Heritability of cellular radiosensitivity: a marker of low-penetrance predisposition genes in breast cancer?

Many inherited cancer-prone conditions show an elevated sensitivity to the induction of chromosome damage in cells exposed to ionizing radiation, indicative of defects in the processing of DNA damage. We earlier found that 40% of patients with breast cancer and 5%-10% of controls showed evidence of enhanced chromosomal radiosensitivity and that this sensitivity was not age related. We suggested that this could be a marker of cancer-predisposing genes of low penetrance. To further test this hypothesis, we have studied the heritability of radiosensitivity in families of patients with breast cancer. Of 37 first-degree relatives of 16 sensitive patients, 23 (62%) were themselves sensitive, compared with 1 (7%) of 15 first-degree relatives of four patients with normal responses. The distribution of radiosensitivities among the family members showed a trimodal distribution, suggesting the presence of a limited number of major genes determining radiosensitivity. Segregation analysis of 95 family members showed clear evidence of heritability of radiosensitivity, with a single major gene accounting for 82% of the variance between family members. The two alleles combine in an additive (codominant) manner, giving complete heterozygote expression. A better fit was obtained to a model that includes a second, rarer gene with a similar, additive effect on radiosensitivity, but the data are clearly consistent with a range of models. Novel genes involved in predisposition to breast cancer can now be sought through linkage studies using this quantitative trait.

Mononucleotide microsatellite instability and germline MSH6 mutation analysis in early onset colorectal cancer

Germline mutations in the MSH2 and MLH1 mismatch repair genes account for most cases of hereditary non-polyposis colon cancer syndrome (HNPCC). In addition, germline MSH2 and MLH1 mutations have been detected in patients with non-HNPCC early onset colorectal cancer. Germline MSH6 mutations appear to be rare in classical HNPCC families, but their frequency in young colorectal cancer cases has not been studied previously. In a population based study of early onset colorectal cancer (<50 years) investigated for tumour microsatellite instability (MSI), we identified a subgroup of tumours with MSI for mono- but not dinucleotide repeat markers (m-MSI+ group). In contrast to tumours with classical MSI for dinucleotide markers (d-MSI+), the m-MSI+ group cancers were mainly left sided (6/7). As MSH6 mutations in yeast and human cell lines are associated with weak (and preferential mononucleotide) MSI, the complete MSH6 gene coding region was sequenced in blood DNA from the five m-MSI+ cases available for analysis. A germline nonsense mutation was identified in an isolated case of early onset colorectal cancer (age 43 years). These results support previous findings that germline MSH6 mutations may not be associated with classical MSI and suggest a role for germline MSH6 mutations in isolated early onset colorectal cancer.

Ectopic pregnancies in two consecutive menstrual cycles

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Differences among Helicobacter pylori strains isolated from three different populations and demonstrated by restriction enzyme analysis of an internal fragment of the conserved gene hpaA

BACKGROUND

Our goal was to test the idea that Helicobacter pylori genotypes vary from one population to another.

METHODS

Analysis of Sau3A and HinfI restriction fragment-length polymorphism (RFLP) in a 375-bp polymerase chain reaction amplicon of hpaA was used to compare 31 H. pylori isolates from a relatively small and genetically homogeneous population (Goteborg, Sweden) with those of large, genetically heterogeneous populations located in two different countries (50 isolates from Houston, TX, and 69 isolates from Minas Gerais, a state in the southeastern region of Brazil).

RESULTS

Five different Sau3A and three different HinfI restriction patterns were found; different combinations of these comprise 10 different RFLP types, I through X. The RFLP types found in the United States and Brazil collections were very similar, except for two Brazil isolates belonging to type VIII and five Brazil isolates belonging to type X, neither type found in the United States. The overall profile of H. pylori isolates from Sweden was remarkably different, with 18 of 31 (58%) having a new Sau3A restriction pattern, termed gS; 10 of these 18 isolates had HinfI restriction pattern E (RFLP type VIII), and 8 had HinfI restriction pattern F (RFLP type IX). No isolates from Sweden belonged to RFLP type III or type X.

