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

IMiDs induce FAM83F degradation via an interaction with CK1α to attenuate Wnt signalling

Immunomodulatory imide drugs (IMiDs) bind CRBN, a substrate receptor of the Cul4A E3 ligase complex, enabling the recruitment of neo-substrates, such as CK1α, and their degradation via the ubiquitinproteasome system. Here, we report FAM83F as such a neo-substrate. The eight FAM83 proteins (A-H) interact with and regulate the subcellular distribution of CK1α. We demonstrate that IMiD-induced FAM83F degradation requires its association with CK1α. However, no other FAM83 protein is degraded by IMiDs. We have recently identified FAM83F as a mediator of the canonical Wnt signalling pathway. The IMiD-induced degradation of FAM83F attenuated Wnt signalling in colorectal cancer cells and removed CK1α from the plasma membrane, mirroring the phenotypes observed with genetic ablation of FAM83F. Intriguingly, the expression of FAM83G, which also binds to CK1α, appears to attenuate the IMiD-induced degradation of CK1α, suggesting a protective role for FAM83G on CK1α. Our findings reveal that the efficiency and extent of target protein degradation by IMiDs depends on the nature of inherent multiprotein complex in which the target protein is part of.

In patients with a positive family history of familial adenomatous polyposis can the condition be diagnosed from the presence of congenital hypertrophy of the retinal pigment epithelium detected via an eye examination: A systematic review

In classic familial adenomatous polyposis (FAP) adenomas become malignant. Congenital hypertrophy of the retinal pigment epithelium (CHRPE) is a retinal pigmented lesion and is the earliest and most common potential extraintestinal manifestation of FAP. This review aims to summarize and analyse all of the published data on CHRPE in patients with classic FAP and then ascertain whether these patients should undergo a relatively cheap and non-invasive dilated fundus examination to screen for CHRPE. Adhering to Preferred Reporting Items for Systematic Reviews and Meta Analyses guidelines our database search identified 102 relevant articles of which 13 were selected for further analysis. The percentage of FAP patients with CHRPE was found to be 80.00%, whereas the percentage of at-risk patients with CHRPE was 31.12%. Despite various statistically significant findings, CHRPE alone cannot be used as a surrogate for diagnosing FAP in those with a positive family history. The authors advocate a combined approach of eye examinations, colonoscopy and genetic testing.

Review article: genetic testing and counselling for hereditary colorectal cancer

Colorectal cancer is the second leading cause of cancer death, after lung cancer, in the USA. The great majority (80%) of patients with colorectal cancer have sporadic disease with no evidence of having inherited the disorder. In the remaining 20%, a potentially definable genetic component exists. With the discovery of gene mutations related to hereditary colorectal cancer, risk assessment based on genetic test results is now feasible. The following review focuses on the two well-described colorectal cancer genetic syndromes-familial adenomatous polyposis and hereditary nonpolyposis colorectal cancer, the process of genetic counselling, currently available genetic tests, and indications for their use.

Cost comparison of predictive genetic testing versus conventional clinical screening for familial adenomatous polyposis

BACKGROUND

Mutations of the APC gene cause familial adenomatous polyposis (FAP), a hereditary colorectal cancer predisposition syndrome.

AIMS

To conduct a cost comparison analysis of predictive genetic testing versus conventional clinical screening for individuals at risk of inheriting FAP, using the perspective of a third party payer.

METHODS

All direct health care costs for both screening strategies were measured according to time and motion, and the expected costs evaluated using a decision analysis model.

RESULTS

The baseline analysis predicted that screening a prototype FAP family would cost $4975/ pound3109 by molecular testing and $8031/ pound5019 by clinical screening strategy, when family members were monitored with the same frequency of clinical surveillance (every two to three years). Sensitivity analyses revealed that the genetic testing approach is cost saving for key variables including the kindred size, the age of screening onset, and the cost of mutation identification in a proband. However, if the APC mutation carriers were monitored at an increased (annual) frequency, the cost of the genetic screening strategy increased to $7483/ pound4677 and was especially sensitive to variability in age of onset of screening, family size, and cost of genetic testing of at risk relatives.

