Jaran Apold

Clinical findings with implications for genetic testing in families with clustering of colorectal cancer.

BACKGROUND Germ-line mutations in DNA mismatch-repair genes (MSH2, MLH1, PMS1, PMS2, and MSH6) cause susceptibility to hereditary nonpolyposis colorectal cancer. We assessed the prevalence of MSH2 and MLH1 mutations in families suspected of having hereditary nonpolyposis colorectal cancer and evaluated whether clinical findings can predict the outcome of genetic testing. METHODS We used denaturing gradient gel electrophoresis to identify MSH2 and MLH1 mutations in 184 kindreds with familial clustering of colorectal cancer or other cancers associated with hereditary nonpolyposis colorectal cancer. Information on the site of cancer, the age at diagnosis, and the number of affected family members was obtained from all families. RESULTS Mutations of MSH2 or MLH1 were found in 47 of the 184 kindreds (26 percent). Clinical factors associated with these mutations were early age at diagnosis of colorectal cancer, the occurrence in the kindred of endometrial cancer or tumors of the small intestine, a higher number of family members with colorectal or endometrial cancer, the presence of multiple colorectal cancers or both colorectal and endometrial cancers in a single family member, and fulfillment of the Amsterdam criteria for the diagnosis of hereditary nonpolyposis colorectal cancer (at least three family members in two or more successive generations must have colorectal cancer, one of whom is a first-degree relative of the other two; cancer must be diagnosed before the age of 50 in at least one family member; and familial adenomatous polyposis must be ruled out). Multivariate analysis showed that a younger age at diagnosis of colorectal cancer, fulfillment of the Amsterdam criteria, and the presence of endometrial cancer in the kindred were independent predictors of germ-line mutations of MSH2 or MLH1. These results were used to devise a logistic model for estimating the likelihood of a mutation in MSH2 and MLH1. CONCLUSIONS Assessment of clinical findings can improve the rate of detection of mutations of DNA mismatch-repair genes in families suspected of having hereditary nonpolyposis colorectal cancer.

Immunochemical analysis of cod fish allergen M: locations of the immunoglobulin binding sites as demonstrated by the native and synthetic peptides.

The major allergen of codfish (Allergen M) is a muscle protein belonging to the family of calcium binding parvalbumins. The primary structure of the molecule was established and the molecular weight was estimated from the sequence data to be 12,328. Allergen M consists of 113 amino acid residues and one residue of glucose. A molecular arrangement of three domains (AB, CD and EF—the latter two bind one Ca2+ ion each) was described for Allergen M, analogous to carp parvalbumin pI 4.25. The suggested strucutre was based on the extensive intramolecular amino acid homologies and the immunochemical cross‐reactivities of the intact molecule and the two major isolated fragments.

Survival in prospectively ascertained familial breast cancer: analysis of a series stratified by tumour characteristics, BRCA mutations and oophorectomy.

Dedicated clinics have been established for the early diagnosis and treatment of women at risk for inherited breast cancer, but the effects of such interventions are currently unproven. This second report on prospectively diagnosed inherited breast cancer from the European collaborating centres supports the previous conclusions and adds information on genetic heterogeneity and the effect of oophorectomy. Of 249 patients, 20% had carcinoma in situ (CIS), 54% had infiltrating cancer without spread (CaN0) and 26% had cancer with spread (CaN+). Five‐year survival was 100% for CIS, 94% for CaN0 and 72% for CaN+ (p = 0.007). Thirty‐six patients had BRCA1 mutations, and 8 had BRCA2 mutations. Presence of BRCA1 mutation was associated with infiltrating cancer, high grade and lack of oestrogen receptor (p < 0.05 for all 3 characteristics). For BRCA1 mutation carriers, 5‐year survival was 63% vs. 91% for noncarriers (p = 0.04). For CaN0 patients, mutation carriers had 75% 5‐year disease‐free survival vs. 96% for noncarriers (p = 0.01). Twenty‐one of the mutation carriers had undergone prophylactic oophorectomy, prior to or within 6 months of diagnosis in 13 cases. All but 1 relapse occurred in the 15 who had kept their ovaries, (p < 0.01); no relapse occurred in those who had removed the ovaries within 6 months (p = 0.04) Contralateral cancer was more frequently observed in mutation noncarriers, but this finding did not reach statistical significance. Our findings support the concept that BRCA1 cancer is biologically different from other inherited breast cancers. While current screening protocols appear satisfactory for the majority of women at risk of familial breast cancer, this may not be the case for BRCA1 mutation carriers. The observed effect of oophorectomy was striking.