CONCLUSIONS

RFLP typing of a 375-bp polymerase chain reaction-amplified DNA fragment of H. pylori hpaA revealed that H. pylori genotypes can and do vary from one population to another. We conclude that the unique RFLP profile shown by the group of H. pylori isolates from Goteborg is the result of a cohort effect in this relatively small, stable, genetically homogeneous population. Also, the overall similarity between RFLP profiles of the H. pylori isolates from Texas and Minas Gerais coincides with the fact that although geographically distanced, these populations are similar in being large, dynamic, and genetically heterogeneous.

Probability of bilateral disease in people presenting with a unilateral vestibular schwannoma

BACKGROUND

Some 4%-5% of those who develop vestibular schwannomas have neurofibromatosis type 2 (NF2). Although about 10% of these patients present initially with a unilateral vestibular schwannoma, the risk for a patient with a truly sporadic vestibular schwannoma developing contralateral disease is unknown.

METHODS

A United Kingdom survey of 296 patients with NF2 was reviewed for laterality of vestibular schwannoma at presentation and the presence of other NF2 related features. The time to presentation of bilateral disease was calculated for patients presenting with a unilateral tumour. Mutation analysis of the NF2 gene was carried out on all available cases presenting initially with unilateral disease.

RESULTS

Of 240 patients with NF2 with vestibular schwannomas, 45 (18%; 32 sporadic, 13 familial) had either a unilateral tumour or delay in detection between the first and contralateral tumours. Among those tested for NF2 mutations, eight of 27 and nine of 13 were identified among sporadic and familial cases respectively. Sporadic cases showed a high female to male ratio and 19 of 32 have not as yet developed a contralateral tumour (mean 4.1 years after diagnosis of the first). Thirteen of 32 sporadic patients developed a contralateral tumour (mean 6.5 years after the first tumour diagnosis, range 0-22 years) compared with 11 of 13 familial patients (mean delay 5 years, range 0-16 years). Seven of the 45 patients had neither a family history of NF2 nor evidence of related tumours at initial presentation (six before the age of 35 years).

CONCLUSION

The risk of patients with sporadic unilateral vestibular schwannomata developing a contralateral tumour in the absence of family history or other features of NF2 is low, but those presenting with other neurogenic tumours in addition to vestibular schwannoma are at high risk of harbouring an NF2 mutation in at least a proportion of their somatic cells.

Germline mutations of the LKB1 (STK11) gene in Peutz-Jeghers patients

Germline mutations of the LKB1 (STK11) serine/threonine kinase gene (chromosome 19p13.3) cause Peutz-Jeghers syndrome, which is characterised by hamartomas of the gastrointestinal tract and typical pigmentation. Peutz-Jeghers syndrome carries an overall risk of cancer that may be up to 20 times that of the general population. Here, we report the results of a screen for germline LKB1 mutations by DNA sequencing in 12 Peutz-Jeghers patients (three sporadic and nine familial cases). Mutations were found in seven (58%) cases, in exons 1, 2, 4, 6, and 9. Five of these mutations, two of which are identical, are predicted to lead to a truncated protein (three frameshifts, two nonsense changes). A further mutation is an in frame deletion of 6 bp, resulting in a deletion of lysine and asparagine; the second of these amino acids is conserved between species. The seventh mutation is a missense change in exon 2, converting lysine to arginine, affecting non-conserved amino acids and of uncertain functional significance. Despite the fact that Peutz-Jeghers syndrome is usually an early onset disease with characteristic clinical features, predictive and diagnostic testing for LKB1 mutations will be useful for selected patients in both familial and non-familial contexts.

The accuracy of diagnoses as reported in families with cancer: a retrospective study

Assessment of risk of developing hereditary cancer and subsequent clinical surveillance is largely based on family history. It is considered standard practice to confirm as many diagnoses as possible in cancer families. Our aim was (1) to assess inaccuracies in reporting of cancers by families, (2) to assess the need for confirmation of diagnosis, and (3) to estimate how many families would have been entered unnecessarily or excluded from screening. A retrospective study of 595 case notes was performed in two centres. Methods of confirmation included information from the cancer registries, death certificates, hospital notes, and histopathological records. Accuracy varied by site of cancer and by the closeness of the relationship to the affected person. Reported abdominal malignancies were inaccurate in 20%, whereas 5% of reported breast cancers were inaccurate. In two families the family history of cancer proved fictitious. Management was altered in 231213 (11%) families following cancer confirmation. The results of the study favour verification of cancer diagnoses particularly if decisions regarding surveillance or prophylactic surgery are based on the family history.

