Germline PKHD1 mutations are protective against colorectal cancer

The autosomal recessive polycystic kidney disease (ARPKD) gene, PKHD1, has been implicated in the genesis or growth of colorectal adenocarcinoma, as a high level of somatic mutations was found in colorectal tumor tissue. To determine whether carriers of a single PKHD1 mutation are at increased risk of colorectal carcinoma, we assessed the prevalence of the commonest European mutation, T36M. First, we assayed a European cohort of ARPKD patients and found T36M was responsible for 13.1% of mutations. We then investigated two European cohorts with colorectal adenocarcinoma versus two control cohorts of similar age and gender. Screening for the most common PKHD1 mutation, T36M, we detected 15:3,603 (0.42%) controls versus 1:3,767 (0.027%) colorectal cancer individuals, indicating that heterozygous PKHD1 mutations are not a risk factor and are protective (p=0.0002). We also show that the carriage rate for PKHD1 mutations in the European population is higher than previous accepted at 3.2% (1:31 genomes).     

Germline mutations in the MYH gene in Swedish familial and sporadic colorectal cancer

Biallelic germline mutations in the base excision repair gene MYH have been shown to predispose to a proportion of multiple colorectal adenomas and cancer. To evaluate the contribution of MYH mutations to non- FAP, non-HNPCC familial colorectal cancer, 84 unrelated Swedish individuals affected with colorectal cancer from such families were screened for germline mutations in the coding sequence of the gene. None of the cases was found to carry any pathogenic sequence change. We then determined the prevalence of the two most common pathogenic MYH mutations found in Caucasians, Y165C and G382D, in 450 Swedish sporadic colorectal cancer cases and 480 Swedish healthy controls. The frequency of both variants in Swedish cases and controls was similar to those previously reported. In addition, we found that previously unknown sequence variations at the position of amino acid 423 (R423Q, R423P, and R423R) appear to occur more frequently in cases than in controls (p = 0.02), a finding that warrants future studies.     

Germline BRCA1 mutations predispose to pancreatic adenocarcinoma

Although the association of germline BRCA2 mutations with pancreatic adenocarcinoma is well established, the role of BRCA1 mutations is less clear. We hypothesized that the loss of heterozygosity at the BRCA1 locus occurs in pancreatic cancers of germline BRCA1 mutation carriers, acting as a “second-hit” event contributing to pancreatic tumorigenesis. Seven germline BRCA1 mutation carriers with pancreatic adenocarcinoma and nine patients with sporadic pancreatic cancer were identified from clinic- and population-based registries. DNA was extracted from paraffin-embedded tumor and nontumor samples. Three polymorphic microsatellite markers for the BRCA1 gene, and an internal control marker on chromosome 16p, were selected to test for the loss of heterozygosity. Tumor DNA demonstrating loss of heterozygosity in BRCA1 mutation carriers was sequenced to identify the retained allele. The loss of heterozygosity rate for the control marker was 20%, an expected baseline frequency. Loss of heterozygosity at the BRCA1 locus was 5/7 (71%) in BRCA1 mutation carriers; tumor DNA was available for sequencing in 4/5 cases, and three demonstrated loss of the wild-type allele. Only 1/9 (11%) sporadic cases demonstrated loss of heterozygosity at the BRCA1 locus. Loss of heterozygosity occurs frequently in pancreatic cancers of germline BRCA1 mutation carriers, with loss of the wild-type allele, and infrequently in sporadic cancer cases. Therefore, BRCA1 germline mutations likely predispose to the development of pancreatic cancer, and individuals with these mutations may be considered for pancreatic cancer-screening programs.     

