Japanese Journal of Clinical Oncology 30:82-88 (2000)
© 2000 Foundation for Promotion of Cancer Research
The Relationship Between Frequencies of Extracolonic Manifestations and the Position of APC Germline Mutation in Patients with Familial Adenomatous Polyposis
1Second Department of Surgery, Tokyo Medical and Dental University, Tokyo, 2Hereditary Tumor Research Project, Tokyo Metropolitan Komagome Hospital, Tokyo, 3Department of Surgery, Kyoundo Hospital, Sasaki Institute, Tokyo and 4Hyogo College of Medicine, Hyogo, Japan
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAcknowledgmentREFERENCES |
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Background: Familial adenomatous polyposis (FAP) patients develop various extracolonic lesions; however, the relationship between germline mutation of the APC gene and extracolonic manifestations is mostly unknown. To examine the genotype–phenotype relationship, we compared the APC mutation and clinical data.
Methods: Germline mutations from codon 157 to 1465 of the APC gene were identified in 39 families of FAP and clinical data were collected from 80 patients of these families. Germline mutations were classified into two groups: mutations from exon 4 to 9 (codon 157 to 416, Group 1) and those from exon 10 to 15H (codon 564 to 1465, Group 2). The complication rates of extracolonic manifestations were compared between these two groups.
Results: Frequencies of duodenal polyps and gastric adenomas in Group 2 were higher than those in Group 1 (p < 0.0001 and p < 0.0004, respectively) and development of osteoma was more frequent in Group 2 (p = 0.01). The number of colorectal polyps and retinal pigments also correlated with the germline mutation, which was consistent with previous reports. However, such correlations were less obvious with regard to gastric fundic polyps, desmoid tumors, soft tissue tumors and colorectal cancer.
Conclusion: There are two types with regard to extracolonic manifestations of FAP: one is more severely affected according to the position of germline mutation of the APC gene and the other is not affected.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAcknowledgmentREFERENCES |
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Familial adenomatous polyposis (FAP) is an autosomal dominant disease with high penetrance, characterized by multiple colorectal adenomatous polyps. About 90% of FAP patients develop colorectal cancer before the age of 60, if left untreated (1). Presymptomatic and prophylatic surgical treatment to prevent colorectal cancer is essential for this disease. However, the disease is not confined to the colon and rectum. Extracolonic manifestations include gastroduodenal polyps, osteomas, desmoid tumors, soft tissue tumors, congenital hypertrophic retinal pigment epithelium (CHRPE) lesions and malignant tumors in other organs (1, 2).
FAP patients are clinically divided into two types according to the number of colorectal polyps. The profuse type develops >5000 colorectal polyps per patient and the sparse type <5000 (3). Additonally, FAP patients with few colorectal polyps have also been found and classified as the attenuated type (4). It has been suggested that germline mutation between codons 1250 and 1464 tends to co-exist with the profuse type (5) and when the mutation is located near the 5' end (codons 97–157) it is related to the attenuated type (4). The CHRPE lesions have previously been reported to be absent when the germline mutation occurs before exon 9, but present when it occurs after exon 9 (6).
Duodenal and gastric adenomatous lesions are among the most common conditions associated with FAP in addition to colorectal polyps (1,7–9).
This study was aimed at examining whether there is a relationship between the position of germline mutation in the APC gene (10–14) and manifestations of duodenal and gastric adenomas and other extracolonic lesions associated with FAP.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAcknowledgmentREFERENCES |
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FAP Patients
Thirty-nine unrelated Japanese FAP families were examined for germline mutation of the APC gene. Germline mutations were classified into two groups according to the previously reported borderline in APC gene for manifestation of CHRPE (6): Group 1, mutation from exon 4 to 9 (codon 157 to 416); Group 2, mutation from exon 10 to 15H (codon 564 to 1465). There was no mutation detected on exons 10–12 in the present study. Clinical data were obtained from 80 patients of these families at the ages indicated in Table 1. Patients under 20 years old were excluded, because extracolonic lesions may not develop at earlier ages.
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Identification of Germline Mutation of the APC Gene
Peripheral blood samples were obtained from FAP patients after informed consent. DNA samples were extracted from peripheral blood, amplified by polymerase chain reaction (PCR) and analyzed by the single-strand conformation polymorphism (SSCP) method, as described previously (15–17). Primers used to amplify the coding exons were the same as those reported previously (11). When abnormal bands were detected in PCR–SSCP analysis, the DNA fragments were extracted from the corresponding gel, amplified through asymmetric PCR and then sequenced as described (16).