Familial diarrhea syndrome caused by an activating GUCY2C mutation.

BACKGROUND Familial diarrhea disorders are, in most cases, severe and caused by recessive mutations. We describe the cause of a novel dominant disease in 32 members of a Norwegian family. The affected members have chronic diarrhea that is of early onset, is relatively mild, and is associated with increased susceptibility to inflammatory bowel disease, small-bowel obstruction, and esophagitis. METHODS We used linkage analysis, based on arrays with single-nucleotide polymorphisms, to identify a candidate region on chromosome 12 and then sequenced GUCY2C, encoding guanylate cyclase C (GC-C), an intestinal receptor for bacterial heat-stable enterotoxins. We performed exome sequencing of the entire candidate region from three affected family members, to exclude the possibility that mutations in genes other than GUCY2C could cause or contribute to susceptibility to the disease. We carried out functional studies of mutant GC-C using HEK293T cells. RESULTS We identified a heterozygous missense mutation (c.2519G→T) in GUCY2C in all affected family members and observed no other rare variants in the exons of genes in the candidate region. Exposure of the mutant receptor to its ligands resulted in markedly increased production of cyclic guanosine monophosphate (cGMP). This may cause hyperactivation of the cystic fibrosis transmembrane regulator (CFTR), leading to increased chloride and water secretion from the enterocytes, and may thus explain the chronic diarrhea in the affected family members. CONCLUSIONS Increased GC-C signaling disturbs normal bowel function and appears to have a proinflammatory effect, either through increased chloride secretion or additional effects of elevated cellular cGMP. Further investigation of the relevance of genetic variants affecting the GC-C-CFTR pathway to conditions such as Crohns disease is warranted. (Funded by Helse Vest [Western Norway Regional Health Authority] and the Department of Science and Technology, Government of India.).

Screening for familial ovarian cancer: poor survival of BRCA1/2 related cancers

Aim: To assess the effectiveness of annual ovarian cancer screening (transvaginal ultrasound and serum CA125 estimation) in reducing mortality from ovarian cancer in women at increased genetic risk. Patients and methods: A cohort of 3532 women at increased risk of ovarian cancer was screened at five European centres between January 1991 and March 2007. Survival from diagnosis of ovarian cancer was calculated using Kaplan–Meier analysis and compared for proven BRCA1/2 carriers with non-carriers and whether the cancer was detected at prevalence or post-prevalent scan. Screening was performed by annual transvaginal ultrasound and serum CA125 measurement. Results: 64 epithelial ovarian malignancies (59 invasive and 5 borderline), developed in the cohort. 26 tumours were detected at prevalent round; there were 27 incident detected cancers and 11 interval. 65% of cancers were stage 3 or 4, however, stage and survival were little different for prevalent versus post-prevalent cancers. Five year and 10 year survival in 49 BRCA1/2 mutation carriers was 58.6% (95% CI 50.9% to 66.3%) and 36% (95% CI 27% to 45%), which was significantly worse than for 15 non-BRCA carriers (91.8%, 95% CI 84% to 99.6%, both 5 and 10 year survival p = 0.015). However, when borderline tumours were excluded, the difference in survival between carriers and non-carriers was no longer significant. Conclusion: Annual surveillance, by transvaginal ultrasound scanning and serum CA125 measurement, in women at increased familial risk of ovarian cancer is ineffective in detecting tumours at a sufficiently early stage to influence substantially survival in BRCA1/2 carriers.

