% of subjects had a risk below 0.003. An integrated risk analysis may have an important place in screening programmes for FAP.

Normal human chromosome 5, on which a familial adenomatous polyposis gene is located, has tumor suppressive activity

The suppressive activity of normal human chromosome 5 was detected by means of the chromosomal transfer technique using DT cells as recipients. A hybrid clone, which exhibited reduced tumorigenicity, contained chromosomal regions such as 5pter-p15, q21 and q33-qter. Since a familial adenomatous polyposis gene has been reported to be located at 5q21-q22, the suppressive activity of chromosome 5 might be due to this gene.

Stability of critical genetic lesions in human colorectal carcinoma xenografts

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Predictive value of congenital hypertrophy of the retinal pigment epithelium as a clinical marker for familial adenomatous polyposis

One hundred forty-eight members of 53 kindreds with familial adenomatous polyposis (FAP) were examined for congenital hypertrophy of the retinal pigment epithelium (CHRPE) and extracolonic manifestations (ECM) to assess the value of CHRPE as a predictive marker for FAP. Based on eye examination results, the families were divided into 2 groups. In a first group of 34 families, all 61 members diagnosed as having polyps and 13 of the 33 patients at risk had 4 or more lesions distributed in both eyes. By contrast, in a second group of 18 families, all 32 polyposis patients and all 18 members at risk had less than 4 lesions. Extra-colonic manifestations were present in 26 of 34 families in the first group and in 11 of 18 families in the second group. Data on one family with ambiguous ancestry were reviewed separately. The existence of 4 or more CHRPE lesions distributed in both eyes seems to be a congenital marker for FAP, present in 65.4 percent of families. When present in a family: 1) it is found in all diagnosed patients in that family, 2) can therefore be considered predictive for the development of polyps in other family members who carry the trait, and 3) if confirmed by longer follow-up, may possibly preclude members without the trait from further evaluation and surveillance.

A clinicopathologic study of the eyes in familial adenomatous polyposis with extracolonic manifestations (Gardner's syndrome)

The eyes of a 51-year-old woman with familial adenomatous polyposis and extracolonic manifestations (Gardner's syndrome) were obtained postmortem and studied by light microscopy and by transmission and scanning electron microscopy. We found a generalized abnormality in melanogenesis of the retinal pigment epithelium and at least three types of pigmented lesions. The histologic findings in one type of lesion were consistent with congenital hypertrophy of the retinal pigment epithelium or benign pigmented nevus of the retinal pigment epithelium. The other two types of lesion were most consistent with hamartomatous malformations of the retinal pigment epithelium featuring cellular hypertrophy, hyperplasia, and rarely retinal invasion and formation of a minute mushroom-shaped tumor. These histopathologic findings indicate a generalized effect of the familial adenomatous polyposis gene on the retinal pigment epithelium. This oncogene, which is responsible for tumor formation in the gastrointestinal tract, soft tissues, bone, and other locations in patients with familial adenomatous polyposis, also leads to a generalized defect in melanogenesis and focal lesions of the retinal pigment epithelium.

Evaluation of polymorphic genetic markers for linkage to the familial adenomatous polyposis locus on chromosome 5

A gene associated with the inherited syndrome, familial adenomatous polyposis (FAP), has been localized to the long arm of chromosome 5 near the 5q21-22 region, and markers that identify genetic polymorphisms near this locus are now available. The authors evaluated several of these markers for linkage to the FAP trait in 11 families entered in the Cleveland Clinic Polyposis Registry. The original probe that established linkage to the FAP locus (C11p11) has limited utility for family studies because of low heterozygosity and distance from the FAP gene. Other probes, however, should be useful for assessing FAP inheritance by restriction fragment length polymorphism analysis, for presymptomatic diagnosis of the disease.

