Characterization of POLE c.1373A > T p.(Tyr458Phe), causing high cancer risk.

The cancer syndrome polymerase proofreading-associated polyposis results from germline mutations in the POLE and POLD1 genes. Mutations in the exonuclease domain of these genes are associated with hyper- and ultra-mutated tumors with a predominance of base substitutions resulting from faulty proofreading during DNA replication. When a new variant is identified by gene testing of POLE and POLD1, it is important to verify whether the variant is associated with PPAP or not, to guide genetic counseling of mutation carriers. In 2015, we reported the likely pathogenic (class 4) germline POLE c.1373A > T p.(Tyr458Phe) variant and we have now characterized this variant to verify that it is a class 5 pathogenic variant. For this purpose, we investigated (1) mutator phenotype in tumors from two carriers, (2) mutation frequency in cell-based mutagenesis assays, and (3) structural consequences based on protein modeling. Whole-exome sequencing of two tumors identified an ultra-mutator phenotype with a predominance of base substitutions, the majority of which are C > T. A SupF mutagenesis assay revealed increased mutation frequency in cells overexpressing the variant of interest as well as in isogenic cells encoding the variant. Moreover, exonuclease repair yeast-based assay supported defect in proofreading activity. Lastly, we present a homology model of human POLE to demonstrate structural consequences leading to pathogenic impact of the p.(Tyr458Phe) mutation. The three lines of evidence, taken together with updated co-segregation and previously published data, allow the germline variant POLE c.1373A > T p.(Tyr458Phe) to be reclassified as a class 5 variant. That means the variant is associated with PPAP.

Use of multigene-panel identifies pathogenic variants in several CRC-predisposing genes in patients previously tested for Lynch Syndrome.

BACKGROUND: Many families with a high burden of colorectal cancer fulfil the clinical criteria for Lynch Syndrome. However, in about half of these families, no germline mutation in the mismatch repair genes known to be associated with this disease can be identified. The aim of this study was to find the genetic cause for the increased colorectal cancer risk in these unsolved cases. MATERIALS AND METHODS: To reach the aim, we designed a gene panel targeting 112 previously known or candidate colorectal cancer susceptibility genes to screen 274 patient samples for mutations. Mutations were validated by Sanger sequencing and, where possible, segregation analysis was performed. RESULTS: We identified 73 interesting variants, of whom 17 were pathogenic and 19 were variants of unknown clinical significance in well-established cancer susceptibility genes. In addition, 37 potentially pathogenic variants in candidate colorectal cancer susceptibility genes were detected. CONCLUSION: In conclusion, we found a promising DNA variant in more than 25 % of the patients, which shows that gene panel testing is a more effective method to identify germline variants in CRC patients compared to a single gene approach.

Current clinical criteria for Lynch syndrome are not sensitive enough to identify MSH6 mutation carriers.

BACKGROUND: Reported prevalence, penetrance and expression of deleterious mutations in the mismatch repair (MMR) genes, MLH1, MSH2, MSH6 and PMS2, may reflect differences in the clinical criteria used to select families for DNA testing. The authors have previously reported that clinical criteria are not sensitive enough to identify MMR mutation carriers among incident colorectal cancer cases. OBJECTIVE: To describe the sensitivity of the criteria when applied to families with a demonstrated MMR mutation. METHODS: Families with an aggregation of colorectal cancers were examined for deleterious MMR mutations according to the Mallorca guidelines. All families with a detected MMR mutation as of November 2009 were reclassified according to the Amsterdam and Bethesda criteria. RESULTS: Sixty-nine different DNA variants were identified in a total of 129 families. The original Amsterdam clinical criteria were met by 38%, 12%, 78% and 25% of families with mutations in MSH2, MSH6, MLH1 and PMS2, respectively. Corresponding numbers for the revised Amsterdam criteria were 62%, 48%, 87% and 38%. Similarly, each of the four clinical Bethesda criteria had low sensitivity for identifying MSH6 or PMS2 mutations. CONCLUSION: Amsterdam criteria and each of the Bethesda criteria were inadequate for identifying MSH6 mutation-carrying kindreds. MSH6 mutations may be more common than currently assumed, and the penetrance/expression of MSH6 mutations, as derived from families meeting current clinical criteria, may be misleading. To increase detection rate of MMR mutation carriers, all cancers in the Lynch syndrome tumour spectrum should be subjected to immunohistochemical analysis and/or analysis for microsatellite instability.

