Inherited Germline Mutations Research Articles

CDH-1 germ line mutations in diffuse gastric and infiltrating ductal breast cancer

e22218 Background: Hereditary Diffuse Gastric Cancer (HDGC) syndrome is characterized by the predisposition to gastric cancer of the diffuse type and to breast cancer of the lobular type. The autosomal dominantly inherited germline mutations of the E- cadherin (CDH1) gene are the defects underlying the HDGC syndrome. The median age of onset for diffuse gastric cancer is 38 years. CDH1 mutations are highly penetrant, conferring a cumulative risk of diffuse gastric cancer of 75%. Methods: Genomic DNA was purified from peripheral blood leukocytes following standard chloroform extraction. The complete coding sequences of the CDH1-gene, including splice junctions, were amplified by Polymerase Chain Reaction (PCR) and electrophorized in an ABI Prism 310 Genetic Analyzer. Results: A pathogenic mutation located on exon 7 of the CDH1 gene was identified in a female patient diagnosed with bilateral breast cancer at the age of 36. She underwent bilateral mastectomy for an infiltrating ductal adenocarcinoma of the left breast and in situ lobular of the right breast. At the age of 45 the patient underwent gastrectomy for diffuse type gastric adenocarcinoma. She had a positive family history for breast and gastric cancer from both sides, but without meeting the absolute clinical criteria for hereditary diffuse gastric cancer syndrome. The nonsense mutation found was probably maternally inherited, since the maternal grandmother was diagnosed with breast cancer at the age of 38. Conclusions: The selection process of patients for genetic testing for the HDGC syndrome is not quite clear at the moment, as it is apparent that more types of breast cancer and not only lobular, can be associated with the syndrome. Criteria should be more flexible in respects to the histopathology of the cancer type. This is the first CDH1 mutation identified in a Greek patient. No significant financial relationships to disclose.

Genetic testing in gastroenterology: Lynch syndrome

Lynch syndrome/Hereditary non-polyposis colorectal cancer is caused by inherited germline mutations in mismatch repair (MMR) genes, and accounts for 2-5% of colorectal cancers (CRC) . It is characterized by young onset CRC and an increased risk for gynaecologic, urinary tract and gastrointestinal cancers. Family history evaluation is crucial in the early identification of individuals at risk for Lynch syndrome. Individuals whose family history includes multiple relatives with cancer, two or more primary cancers, or component tumours diagnosed at a young age, should undergo genetic evaluation for Lynch syndrome. Guidelines recommend initial evaluation of the tumour with immunohistochemistry or microsatellite instability testing followed by germline testing for mutations in MMR genes in those with abnormal results. Genetic test results can guide screening recommendations for patients and their families. However, results are not always conclusive and in such cases recommendations for cancer screening should be individualized on the basis of personal and family history.

In vivo proliferation advantage of genetically corrected hematopoietic stem cells in a mouse model of Fanconi anemia FA-D1

AbstractFanconi anemia (FA) is an inherited recessive DNA repair disorder mainly characterized by bone marrow failure and cancer predisposition. Studies in mosaic FA patients have shown that reversion of one inherited germ-line mutation resulting in a functional allele in one or a few hematopoietic stem cells (HSCs) can lead to the proliferation advantage of corrected cells, thus over time normalizing the hematologic status of the patient. In contrast to these observations, it is still unclear whether ex vivo genetic correction of FA HSCs also provides a similar proliferation advantage to FA HSCs. Using an FA mouse model with a marked hematopoietic phenotype, the FA-D1 (Brca2Δ27/Δ27) mice, we demonstrate that the lentivirus-mediated gene therapy of FA HSCs results in the progressive expansion of genetically corrected clones in mild-conditioned FA-D1 recipients. Consistent with these data, hematopoietic progenitors from FA recipients progressively became mitomycin C resistant and their chromosomal instability was reverted. No evidence of myelodysplasia, leukemias, or abnormal clonal repopulation was observed at multiple time points in primary or secondary recipients. Our results demonstrate that ectopic expression of BRCA2 confers a beneficial in vivo proliferation advantage to FA-D1 HSCs that enables the full hematopoietic repopulation of FA recipients with genetically corrected cells.