The value of screening and central registration of families with familial adenomatous polyposis. A study of 82 families in The Netherlands

In 1984 a national registry of families with familial adenomatous polyposis was set up in The Netherlands to promote screening in those families. Eight-two families had been registered by the end of 1988. Analysis of the pedigrees showed that 204 family members at risk had not yet been screened. The diagnosis of familial adenomatous polyposis was histologically confirmed in 230 patients. These patients were subdivided into two groups. Group A comprised patients with familial adenomatous polyposis referred because they were symptomatic, and Group B relatives of these patients who were found by screening to have familial adenomatous polyposis. The authors compared these groups with respect to the occurrence of colorectal carcinoma. Fifty-four patients were found to have a colorectal carcinoma at the time of diagnosis of familial adenomatous polyposis, i.e., 49 of the 104 patients in Group A (47 percent) and five of the 126 patients in Group B (4 percent). The average age at diagnosis of the 104 patients in Group A was 35 years (range, 13 to 66 years) and that of the 126 patients in Group B was 24 years (range, 8 to 59 years). By the age of 40 years, 90 percent of the patients in group B had been diagnosed. Late onset of familial adenomatous polyposis was found in four families. Endoscopy and/or radiography of the upper digestive tract were (was) performed in 44 of the 230 patients. Nineteen patients (43 percent) were found to have polyps in the stomach or duodenum, or both. In our series, only one patient died from cancer of the upper digestive tract (ampullary carcinoma). These results show conclusively that screening leads to the early detection of familial adenomatous polyposis. The value of a national registry is proved by the finding of many at-risk family members who had not previously been screened. Screening should start between the ages of 10 and 12 and should continue up to the age of 50. In the rare cases of families with an apparently late onset of familial adenomatous polyposis, screening should be continued up to age 60. More studies are needed to determine the natural history of polyps in the upper digestive tract.

Facioscapulohumeral muscular dystrophy gene in Dutch families is not linked to markers for familial adenomatous polyposis on the long arm of chromosome 5

Cosegregation of facioscapulohumeral muscular dystrophy (FSHD) and familial adenomatous polyposis (FAP) has been described in two small families. The gene for FAP is located on the long arm of chromosome 5. We studied two large Dutch families with FSHD and found no evidence for linkage with gene markers closely linked to FAP. These results strongly suggest that the FSHD gene segregating in the Dutch families is not localized close to the FAP locus on chromosome 5.

Lessons from the genetics of colon cancer

Remarkable advances in the understanding of specific inherited and acquired genetic events that are important in colonic carcinogenesis have occurred in the last several years. Studies of the population genetics of colon cancer have determined that the gene responsible for familial adenomatous polyposis (FAP), and Gardner's syndrome has been localized on the long arm of chromosome 5 and have more clearly defined the importance of genetic influences in 'sporadic' colon cancer. Studies of the molecular genetics of colon cancer have identified acquired alterations in oncogenes such as the K-ras gene and in putative tumor suppressor genes such as the FAP gene on chromosome 5, the p53 gene on chromosome 17, and the DCC gene on chromosome 18, which appear to mediate important steps in the adenoma-dysplasia-carcinoma sequence. Some of these research advances (FAP gene carriage) are already being used clinically to identify individuals at risk for colon cancer, and they offer great promise for the future of both prevention and therapeutic programs.

Presymptomatic diagnosis of familial adenomatous polyposis by bridging DNA markers

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.

CpG island clones from a deletion encompassing the gene for adenomatous polyposis coli

Adenomatous polyposis coli (APC), a dominantly inherited disorder, has been mapped to chromosome 5q15-q21 by family linkage studies. Cells from patients with deletions in this region, in one case associated with polyposis in a family, have been used to construct human hamster hybrid cell lines that retain either the normal or deleted chromosome 5. These lines have been used to identify markers from the region of the polyposis gene obtained by cloning the ends of 0.5- to 2-megabase BssHII fragments purified by pulsed-field gel electrophoresis. Three markers are described that map within the deletions and must therefore be close to the APC gene.

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.

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.