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PubMed2003

Reprogramming of primordial germ cells begins before migration into the genital ridge, making these cells inadequate donors for reproductive cloning.

Germ cells undergo epigenetic modifications as they develop, which suggests that they may be ideal donors for nuclear transfer (cloning). In this study, nuclei from confirmed embryonic germ cells were used as donors to determine whether they are competent for cloning and at which stage they are most competent. Embryos cloned from migrating 10.5-days-postcoitum (dpc) primordial germ cells (PGCs) showed normal morphological development to midgestation but died shortly thereafter. In contrast, embryos cloned from later-stage germ cells were developmentally delayed at midgestation. Thus, donor germ cell age inversely correlated with the developmental stage attained by cloned embryos. The methylation status of the H19- and Snrpn-imprinting control regions in germ cell clones paralleled that of the donors, and revealed that demethylation, or erasure of imprints, was already initiated in PGCs at 10.5 dpc and was complete by 13.5 dpc. Similarly, clones derived from male 15.5-dpc germ cells showed increased methylation correlating with the initiation of de novo methylation that resets imprints at this stage, and clones from neonatal germ cells showed nearly complete methylation in the H19 imprinting control region. These results indicate that the epigenetic state of the donor nucleus is retained in cloned embryos, and that germ cells are therefore inadequate nuclear donors for cloning because they are either erasing or resetting epigenetic patterns.

Animals↗

PubMed1999

DNA methylation changes and multiple myeloma.

In contrast to classical mutations, DNA methylation is a mechanism of changing the base sequence without altering the coding function of a gene. The interplay between this epigenetic modification and classical mutations plays an important role in tumorigenesis. Global genomic hypomethylation has been associated with the induction of chromosomal instability, which is commonly seen in solid tumors and multiple myeloma. De novo methylation of CpG islands on the promoter region may contribute to the progressive inactivation of growth-inhibitory genes resulting in the clonal selection of cells with growth advantage. Recently, alteration of p16 and p15 solely by hypermethylation has been detected in high frequencies hitherto unreported in multiple myeloma (MM). Hypermethylation of p16 has been shown to be associated with plasmablastic disease (p=0.026) in primary MM and transcriptional silencing of p16 and p15 has also been found to correlate with hypermethylation of these genes in MM-derived cell lines. Our results in studies with cell lines and primary MM support the fact that hypermethylation of p16 and p15 plays an important role in MM tumorigenesis. Because of its high frequency, the presence of hypermethylation of p16 may prove to be a useful tumor marker for the majority of MM patients. Promoters silenced by methylation can be reactivated by treatment with the demethylating agent 5-aza-2'deoxycytidine. The reversibility of this epigenetic inactivation of the p16 and p15 genes in MM may also provide a broad clinical application in the development of new therapeutic interventions in this uniformly fatal form of cancer.

Carrier Proteins↗

PubMed2005

DNA methylation and cancer therapy: new developments and expectations.

PURPOSE OF REVIEW: In addition to having genetic causes, cancer can also be considered an epigenetic disease. The main epigenetic modification is DNA methylation, and patterns of aberrant DNA methylation are now recognized to be a common hallmark of human tumors. One of the most characteristic features is the inactivation of tumor-suppressor genes by CpG-island hypermethylation of the CpG islands located in their promoter regions. These sites, among others, are the targets of DNA-demethylating agents, the promising chemotherapeutic drugs that are the focus of this article. RECENT FINDINGS: Four exciting aspects have recently arisen at the forefront of the advancements in this field: first, the development of new compounds with DNA-demethylating capacity that are less toxic (for example, procaine) and may be administered orally (for example, zebularine); second, a better knowledge of the molecular mechanisms underlying the action of these drugs for particular genes and throughout the genome; third, the establishment of more reliable techniques to measure the effects of these drugs in clinical samples, such as high-performance capillary electrophoresis; and fourth, a decisive effort in the clinical trials that has merited the approval of 5-azacytidine by the U.S. Food and Drug Administration for the treatment of myelodysplastic syndrome. SUMMARY: We are at the dawn of an era when epigenetic drugs will be an important weapon in our arsenal in the war against cancer. Hematological malignancies have provided a promising starting point, but studies will surely extend to all solid tumors. However, we need to continue our research to develop more specific DNA-demethylating agents, to understand their biologic effects, and to determine whether they may be successfully combined with other epigenetic drugs, such as the inhibitors of histone deacetylases, and classic chemotherapy compounds.

Antineoplastic Agents↗

PubMed2006

Rejuvenation by shoot apex culture recapitulates the developmental increase of methylation at the maize gene Pl-Blotched.