A large novel deletion in the APC promoter region causes gene silencing and leads to classical familial adenomatous polyposis in a Manitoba Mennonite kindred

Familial adenomatous polyposis (FAP) is an autosomal dominant syndrome caused by the inheritance of germline mutations in the APC tumour suppressor gene. The vast majority of these are nonsense and frameshift mutations resulting in a truncated protein product and abnormal function. While APC promoter hypermethylation has been previously documented, promoter-specific deletion mutations have not been reported. In a large Canadian Mennonite polyposis kindred, we identified a large novel germline deletion in the APC promoter region by linkage analysis and MLPA. By RT-PCR and sequence analysis, this mutation was found to result in transcriptional silencing of the APC allele. A few genetic disorders have been characterized as over-represented in the Manitoba Mennonite population, however, the incidence of cancer has not been recognized as increased in this population as compared to other Manitoba ethnic groups. This study strengthens the likelihood that this novel APC promoter mutation is linked to this unique population as a founder mutation.

Colonic Adenomatous Polyposis Syndromes: Clinical Management

Colorectal cancer is one of the major causes of cancer deaths in both men and women. It is estimated that 5 to 10% of patients with colorectal cancer have an inherited germline mutation that predisposes them to cancer. Hereditary colorectal cancer syndromes can be divided into those associated with colonic polyposis - familial adenomatous polyposis (FAP), attenuated familial adenomatous polyposis (aFAP), and MYH associated polyposis (MAP), and those not associated with colonic polyposis - hereditary nonpolyposis colon cancer (HNPCC). The hereditary polyposes are usually easier to diagnose than HNPCC, but their higher penetrance and variable phenotype pose some difficult problems in management and surveillance. The timing and type of surgical intervention, the management of desmoid risk, the treatment of rectal or pouch neoplasia, and the management of duodenal neoplasia are all questions that must be addressed in patients with FAP or MAP.

Promoter hypermethylation of BRCA1 correlates with absence of expression in hereditary breast cancer tumors

Germline mutations in BRCA1 account for a low proportion of hereditary cases in diverse populations. Several efforts have been made to find new genes involved in the inheritance of breast cancer with no success until today. The participation of BRCA1 in the development of breast cancer has been proposed in several studies where hypermethylation of its promoter and a decrease in expression has been reported for sporadic cases and one study on familial cases. To explore the participation of BRCA1 in hereditary carcinogenesis through a different mechanism than the inheritance of germline mutations, we studied the methylation status of its promoter in breast tumors, from patients previously screened for BRCA1/BRCA2 germline mutations. We also determined the presence of the BRCA1 protein in these tumors and correlated both events with tumor grade, hormone receptors and ERBB2 presence. Promoter hypermethylation of the BRCA1 gene was detected in 51% of our biopsies, among which 67% did not express the respective protein. This result leads us to suggest that hypermethylation could be considered as an inactivating mechanism for BRCA1 expression, either as a first or second hit. Moreover, a number of biopsies with absence of expression on BRCA1 showed negative detection of estrogen and progesterone receptors, a similar phenotype to BRCA1 mutated breast tumors.

Constitutive deficiency in DNA mismatch repair: is it time for Lynch III?

