Peutz-Jeghers syndrome: intriguing suggestion of gastrointestinal cancer prevention from surveillance.

BACKGROUND: Peutz-Jeghers syndrome is characterized by GI polyps and mucocutaneous pigmentation and carries an increased risk of GI cancer. GI polyps may bleed or cause intussusception. Luminal GI surveillance is recommended, but there are few data detailing outcomes from GI surveillance in Peutz-Jeghers syndrome. OBJECTIVE: This study aimed to assess outcomes from GI surveillance in patients with Peutz-Jeghers syndrome. DESIGN: This study is a retrospective review, using hospital and registry notes and endoscopy and histology reports. SETTING: The investigation was conducted at a tertiary referral center. PATIENTS: All patients with Peutz-Jeghers syndrome who were followed up at St Mark's hospital were included. MAIN OUTCOME MEASURES: The primary outcomes measured were surveillance procedures performed, complications, and long-term outcomes. RESULTS: Sixty-three patients from 48 pedigrees were included; the median age when patients were first seen was 20 years (range, 3-59). Only baseline investigations were performed in 12 patients. The remaining patients were followed up for 683 patient years, a median of 10 years (range, 2-41). Seven hundred seventy-six procedures were performed to assess the GI tract. These led to 5 double-balloon enteroscopies, 1 push enteroscopy, and 71 surgical procedures. Of the surgical procedures, 20 were performed as a result of baseline investigations, 12 arose from investigations of symptoms, and 39 were due to surveillance of asymptomatic patients. No emergency surgical interventions were performed. No luminal GI cancers were diagnosed. Of the 2461 polypectomies performed, 6 polyps contained atypia or dysplasia. Six complications arose from endoscopy or surgical intervention, requiring 5 laparotomies to manage these complications. CONCLUSION: GI surveillance in Peutz-Jeghers syndrome is relatively safe and avoids the need for emergency surgery for small-bowel polyps. The lack of GI cancers may reflect that surveillance and polypectomy have prevented cancer from developing, although the detection of neoplasia or dysplasia is uncommon.

Risk factors predicting intra-abdominal desmoids in familial adenomatous polyposis: a single centre experience.

BACKGROUND: Desmoids are myofibroblastic proliferations occurring in 15% of patients with familial adenomatous polyposis (FAP), 70% being intra-abdominal desmoids (IAD). Since the morbidity and mortality due to desmoids is almost entirely attributable to IAD, we aimed to identify specifically risk factors predicting IAD development in FAP. METHODS: We undertook a retrospective review of our institutional database. Multivariate analysis was performed, and hazard ratios (HR) calculated for variables including female gender, 3' APC mutation, surgical intervention for FAP (colectomy with ileo-rectal anastomosis or restorative proctocolectomy), age at surgery and family history (FH) of desmoids. RESULTS: Of the 558 patients analysed, 49 (9%) developed IAD; 22 (4%) diagnosed intra-operatively and 27 (5%) developing over a median post-operative period of 34 (7-120) months. 75% of IAD had developed before age 40. A 3' APC mutation (HR 5.2, 95% CI 2.1-13.3, P = 0.001), positive FH (HR 2.5, 95% CI 1.4-4.6, P = 0.003) and female gender (HR 1.9, 95% CI 1.0-3.5, P = 0.04) were found to be predictive of IAD development. No significant difference in IAD risk was detected between the type of surgical intervention (P = 0.37) or age at surgery (P = 0.29). CONCLUSIONS: Our analysis confirms 3' APC mutation to be the most significant risk factor for IAD development. The independent association between positive FH and IAD risk suggests the existence of modifier genes, independent of the APC genotype-phenotype correlation. Few of these risk factors can be meaningfully modified. Delaying prophylactic surgery may be appropriate in female patients with a 3' APC mutation and attenuated polyposis.

Comparison of outcomes of ileal pouch-anal anastomosis for familial adenomatous polyposis with and without previous ileorectal anastomosis.