Surveillance for familial breast cancer : Differences in outcome according to BRCA mutation status

Women with a family history of breast cancer are commonly offered regular clinical or mammographic surveillance from age 30. Data on the efficacy of such programmes are limited. Clinical, pathological and outcome data were recorded on all breast and ovarian cancers diagnosed within familial breast cancer surveillance programmes at collaborating centers in Norway and the UK up to the end of 2005. These have been analyzed according to the mutation status of the affected women (BRCA1+ve, BRCA2+ve or mutation‐negative). Breast cancer was diagnosed in 442 patients subsequently followed for a total of 2095 years. Eighty‐nine (20%) had BRCA1 mutations, 35 (8%) BRCA2 mutations and in 318 (72%) no mutation could be detected (“mut neg”). Five‐year survival in BRCA1 was 73% compared to 96% in BRCA2 and 92% in mut neg (p = 0.000). Among BRCA1 mutation‐carriers, 5‐year survival was 67% for cases diagnosed as carcinoma in situ, 84% for node‐negative invasive cancers and 58% for those with nodal involvement (p > 0.05). For BRCA2 mutation‐carriers the corresponding figures were 100, 100 and 90% (p > 0.05), while for mut neg women they were 100, 97 and 71% (p = 0.03). Regular surveillance in women at increased familial risk of breast cancer is associated with a good outcome if they carry BRCA2 mutations or no detectable mutation. Carriers of BRCA1 mutations fare significantly worse, even when their tumors are diagnosed at an apparently early stage. The differences in outcome associated with different genetic causes of disease were associated with demonstrated differences in tumor biology. The findings demonstrate the outcome for genetically different breast cancers detected within a programme for early diagnosis and treatment, which is relevant to genetic counseling when women at risk have to chose between the options for preventing death from inherited breast cancer.

Efficacy of early diagnosis and treatment in women with a family history of breast cancer. European Familial Breast Cancer Collaborative Group.

Protocols for activity aiming at early diagnosis and treatment of inherited breast or breast-ovarian cancer have been reported. Available reports on outcome of such programmes are considered here. It is concluded that the ongoing activities should continue with minor modifications. Direct evidence of a survival benefit from breast and ovarian screening is not yet available. On the basis of expert opinion and preliminary results from intervention programmes indicating good detection rates for early breast cancers and 5-year survival concordant with early diagnosis, we propose that women at high risk for inherited breast cancer be offered genetic counselling, education in ‘breast awareness’ and annual mammography and clinical expert examination from around 30 years of age. Mammography every second year may be sufficient from 60 years on. BRCA1 mutation carriers may benefit from more frequent examinations and cancer risk may be reduced by oophorectomy before 40–50 years of age. We strongly advocate that all activities should be organized as multicentre studies subjected to continuous evaluation to measure the effects of the interventions on long-term mortality, to match management options more precisely to individual risks and to prepare the ground for studies on chemoprevention.

PKU mutation (D143G) associated with an apparent high residual enzyme activity: Expression of a kinetic variant form of phenylalanine hydroxylase in three different systems

We have used three complementary in vitro systems to express the human phenylalanine hydroxylase (PAH) gene at high levels. Recombinant PAH was expressed in Escherichia coli (as a fusion protein), in human kidney cells and in a cell‐free in vitro transcription‐translation system. These systems were used to characterize a novel kinetic variant form (D143G) of the enzyme. The recombinant D143G mutant enzyme had the same physicochemical properties as the wild‐type PAH and was stable when expressed in eukaryotic cells. Enzyme activity studies of the D143G mutant enzyme, produced in the three expression systems, revealed a kinetic variant form with reduced affinity for L‐Phe (about 2.4‐fold increase in the S0.5 value) as well as reduced affinity for tetrahydrobiopterin (BH4) (about 2‐fold increase in the apparent Km). At standard assay conditions (1 mM L‐Phe, 75 μM BH4) the residual activity of the mutant enzyme was high and variable (52%, 33%, and 102%) when analysed in the three different systems. The high residual activities of the mutant enzyme obtained at these conditions were not in agreement with the classical PKU phenotype found in a patient compound heterozygous for the termination mutation G272X and the novel D143G mutation. However, when the D143G mutant enzyme was assayed at lower concentrations of L‐Phe (100–300 μM) and BH4 (10 μM) the residual activities were compatible with severely reduced hydroxylation of L‐Phe and the classical PKU phenotype.