Germline p53 mutations in a cohort with childhood sarcoma: sex differences in cancer risk

To characterize cancer risk in heterozygous p53 mutation carriers, we analyzed cancer incidence in 56 germline p53 mutation carriers and 3,201 noncarriers from 107 kindreds ascertained through patients with childhood soft-tissue sarcoma who were treated at the University of Texas M. D. Anderson Cancer Center. We systematically followed members in these kindreds for cancer incidence for >20 years and evaluated their p53 gene status. We found seven kindreds with germline p53 mutations that include both missense and truncation mutation types. Kaplan-Meier analysis showed similar cancer risks between 21 missense and 35 truncation p53 mutation carriers (log-rank chi(2)=0.04; P=.84). We found a significantly higher cancer risk in female carriers than in male carriers (log-rank chi(2)=12.1; P<.001), a difference not explained by an excess of sex-specific cancer. The calculated standardized incidence ratio (SIR) showed that mutation carriers had a risk for all types of cancer that was much higher than that for the general population (SIR = 41.1; 95% confidence interval [CI] 29.9-55.0) whereas noncarriers had a risk for all types of cancer that was similar to that in the general population (SIR = 0.9; 95% CI 0.8-1.0). The calculated SIRs showed a >100-fold higher risk of sarcoma, female breast cancer, and hematologic malignancies for the p53 mutation carriers and agreed with the findings of an earlier segregation analysis based on the same cohort. These results quantitatively illustrated the spectrum of cancer risk in germline p53 mutation carriers and will provide valuable reference for the evaluation and treatment of patients with cancer.     

Germline DDX41 mutations cause ineffective hematopoiesis and myelodysplasia

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Germline polymorphism of cancer susceptibility genes in gynecologic cancer

The multifactorial process of carcinogenesis involves mutations in oncogenes, or tumor suppressor genes, as well as the influence of environmental etiological factors. Common DNA polymorphisms in low penetrance genes have emerged as genetic factors that seem to modulate an individual’s susceptibility to malignancy. Genetic studies, which lead to a true association, are expected to increase understanding of the pathogenesis of each malignancy and to be a powerful tool for prevention and prognosis in the future. Here, we review the findings of genetic association studies of gene polymorphisms in gynecologic cancer with special reference to glutathione-S-transferase, FAS/CD95 and p53 genes including our recent research results.     

Germline autonomy of maternal-effect mutations altering the embryonic body pattern of Drosophila

Nine maternal-effect loci Drosophila melanogaster were tested in germline mosaics to determine whether the wildtype gene activity is required in somatic or germline components of the maternal ovary. Mutations in these loci affect the anterior-posterior or dorso-ventral body pattern. In all nine loci (torso, trunk, exuperantia, vasa, valois, staufen, tudor, dorsal, Toll) a mutant genotype in the germ cells is sufficient to produce all aspects of the mutant embryonic phenotype, even when those germ cells are surrounded by wildtype somatic tissues.     

Germline mutations of KIT in gastrointestinal stromal tumor (GIST) and mastocytosis

Somatic mutations of KIT are frequently found in mastocytosis and gastrointestinal stromal tumor (GIST), while germline mutations of KIT are rare, and only found in few cases of familial GIST and mastocytosis. Although ligand-independent activation is the common feature of KIT mutations, the phenotypes mediated by various germline KIT mutations are different. Germline KIT mutations affect different tissues such as interstitial cells of Cajal (ICC), mast cells or melanocytes, and thereby lead to GIST, mastocytosis, or abnormal pigmentation. In this review, we summarize germline KIT mutations in familial mastocytosis and GIST and discuss the possible cellular context dependent transforming activity of KIT mutations.     

Germline mutations of the MYH gene in Japanese patients with multiple colorectal adenomas

Germline mutations of the MYH gene have been revealed to associate with the recessive inheritance of multiple colorectal adenomas in Caucasian population. However, MYH mutations in Japanese patients have not yet been clarified. In an assessment of MYH mutations, we examined 35 Japanese patients with multiple colorectal adenomas who had neither dominant inheritance of colorectal tumors, nor germline APC mutations. One patient had a homozygous biallelic MYH mutation, R231C and three independent patients had monoallelic MYH mutations at a splice-site on exon 11 (IVS10-2 A to G). These four patients had 21 to around 100 colorectal adenomas and 1-3 synchronous colorectal carcinomas. The most common mutations in Caucasian patients, Y165C and G382D, were not detected in our Japanese cases. The MYH mutations detected in Japanese patients were novel and different from those detected among Caucasian, Indian and Pakistani patients, which suggests the existence of ethnic differentiation in MYH mutations.     