CONCLUSIONS

In FAP kindreds, a predictive genetic testing strategy costs less than conventional clinical screening, provided that the frequency of surveillance is identical using either strategy. An additional significant benefit is the elimination of unnecessary colonic examinations for those family members found to be non-carriers.

Molecular analysis of the APC gene in 205 families: extended genotype-phenotype correlations in FAP and evidence for the role of APC amino acid changes in colorectal cancer predisposition

BACKGROUND/AIMS

The development of colorectal cancer and a variable range of extracolonic manifestations in familial adenomatous polyposis (FAP) is the result of the dominant inheritance of adenomatous polyposis coli (APC) gene mutations. In this study, direct mutation analysis of the APC gene was performed to determine genotype-phenotype correlations for nine extracolonic manifestations and to investigate the incidence of APC mutations in non-FAP colorectal cancer.

METHODS

The APC gene was analysed in 190 unrelated FAP and 15 non-FAP colorectal cancer patients using denaturing gradient gel electrophoresis, the protein truncation test, and direct sequencing.

RESULTS

Chain terminating signals were only identified in patients belonging to the FAP group (105 patients). Amino acid changes were identified in four patients, three of whom belonged to the non-FAP group of colorectal cancer patients. Genotype-phenotype correlations identified significant differences in the nature of certain extracolonic manifestations in FAP patients belonging to three mutation subgroups.

CONCLUSIONS

Extended genotype-phenotype correlations made in this study may have the potential to determine the most appropriate surveillance and prophylactic treatment regimens for those patients with mutations associated with life threatening conditions. This study also provided evidence for the pathological nature of amino acid changes in APC associated with both FAP and non-FAP colorectal cancer patients.

An overview of clinical molecular genetics

Clinical molecular genetics has recently become recognized as a diagnostic discipline. This article covers the evolution, structure, and possible forward development of clinical molecular genetics. Topics covered include general test categories, introducing new tests, laboratory facilities, staffing and training, and overview of quality issues.

Uptake of genetic testing for cancer predisposition

Although there has been much debate about the uptake and effects of predictive testing for common cancers, such as breast and colon cancer, little has been published on the more classical tumour predisposing conditions, such as von Hippel-Lindau disease and familial adenomatous polyposis. Since 1990 the genetics departments in Manchester and Cambridge have had a genetic register for cancer predisposing syndromes and presymptomatic testing for these conditions has been offered once this has become possible. To investigate the factors that might influence uptake of genetic testing in familial cancer syndromes we have reviewed our experience. Demand for predictive testing has generally been high, but men had a lower uptake (77%) than a comparable group of women (93%) (p < 0.01).

Molecular screening of families affected by familial adenomatous polyposis (FAP)

OBJECTIVES

To assess the risk of developing familial adenomatous polyposis (FAP) in presymptomatic individuals using APC gene flanking and intragenic polymorphic markers.

SETTING

Twenty families enrolled in the Italian Registry of Polyposis comprising a total of 217 individuals, including 53 (24%) presymptomatic subjects with a 50% a priori risk of FAP, were analysed. Direct analysis techniques had previously failed to identify the FAP mutation in these families.

METHODS

DNA isolated from peripheral mononuclear blood cells and tissue sections was analysed by the polymerase chain reaction and a panel of seven highly polymorphic markers--YN5.64, CB83, CB26, LNS, APC1458.5, MBC, 37AB. Amplification products were separated by a modified denaturing gel electrophoresis method.

RESULTS

The haplotype associated with the disease was identified in 18 families (90%). The segregation of the FAP haplotype in these kindreds showed that 10 presymptomatic individuals had inherited the FAP mutation and carried a high risk of developing the disease. The remaining two families were not informative because of the lack of a sufficient number of probands or biological specimens.

CONCLUSIONS

These data indicate that indirect analysis with linked DNA markers has a high rate of success in defining the risk of FAP of presymptomatic subjects, provided that a sufficient number of probands or samples is available. Uninformative families accounted for 10% of the total, indicating that linkage analysis may still have higher sensitivity than direct mutation analysis techniques. The combined use of both approaches should be implemented, however, to enhance further the application of molecular genetics to the screening of families with FAP.

