Jill D. Brensinger

The use and interpretation of commercial APC gene testing for familial adenomatous polyposis

BACKGROUND The use of commercially available tests for genes linked to familial cancer has aroused concern about the impact of these tests on patients. Familial adenomatous polyposis is an autosomal dominant disease caused by a germ-line mutation of the adenomatous polyposis coli (APC) gene that causes colorectal cancer if prophylactic colectomy is not performed. We evaluated the clinical use of commercial APC gene testing. METHODS We assessed indications for APC gene testing, whether informed consent was obtained and genetic counseling was offered before testing, and the interpretation of the results through telephone interviews with physicians and genetic counselors in a nationwide sample of 177 patients from 125 families who underwent testing during 1995. RESULTS Of the 177 patients tested, 83.0 percent had clinical features of familial adenomatous polyposis or were at risk for the disease-both valid indications for being tested. The appropriate strategy for presymptomatic testing was used in 79.4 percent (50 of 63 patients). Only 18.6 percent (33 of 177) received genetic counseling before the test, and only 16.9 percent (28 of 166) provided written informed consent. In 31.6 percent of the cases the physicians misinterpreted the test results. Among the patients with unconventional indications for testing, the rate of positive results was only 2.3 percent (1 of 44). CONCLUSIONS Patients who underwent genetic tests for familial adenomatous polyposis often received inadequate counseling and would have been given incorrectly interpreted results. Physicians should be prepared to offer genetic counseling if they order genetic tests.

Variable phenotype of familial adenomatous polyposis in pedigrees with 3' mutation in the APC gene

Background—Germline mutation in the adenomatous polyposis coli (APC) gene on chromosome 5 causes familial adenomatous polyposis. “Attenuated” phenotype has been reported with mutation in the 5′ end of the gene (5′ to codon 158), but genotype-phenotype relations at the 3′ end (3′ to codon 1596) have not been described fully. Aims—To describe and compare colorectal and extracolonic phenotypes in a case series of families with mutation in the 3′ end of the APC gene. Methods—Thirty one at risk or affected members from four families with a mutation in the APC gene located at codon 1979 or 2644 were evaluated. Results—Variable intrapedigree colorectal phenotype was observed: some members at older age had oligopolyposis (fewer than one hundred colorectal adenomas) whereas other members had classic polyposis at young age. Colorectal cancer was diagnosed at older mean age (50 (7) years) in the four families than in classic FAP pedigrees (39 (14) years). Extracolonic lesions characteristic of FAP occurred with 3′ APC mutations, but variability in intrapedigree and interpedigree extracolonic phenotype and dissociation of severity of extracolonic manifestations from number of colorectal polyps was noted. Conclusions—Families with 3′ mutations of the APC gene exhibit variable intrapedigree phenotype similar to the heterogeneity noted in families with proximal 5′ mutations. Genotyping of FAP and oligopolyposis pedigrees can guide appropriate surveillance of the upper and lower gastrointestinal tract in affected members.

Phenotypic expression of disease in families that have mutations in the 5' region of the adenomatous polyposis coli gene