Germline E-cadherin gene (CDH1) mutations predispose to familial gastric cancer and colorectal cancer

Inherited mutations in the E-cadherin gene ( CDH1 ) were described recently in three Maori kindreds with familial gastric cancer. Familial gastric cancer is genetically heterogeneous and it is not clear what proportion of gastric cancer susceptibility in non-Maori populations is due to germline CDH1 mutations. Therefore, we screened eight familial gastric cancer kindreds of British and Irish origin for germline CDH1 mutations, by SSCP analysis of all 16 exons and flanking sequences. Each family contained: (i) two cases of gastric cancer in first degree relatives with one affected before age 50 years; or (ii) three or more cases of gastric cancer. Novel germline CDH1 mutations (a nonsense and a splice site) were detected in two families (25%). Both mutations were predicted to truncate the E-cadherin protein in the signal peptide domain. In one family there was evidence of non-penetrance and susceptibility to both gastric and colorectal cancer; thus, in addition to six cases of gastric cancer, a CDH1 mutation carrier developed colorectal cancer at age 30 years. We have confirmed that germline mutations in the CDH1 gene cause familial gastric cancer in non-Maori populations. However, only a minority of familial gastric cancers can be accounted for by CDH1 mutations. Loss of E-cadherin function has been implicated in the pathogenesis of sporadic colorectal and other cancers, and our findings provide evidence that germline CDH1 mutations predispose to early onset colorectal cancer. Thus, CDH1 should be investigated as a cause of inherited susceptibility to both gastric and colorectal cancers.

A clinical study of type 1 neurofibromatosis in north west England

A clinical study of patients on the North West Regional Genetic Register with neurofibromatosis type 1 (NF1) identified 523 affected cases from 304 families. In those for whom relevant information was available, 86.7% (383 of 442) had more than six café au lait patches, 83.8% (310 of 370) had axillary freckling, 42.3% (151 of 357) had inguinal freckling, and 63% (157 of 249) had Lisch nodules. Cutaneous neurofibromas were present in 59.4% (217 of 365) and 45.5% (150 of 330) were noted to have subcutaneous tumours. Plexiform neurofibromas were present in 15.3% (80 of 523). A positive family history of NF1 was found in 71.2% (327 of 459) and 28.8% (132 of 459) of affected patients were considered to be the result of a new mutation. Learning difficulties of varying severity occurred in 62% (186 of 300). CNS tumours associated with NF1 were reported in 9.4% (49) of patients, optic gliomas occurring in 25 of these, 4.8% of patients. Some degree of scoliosis was reported for 11.7% (61), 1.9% (10) had pseudoarthrosis, 4.3% (23) had epilepsy, and 2.1% (11) had spinal neurofibromas. Actuarial analyses were carried out for both optic glioma and malignant nerve sheath tumours and the data are presented.

A common MSH2 mutation in English and North American HNPCC families: origin, phenotypic expression, and sex specific differences in colorectal cancer

The frequency, origin, and phenotypic expression of a germline MSH2 gene mutation previously identified in seven kindreds with hereditary non-polyposis cancer syndrome (HNPCC) was investigated. The mutation (A-->T at nt943+3) disrupts the 3' splice site of exon 5 leading to the deletion of this exon from MSH2 mRNA and represents the only frequent MSH2 mutation so far reported. Although this mutation was initially detected in four of 33 colorectal cancer families analysed from eastern England, more extensive analysis has reduced the frequency to four of 52 (8%) English HNPCC kindreds analysed. In contrast, the MSH2 mutation was identified in 10 of 20 (50%) separately identified colorectal families from Newfoundland. To investigate the origin of this mutation in colorectal cancer families from England (n=4), Newfoundland (n=10), and the United States (n=3), haplotype analysis using microsatellite markers linked to MSH2 was performed. Within the English and US families there was little evidence for a recent common origin of the MSH2 splice site mutation in most families. In contrast, a common haplotype was identified at the two flanking markers (CA5 and D2S288) in eight of the Newfoundland families. These findings suggested a founder effect within Newfoundland similar to that reported by others for two MLH1 mutations in Finnish HNPCC families. We calculated age related risks of all, colorectal, endometrial, and ovarian cancers in nt943+3 A-->T MSH2 mutation carriers (n=76) for all patients and for men and women separately. For both sexes combined, the penetrances at age 60 years for all cancers and for colorectal cancer were 0.86 and 0.57, respectively. The risk of colorectal cancer was significantly higher (p<0.01) in males than females (0.63 v 0.30 and 0.84 v 0.44 at ages 50 and 60 years, respectively). For females there was a high risk of endometrial cancer (0.5 at age 60 years) and premenopausal ovarian cancer (0.2 at 50 years). These intersex differences in colorectal cancer risks have implications for screening programmes and for attempts to identify colorectal cancer susceptibility modifiers.