Mutation screening in a Norwegian cohort with pheochromocytoma.

Pheochromocytomas (PHEOs) are neuroendocrine tumours, originating from chromaffin cells in the adrenal medulla. They are either sporadic or hereditary. It is important to identify the hereditary cases, so that patients and relatives with germline mutations can be offered regular surveillance. The objective of this study was the detection of pathogenic germline mutations in a cohort of Norwegian PHEO patients. Blood samples and/or formalin-fixed, paraffin-embedded tissue specimens, were collected from 60 patients who were operated upon between 1986 and 2004 at two university hospitals in Norway. DNA mutation analyses were performed successfully in the 42 blood samples and in one of the paraffin-embedded tissue specimen in VHL, RET, SDHB, SDHC, SDHD and NF1. In all, 32 different DNA variants were observed, of which 8 were classified as pathogenic (19 %), or possibly pathogenic; three in NF1, two in RET and VHL and one in SDHB. Two variants were observed in one patient, one in SDHB and one in NF1. Three of these variants are, to the best of our knowledge, new ones; two in NF1 [c.950_51insGCTGA, (p.Glu318LeufsX59) and c.1588G > A, (p.Val530Ile)] and one in VHL (c.308C > T, p.Pro103Leu). In conclusion the overall incidence of germline mutations in genes associated with familial PHEO was found to be of the same order of magnitude in the present Norwegian series as in those from other countries. Two new NF1 variants and one new VHL gene variant were detected.

High penetrances of BRCA1 and BRCA2 mutations confirmed in a prospective series.

Penetrances of BRCA1 and BRCA2 mutations have been derived from retrospective studies, implying the possibility of ascertainment biases to influence the results.We have followed women at risk for breast and/or ovarian cancer for two decades, and report the prospectively observed age-related annual incidence rates to contract breast or ovarian cancer for women with deleterious BRCA1 or BRCA2 mutations based on 4830 observation years. Patients were grouped according to mutation, age and having/not having had previous cancer.In women not having had previous cancer and aged 40-59 years, the annual incidence rate to contract breast or ovarian cancer in those having the most frequent BRCA1 founder mutations was 4.0%, for women in this age group and with less frequent BRCA1 mutations annual incidence rate was 5.9%, and for women with BRCA2 mutations 3.5%.The observed figures may be used for genetic counseling of healthy mutation carriers in the respective age groups. The results may indicate that less frequent BRCA1 mutations have higher penetrances than BRCA1 founder mutations.

A homozygote splice site PMS2 mutation as cause of Turcot syndrome gives rise to two different abnormal transcripts.

Turcot syndrome is a rare, inherited disease predisposing of tumours in the central nerve system and in the colorectal system. This report describes a Turcot patient with an extraordinary clinical history. The patient is still alive at the age of 43. She was operated at the age of 10 by brain tumour and at the age of 16 by colorectal cancer. She has since then been treated for multiple cancers (gastrointestinal, endometrial, basal cell carcinomas), and removal of adenomatous polyps at several occasions. The aim of this work was to investigate if there was any specific genotype that explains her remarkable clinical history. Microsatellite instability and immunohistochemistry analysis for four DNA mismatch repair proteins were performed. DNA mutation analysis was done for genes involved in polyposis and mismatch repair by denaturing high performance liquid chromatography and sequencing. cDNA analysis was carried out for the mismatch repair gene PMS2. The patients genotype was found to be a homozygous splice site mutation in the PMS2 gene, c.989-1G

Living with multiple endocrine neoplasia type 1: decent care-insufficient medical and genetic information: a qualitative study of MEN 1 patients in a Swedish hospital.

This qualitative study explores how 29 Swedish patients with Multiple Endocrine Neoplasia type 1 (MEN1) experience living with the condition, appraisal of the clinical follow-up program, and surveys their future expectations. The aim of this study is to build knowledge about this patient group in order to provide optimal care. The participants describe physical, psychological, and social limitations in their daily activities and how these limitations influence quality of life. Our findings indicate that a majority of patients have adjusted to their situation, describing themselves as being healthy despite physical symptoms and treatment. The participants received decent care in the clinical follow-up program, - however, greater effort should be put into patient information. These patients might benefit from genetic counseling. Health professionals involved should recognize their potential impact and influence on a patient's ability to adjust to these circumstances. Antonovsky's Sense of Coherence theory is used to discuss these findings.