Familial adenomatous polyposis is a dominant autosomal disease that is caused by germline mutations of the adenomatous polyposis coli gene, which is located on the long arm of chromosome 5 in band q21 [1-4]. The familial adenomatous polyposis phenotype is usually characterized by the development of hundreds of colorectal adenomas in young adults [5]. If prophylactic colectomy is not done, most patients will develop colorectal cancer by the sixth decade of life [6]. In 1988, Lynch and colleagues [7] first described a cancer-prone family with many members who had fewer than 100 adenomas. The adenomas were flat in appearance and were located primarily in the right side of the colon. After molecular examinations of this family and six others with similar characteristics were done [8-10], a mutation was found in the adenomatous polyposis coli gene. This variant of familial adenomatous polyposis was named attenuated adenomatous polyposis coli by Spirio and colleagues [11]. The clinical characteristics of this attenuated variant include few adenomas, marked phenotypic variation within families, and onset of colorectal cancer occurring approximately 15 years later than in classic familial adenomatous polyposis but 10 years earlier than in sporadic colorectal cancer [10, 12]. When studying seven families that had an attenuated phenotype, Spirio and colleagues [11] found four different mutations of the adenomatous polyposis coli gene. These mutations were frame-shifts or changes to single base pairs, and they predicted truncated gene products (proteins) that are similar to the mutations that are found in classic familial adenomatous polyposis. However, these truncations were located very close to the 5 end of the gene in codons 85 to 157. With data from three other families that were studied by Olschwang and coworkers [13] and Fodde and associates [14], Spirio and colleagues concluded that mutations that were proximal to codon 158 predicted the attenuated phenotype whereas mutations that were distal to codon 167 were associated with classic familial adenomatous polyposis [10] (Figure 1). However, the clinical features of families that have mutations at various sites in the 5 region of the adenomatous polyposis coli gene have not been compared in detail. Figure 1. The adenomatous polyposis coli gene. In this study, we examined the phenotype of seven families with mutations in the adenomatous polyposis coli gene that occurred toward the 5 end, relative to codon 158 (proximal 5 families). These findings were compared with those of seven families with mutations that were immediately downstream from codon 158, in codons 179 to 625 (distal 5 families). Methods Patient Evaluation At the time of this study, The Johns Hopkins Polyposis Registry contained information from 340 families with familial adenomatous polyposis that was initially gathered from a five-state region in the United States beginning in 1972. After informed consent was obtained, at least one member with familial adenomatous polyposis from each of 112 families was evaluated for a mutation of the adenomatous polyposis coli gene. These 112 families were the first to be consecutively enrolled in the Johns Hopkins Registry that had an affected member who was available for genetic testing. Genotype was analyzed in leukocyte DNA, RNA, or both from peripheral blood. The analysis was done by the in vitro synthesized protein (IVSP) assay, by cloning and sequencing the entire coding region of the gene, or by both methods as described elsewhere [15-17]. (The in vitro synthesized protein assay has replaced DNA sequencing for routine detection of adenomatous polyposis coli mutations and is the only test that is clinically available to detect mutations of the adenomatous polyposis coli gene.) Medical and family information was obtained from patients through a standard registry questionnaire and a review of medical records. The clinical diagnosis of familial adenomatous polyposis in a family was verified by the clinical and pathologic criterion of 100 or more colorectal adenomas in a phenotypically affected member [5]. Phenotypically affected members of a family were assumed to have the same mutation as the affected member who was analyzed. All data were entered into computer data-bases using dBase (Borland, Scotts Valley, California) and pedigree analysis software (Cyrillic, Cherwell Scientific Publishing, Oxford, United Kingdom). The following clinicopathologic variables were analyzed for each family member: sex; age at diagnosis of familial adenomatous polyposis; number of colorectal adenomas that were found at the first colorectal examination, recorded as fewer than 100 polyps or at least 100 polyps (polyposis); number of colorectal adenomas that were found at the first colorectal examination when the patient was 35 years of age or younger (95% of patients with familial adenomatous polyposis have more than 100 adenomas by 36 years of age [6]); predominant anatomical