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.

Presymptomatic diagnosis in families with adenomatous polyposis using highly polymorphic dinucleotide CA repeat markers flanking the APC gene

A panel of five multiallelic and highly informative dinucleotide CA repeat markers flanking the APC gene was used for presymptomatic diagnosis of familial adenomatous polyposis coli (FAP). Marker regions were amplified by PCR. DNA fragments were separated by electrophoresis in denaturing polyacrylamide gels and visualised by ethidium bromide staining. Two or more markers were found to be informative in all nine families tested, and all 23 persons at risk could be diagnosed as affected or unaffected by the disease gene, the probability being > 99.9% in 14 cases from six families in which flanking markers were informative. We found no indication for locus heterogeneity of the disease in our sample. The polyposis phenotype and its extracolonic manifestations co-segregated with a distinct haplotype determined by the markers flanking the APC gene. In one family with no remaining living affected members, we could infer the high risk haplotype from genotyping of first degree relatives. The segregation of this haplotype is consistent with the occurrence of CHRPEs in the progeny. In a sporadic case we made use of the typical early extracolonic manifestations of the disease (osteomas, desmoids) to identify the high risk haplotype. We conclude from our experience that indirect genotyping of FAP with this particular panel of closely linked and highly polymorphic microsatellite markers is a rapid, efficient, and highly reliable method for presymptomatic diagnosis of FAP.

Unconjugated faecal bile acids in familial adenomatous polyposis analysed by gas-liquid chromatography and mass spectrometry

Previous studies have suggested reduced formation of secondary bile acids in patients with familial adenomatous polyposis (FAP). Developments in the collection, extraction and analysis of faecal bile acids as well as in the accurate diagnosis of FAP by DNA markers prompted reinvestigation of this hypothesis. The median (interquartile range (i.q.r.)) faecal bile acid concentration (3.69 (1.66-5.36) mumol per g dry weight) and daily excretion rate (60.5 (29-149) mumol per g per 24 h) in ten patients with FAP were similar to those of nine control subjects (3.31 (0.65-8.38) mumol per g dry weight and 30.1 (7.9-228) mumol per g per 24 h). Although the median (i.q.r.) concentration of only one bile acid (12-oxo-lithocholic acid) was significantly different between patients with FAP and controls (49 (34-70) versus 0 (0-20) nmol per g dry weight, P = 0.006), the derivatives of chenodeoxycholic acid (3.35 (1.76-5.32) versus 0.51 (0.13-2.37) mumol per g dry weight, P = 0.02) and cholic acid (1.63 (0.42-2.34) versus 0.80 (0.13-3.57) mumol per g dry weight, P = 0.006) were increased in those with polyposis. These results show increased bacterial biotransformation of faecal bile acids in patients with FAP.

Loss of heterozygosity of the retinoblastoma and adenomatous polyposis susceptibility gene loci and in chromosomes 10p, 10q and 16q in human prostate cancer

OBJECTIVE

To examine prostate tumours for losses of known or suspected tumour suppressor genes to determine some of the important events in the genesis of this common cancer.

MATERIALS AND METHODS

Paired tumour and blood samples were obtained from 21 patients who underwent transurethral resection of malignant prostate glands for urinary outflow obstruction. Paired tumour and normal tissue (leucocytes) DNA was extracted and examined for possible losses of several known or suspected tumour suppressor genes, using restriction fragment length polymorphism techniques to detect loss of heterozygosity.

RESULTS

Deletions of the retinoblastoma susceptibility gene (RB1) locus were found in six of nine informative cases using two intragenic probes (p68RS2.0 and p123m1.8). The locus related to the familial adenomatous polyposis susceptibility (APC) gene demonstrated loss of heterozygosity in three of seven informative cases using the EF5.44 probe. Losses were also noted in loci on chromosome 10p in four of 19 informative cases (probe cTBQ7), chromosome 10q in eight out of 19 informative cases (probes EFD75 and D10S90) and in 16q in three of 17 informative cases (probe D16S7).