BACKGROUND: It is reported that previous colectomy and ileorectal anastomosis (IRA) has no effect on postoperative complications and functional outcomes of secondary proctectomy and ileal pouch-anal anastomosis (IPAA) in patients with familial adenomatous polyposis (FAP). This retrospective study re-examined the question in a single centre. METHODS: Some 185 patients were grouped by either IPAA as the initial prophylactic surgical procedure (primary IPAA) or IPAA preceded by IRA (secondary IPAA). Data on functional outcomes were available for 104, 83 and 56 patients at years 1, 5 and 10 respectively. RESULTS: The 78 patients who had secondary IPAA were older at the time of operation than the 107 who underwent primary IPAA (35.7 versus 29.2 years; P < 0.001). Six (8 per cent) of the secondary IPAA procedures could not be completed. Otherwise, apart from more wound infections in the secondary IPAA group (9 versus 0.9 per cent in the primary IPAA group; P = 0.012), there were no significant differences in rates of complications, functional outcomes, desmoid disease or pouch failure. CONCLUSION: Conversion from IRA to IPAA may not be possible in patients with FAP. Where conversion is successful, pouch outcomes are similar but wound infections are more frequent.

A 10-year review of surgery for desmoid disease associated with familial adenomatous polyposis.

BACKGROUND: Desmoid tumours affect 10-25 per cent of patients with familial adenomatous polyposis and represent a major cause of morbidity and mortality. Surgery for intra-abdominal desmoids has traditionally been used as a last resort or to manage obstructive complications. The aim was to review 10 years of desmoid surgery in patients with familial adenomatous polyposis from a single centre. METHODS: Patients who had surgery for desmoid disease between 1994 and 2004 were identified from the Polyposis Registry database and their hospital notes reviewed. RESULTS: Twenty patients had surgery to remove 32 desmoid tumours (16 intra-abdominal, 12 abdominal wall, four extra-abdominal). Complete clearance was achieved in 19 tumours and, of these, clinically significant recurrence occurred in eight. There was no difference in recurrence rates for site or sex. There was no operative mortality. Intra-abdominal desmoid resection was associated with a mean resection of 45.55 (range 10-200) cm of small bowel. One patient required long-term parenteral feeding. Median follow-up was 5 (range 0.6-10) years. During this period, one patient died (metastatic duodenal cancer); there was no mortality from desmoid disease. CONCLUSION: Surgery for intra-abdominal desmoids in selected patients is less hazardous than previously reported. Surgery for abdominal wall and extra-abdominal tumours is safe. However, disease recurrence remains a major problem.

Disease severity and genetic pathways in attenuated familial adenomatous polyposis vary greatly but depend on the site of the germline mutation.

BACKGROUND: Attenuated familial adenomatous polyposis (AFAP) is associated with germline mutations in the 5', 3', and exon 9 of the adenomatous polyposis coli (APC) gene. These mutations probably encode a limited amount of functional APC protein. METHODS AND RESULTS: We found that colonic polyp number varied greatly among AFAP patients but members of the same family tended to have more similar disease severity. 5' Mutants generally had more polyps than other patients. We analysed somatic APC mutations/loss of heterozygosity (LOH) in 235 tumours from 35 patients (16 families) with a variety of AFAP associated germline mutations. In common with two previous studies of individual kindreds, we found biallelic changes ("third hits") in some polyps. We found that the "third hit" probably initiated tumorigenesis. Somatic mutation spectra were similar in 5' and 3' mutant patients, often resembling classical FAP. In exon 9 mutants, in contrast, "third hits" were more common. Most "third hits" left three 20 amino acid repeats (20AARs) on the germline mutant APC allele, with LOH (or proximal somatic mutation) of the wild-type allele; but some polyps had loss of the germline mutant with mutation leaving one 20AAR on the wild-type allele. CONCLUSIONS: We propose that mutations, such as nt4661insA, that leave three 20AARs are preferentially selected in cis with some AFAP mutations because the residual protein function is near optimal for tumorigenesis. Not all AFAP polyps appear to need "three hits" however. AFAP is phenotypically and genetically heterogeneous. In addition to effects of different germline mutations, modifier genes may be acting on the AFAP phenotype, perhaps influencing the quantity of functional protein produced by the germline mutant allele.

Evidence for genetic predisposition to desmoid tumours in familial adenomatous polyposis independent of the germline APC mutation.