Hereditary non-polyposis colorectal cancer (HNPCC), also known as Lynch syndrome types I and II, and the related subtypes Turcot and Muir-Torre syndrome, have all been associated with inheritance of germ line mutations in the DNA mismatch repair (MMR) genes. Fifty individuals have recently been identified with an early onset of a different spectrum of cancers associated with inheritance of two MMR mutations--resulting either in a constitutive loss of MMR function, or greatly impaired MMR function. In contrast to Lynch I and II individuals, individuals with inheritance of homozygous or compound heterozygous mutations in the MMR genes that result in a complete lack of protein, present with hematological and brain malignancies in the first decade of life. Biallelic mutations with compromised but residual protein function present with a broader spectrum of cancers (brain, hematological or gastrointestinal) in the second to fourth decades of life. We propose that inheritance of two MMR mutations in an individual and the unique tumor spectrum that occurs with an early onset should be defined separately from Lynch syndrome I and II, or the subtypes Turcot and Muir-Torre. We suggest Lynch III as an appropriate name for identifying individuals with constitutively compromised MMR associated with biallelic mutations.

Function and Malfunction of Hematopoietic Stem Cells in Primary Bone Marrow Failure Syndromes

Hematopoietic stem cells (HSCs) are responsible for the production of mature blood cells in bone marrow; peripheral pancytopenia is a common clinical presentation resulting from several different conditions, including hematological or extra-hematological diseases (mostly cancers) affecting the marrow function, as well as primary failure of hematopoiesis. Primary bone marrow failure syndromes are a heterogeneous group of diseases with specific pathogenic mechanisms, which share a profound impairment of the hematopoietic stem cell pool resulting in global or selective marrow aplasia. Constitutional marrow failure syndromes are conditions caused by intrinsic defects of HSCs; they are due to inherited germline mutations accounting for specific phenotypes, and often involve also organs and systems other than hematopoiesis. By contrast, in acquired marrow failure syndromes hematopoietic stem cells are thought to be intrinsically normal, but subjected to an extrinsic damage affecting their hematopoietic function. Direct toxicity by chemicals or radiation, as well as association with viruses and other infectious agents, can be sometimes demonstrated. In idiopathic Aplastic Anemia (AA) immunological mechanisms play a pivotal role in damaging the hematopoietic compartment, resulting in a depletion of the hematopoietic stem cell pool. Clinical and experimental evidences support the presence of a T cell-mediated immune attack, as confirmed by clonally expanded lymphocytes, even if the target antigens are still undefined. However, this simple model has to be integrated with recent data showing that, even in presence of an extrinsic damage, preexisting mutations or polymorphisms of genes may constitute a genetic propensity to develop marrow failure. Other recent data suggest that similar antigen-driven immune mechanisms may be involved in marrow failure associated with lymphoproliferative or autoimmune disorders characterized by clonal expansion of T lymphocytes, such as Large Granular Lymphocyte leukemia. In this wide spectrum, a unique and intriguing condition is Paroxysmal Nocturnal Hemoglobinuria (PNH); even in presence of a somatic mutation of the PIG-A gene carried by one or more HSCs and their progeny, the typical marrow failure in PNH is likely due to pathogenic mechanisms similar to those involved in AA, and not to the intrinsic abnormality conferred to the clonal population by the PIG-A mutation. The study of hematopoietic stem cell function in marrow failure syndromes provides hints for specific molecular pathways disturbed in many diseases of hematopoietic and non-hematopoietic stem cells. Beyond the specific interest of investigators involved in the field of these rare diseases, marrow failure syndromes represent a model that provides intriguing insight into quantity and function of normal hematopoietic stem cells, improving our knowledge on stem cell biology.

Cellular functions of the BRCA tumour-suppressor proteins

Inherited germline mutations in either BRCA1 or BRCA2 confer a significant lifetime risk of developing breast or ovarian cancer. Defining how these two genes function at the cellular level is essential for understanding their role in tumour suppression. Although BRCA1 and BRCA2 were independently cloned over 10 years ago, it is only in the last few years that significant progress has been made towards understanding their function in cells. It is now widely accepted that both genes play critical roles in the maintenance of genome stability. Evidence implicates BRCA2 as an integral component of the homologous recombination machinery, whereas BRCA1 is an E3 ubiquitin ligase that has an impact on DNA repair, transcriptional regulation, cell-cycle progression and meiotic sex chromosome inactivation. In this article, I will review the most recent advances and provide a perspective of potential future directions in this field.