Survival in women with MMR mutations and ovarian cancer; A multicentre study in Lynch Syndrome kindreds

Background Women with a germline mutation in one of the MMR genes MLH1, MSH2 or MSH6 reportedly have 4–12% lifetime risk of ovarian cancer, but there is limited knowledge on survival. Prophylactic bilateral salpingo-oophorectomy (PBSO) has been suggested for preventing this condition. Aim The purpose of this retrospective multicentre study was to describe survival in carriers of pathogenic mutations in one of the MMR genes, and who had contracted ovarian cancer. Methods Women who had ovarian cancer, and who tested positive for or were obligate carriers of an MMR mutation, were included from 11 European centres for hereditary cancer. Most women had not attended for gynaecological screening. Crude and disease specific survival was calculated by the Kaplan–Meier algorithm. Results Among the 144 women included, 81.5% had FIGO stage 1 or 2 at diagnosis. 10 year ovarian cancer specific survival independent of staging was 80.6%, compared to less than 40% that is reported both in population based series and in BRCA mutation carriers. Disease specific 30 year survival for ovarian cancer was 71.5%, and for all hereditary non-polyposis colon cancer (HNPCC)/Lynch syndrome related cancers including ovarian cancer it was 47.3%. Conclusions In the series examined, infiltrating ovarian cancer in Lynch syndrome had a better prognosis than infiltrating ovarian cancer in BRCA1/2 mutation carriers or in the general population. Lifetime risk of ovarian cancer of about 10% and a risk of dying of ovarian cancer of 20% gave a lifetime risk of dying of ovarian cancer of about 2% in female MMR mutation carriers.

PKU mutation G46S is associated with increased aggregation and degradation of the phenylalanine hydroxylase enzyme

The G46S mutation in the phenylalanine hydroxylase (PAH) gene was identified by fluorescence‐based single‐strand conformation polymorphism (F‐SSCP) analysis on phenylketonuria (PKU) haplotype 5.9 alleles. DNA sequencing of PAH exon 2 revealed a G‐to‐A transition in cDNA position 136. G46S mutations were present on 17 of 236 Norwegian PKU alleles (7.2%) and on 8 of 176 Swedish PKU alleles (4.5%). Analysis of all 13 exons with the flanking regions further detected a 1316‐35c>t polymorphism (PAH intron 12), associated with both G46S and haplotype 5.9. Three patients were homozygous for the G46S mutation, two were untreated and had mild and severe mental retardation, respectively. The G46S mutation was introduced in the PAH cDNA by site‐directed mutagenesis and expressed in three different systems (the pMAL/Escherichia coli system, the pcDNA3/human embryonic kidney (A293) cells, and the pcDNA3/TnT coupled in vitro transcription‐translation system). The mutant recombinant E. coli fusion protein was recovered in high yield and with a specific activity of the purified tetrameric form, which was higher than the wild‐type activity. After transient expression in A293 cells, the amount of the G46S protein was only about 3% of the wild type at equal PAH mRNA levels. The fusion protein cleaved by restriction protease factor Xa, as well as the enzyme produced by in vitro transcription‐translation, revealed an abnormal susceptibility to form catalytically inactive high‐molecular‐mass aggregates of the enzyme. This aggregation, followed by an increased cellular degradation of the G46S mutant enzyme, is compatible with the clinical/metabolic phenotype of the affected homozygous and compound heterozygous patients.