CONCLUSION

These findings suggest that losses of the RB1 and APC tumour suppressor genes and suspected tumour suppressor genes on 10p, 10q and 16q may be important events in the genesis of prostatic tumours.

Biliary bile acid profiles in patients with familial adenomatous polyposis before and after colectomy

The development of colorectal polyps and cancer in patients with familial adenomatous polyposis (FAP) is directly linked to inactivation of the APC gene. Other, epigenetic, mechanisms may be involved in tumorigenesis and a previous study suggested that an intrinsic difference in the biliary bile acid profile of untreated patients with FAP persisted after colectomy. Gas chromatography and gas chromatography-mass spectrometry were used to examine the biliary bile acid profiles of four groups of patients with normal gallbladders: 20 patients with an intact colon comprising 12 with FAP and eight controls; and 26 patients after colectomy comprising 12 with FAP and 14 controls. Comparison of ten different bile acids from both amidate fractions (glycine and taurine) revealed a small increase in the molar percentage of a minor bile acid (12-oxolithocholic acid) in patients with FAP and an intact colon compared with the matching control group. Colectomy was associated with a dramatic reduction in levels of secondary bile acids but with little difference between patients with FAP and controls.

Combined use of molecular and biomarkers for presymptomatic carrier risk assessment in familial adenomatous polyposis: implications for screening guidelines

Predictive carrier testing for the inherited disorder of familial adenomatous polyposis (FAP) can be conducted using DNA markers linked to the FAP locus. The presence of characteristic hypertrophic retinal lesions has been advocated as useful biomarkers for FAP. We have compared molecular linkage and retinal screening techniques by evaluating the presymptomatic carrier risk of 40 at-risk individuals from 15 FAP families. Linkage analysis was informative in all and retinal lesion analysis in 25 cases. For informative at-risk population, predictive diagnosis by both techniques was completely concordant and identified 15 members at "high" and 10 at "low" risk of inheriting FAP. Because of the unique advantages offered by each technique, a strategy integrating both techniques will increase the number of FAP families that can be screened presymptomatically. Identification of individuals at high risk of polyposis will improve their clinical surveillance and further reduce the incidence of colorectal cancer in FAP families.

Exon eight APC mutations account for a disproportionate number of familial adenomatous polyposis families

The familial adenomatous polyposis gene, APC, has recently been identified. Detection of APC mutations will facilitate genetic screening in family members at risk for this disease. The length of APC makes it impractical to examine the entire coding sequence in each new family encountered. Identification of mutation cluster regions within the gene has therefore become a priority. Initial reports suggested that exon eight might contain a disproportionate number of mutations. This study describes direct sequencing of exon eight in 21 unrelated Australians with familial adenomatous polyposis. Mutations were detected in three of the 21 subjects (14%). Two were previously described point mutations changing an arginine to a stop codon. The third was a novel two base-pair deletion producing a frameshift and downstream stop codon. All three mutations segregated with the disease gene in their respective families. Three at risk children from two of these families were studied and shown not to have inherited the disease producing mutation. These results confirm that exon eight is a frequent site of mutation in familial adenomatous polyposis and should be examined routinely in families requesting genetic screening.

The role of congenital hypertrophy of the retinal pigment epithelium in screening for familial adenomatous polyposis

Retinal examination by indirect ophthalmoscopy was performed on seventy members from 20 kindreds demonstrating the clinical manifestations of familial adenomatous polyposis and forty controls. Thirty-four of 43 affected patients manifested CHRPE lesions compared with 2 of 27 at risk and 2 of 40 controls giving a sensitivity of 79% and specificity of 95% based on the control group. The difference between the affected and at risk groups was significant (Chi-squared = 34.098, 1 df, P = 0.001). The low sensitivity and variation in incidence of CHRPE in FAP patients and general population documented in the world literature prevent its use as a sole marker for the condition. With advances in knowledge of the disease at a molecular level it is now possible to alter risks for families by DNA analysis. There remain a number of patients in whom such techniques do not significantly alter risks. In these families by combining the results of DNA analysis, sigmoidoscopy and retinal examination it may be possible to alter risks by a significant degree. Retinal examination should be reserved for those families in whom risks cannot be altered sufficiently by DNA analysis alone.