A de novo MLH1 germ line mutation in a 31‐year‐old colorectal cancer patient

Hereditary nonpolyposis colorectal cancer is an autosomal dominant cancer predisposition syndrome caused by inherited germ line mutations in DNA mismatch repair genes, predominantly MSH2 and MLH1. Here we report the first proven de novo germ line mutation in MLH1 (c.666dupA) identified in a 31-year-old colorectal cancer patient with the alteration being present in a heterozygous state in all three germ layers and homozygously in his colon cancer. The mutation was absent in both biological parents and all sibs available. Despite extensive polymorphic marker analysis, the parental origin of c.666dupA could not be conclusively determined, representing either a single mutational event in a parental germ cell or (maternal) gonadal mosaicism. Although rare, consequential application of the Bethesda guidelines for genetic testing should allow the clinician to readily identify colorectal cancer patients below age 50 years who carry de novo mismatch repair gene mutations.

Screening for Early Pancreatic Neoplasia in High-Risk Individuals: A Prospective Controlled Study

Individuals with a strong family history of pancreatic cancer and persons with Peutz-Jeghers syndrome (PJS) have an increased risk for pancreatic cancer. This study screened for early pancreatic neoplasia and compared the pancreatic abnormalities in high-risk individuals and control subjects. High-risk individuals with PJS or a strong family history of pancreatic cancer were prospectively evaluated with baseline and 12-month computed tomography (CT) scan and endoscopic ultrasonography (EUS). If EUS was abnormal, EUS-fine-needle aspiration and endoscopic retrograde cholangiopancreatography (ERCP) were performed. Surgery was offered to patients with potentially neoplastic lesions. Radiologic findings and pathologic diagnoses were compared. Patients undergoing EUS and/or ERCP for benign non-pancreatic indications were concurrently enrolled as control subjects. Seventy-eight high-risk patients (72 from familial pancreatic cancer kindreds, 6 PJS) and 149 control patients were studied. To date, 8 patients with pancreatic neoplasia have been confirmed by surgery or fine-needle aspiration (10% yield of screening); 6 patients had 8 benign intraductal papillary mucinous neoplasms (IPMNs), 1 had an IPMN that progressed to invasive ductal adenocarcinoma, and 1 had pancreatic intraepithelial neoplasia. EUS and CT also diagnosed 3 patients with 5 extrapancreatic neoplasms. At EUS and ERCP abnormalities suggestive of chronic pancreatitis were more common in high-risk patients than in control subjects. Screening EUS and CT diagnosed significant asymptomatic pancreatic and extrapancreatic neoplasms in high-risk individuals. IPMN should be considered a part of the phenotype of familial pancreatic cancer. Abnormalities suggestive of chronic pancreatitis are identified more commonly at EUS and ERCP in high-risk individuals.

BRCA1 Promoter Methylation in Sporadic Breast Cancer Is Associated with Reduced BRCA1 Copy Number and Chromosome 17 Aneusomy