BACKGROUND: Many patients with familial adenomatous polyposis (FAP) die from desmoid tumours which can arise spontaneously but often appear to be surgically induced by prophylactic colectomy. FAP results from germline adenomatous polyposis coli (APC) gene mutations and desmoids arise following biallelic APC mutation, with one change usually occurring distal to the second beta-catenin binding/degradation repeat of the gene (3' to codon 1399). We have suggested that because families with germline mutations in this region already have the requisite change, they are more likely to develop desmoids. However, there are families with 5' germline mutations where desmoids are common. PATIENTS AND METHODS: We examined desmoid risk dependent on germline APC mutation, sex, history of abdominal surgery, and family history in FAP patients from the St Mark's Hospital Polyposis Registry. RESULTS: Overall desmoid prevalence was 15%. Desmoids tended to cluster in susceptible individuals, irrespective of the germline APC mutation. Independent predictors of increased desmoid risk were: germline mutation distal to codon 1399; any family history of disease; and a strong family history of desmoids. A family history of multiple desmoids (>1) increased an individual's own risk of multiplicity. Females had twice the odds of developing desmoids compared with males. There was no significant interaction between any of the three explanatory variables. CONCLUSIONS: Our results indicate the influence of unknown genetic factors independent of APC in susceptibility to desmoid tumours in FAP. The data have implications in terms of clinical management of FAP patients and assessing the balance between chemoprevention and prophylactic colectomy.

Analysis of candidate modifier loci for the severity of colonic familial adenomatous polyposis, with evidence for the importance of the N-acetyl transferases.

BACKGROUND: We have recently shown that the severity of human colonic familial adenomatous polyposis (FAP) varies in a manner consistent with the action of modifier genes. These modifier genes may harbour common alleles which increase the risk of colorectal cancer (CRC) in the general population. Analyses have suggested several common polymorphisms as risk alleles for CRC. METHODS: We determined the association between the severity of colonic FAP (151 patients) and polymorphisms in MTHFR, NAT1, NAT2, GSTM, GSTT, cyclin D1, E-cadherin, and APC. All of these loci have been suggested as influencing the risk of CRC. Colonic FAP severity was quantitated as the number of polyps per colectomy specimen, standardised for colon size. We analysed the relationship between disease severity and genotype at the polymorphic site, making allowance for the position of the germline APC mutation. RESULTS: We identified significant associations between more severe disease and the absence of the NAT1*10 genotype in the whole group of patients. In a subset of patients with germline mutations in the so-called "mutation cluster region", there was an association between more severe disease and the presence of NAT2*fast alleles. In the whole patient set, a relatively strong association existed between more severe disease and possession of both the NAT1*non-10 and NAT2*fast genotypes. There was weak evidence for an association between the APCT1493C allele and more severe disease in the whole patient group. No consistent association with disease severity was found for the other polymorphisms. CONCLUSION: The severity of colonic FAP may be modified by alleles at the NAT1 and/or NAT2 loci. The identity of any functional variation remains unknown as NAT1*10 appears to be non-functional and there is linkage disequilibrium between alleles at multiple sites within these loci which are adjacent on chromosome 8p22. While evidence from this study cannot be conclusive, our data suggest that NAT1 and NAT2 variants may explain an approximately twofold increase in polyp number in the FAP colon.

Further observations on LKB1/STK11 status and cancer risk in Peutz-Jeghers syndrome.

Germline mutations in the LKB1/STK11 tumour suppressor gene cause Peutz-Jeghers syndrome (PJS), a rare dominant disorder. In addition to typical hamartomatous gastrointestinal polyps and pigmented perioral lesions, PJS is associated with an increased risk of tumours at multiple sites. Follow-up information on carriers is limited and genetic heterogeneity makes counselling and management in PJS difficult. Here we report the analysis of the LKB1/STK11 locus in a series of 33 PJS families, and estimation of cancer risks in carriers and noncarriers. Germline mutations of LKB1/STK11 were identified in 52% of cases. This observation reinforces the hypothesis of a second PJS locus. In carriers of LKB1/STK11 mutations, the risk of cancer was markedly elevated. The risk of developing any cancer in carriers by age 65 years was 47% (95% CI: 27-73%) with elevated risks of both gastrointestinal and breast cancer. PJS with germline mutations in LKB1/STK11 are at a very high relative and absolute risk of multiple gastrointestinal and nongastrointestinal cancers. To obtain precise estimates of risk associated with PJS requires further studies of genotype-phenotype especially with respect to LKB1/STK11 negative cases, as this group is likely to be heterogeneous.