Analysis of faecal neutral sterols in patients with familial adenomatous polyposis by gas chromatography-mass spectrometry

Previous studies have suggested that patients with familial adenomatous polyposis (FAP) have increased faecal excretion of cholesterol but a reduction in cholesterol metabolites. It was consequently proposed that the degree of faecal cholesterol degradation could be used as a means of diagnosis. Developments in the extraction and analysis of faecal neutral sterols as well as the accurate means of diagnosing FAP by DNA analysis and indirect ophthalmoscopy has necessitated a re-examination of this proposal. Faecal neutral sterols were analysed in 10 patients with untreated FAP following a complete 5-day stool collection and compared with 9 healthy control subjects (including 4 siblings) closely matched for age and sex. The median [25 and 75, percentiles] stool wet weights were similar between the FAP (97.5 [69, 192] g.24 h-1) and the control (116 [61.5, 137] g.24 h-1) groups. Faecal cholesterol concentration was similar in the two groups (FAP = 2.3 [1.4, 4.2]; control = 3.5 [1.0, 6.0] mumol.g-1 dry wt) as was the concentration of total neutral sterols not including plant sterols (FAP = 17.2 [13.4, 21.0]; control = 18.2 [7.4, 21.6] mumol.g-1 dry wt). There were no significant differences in the proportions of cholesterol metabolised between the FAP (82.3 [74.2, 93.5]%) and control (72.1 [5.7, 81.3]%) groups. This study does not support the notion that faecal neutral sterol metabolism is uniquely different in patients with FAP.

Non-penetrance and late appearance of polyps in families with familial adenomatous polyposis

One case of non-penetrance of the familial adenomatous polyposis (FAP) gene at 59 years of age and late onset of polyps on endoscopy and biopsy in this and two other families is described. Screening protocols should include dental screening as well as indirect ophthalmoscopy and endoscopy to detect minimal manifestations of the gene. In the absence of a specific DNA predictive test, bowel screening should continue well beyond 30 years of age.

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.

Familial transitional cell carcinoma and the Lynch syndrome II

A family is presented in which 4 male siblings developed transitional cell carcinoma (TCC). Four upper tract tumours occurred in 3 and in the fourth the tumour was intravesical. Two of these patients also had colorectal adenocarcinoma. There were 2 other relatives in the pedigree with large bowel cancer. It is suggested that this is an example of Lynch Syndrome II, a hereditary non-polyposis colorectal cancer with extracolonic cancer sites. The implications regarding the screening, surveillance and detection of possible carrier status in healthy relatives is discussed.

Evaluation of molecular genetic diagnosis in the management of familial adenomatous polyposis coli: a population based study

A population based clinical and molecular genetic study of familial adenomatous polyposis coli (FAPC) was performed to investigate the value of molecular genetic analysis and ophthalmological assessment in the presymptomatic diagnosis of FAPC. The point prevalence of affected patients was 2.62 x 10(-5) (1/38,000) and the minimum heterozygote prevalence was estimated at 3.8 x 10(-5) (1/26,000). Eight of 33 (24%) probands were new mutations. Forty-eight asymptomatic relatives at 50% prior risk aged between 10 and 40 years were assessed for risk modification with linked DNA markers: in nine subjects (18%) the family structure was unsuitable for linkage based analysis, but 32 subjects were informative with a panel of intragenic and closely linked markers (25 had a combined age/DNA related risk of < 1% (low risk group) and seven were at high risk (DNA predicted risk > 99%)). Ophthalmological assessment for CHRPEs showed that 27/43 (63%) affected patients and high risk relatives and 0/18 low risk relatives had more than three CHRPEs. Interfamilial variation in CHRPE expression was apparent. This study has shown that DNA based risk modification with intragenic and closely linked DNA markers is informative in most FAPC families. In addition to the clinical benefits of presymptomatic diagnosis for FAPC, the reduction in screening for low risk relatives (365 person years in the present study) means that molecular genetic diagnosis of FAPC is a cost effective procedure.