To explore the molecular mechanisms for the similarities between inherited and noninherited forms of breast cancer, we tested the hypothesis that inactivation of BRCA1 by promoter hypermethylation is associated with reduced gene copy number and chromosome 17 aneusomy as observed in tumors from BRCA1 mutation carriers. Using a combination of methylation-specific PCR analysis and fluorescence in situ hybridization, we observed varying degrees of promoter methylation in 39 of 131 (29.8%) primary tumors. Despite significant tumor heterogeneity, mean copy numbers of BRCA1 and CEP17 per cell were lower in methylated cases compared with unmethylated cases [1.78 versus 2.30 (P = 0.001) and 1.85 versus 2.29 (P = 0.005), respectively]. Methylation was more frequently observed in younger women (P = 0.05) with high-grade (P = 0.001), estrogen receptor-negative (P = 0.04), and progesterone receptor-negative (P = 0.01) tumors. Moreover, methylation was associated with reduced or absent BRCA1 transcripts, which was reversible in the heavily BRCA1-methylated cell line UACC3199 following treatment with 5-aza-2'-deoxycytidine and trichostatin A. We identified five CpGs at positions -533, -355, -173, -21, and +44 as critical in the reexpression of BRCA1. We conclude that BRCA1 methylation contributes to a subset of sporadic breast cancers with the resulting molecular and clinicopathologic phenotype similar to that of hereditary BRCA1-associated breast cancers. Our data support a model of carcinogenesis in which BRCA1 promoter methylation may serve as a "first hit," much like an inherited germ line mutation, and promote tumor progression down a restricted set of molecular pathways.

Mortality rate of adrenocortical tumors in children under 15 years of age in Curitiba, Brazil

Several reports refer to an increased frequency of adrenal cortex tumors (ACT) among children in Southern Brazil, yet all data have been derived from hospital-based registries. An inherited germline mutation in the p53 gene (TP53 R337H) is detected in virtually all children with ACT in this region and accounts for the excess cases observed. We reviewed all death certificates that mentioned ACT or adrenal neuroblastoma (NB) and which were reported to the Paraná State Department of Health between 1998 and 2003, for individuals younger than 15 years who resided in the Curitiba metropolitan region. Eight deaths from ACT and ten from NB were identified. The age-standardized mortality rate per million children <15 years of age in the Curitiba metropolitan region during the years 1998-2003 was 1.6 (95% confidence interval (CI) 1.4, 1.8) for ACT and 2.3 (95% CI 2.0, 2.5) for NB. The ratio of the adrenal NB and ACT age-adjusted mortality rates was 1.43. The incidence of ACT estimated from the mortality data, assuming an ACT survival rate of 0.542, was 3.5 (95% CI 2.9, 4.2). Our investigation of population-based mortality confirms the evidence from hospital-based registries of a clustering of ACT in Southern Brazil. In addition, our data suggest that the incidence of ACT in this region is about 12-18 times the incidence reported in the United States and Europe.

Inherited colorectal cancer syndromes.

Colorectal cancer is one of the major causes of cancer deaths in both men and women. It is estimated that approximately 5% to 10% of patients with colorectal cancer have an inherited germline mutation that predisposes them to cancer. Clinically, hereditary colorectal cancer syndromes can be divided into those associated with colonic polyposis (familial adenomatous polyposis, attenuated familial adenomatous polyposis, and MYH-associated polyposis) and those not associated with colonic polyposis (hereditary nonpolyposis colon cancer). Treatment options for these patients include multiple aggressive screening regimens, chemopreventive medications, and prophylactic surgery. Selection of the appropriate management approach is best made using information obtained from the patient's clinical examination, the family medical history, and genetic evaluation. Compliance is improved when patients completely understand their disease and participate fully in the formulation of the treatment plan. Although not proved, it seems reasonable that this approach may prevent the poor outcomes so frequently associated with inherited cancer syndromes.

Genetic Mapping of a Third Li-Fraumeni Syndrome Predisposition Locus to Human Chromosome 1q23

Li-Fraumeni syndrome (LFS) is a clinically and genetically heterogeneous inherited cancer syndrome. Most cases ( approximately 70%) identified and characterized to date are associated with dominantly inherited germ line mutations in the tumor suppressor gene TP53 (p53) in chromosome 17p13.1. In a subset of non-p53 patients with LFS, CHEK2 in chromosome 22q11 has been identified as another predisposing locus. Studying a series of non-p53 LFS kindred, we have shown that there is additional genetic heterogeneity in LFS kindred with inherited predisposition at loci other than p53 or CHEK2. Using a genome-wide scan for linkage with complementing parametric and nonparametric analysis methods, we identified linkage to a region of approximately 4 cM in chromosome 1q23, a genomic region not previously implicated in this disease. Identification ofa third predisposing gene and its underlying mutation(s) should provide insight into other genetic events that predispose to the genesis of the diverse tumor types associated with LFS and its variants.