Germline met mutations in mice reveal mutation- and background-associated differences in tumor profiles

Background

The receptor tyrosine kinase Met is involved in the progression and metastasis of numerous human cancers. Although overexpression and autocrine activation of the Met signaling pathway are commonly found in human cancers, mutational activation of Met has been observed in small cell and non-small cell lung cancers, lung adenocarcinomas, renal carcinomas, and mesotheliomas.

Methodology/Principal Findings

To investigate the influence of mutationally activated Met in tumorigenesis, we utilized a novel mouse model. Previously, we observed that various Met mutations developed unique mutation-specific tumor spectra on a C57BL/6 background. Here, we assessed the effect of genetic background on the tumorigenic potential of mutationally activated Met. For this purpose, we created congenic knock-in lines of the Met mutations D1226N, M1248T, and Y1228C on the FVB/N background. Consistent with the mutation-specific tumor spectra, several of the mutations were associated with the same tumor types as observed on C57BL/6 background. However, on the FVB/N background most developed a high incidence of mammary carcinomas with diverse histopathologies.

Conclusions/Significance

This study demonstrates that on two distinct mouse backgrounds, Met is able to initiate tumorigenesis in multiple cell types, including epithelial, hematopoietic, and endothelial. Furthermore, these observations emphasize that even a modest increase in Met activation can initiate tumorigenesis with both the Met mutational spectra and host background having profound influence on the type of tumor generated. Greater insight into the interaction of genetic modifiers and Met signaling will significantly enhance our ability to tailor combination therapies for Met-driven cancers.     

Germline mutations of tetranucleotide DNA repeats in families with normal children and reproductive pathology

We have previously reported a high rate of tetranucleotide DNA repeat mutations, including mutations of both germline and somatic origin, in spontaneous human abortuses. To analyze in more detail mutational microsatellite (MS) variability in meiosis and its possible association with disturbed embryonic development, we have conducted a comparative study of mutation rates of a complex of 15 autosomal tetranucleotide MSs in 55 families with healthy children and in 103 families that have had spontaneous abortuses with normal karyotypes. In the families with miscarriage, the gametic MS mutation rate was higher than in the families with normal reproductive function (4.36 x 10(-3) versus 2.32 x 10(-3) per locus per gamete per generation), but this difference was statistically nonsignificant (P = 0.25). No association of MS mutations with familiar miscarriage was found. Mutations at the MS loci studied were recorded almost 3 times as often in spermatogenesis as in oogenesis, which is likely to result from a greater number of DNA replication cycles in male germline cell precursors than in female ones. Mutations increasing and reducing the MS sequence length appeared at virtually the same rate. Changes in MS DNA sequence length per one repeated element, i.e., single-step mutations (93% of cases) exceeded all other events of allele length change. The highest number of mutations (81.2%) was found in longer alleles. This distribution of mutations by size, direction, and parental origin corresponds to the multistep mutation model of their emergence via mechanism of DNA strand slippage during replication.     