Neurofibromatosis type 2: genetic and clinical features

For decades, neurofibromatosis type 2 (NF2) was misclassified with the more common neurofibromatosis type 1 (NF1), until 1987 when it was found via genetic linkage analysis that the gene for NF1 was localized to chromosome 17 and the gene for NF2 was localized to chromosome 22. Large, population-based studies have shown that vestibular schwannomas (VS), the hallmark of NF2, do not occur at increased frequency in patients with NF1. Typical clinical features of NF2 are bilateral VS or a family history of NF2, plus either unilateral VS or any two of the following: meningioma, glioma, neurofibroma, schwannoma or posterior subcapsular lenticular opacities. Presymptomatic genetic tests are now possible in the majority of families, and it is hoped that somatic gene therapy will be developed for the treatment of this disease.

The pathology of familial breast cancer: Clinical and genetic counselling implications of breast cancer pathology

Approximately 5% of all breast cancers are due to one of the high-risk breast cancer genes BRCA1 and BRCA2, or possibly to a third or fourth moderate- to high-risk gene(s). A further proportion of cases arise in the presence of a less striking family history, with later average age at onset and lower penetrance: familial breast cancer. Bilaterality is a recognized feature of hereditary breast cancer. Cancers often present at an early age, with the contralateral risk high within 10 years. Proof that bilateral malignancies are separate primaries can be difficult histologically, however, especially within 3 years. The recent finding of specific pathological features related to BRCA1 and, to a lesser extent, BRCA2 mutations means that, in addition to bilaterality and family history, a pathological element can be entered into the risk calculation for the presence of BRCA1/BRCA2 mutations. This will facilitate the targeting of mutation testing to families in which a positive result is most likely, and may subsequently influence the clinical management of these families.

Utilisation of prophylactic mastectomy in 10 European centres

Increasingly women at high risk of breast cancer are opting for prophylactic surgery to reduce their risks. Data from 10 European centres that offer a risk counselling and screening service to women at risk show different approaches to the option of preventive surgery, although most centres adhere to a protocol including at least two risk counselling sessions and a psychological assessment. Thus far the combined centres have data on 174 women who have undergone prophylactic mastectomy with in excess of 400 women years of follow up. Operations were carried out on women with lifetime risks of 25-80%, with an average annual expected incidence rate of 1% per women. No breast cancers have occurred in this cohort. Long term follow up on an extended group of women will be necessary to truly address the risk of subsequent breast cancer and the psychological sequelae.

Genetics of cancer: current knowledge and future possibilities

For many years there has been scepticism among clinicians and cancer epidemiologists as to whether cancer was a genetic disease or could be hereditary. It is only in the last 10 years that developments in molecular biology have proven the hereditary nature of a small proportion of certain common cancers. That cancer is now indisputably 'genetic' at the cellular level is beyond dispute.

Differential diagnosis of type 2 neurofibromatosis: molecular discrimination of NF2 and sporadic vestibular schwannomas

Patients who present with unilateral vestibular schwannomas either at a young age or with additional features of type 2 neurofibromatosis (NF2) are at risk of developing bilateral disease and transmitting a risk of neurogenic tumours to their offspring. We have identified 15 patients from a series of 537 with unilateral vestibular schwannomas who also had one or more of the following: other tumours (10/15), features of NF2 (3/15), or a family history of neurogenic tumours (5/15). No germline NF2 mutations were detected and in 7/9 cases where tumour material was available for analysis a germline mutation in the NF2 gene has been excluded. Although a possibility of gonosomal mosaicism still exists, exclusion tests for the offspring are now possible. We suggest a general strategy, based on analysis of tumour DNA, for distinguishing sporadic and familial cases of tumours caused by two hit mechanisms. Application of this strategy suggests that most instances of unilateral vestibular schwannoma which do not fulfil criteria for NF2 represent chance occurrences.