Epidemiology and prevention of pancreatic cancer.

Pancreatic cancer is an uncommon tumor, but because the mortality rate approaches 100%, this form of cancer has now become a common cause of cancer mortality. In the United States it is the fourth most frequent cause of cancer mortality; in Japan it ranks as the fifth commonest cause of death from cancer. Smoking is the major known risk factor for pancreatic cancer, accounting for approximately 25-30% of all cases. Some of the time-dependent changes in the frequency of pancreatic cancer can be explained by smoking trends. Aggressive public health measures to control smoking would substantially reduce the burden of pancreatic cancer. Dietary factors are less important for pancreatic cancer than for other digestive tract tumors, but consumption of a diet with adequate quantities of fruits and vegetables, plus control of calories either by dietary measures or by exercise will help to prevent this lethal tumor. There are more than a dozen inherited germline mutations that increase the risk of pancreatic cancer. Of these, hereditary pancreatitis confers the greatest risk, while BRCA2 mutations are the commonest inherited disorder. In addition to germline defects, there are several common polymorphisms in genes that control detoxification of environmental carcinogens that may alter the risk of pancreatic cancer. More research will be needed in this area, to explain and to clarify the interaction between genes and environmental factors.

Spontaneous Immortalization of Clinically Normal Colon-Derived Fibroblasts from a Familial Adenomatous Polyposis Patient

Normal human diploid cells do not spontaneously immortalize in culture, but instead enter replicative senescence after a finite number of population doublings. Ablation of key checkpoint arrest or cancersuppressor genes, through dominantly inherited germline mutation (p53+/-, Li-Fraumeni) or viral oncogene expression (SV40 large T, HPV16/18, E6/E7) can lead to escape from senescence, additional doublings, entrance into crisis phase, where immortal clones emerge at low frequency. In the vast majority of cases, telomerase is reactivated and telomeres are stabilized. Here we describe the spontaneous immortalization of clinically normal fibroblasts derived from colonic stroma of a familial adenomatous polyposis (FAP) patient. The preimmortal (C26C) and the spontaneously immortalized derivative (C26Ci) cells are heterozygous for a characterized germline mutation in exon 15 of the adenomatous polyposis coli gene. Immortalization was accompanied by spontaneous reactivation of endogenous telomerase and establishment of telomeres at presenescent lengths. Normal checkpoint behavior is retained and a diploid karyotype is maintained. These cells provide a valuable new addition to the limited number of spontaneously immortalized human cell types, particularly fibroblast cells, will be useful in experimentally determining the functional pathways in neoplastic development and in the identification of potential molecular targets for cancer chemoprevention.

Spontaneous immortalization of clinically normal colon-derived fibroblasts from a familial adenomatous polyposis patient.

Normal human diploid cells do not spontaneously immortalize in culture, but instead enter replicative senescence after a finite number of population doublings. Ablation of key checkpoint arrest or cancer-suppressor genes, through dominantly inherited germline mutation (p53+/-, Li-Fraumeni) or viral oncogene expression (SV40 large T, HPV16/18, and E6/E7) can lead to escape from senescence, additional doublings, and entrance into crisis phase, where immortal clones emerge at low frequency. In the vast majority of cases, telomerase is reactivated and telomeres are stabilized. Here we describe the spontaneous immortalization of clinically normal fibroblasts derived from colonic stroma of a familial adenomatous polyposis (FAP) patient. The preimmortal (C26C) and the spontaneously immortalized derivative (C26Ci) cells are heterozygous for a characterized germline mutation in exon 15 of the adenomatous polyposis coli gene. Immortalization was accompanied by spontaneous reactivation of endogenous telomerase and establishment of telomeres at presenescent lengths. Normal checkpoint behavior is retained and a diploid karyotype is maintained. These cells provide a valuable new addition to the limited number of spontaneously immortalized human cell types, particularly fibroblast cells, and will be useful in experimentally determining the functional pathways in neoplastic development and in the identification of potential molecular targets for cancer chemoprevention.