Assessment of the value of congenital hypertrophy of the retinal pigment epithelium as an ocular marker for familial adenomatous polyposis coli

The presence of bilateral, multiple patches of congenital hypertrophy of the retinal pigment epithelium (CHRPE) is cited as an early phenotypic marker of the familial adenomatous polyposis coli (FAPC) gene. However, the degree of concordance between CHRPE and the presence of familial adenomatous polyposis (FAP) has not been adequately assessed in individual families. We studied the eyes of 28 members of a single kindred spanning three generations with FAPC; 14 were affected and 14 unaffected but 'at risk'. Six affected and 8 unaffected at risk individuals possessed a total of 34 retinal lesions, 17 in each group. Two affected individuals and 1 at risk individual had the classical pattern of CHRPE associated with FAPC. The sensitivity of CHRPE as an ocular marker for FAPC in this kindred was 14.2%. Our findings have implications for the use of CHRPE for the presymptomatic screening of family members at risk of FAPC. Therefore, ocular examination should not replace colonoscopic screening in an individual at risk of FAPC.

Carcinoma of the thyroid gland and Gardner's syndrome

A patient known to be suffering from Gardner's syndrome who developed carcinoma of the thyroid gland is presented. A review of the literature reveals that this relationship is not fortuitous and that it has the following characteristics: female predominance (89%), youth (< 30 years in 78%), papillary form (88%), multicentricity (70%) and thyroid carcinoma preceding diagnosis of hereditary polyposis in 30%. Hereditary polyposis patients affected by familial polyposis coli are at significant risk of developing extracolonic malignant tumours, and require life-long surveillance. Palpation of the thyroid gland and possibly ultrasound examination of the neck should be part of the routine follow up of these patients.

An audit of restorative proctocolectomy

A total of 168 restorative proctocolectomies have been performed without mortality during the past nine years. Morbidity from pelvic sepsis (12%), ileoanal stricture (15%), and pouch related fistulas (16%) have become less with increasing experience of the operation. Pouch excision, which occurred in 30% of the first 50 patients was undertaken in only 4% in the last 68 patients. Despite this, intestinal obstruction (18%) continues to complicate the operation. We have abandoned restorative proctocolectomy after failed ileorectal anastomosis in patients with slow transit constipation as half have now requested pouch excision because of poor results. Failure to identify Crohn's disease continues to influence the outcome: in 10 patients now known to have Crohn's disease six developed post operative fistulas, three have required pouch excision. Sexual impairment has occurred in three male patients (4%). Ten women had children after operation, eight uncomplicated vaginal deliveries occurred without impaired continence. Seven of nine patients over 60 years of age have had a successful outcome. Our data also indicate that the operation may be justified in distal disease if urgency is socially inconvenient. Frequency of defecation is usually less than three per 24 hours in patients with familial adenomatous polyposis but remains variable in those with ulcerative colitis.

Presymptomatic direct detection of adenomatous polyposis coli (APC) gene mutations in familial adenomatous polyposis

The recent identification of the familial adenomatous polyposis (FAP) gene (designated as APC) enables conclusive genetic testing of at-risk family members for the specific mutation in families in which the germline gene mutation has been characterized. Presymptomatic molecular diagnosis of FAP was performed by direct direction of mutations in lymphocyte DNA in four families. Each of the families has a different mutation of the APC gene. Twenty-seven offspring of affected individuals (a priori risk of 50%) were tested. Ten of the 27 had already developed clinical features of FAP. Of the remaining seventeen, two had had a negative colon exams at an early age, and nine had never had colon exams (mean age, 12.1 +/- 3.1 SD years). Six children from this group (54%) were found to carry their affected parent's mutation. No change in the conventional FAP colon screening regimen is recommended for these children. In contrast, when direct tests indicate that an individual does not have the FAP mutation, we recommend that screening be decreased. Reduction of uncertainty for at-risk FAP family members is an important benefit of genetic testing.