Analysis of chromosomal instability in human colorectal adenomas with two mutational hits at APC.

In vitro data show that the adenomatous polyposis coli (APC) protein associates with the mitotic spindle and that mouse embryonic stem cells with biallelic Apc mutations are karyotypically unstable. These findings led to suggestions that APC acts in chromosomal segregation and that APC inactivation leads to chromosomal instability (CIN). An alternative hypothesis based on allelic loss studies in colorectal adenomas proposes that CIN precedes and contributes to genetic changes at APC. We determined whether colorectal adenomas with two mutations at APC show features consistent with these models by studying 55 lesions (average size 5 mm; range 1-13 mm) from patients with familial adenomatous polyposis. A variety of methods was used depending on available material, including flow cytometry, comparative genomic hybridization, and loss of heterozygosity (LOH) analysis. Selected adenomas were assessed for proliferative activity by Ki-67 immunocytochemistry. Seventeen of 20 (85%) tumors were diploid, two were near-diploid, and one was hypotetraploid. Just one (near-diploid) tumor showed increased proliferative activity. LOH was found occasionally on chromosome 15q (2 of 49 tumors), but not on chromosome 18q (0 of 48). In 20 adenomas, LOH at APC was associated with loss at 5q but not 5p markers, with the former encompassing a minimum of 20 Mb. However, three of these lesions analyzed by comparative genomic hybridization displayed normal profiles, suggesting, together with other data, that the mechanism of LOH at APC is probably somatic recombination. Our results therefore do not support the hypothesis that CIN precedes APC mutations in tumorigenesis. Regarding the model in which APC mutations lead directly to CIN, if APC mutations do have this effect in vivo, it must be subtle. Alternatively, CIN associated with APC mutations might be essentially an in vitro phenomenon.

Explaining variation in familial adenomatous polyposis: relationship between genotype and phenotype and evidence for modifier genes.

BACKGROUND: Familial adenomatous polyposis (FAP) is characterised by variable phenotypic expression. Part of this is attributable to a relationship between APC genotype and phenotype but there remains significant intrafamilial variation. In the Min mouse model of FAP, differences in the severity of gastrointestinal polyposis result from the action of modifier genes. AIMS: To determine whether phenotypic variation in human FAP has an inherited component consistent with the action of modifier genes. METHOD: We systematically examined polyp numbers in colectomy specimens from patients with classical FAP. Variation both between and within families was analysed. Formal modelling of the segregation of disease severity in families was performed RESULTS: There was strong evidence for a relationship between site of mutation and the number of colorectal polyps, with germline mutations in the "cluster region" causing the most severe disease and those with mutations between codons 1020 and 1169 having the mildest disease. In addition to this genotype-phenotype relationship, we found evidence for non-APC linked genetic modifiers of disease expression. First degree relatives had more similar polyp counts than more distant relatives. Formal modelling of the segregation of disease severity in families revealed further evidence for the action of modifier genes, with a best fit to a mixed model of inheritance. CONCLUSION: Our data provide good evidence to support the hypothesis that modifier genes influence the severity of FAP in humans.

Whole-gene APC deletions cause classical familial adenomatous polyposis, but not attenuated polyposis or "multiple" colorectal adenomas.