Polycythemia and oxygen sensing

Polycythemias can be differentiated based on the responsiveness of erythroid progenitors to circulating cytokines. Primary polycythemias are characterized by an augmented response due to acquired somatic or inherited germ-line mutations that are expressed within hematopoietic progenitors causing increased proliferation or decreased apoptosis and resulting in accumulation of red blood cells. In terms of oxygen requirements, primary polycythemias can be viewed as the production of hemoglobin fully dissociated from the tissue oxygen needs and from the oxygen sensing pathway. Polycythemia vera (PV) is the most common primary polycythemia. PV bone marrow progenitors cells can form erythroid colonies in the absence of exogenous erythropoietin in vitro. These endogenous erythroid colonies (EEC) are useful in differentiating PV and secondary polycythemias. They also can differentiate PV where this feature is independent of Epo signalling from primary familial and congenital polycythemia. In this autosomal dominant primary polycythemia, at variance with PV, EEC formation is abolished by anti-Epo and anti-Epo receptor neutralising antibodies. Mutations of the EPOR have been described and resulted in nine cases in truncated EPORs lacking the cytoplasmic carboxy-terminal of the receptor which possesses a negative growth regulatory domain. However, recent data suggest that different mutations may cause PFCP in most cases. Secondary polycythemia can be viewed as either physiological response to satisfy the oxygen needs of the tissues, resulting for instance from high affinity hemoglobins or BPG mutase deficiency, or as the result of germ-line or somatic mutations disturbing the oxygen sensing pathway or its target: Epo. Chuvash polycythemia is a frequently symptomatic disorder with an autosomal recessive inheritance and inappropriately high Epo levels. The erythroid progenitors are hypersensitive to Epo linking this condition to both primary and secondary polycythemia. A germline missense mutation at nucleotide 598 in both alleles of the von Hippel–Lindau gene results in increased hypoxia inducible factor-1 (HIF-1) expression in normoxic conditions. HIF-1 controls the expression of many genes including Epo. Identifying causal defects in other situations like post-renal transplant erythrocytosis and cases of autosomal dominant polycythemia with high Epo levels will help further understanding of the regulation of erythropoiesis.

PKD1 intron 21: triplex DNA formation and effect on replication.

Although autosomal dominant polycystic kidney disease is transmitted in an autosomal dominant fashion, there is evidence that the pathophysiology of cystogenesis involves a second hit somatic mutation superimposed upon the inherited germline mutation within the renal tubule cells. The polypurine.polypyrimidine (Pu.Py) tract of PKD1 intron 21 may play a role in promoting somatic mutations. To better characterize this tract and to evaluate its potential to participate in mutagenesis, we investigated the thermodynamics of intramolecular triplex formation by 15 Pu.Py mirror repeat tracts from PKD1 intron 21 by 2D gel electrophoresis. We demonstrate that intramolecular triplexes form with modest superhelical tensions for all the tracts examined. Primer extension studies demonstrated significant polymerase arrest within the Pu.Py tracts in one direction of replication only. We found correlation between polymerization arrest and both the potential length of the triplex and superhelical tension of intramolecular triplex formation. The presence of a Pu.Py tract also led to a replication blockade and double-strand breakage using an SV40 in vitro replication assay with HeLa cell extracts. During DNA replication, the G-rich template of the PKD1 Pu.Py tracts may form a triplex structure with the nascent strand, thereby blocking replication and potentially leading to recombination and mutation.