Duodenal Polyps
Duodenal polyps were examined by a side-viewing video-endoscope, to the second part of the duodenum. The extent of duodenal polyps was classified into four groups according to polyp number: no polyps (–), 1–4 polyps (+), 5–20 polyps (++) and >20 polyps (+++).
Gastric Polyps
Gastric polyps were observed by a front-viewing video-endoscope. Any polyps in the antral region were biopsied and examined for adenomatous changes. The extent of gastric polyps (both adenomatous polyps and fundic gland polyps) was classified into four groups: no polyps (–), 1–4 polyps (+), 5–20 polyps (++) and >20 polyps (+++).
Colorectal Polyps
The extent of colorectal polyps was classified into three groups: <100 polyps (+), 100–5000 polyps (++) and >5000 polyps (+++).
Osteoma, Desmoid Tumor and Soft Tissue Tumors
Absence (–) or presence (+) of these tumors was noted.
CHRPE Lesions
The retina was examined by an experienced ophthalmologist and the number of pigmented lesions was determined as described previously (18).
Colorectal Cancer
The number of colorectal cancers detected was recorded.
Statistical Method
The frequency of extracolonic manifestations was compared in patients having APC germline mutation before and after exon 9 (Groups 1 and 2), using Fisher’s exact probability test. Calculation was done with respect to the extent of manifestation by categorizing the cases as follows: with and without extracolonic manifestation; and low and high extent of manifestation.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAcknowledgmentREFERENCES |
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Informative clinical data were obtained from 80 FAP patients from 39 unrelated families, as shown in Table 1. With respect to APC germline mutation, we detected frameshift and nonsense mutations in our patients, but no missense or in-frame deletion was detected by the PCR–SSCP method. The frequencies of extracolonic manifestations were compared in patients having APC mutation before and after exon 9, which has been reported as a borderline for manifestation of CHRPE (6).
Duodenal polyps were analyzed in 62 patients from 30 families (Table 2). Ten families (20 informative patients) had APC gene mutations from exon 4 to 9 (Group 1) and 20 families (42 informative patients) had them from exon 13 to 15H (Group 2). When the extent of manifestation was compared between absence (–) and presence (+, ++ and +++), four of 20 (20%) patients in Group 1 had duodenal polyps, whereas 31 of 42 (74%) patients in Group 2 had duodenal polyps (p = 0.0001). When the extent was compared between low (– and +) and high (++ and +++), no patients (0%) in Group 1 showed a high extent, whereas 28 of 42 (67%) patients in Group 2 showed a high extent (p = 0.0000002). The mean age of the patients examined was 39.4 years for Group 1 and 34.9 years for Group 2.
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Gastric adenomas were analyzed in 69 patients from 35 families (Table 3). Eleven families (21 informative patients) had the mutation from exon 4 to 9 (Group 1) and 24 families (48 informative patients) had the mutation from exon 13 to 15H (Group 2). A comparison between absence (–) and presence (+, ++ and +++) of gastric adenomas revealed that two of 21 (10%) patients in Group 1 had gastric adenomas, whereas 26 of 48 (54%) patients in Group 2 had adenomas (p = 0.0004). When compared between low (– and +) and high (++ and +++), no patient (0%) in Group 1 had a high extent, whereas 20 of 48 (42%) patients in Group 2 showed high extent (p = 0.0001). The mean age of the patients in Group 1 was 38.7 years and that in Group 2 was 35.5 years. However, the manifestation of gastric fundic polyps (Table 6) did not correlate with the position of the APC gene mutation (between absence and presence and between low and high: p = 0.2 and 0.6, respectively).
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Colorectal polyp densities were evaluated in 39 families. In 11 families with the APC germline mutation between codons 1250 and 1311, all the members developed profuse-type colorectal polyps. In the remaining 28 families with the mutation either before codon 1250 or after codon 1311, all members except one showed the sparse type or the attenuated type. The one case with mutation at codon 1102 had the profuse type. Three patients with mutation between codons 157 and 175 showed the attenuated type.
CHRPE lesions were evaluated in 21 families (Table 5). In Group 1, all five patients showed no CHRPE lesions. In contrast, 17 of 20 (85%) patients in Group 2 showed CHRPE (p = 0.001).
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Absence or presence of osteoma (Table 4) had a weak correlation with the position of APC germline mutation. Two of 14 (14%) patients in Group 1 had osteomas, whereas 20 of 38 (53%) patients in Group 2 had osteomas (p = 0.01). The mean age of the patients examined in Group 1 was 38.1 years and in Group 2 36.0 years.