Familial adenomatous polyposis (FAP) is a dominantly inherited colorectal tumor predisposition that results from germ-line mutations in the APC gene (chromosome 5q21). FAP shows substantial phenotypic variability: classical polyposis patients develop more than 100 colorectal adenomas, whereas those with attenuated polyposis (AAPC) have fewer than 100 adenomas. A further group of individuals, so-called "multiple" adenoma patients, have a phenotype like AAPC, with 3-99 polyps throughout the colorectum, but mostly have no demonstrable germ-line APC mutation. Routine mutation detection techniques fail to detect a pathogenic APC germ-line mutation in approximately 30% of patients with classical polyposis and 90% of those with AAPC/multiple adenomas. We have developed a real-time quantitative multiplex PCR assay to detect APC exon 14 deletions. When this technique was applied to a set of 60 classical polyposis and 143 AAPC/multiple adenoma patients with no apparent APC germ-line mutation, deletions were found exclusively in individuals with classical polyposis (7 of 60, 12%). Fine-mapping of the region suggested that the majority (6 of 7) of these deletions encompassed the entire APC locus, confirming that haploinsufficiency can result in a classical polyposis phenotype. Screening for germ-line deletions in APC mutation-negative individuals with classical polyposis seems warranted.

Germline mutations in BMPR1A/ALK3 cause a subset of cases of juvenile polyposis syndrome and of Cowden and Bannayan-Riley-Ruvalcaba syndromes.

Juvenile polyposis syndrome (JPS) is an inherited hamartomatous-polyposis syndrome with a risk for colon cancer. JPS is a clinical diagnosis by exclusion, and, before susceptibility genes were identified, JPS could easily be confused with other inherited hamartoma syndromes, such as Bannayan-Riley-Ruvalcaba syndrome (BRRS) and Cowden syndrome (CS). Germline mutations of MADH4 (SMAD4) have been described in a variable number of probands with JPS. A series of familial and isolated European probands without MADH4 mutations were analyzed for germline mutations in BMPR1A, a member of the transforming growth-factor beta-receptor superfamily, upstream from the SMAD pathway. Overall, 10 (38%) probands were found to have germline BMPR1A mutations, 8 of which resulted in truncated receptors and 2 of which resulted in missense alterations (C124R and C376Y). Almost all available component tumors from mutation-positive cases showed loss of heterozygosity (LOH) in the BMPR1A region, whereas those from mutation-negative cases did not. One proband with CS/CS-like phenotype was also found to have a germline BMPR1A missense mutation (A338D). Thus, germline BMPR1A mutations cause a significant proportion of cases of JPS and might define a small subset of cases of CS/BRRS with specific colonic phenotype.

Analysis of genetic and phenotypic heterogeneity in juvenile polyposis.

BACKGROUND: Juvenile polyposis syndrome (JPS) is characterised by gastrointestinal (GI) hamartomatous polyposis and an increased risk of GI malignancy. Juvenile polyps also occur in the Cowden (CS), Bannayan-Ruvalcaba-Riley (BRRS) and Gorlin (GS) syndromes. Diagnosing JPS can be problematic because it relies on exclusion of CS, BRRS, and GS. Germline mutations in the PTCH, PTEN and DPC4 (SMAD4) genes can cause GS, CS/BRRS, and JPS, respectively. AIMS: To examine the contribution of mutations in PTCH, PTEN, and DPC4 (SMAD4) to JPS. METHODS: Forty seven individuals from 15 families and nine apparently sporadic cases with JPS were screened for germline mutations in DPC4, PTEN, and PTCH. RESULTS: No patient had a mutation in PTEN or PTCH. Five different germline mutations were detected in DPC4; three of these were deletions, one a single base substitution creating a stop codon, and one a missense change. None of these patients had distinguishing clinical features. CONCLUSIONS: Mutations in PTEN and PTCH are unlikely to cause juvenile polyposis in the absence of clinical features indicative of CS, BRRS, or GS. A proportion of JPS patients harbour DPC4 mutations (21% in this study) but there remains uncharacterized genetic heterogeneity in JPS.

Desmoid tumours complicating familial adenomatous polyposis.