Current policies for surveillance and management in women at risk of breast and ovarian cancer: a survey among 16 European family cancer clinics. European Familial Breast Cancer Collaborative Group

The recent isolation of breast cancer predisposing genes (BRCA1 and BRCA2) allows the identification of carriers within affected families. These carriers have a 50-85% risk of developing breast or ovarian cancer and need careful follow-up. The purpose of this study was to evaluate the management and screening protocols implemented in high risk families at various family cancer clinics in Europe. A questionnaire was mailed to the members of the European Familial Breast Cancer Collaborative Group (n = 30) requesting information on the following issues: indication for surveillance of breasts and ovaries, the recommended protocol, coordination of the screening examination, prophylactic surgery, the specific management of breast cancer in a mutation carrier and the use of oestrogen. 16 centres from nine countries responded. Most centres recommend surveillance of the breasts if the lifetime risk exceeds 15-20%. The surveillance protocol that is generally advised comprises monthly self breast examination, examination by a specialist every 6 months and annual mammography, all starting from an age between 25 and 35 years. Surveillance of the ovaries is recommended in BRCA1 and BRCA2-mutation carriers, in members from breast/ovarian cancer families and in some centres in 'breast cancer only' families with an early onset of breast cancer. The recommended protocol includes gynaecological examination, sonography and estimation of CA-125 at yearly intervals starting from the age 30-35 years. Prophylactic mastectomy is considered for proven mutation carriers in some centres. Most centres consider prophylactic oophorectomy in mutation carriers and some centres also consider it for members of breast/ovarian cancer families. This survey provides insight into the guidelines for surveillance and management of familial breast cancer used at various family cancer clinics in Europe; this insight may contribute to the appropriate management of these high risk women. It should be emphasised that most recommendations are based on experts' opinion rather than on any specific studies.

Helicobacter pylori cagA status and s and m alleles of vacA in isolates from individuals with a variety of H. pylori-associated gastric diseases

The cagA gene was detected in 100% of 16 Helicobacter pylori isolates from patients with gastric carcinoma versus 78% of 18 isolates from patients with duodenal ulcers (P = 0.344) and only 64% of 22 isolates from patients with gastritis only (P = 0.005) in Brazil. Also, there was a significant association between isolation of cagA+ s1-type vacA H. pylori in cases of stomach cancer and ulcers as opposed to cases of gastritis only (P = 0.004), but this was not true in Houston (P = 0.238), where 94% of all isolates were cagA+.

A novel TP53 splicing mutation in a Li-Fraumeni syndrome family: a patient with Wilms' tumour is not a mutation carrier

We report a Li-Fraumeni syndrome family in which we have detected a splice acceptor mutation in intron 3 of TP53. The mutation affects one of the invariant residues at the splice acceptor site, as a result of which two aberrant transcripts are produced. A child with Wilms' tumour aged 3 years in this family was shown not to be a mutation carrier.

Cancer phenotype correlates with constitutional TP53 genotype in families with the Li-Fraumeni syndrome

The Li-Fraumeni cancer predisposition syndrome is associated with germline TP53 mutations in the majority of families. We have investigated cancer incidence in 34 Li-Fraumeni families, according to their constitutional TP53 mutation status. Families with germline missense mutations in the core DNA binding domain showed a more highly penetrant cancer phenotype than families with other TP53 mutations or no mutation. Cancer phenotype in families carrying such mutations was characterized by a higher cancer incidence and earlier ages at diagnosis, especially of breast cancer and brain tumours, compared with families carrying protein truncating or other inactivating mutations (P=0.03 for all cancers, P=0.006 for breast cancers, P=0.05 for brain tumours). Proband cancers showed significantly younger ages at diagnosis in those with missense mutations in the DNA binding domain than in those with protein inactivating mutations (P=0.031). In individuals with the former type of mutation, there was a significantly lower proportion of tumours which showed loss of the wild-type TP53 allele (P=0.004). These results are consistent with observations in experimental systems which demonstrate that certain mutations exhibit gain of function and/or dominant-negative properties. Our results support an enhanced oncogenic potential for such mutations in human populations.