Germline EPHB2 receptor variants in familial colorectal cancer

Familial clustering of colorectal cancer occurs in 15-20% of cases, however recognized cancer syndromes explain only a small fraction of this disease. Thus, the genetic basis for the majority of hereditary colorectal cancer remains unknown. EPHB2 has recently been implicated as a candidate tumor suppressor gene in colorectal cancer. The aim of this study was to evaluate the contribution of EPHB2 to hereditary colorectal cancer. We screened for germline EPHB2 sequence variants in 116 population-based familial colorectal cancer cases by DNA sequencing. We then estimated the population frequencies and characterized the biological activities of the EPHB2 variants identified. Three novel nonsynonymous missense alterations were detected. Two of these variants (A438T and G787R) result in significant residue changes, while the third leads to a conservative substitution in the carboxy-terminal SAM domain (V945I). The former two variants were found once in the 116 cases, while the V945I variant was present in 2 cases. Genotyping of additional patients with colorectal cancer and control subjects revealed that A438T and G787R represent rare EPHB2 alleles. In vitro functional studies show that the G787R substitution, located in the kinase domain, causes impaired receptor kinase activity and is therefore pathogenic, whereas the A438T variant retains its receptor function and likely represents a neutral polymorphism. Tumor tissue from the G787R variant case manifested loss of heterozygosity, with loss of the wild-type allele, supporting a tumor suppressor role for EPHB2 in rare colorectal cancer cases. Rare germline EPHB2 variants may contribute to a small fraction of hereditary colorectal cancer.     

Germline mutations and variants in the succinate dehydrogenase genes in Cowden and Cowden-like syndromes

Individuals with PTEN mutations have Cowden syndrome (CS), associated with breast, thyroid, and endometrial neoplasias. Many more patients with features of CS, not meeting diagnostic criteria (termed CS-like), are evaluated by clinicians for CS-related cancer risk. Germline mutations in succinate dehydrogenase subunits SDHB-D cause pheochromocytoma-paraganglioma syndrome. One to five percent of SDHB/SDHD mutation carriers have renal cell or papillary thyroid carcinomas, which are also CS-related features. SDHB-D may be candidate susceptibility genes for some PTEN mutation-negative individuals with CS-like cancers. To address this hypothesis, germline SDHB-D mutation analysis in 375 PTEN mutation-negative CS/CS-like individuals was performed, followed by functional analysis of identified SDH mutations/variants. Of 375 PTEN mutation-negative CS/CS-like individuals, 74 (20%) had increased manganese superoxide dismutase (MnSOD) expression, a manifestation of mitochondrial dysfunction. Among these, 10 (13.5%) had germline mutations/variants in SDHB (n = 3) or SDHD (7), not found in 700 controls (p < 0.001). Compared to PTEN mutation-positive CS/CS-like individuals, those with SDH mutations/variants were enriched for carcinomas of the female breast (6/9 SDH versus 30/107 PTEN, p < 0.001), thyroid (5/10 versus 15/106, p < 0.001), and kidney (2/10 versus 4/230, p = 0.026). In the absence of PTEN alteration, CS/CS-like-related SDH mutations/variants show increased phosphorylation of AKT and/or MAPK, downstream manifestations of PTEN dysfunction. Germline SDH mutations/variants occur in a subset of PTEN mutation-negative CS/CS-like individuals and are associated with increased frequencies of breast, thyroid, and renal cancers beyond those conferred by germline PTEN mutations. SDH testing should be considered for germline PTEN mutation-negative CS/CS-like individuals, especially in the setting of breast, thyroid, and/or renal cancers.     

Germline mutation in ATR in autosomal- dominant oropharyngeal cancer syndrome

ATR (ataxia telangiectasia and Rad3 related) is an essential regulator of genome integrity. It controls and coordinates DNA-replication origin firing, replication-fork stability, cell-cycle checkpoints, and DNA repair. Previously, autosomal-recessive loss-of-function mutations in ATR have been demonstrated in Seckel syndrome, a developmental disorder. Here, however, we report on a different kind of genetic disorder that is due to functionally compromised ATR activity, which translates into an autosomal-dominant inherited disease. The condition affects 24 individuals in a five-generation pedigree and comprises oropharyngeal cancer, skin telangiectases, and mild developmental anomalies of the hair, teeth, and nails. We mapped the disorder to a ～16.8 cM interval in chromosomal region 3q22-24, and by sequencing candidate genes, we found that ATR contained a heterozygous missense mutation (c.6431A>G [p.Gln2144Arg]) that segregated with the disease. The mutation occurs within the FAT (FRAP, ATM, and TRRAP) domain-which can activate p53-of ATR. The mutation did not lead to a reduction in ATR expression, but cultured fibroblasts showed lower p53 levels after activation of ATR with hydroxyurea than did normal control fibroblasts. Moreover, loss of heterozygosity for the ATR locus was noted in oropharyngeal-tumor tissue. Collectively, the clinicopathological and molecular findings point to a cancer syndrome and provide evidence implicating a germline mutation in ATR and susceptibility to malignancy in humans.     