BACKGROUND: Desmoid tumours are one of the most important and intriguing extracolonic manifestations of familial adenomatous polyposis (FAP). They have been studied only in small numbers of patients. METHODS: Patients with FAP who also had desmoid tumour were identified from a polyposis registry database and their hospital notes were reviewed. RESULTS: There were 166 desmoids in 88 patients (median age 32 (interquartile range 22-38) years; 51 (58 per cent) female); 83 tumours (50 per cent) were within the abdomen and 80 (48 per cent) were in the abdominal wall. All but 16 individuals (18 per cent) had already undergone abdominal surgery, which was significantly more recent in women (P = 0.01, Mann-Whitney U test). Intra-abdominal desmoids caused small bowel and ureteric obstruction and resulted in ten deaths; survival was significantly poorer than in patients with abdominal wall desmoid alone (chi2 = 3. 93, 1 d.f., P = 0.047, log rank test), and eight of 22 patients who underwent resection of intra-abdominal desmoid died in the perioperative period. CONCLUSION: Abdominal wall desmoids caused no deaths or significant morbidity; although recurrence was common after excision, the treatment was safe. Intra-abdominal desmoids can cause serious complications and treatment is often unsuccessful; in particular, surgery for desmoids at this site is hazardous.

The type of somatic mutation at APC in familial adenomatous polyposis is determined by the site of the germline mutation: a new facet to Knudson's 'two-hit' hypothesis.

APC is often cited as a prime example of a tumor suppressor gene. Truncating germline and somatic mutations (or, infrequently, allelic loss) occur in tumors in FAP (familial adenomatous polyposis). Most sporadic colorectal cancers also have two APC mutations. Clues from attenuated polyposis, missense germline variants with mild disease and the somatic mutation cluster region (codons 1,250-1,450) indicate, however, that APC mutations might not result in simple loss of protein function. We have found that FAP patients with germline APC mutations within a small region (codons 1,194-1,392 at most) mainly show allelic loss in their colorectal adenomas, in contrast to other FAP patients, whose 'second hits' tend to occur by truncating mutations in the mutation cluster region. Our results indicate that different APC mutations provide cells with different selective advantages, with mutations close to codon 1,300 providing the greatest advantage. Allelic loss is selected strongly in cells with one mutation near codon 1,300. A different germline-somatic APC mutation association exists in FAP desmoids. APC is not, therefore, a classical tumor suppressor. Our findings also indicate a new mechanism for disease severity: if a broader spectrum of mutations is selected in tumors, the somatic mutation rate is effectively higher and more tumors grow.

Attenuated adenomatous polyposis coli: the role of ascertainment bias through failure to dye-spray at colonoscopy.

PURPOSE: The aim of this study is to show that the diagnosis of attenuated adenomatous polyposis coli must be made with caution and certainly only after adequate colonic examination with dye-spray. METHODS: Four patients thought to have attenuated adenomatous polyposis coli on the basis of family history and the identification of fewer than 100 polyps on simple colonoscopy underwent colonoscopy with dye-spray. RESULTS: All four individuals were found to have more than 100 polyps when dye-spray was used, confirming a diagnosis of classical familial adenomatous polyposis. CONCLUSIONS: The diagnosis of familial adenomatous polyposis may be missed altogether or incorrectly assigned as attenuated adenomatous polyposis coli if dye-spray is not used at colonoscopy. Patients with a family history of familial adenomatous polyposis or colorectal cancer should be considered for dye-spray before the diagnosis of familial adenomatous polyposis is excluded or one of attenuated adenomatous polyposis coli is made.

Screening SMAD1, SMAD2, SMAD3, and SMAD5 for germline mutations in juvenile polyposis syndrome.

BACKGROUND AND AIMS: Juvenile polyps occur in several Mendelian disorders, whether in association with gastrointestinal cancer alone (juvenile polyposis syndrome, JPS) or as part of known syndromes (Cowden, Gorlin, and Bannayan-Zonana) in association with developmental abnormalities, dysmorphic features, or extraintestinal tumours. Recently, some JPS families were shown to harbour germline mutations in the SMAD4 (DPC4) gene, providing further evidence for the importance of the TGFbeta signalling pathway in colorectal cancer. There remains, however, considerable, unexplained genetic heterogeneity in JPS. Other members of the SMAD family are excellent candidates for JPS, especially SMAD2 (which, like SMAD4, is mutated somatically in colorectal cancers), SMAD3 (which causes colorectal cancer when "knocked out" in mice), SMAD5, and SMAD1. METHODS: SMAD1, SMAD2, SMAD3, and SMAD5 were screened for germline mutations in 30 patients with JPS and without SMAD4 mutations. RESULTS: No mutations were found in any of these genes. A G-A C89Y polymorphism with possible effects on protein function was found in SMAD3, but the frequencies of the G and A alleles did not differ between patients with JPS and controls. CONCLUSIONS: It remains to be determined whether or not this polymorphism is involved in a minor predisposition to colorectal or other carcinomas. SMAD4 may be the only member of the SMAD family which causes JPS when mutant in the germline. The other genes underlying JPS remain to be identified.