distribution of polyps, recorded as right-sided (proximal to splenic flexure), left-sided (distal to splenic flexure), or uniform; age at diagnosis of colorectal cancer; and anatomical location of colorectal cancer. Statistical Analysis Differences in the number of polyps found at first examination and the number of polyps found during examination when patients were younger than 36 years of age were evaluated by using the chi-square test. Differences in mean age were evaluated by using a t-test. Analysis for intrafamilial clustering of phenotype was done by using nested analysis of variance. The rate of development of colorectal cancer was compared between groups by Kaplan-Meier analysis with log-rank tests. A P value less than 0.05 was considered statistically significant. The True Epistat software package (Epistat Services, Richardson, Texas) was used for all analyses. Results Mutations in the Adenomatous Polyposis Coli Gene in 5 Families Of 112 families with familial adenomatous polyposis and known mutations of the adenomatous polyposis coli gene, 7 (6%) were found to have a mutation toward the 5 end of the adenomatous polyposis coli gene relative to codon 158. Seven others had a mutation downstream from codon 158, in codons 179 to 625. The site of mutation in proximal 5 and distal 5 families is shown in Table 1 and Figure 1. Point and frameshift mutations were noted. Table 1. Germline Mutations in the Adenomatous Polyposis Coli Gene in Families with Proximal 5 and Distal 5 Mutation of the Adenomatous Polyposis Coli Gene We evaluated the possibility of common ancestry by searching for surname, date of birth, and country of origin of the oldest members of all 14 families by using the extensive genealogy records maintained by the Church of Jesus Christ of Latter-Day Saints. No common ancestry could be established in the families described. Clinical Features of Proximal 5 and Distal 5 Families The clinical features of the families are described in Table 2. Demographic characteristics, mean age at diagnosis of familial adenomatous polyposis, age at first examination of the colon, and age at diagnosis of familial adenomatous polyposis in the proband of each family did not significantly differ between the proximal 5 and distal 5 families. Nested analysis of variance for age at diagnosis of familial adenomatous polyposis grouped by proximal 5 or distal 5 site and by family also showed no evidence of intrafamilial clustering (F = 1.25; P = 0.27). The intraclass coefficient (r = 0.049) reflects a modest contribution of intrafamilial variation to the overall variance. In contrast, the colonic phenotypes differed between proximal 5 and distal 5 families. Eight of 17 phenotypically affected patients (47%) in proximal 5 families were found to have fewer than 100 adenomas during their first colorectal examination; only 9 of 48 patients (19%) in distal 5 families had similar findings (P = 0.029). Seven of 12 patients in proximal 5 families who were 35 years of age or younger had fewer than 100 polyps compared with 7 of 39 (18%) patients in distal 5 families (P = 0.010). In family 3, two patients who had a mutation of the adenomatous polyposis coli gene at codon 140 had no adenomas found by colonoscopy done in the third decade of life (when the disease is usually evident). Nevertheless, in proximal 5 families, all but one patient who were older than 45 years of age had polyposis; in six of seven families, at least one member had the phenotype for classic familial adenomatous polyposis. Thus, the phenotype was heterogenous in the family rather than attenuated in all of its members. Table 2. Characteristics of Proximal 5 and Distal 5 Families In proximal 5 families, polyp distribution was predominantly right-sided in 4 patients (24%), uniform in 10 patients (59%), and left-sided in 3 patients (18%). In contrast, polyp distribution in distal 5 families was right-sided in 3 patients (6%), uniform in 44 patients (94%), and left-sided in no patients (P < 0.001) (Table 2). Six of 20 (30%) phenotypically affected patients in four proximal 5 families had colorectal cancer compared with 18 of 53 patients (34%) in distal 5 families (Table 3). The mean age (SD) at diagnosis of colorectal cancer in patients in proximal 5 families was 51 16 years (range, 28 to 75 years). This value was somewhat greater than the mean age in patients in distal 5 families (39 14 years [range, 23 to 71 years]), but the difference was not statistically significant. However, Kaplan-Meier analysis done with a log-rank test showed a statistically significant difference in the cumulative probability of survival without colorectal cancer between the two types of families (P = 0.041) (Figure 2). Patients in proximal 5 families had a higher rate of cancer-free survival. The occurrence of colorectal cancer was related to the number of polyps in patients in the proximal 5 families: Five of the six cases of cancer developed in patients who had the phenotype for classi