Germline mutations of regulator of telomere elongation helicase 1, RTEL1, in Dyskeratosis congenita

Dyskeratosis congenita (DC) is an inherited bone marrow failure and cancer predisposition syndrome caused by aberrant telomere biology. The classic triad of dysplastic nails, abnormal skin pigmentation, and oral leukoplakia is diagnostic of DC, but substantial clinical heterogeneity exists; the clinically severe variant Hoyeraal Hreidarsson syndrome (HH) also includes cerebellar hypoplasia, severe immunodeficiency, enteropathy, and intrauterine growth retardation. Germline mutations in telomere biology genes account for approximately one-half of known DC families. Using exome sequencing, we identified mutations in RTEL1, a helicase with critical telomeric functions, in two families with HH. In the first family, two siblings with HH and very short telomeres inherited a premature stop codon from their mother who has short telomeres. The proband from the second family has HH and inherited a premature stop codon in RTEL1 from his father and a missense mutation from his mother, who also has short telomeres. In addition, inheritance of only the missense mutation led to very short telomeres in the proband’s brother. Targeted sequencing identified a different RTEL1 missense mutation in one additional DC proband who has bone marrow failure and short telomeres. Both missense mutations affect the helicase domain of RTEL1, and three in silico prediction algorithms suggest that they are likely deleterious. The nonsense mutations both cause truncation of the RTEL1 protein, resulting in loss of the PIP box; this may abrogate an important protein–protein interaction. These findings implicate a new telomere biology gene, RTEL1, in the etiology of DC.     

Germline missense mutations affecting KRAS Isoform B are associated with a severe Noonan syndrome phenotype

Noonan syndrome (NS) is a developmental disorder characterized by short stature, facial dysmorphia, congenital heart disease, and multiple skeletal and hematologic defects. NS is an autosomal dominant trait and is genetically heterogeneous. Gain of function of SHP-2, a protein tyrosine phosphatase that positively modulates RAS signaling, is observed in nearly 50% of affected individuals. Here, we report the identification of heterozygous KRAS gene mutations in two subjects exhibiting a severe NS phenotype with features overlapping those of cardiofaciocutaneous and Costello syndromes. Both mutations were de novo and affected exon 6, which encodes the C-terminal portion of KRAS isoform B but does not contribute to KRAS isoform A. Structural analysis indicated that both substitutions (Val152Gly and Asp153Val) perturb the conformation of the guanine ring-binding pocket of the protein, predicting an increase in the guanine diphosphate/guanine triphosphate (GTP) dissociation rate that would favor GTP binding to the KRASB isoform and bypass the requirement for a guanine nucleotide exchange factor.     

Germline mutations of the paired-like homeobox 2B (PHOX2B) gene in neuroblastoma

Neuroblastoma (NB) is a frequent pediatric tumor for which recurrent somatic rearrangements are known. Germline mutations of predisposing gene(s) are suspected on the basis of rare familial cases and the association of NB with other genetically determined congenital malformations of neural crest-derived cells--namely, Hirschsprung disease (HSCR) and/or congenital central hypoventilation syndrome (CCHS). We recently identified the paired-like homeobox 2B (PHOX2B) gene as the major disease-causing gene in isolated and syndromic CCHS, which prompted us to regard it as a candidate gene in NB. Here, we report on germline mutations of PHOX2B in both a familial case of NB and a patient with the HSCR-NB association. PHOX2B, therefore, stands as the first gene for which germline mutations predispose to NB.