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Desmoid tumors (p = 0.1), other soft tissue tumors (p = 0.7) and colorectal cancer (p = 0.08) were not related to the position of APC gene mutation.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAcknowledgmentREFERENCES |
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The present study confirmed that the numbers of colorectal polyps (profuse, sparse or attenuated type) and CHRPE lesions are determined by the position of germline mutation (4–6). In addition, we found that the extent of extracolonic manifestations, such as duodenal polyps and gastric adenoma, was also affected by the position of the germline mutation when we compared the frequency of the manifestation between Group 1 (exons 4–9) and Group 2 (exons 10–15H).
Although duodenal and gastric adenomas are usually found in rather elderly FAP patients, two studies reported that the number of duodenal polyps did not increase with age when patients were over 25 years old (7,8). The mean age of our patients, when their duodenal and stomach examinations were performed, was 36 years. Our data suggest that the number of duodenal adenomas was regulated by the family to which the patients belong, where the regulation is caused by the position of the APC gene mutation. It was previously reported that gastric adenomas were usually observed in association with more severe duodenal adenomas (9). Our data were consistent with the report. On the other hand, we observed that fundic gland polyps of the stomach, desmoid tumors, soft tissue tumors and colonic cancer had no correlations with the mutation position, although osteomas had a weak correlation. These findings suggest that there are two types of manifestations associated with FAP: those more severely affected according to the position of the germline mutation and those not affected. In the former manifestations, the interfamilial difference appears to come from the function of truncated APC protein. The latter may be affected by environmental or time factors rather than the mutation position.
It has been suggested that APC protein, which is truncated downstream of codon 171, forms unstable heterodimers with wild-type APC protein, leading to a relatively large amount of wild-type dimers (19,20). Because of a weak dominant negative effect, members of families having germline mutation before this codon have fewer polyps (4).
An additional site that mediates homo- and hetero-oligomerization with coiled-coil potential was reported around codon 500 (12) (arm repeats in Fig. 1). It is also assumed that the dominant negative effect of truncation is more significant after codon 500 than before it. Patients with germline mutations, which produce mutant APC proteins truncated after codon 500 (mutations after codon 416 in Table 1), developed increased numbers of duodenal polyps and gastric adenomas compared with patients with APC mutation before codon 500 (mutations before codon 564 in Table 1). The frequency of CHRPE lesions may also be affected by this binding site, since it has been reported that CHRPE lesions were absent in patients with the mutation before exon 9 (codons 413–438), but were present in patients with the mutation after exon 9 (6). Our data on CHRPE in Table 1 were consistent with that previous observation.
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Other sites between codons 1014 and 1210 (15 aa repeats in Fig. 1) and 1263 and 2013 (20 aa repeats in Fig. 1) have been found to be involved in the association of the APC protein with catenins (21,22). This association may be involved in regulating transmission of the contact inhibition signal into the cells. The occurrence of the profuse type of colorectal polyps in patients with mutations after codon 1110 (Table 1) suggests that mutant APC proteins truncated after this region may have significant dominant negative effects on the wild-type APC protein, compared with mutant APC proteins truncated before this region. This dominant negative effect may diminish the association that exists between normal APC protein and catenins. However, it is unclear yet why families with germline mutation after codon 1465 do not exhibit the profuse type.
Tissues with frequent proliferation of cells appear to be more susceptible to the dominant negative effect of truncated APC proteins, which may result in a more increased level of hyperproliferation, although visible-sized tumors can develop after somatic mutation occurs in the other allele (13,15–17,23,24). However, with respect to manifestations that are mainly affected by environmental factors, these factors seem to outweigh the effect of germline mutation. The mechanism underlying the correlation between the extent of colonic and extracolonic manifestations and the position of germline mutations should be further examined. Intrafamilial variations that were observed in extracolonic manifestations (Table 1) were difficult to explain by only APC mutation position. Other genetic factors, such as modifiers (25), assumed to modify the phenotypic expression and environmental factors, may also affect the extent of manifestation. The causes of these variations should also be examined further.
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Acknowledgment |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAcknowledgmentREFERENCES |
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This work was supported in part from grants from the Ministry of Health and Welfare of Japan, and Smoking Research Foundation.
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FOOTNOTES |
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+ For reprints and all correspondence: Michiko Miyaki, Hereditary Tumor Research Project, Tokyo Metropolitan Komagome Hospital, 3–18–22 Honkomagome, Bunkyo-ku, Tokyo 113-8677, JapanAbbreviations: APC, adenomatous polyposis coli; FAP, familial adenomatous polyposis; CHRPE, congenital hypertrophic retinal pigment epithelium; PCR, polymerase chain reaction; SSCP, single-strand conformation polymorphism
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONAcknowledgmentREFERENCES |
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Received August 9, 1999; accepted November 2, 1999.
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