Sulindac induced regression of colorectal adenomas in familial adenomatous polyposis: evaluation of predictive factors.

BACKGROUND--Sulindac, a non-steroidal anti-inflammatory drug, causes regression of colorectal adenomas in patients with familial adenomatous polyposis (FAP) but the response is variable. Specific clinical factors predictive of sulindac induced regression have not been studied. METHODS--22 patients with FAP were given sulindac 150 mg orally twice a day. Polyp number and size were determined before treatment and at three months. The relation of nine clinical factors to polyp regression (per cent of baseline polyp number after treatment) was evaluated by univariate and multivariate analysis. RESULTS--After three months of sulindac, polyp number had decreased to 45 per cent of baseline and polyp size to 50 per cent of baseline (p < 0.001 and p < 0.01, respectively). Univariate analysis showed greater polyp regression in older patients (p = 0.004), those with previous colectomy and ileorectal anastomosis (p = 0.001), and patients without identifiable mutation of the APC gene responsible for FAP (p = 0.05). With multivariate regression analysis, response to sulindac treatment was associated with previous subtotal colectomy. CONCLUSIONS--Sulindac treatment seems effective in producing regression of colorectal adenomas of FAP patients with previous subtotal colectomy regardless of baseline polyp number and size. Changed sulindac metabolism, reduced area of the target mucosa, or changed epithelial characteristics after ileorectal anastomosis may explain these findings.

Cost analysis of alternative approaches to colorectal screening in familial adenomatous polyposis

BACKGROUND & AIMS The commercial availability of gene testing for familial adenomatous polyposis (FAP) represents an important advance in screening for inherited colon cancer. We investigated the financial impact of this diagnostic tool on colorectal screening for FAP. METHODS Decision analysis was used to compare per-person costs with third-party payers of three colorectal screening strategies used to diagnose FAP in at-risk persons. The strategies included conventional serial flexible sigmoidoscopy and two different APC gene testing approaches. RESULTS For 1 at-risk relative who begins screening at age 12 years, average screening costs are

Response to genetic counseling and testing for the APC I1307K mutation

2625 when genotyping the proband first,

Very High Risk of Cancer in Familial Peutz—Jeghers Syndrome

2674 when genotyping the at-risk relative first, and

AGA technical review on hereditary colorectal cancer and genetic testing.

3208 for conventional sigmoidoscopy. The cost advantage of genotyping increases as the pedigree size increases. For a pedigree of 5 at-risk relatives, sigmoidoscopy would have to cost less than

Attitudes toward Colon Cancer Gene Testing: Factors Predicting Test Uptake

85.60 (professional plus facility fee) for conventional screening to compete with genotyping. The cost advantage of genotyping is diminished for at-risk relatives who begin FAP screening at older ages. CONCLUSIONS The choice of least expensive FAP screening strategy depends on the cost of flexible sigmoidoscopy, patient age when screening starts, and pedigree size. Genotyping can substantially reduce the cost of FAP screening and, when possible, should start with the proband.

Hepatoblastoma and APC gene mutation in familial adenomatous polyposis.

The APC I1307K gene mutation is associated with increased colorectal cancer (CRC) risk in Ashkenazi Jews. Factors predicting acceptance of this and other hereditary colon cancer mutation tests in a clinical setting are unknown. We analyzed sex, age, family history, personal history, and gene test results of patients at increased risk for cancer who sought cancer risk counseling at the Johns Hopkins (JH) CRC Risk Assessment Clinic (n = 91), and those submitting samples to the JH Pathology Molecular Diagnostic Laboratory (n = 256) for APC I1307K testing. Of patients seen at the JH Clinic, 77/91 (84.6%) elected APC I1307K testing after pretest counseling (acceptors). There were no statistically significant differences in demographic characteristics between acceptors and decliners. In comparison, only 8 of 57 (14.0%) patients offered HNPCC testing proceeded with testing (P < 0.001). Of 256 individuals tested at the JH laboratory, most were male (61.3%) and most had a personal or family history of colorectal cancer or polyps. Test positivity correlated with increasing risk of colorectal cancer. Acceptance of testing for the APC I1307K mutation is high, with more men than women pursuing counseling and testing. The reported association between the APC I1307K mutation and colon cancer risk was supported by a correlation in these data between personal or family history of CRC or polyps and a gene mutation.