Men in breast cancer families: a preliminary qualitative study of awareness and experience

In inherited forms of breast cancer, attention in clinical genetics services has focused on women because they are most at risk of developing cancer. Men at risk of transmitting a predisposing gene mutation are less likely to have a genetic test than the women in these families. This preliminary study investigates the perspective of the brothers of women with familial breast cancer and is based on qualitative analysis of 22 semistructured interviews using an attenuated form of Grounded Theory. There is an awareness among these men (without having had genetic counselling) that the breast cancer in their families is inherited. Some of them harbour fear of developing cancer themselves and many are concerned that their daughters might develop breast cancer. Some appeared to use avoidance as a coping strategy. The men were very often excluded from family conversations about breast cancer. Implications for the provision of genetic counselling for these families are discussed.

Somatic mosaicism: a common cause of classic disease in tumor-prone syndromes? Lessons from type 2 neurofibromatosis

Blood samples from 125 families with classic type 2 neurofibromatosis with bilateral vestibular schwannomas were analyzed for mutations in the NF2 gene. Causative mutations were identified in 52 families. In five families, the first affected individual in the family (the index case) was a mosaic for a disease-causing mutation. Only one of nine children from the three mosaic cases with children are affected. Four of these nine children inherited the allele associated with the disease-causing mutation yet did not inherit the mutation. NF2 mutations were identified in only 27/79 (34%) of sporadic cases, compared with 25/46 (54%) of familial cases (P<.05). In 48 families in which a mutation has not been identified, the index cases have had 125 children, of whom only 29 are affected with NF2 and of whom only a further 21 cases would be predicted to be affected by use of life curves. The 50/125 (40%) of cases is significantly less than the 50% expected eventually to develop NF2 (P<.05). Somatic mosaicism is likely to be a common cause of classic NF2 and may well account for a low detection rate for mutations in sporadic cases. Degrees of gonosomal mosaicism mean that recurrence risks may well be <50% in the index case when a mutation is not identified in lymphocyte DNA.

False family history of breast cancer in the family cancer clinic

AIMS

Awareness of hereditary breast and ovarian cancer in both the general public and the medical profession is increasing. Individuals who may be at risk on the basis of a family history are requesting risk determination and appropriate management in a variety of settings. Risk determination relies largely on pedigree analysis and epidemiological data.

METHODS

We describe five individuals presenting in the family cancer or genetic counselling clinic where a factitious family or personal history led to erroneous risk estimation. Common factors in these families are a history of benign breast disease, poor communication within families, long survival with early onset or bilateral disease, a lack of detailed knowledge of the illness and treatment in close relatives and inconsistencies in the history in repeated consultations.

Genetic and functional studies of a germline TP53 splicing mutation in a Li-Fraumeni-like family

We report an extensive Li-Fraumeni-like family in which there is an unusual spectrum of tumours at relatively late onset. A germline TP53 splice donor mutation in exon 4 is present in all affected family members available for testing. The mutation abolishes correct splicing of intron 4 and techniques of RT-PCR have identified three different aberrant transcripts from the mutant TP53 allele. Using the yeast functional assay to analyse transcripts in cells from a number of family members with the mutant allele, TP53 appears wild-type. Functional studies have been carried out on cells from patients with and without cancer who carry the germline mutation, and on cells from unaffected individuals from the same family who do not carry the mutation. Using a number of functional endpoints known to distinguish between cells carrying mutant or wild-type TP53 alleles, we were unable to discriminate normal (wt/wt) from heterozygous (wt/mut) cells by lymphocyte apoptosis and fibroblast survival following low dose rate ionising radiation exposure. However germline mutation carriers show increased sensitivity to radiation-induced chromosome damage in the G2 phase of the cell cycle, and decreased transient and permanent G1 arrest. These studies demonstrate the importance of fully characterising the effects of TP53 germline mutations, and may explain some of the phenotypic features of this family.