Inherited susceptibility to colorectal adenomas and carcinomas: evidence for a new predisposition gene on 15q14-q22.

BACKGROUND & AIMS: The aim of this study was to evaluate the role of known colorectal adenoma and carcinoma susceptibility genes and to locate a novel susceptibility gene in an Ashkenazi family (SM1311) with dominantly inherited predisposition to colorectal adenomas and carcinomas. METHODS: Clinicopathologic and family history data were collected. Genetic linkage and mutational analyses were used to investigate the genetic basis of the family's disease. RESULTS: Affected members of SM1311 develop multiple tubular, villous, tubulovillous, and/or serrated colorectal adenomas throughout the large bowel, and some develop colon carcinoma. There are no extracolonic features clearly associated with disease in SM1311. We have shown that the family's phenotype does not result from APC mutations (including the I1307K variant) or from genetic changes in the other known genes that predispose to colon cancer. Using genetic linkage analysis, supplemented by allele loss in tumors, we have provided evidence for a new colorectal cancer susceptibility gene, CRAC1 (colorectal adenoma and carcinoma), mapping to chromosome 15q14-q22. CONCLUSIONS: We provide evidence for a novel colorectal adenoma and carcinoma susceptibility gene on chromosome 15q14-q22. Further studies are needed to confirm this localization and to evaluate the contribution of CRAC1 to this disease.

Mutations and impaired function of LKB1 in familial and non-familial Peutz-Jeghers syndrome and a sporadic testicular cancer.

Germline mutations in LKB1 have been reported to underlie familial Peutz-Jeghers syndrome (PJS) with intestinal hamartomatous polyps and an elevated risk of various neoplasms. To investigate the prevalence of LKB1 germline mutations in PJS more generally, we studied samples from 33 unrelated PJS patients including eight non-familial sporadic patients, 20 familial patients and five patients with unknown family history. Nineteen germline mutations were identified, 12 (60%) in familial and four (50%) in sporadic cases. LKB1 mutations were not detected in 14 (42%) patients, indicating that the existence of additional minor PJS loci cannot be excluded. LKB1 is predicted to encode a serine/threonine kinase. To demonstrate the putative Lkb1 kinase function and to study the consequences of LKB1 mutations in PJS and sporadic tumors, we have analyzed the kinase activity of wild-type and mutant Lkb1 proteins. Interestingly, while most of the small deletions or missense mutations resulted in loss-of-function alleles, one missense mutation (G163D) previously identified in a sporadic testicular tumor demonstrated severely impaired but detectable kinase activity.

Mutations in DPC4 (SMAD4) cause juvenile polyposis syndrome, but only account for a minority of cases.

Juvenile polyps are present in a number of Mendelian disorders, sometimes in association only with gastrointestinal cancer [juvenile polyposis syndrome (JPS)] and sometimes as part of known syndromes (Cowden, Gorlin and Banayan-Zonana) in association with developmental abnormalities, dysmorphic features or extra-intestinal tumours. Recently, a gene for JPS was mapped to 18q21.1 and the candidate gene DPC4 (SMAD4) was shown to carry frameshift mutations in some JPS families. We have analysed eight JPS families for linkage to DPC4. Overall, there was no evidence for linkage to DPC4; linkage could be excluded in two of the eight pedigrees and was unlikely in two others. We then tested these eight families and a further 13 familial and sporadic JPS cases for germline mutations in DPC4. Just one germline DPC4 mutation was found (in a familial JPS patient from a pedigree unsuitable for linkage analysis). Like all three previously reported germline mutations, this variant occurred towards the C-terminus of the DPC4 protein. However, our patient's mutation is a missense change (R361C); somatic missense mutations in DPC4 have been reported previously in tumours. We therefore confirm DPC4 as a cause of JPS, but show that there is considerable remaining, uncharacterized genetic heterogeneity in this disease.