Cytosine methylation provides an attractive epigenetic modification for the global maintenance of phases in plant development; however, there are few known examples of specific genes whose methylation status changes in a developmentally regulated manner. Pl-Blotched, an allele of purple plant1 (pl1), which encodes a myb-like transcription factor that regulates anthocyanin production in maize, is one such gene: certain cytosines at the 3' end of this allele are hypomethylated in seedlings, become hypermethylated in organs formed in the adult phase, and are hypomethylated again in the next generation. We tested whether this developmental pattern of low juvenile cytosine methylation followed by higher methylation in adult tissues could also be observed in plants "rejuvenated" via shoot apex culture. We found that cytosine methylation patterns at Pl-Blotched were indeed recapitulated in culture-rejuvenated plants, showing hypomethylation in leaves with juvenile patterns of differentiation (even though they were made by an old meristem) followed by hypermethylation in later-formed leaves. Our results show that methylation status at that locus is determined by the developmental phase of the shoot, rather than by the age of the meristem forming it. These results support the hypothesis that DNA methylation is employed by the plant to maintain an epigenetic state.

Cytosine↗

PubMed1998

Epigenetic reprogramming of the human H19 gene in mouse embryonic cells does not erase the primary parental imprint.

BACKGROUND: Genomic imprinting in mammals is thought to result from epigenetic modifications to chromosomes during gametogenesis, which leads to differential allelic expression during development. There is a requirement for an appropriate experimental system to enable the analysis of the mechanisms of genomic imprinting during embryogenesis. RESULTS: To develop a novel in vitro system for studying the molecular basis of genomic imprinting, we constructed mouse cell lines containing either a paternal or maternal human chromosome 11, by microcell-mediated chromosome transfer. Allele-specific expression and DNA methylation studies revealed that the imprinting status of the human H19 gene was maintained in mouse A9 mono-chromosomal hybrids. Each parental human chromosome was introduced independently into mouse near-diploid immortal fibroblasts (m5S) and two embryonal carcinoma (EC) cell lines (OTF9-63 and P19). The paternal allele of human H19 remained in a repressed state in m5S cells, but was de-repressed in both EC cells. The paternal H19 allele was demethylated extensively in OTF9-63 cells, whereas the only alteration in P19 hybrids was de novo methylation on both alleles in the 3' region. Following in vitro differentiation, the expressed paternal H19 allele was selectively repressed in differentiated derivatives of EC hybrids. CONCLUSION: These results indicated that human imprint marks could function effectively in mouse cells, and that the imprinting process was epigenetically reprogrammed in embryonal carcinoma cells, without erasure of the primary imprint that marked the parental origin. Therefore, these mono-chromosomal hybrids could provide a valuable in vitro system to study the mechanisms involved in the regulation of imprinted gene expression.

Animals↗

PubMed2001

The use of amplified cDNA to investigate the expression of seven imprinted genes in human oocytes and preimplantation embryos.

Imprinted genes are characterized by expression of only one of the two alleles according to its inheritance from the mother or the father. This mono-allelic expression must arise from primary differential epigenetic modification of the parental alleles of the imprinted gene in the spermatozoon and the oocyte. Most of the information on the onset of imprinted gene expression, and on the molecular mechanisms regulating mono-allelic expression, have been derived from studies in the mouse. In this paper, we investigate the expression of seven imprinted genes in human preimplantation development. Due to limitations imposed by the rarity of human embryos available for research, our approach has been to screen amplified cDNA preparations prepared from human unfertilized oocytes and individual embryos at each of the 4-cell, 8-cell and blastocyst stages. Gene-specific primers were used to investigate expression of the imprinted genes by polymerase chain reaction (PCR) analysis of these amplified cDNA. We found that expression is inherently variable in the amplified cDNA from embryo to embryo but the use of several samples at each stage showed that the SNRPN, UBE3A and PEG1 genes are expressed throughout human preimplantation development. This was confirmed by direct analysis by gene-specific reverse transcription-PCR on a limited number of lysed embryos (one gene analysed per embryo). Thus, the amplified cDNA may be used to rapidly identify those imprinted genes expressed in preimplantation development and, hence, those genes amenable to investigation of the epigenetic mechanisms regulating mono-allelic expression. Confirmation of preimplantation expression also identifies those imprinted diseases amenable to preimplantation diagnosis, and the imprinted genes which may be used in assessment of possible perturbations of imprinting following new procedures in assisted reproduction. Our series of single embryo amplified cDNA are established as a valuable resource for comparative studies of gene expression within one embryo and between embryos throughout early human development. The amplified cDNA thus circumvent the need for a continuous supply of human embryos for studies on embryonic gene expression.

DNA, Complementary↗

PubMed1997

Methylation of an ETS site in the intron enhancer of the keratin 18 gene participates in tissue-specific repression.

The activities of ETS transcription factors are modulated by posttranscriptional modifications and cooperation with other proteins. Another factor which could alter the regulation of genes by ETS transcription factors is DNA methylation of their cognate binding sites. The optimal activity of the keratin 18 (K18) gene is dependent upon an ETS binding site within an enhancer region located in the first intron. The methylation of the ETS binding site was correlated with the repression of the K18 gene in normal human tissues and in K18 transgenic mouse tissues. Neither recombinant ETS2 nor endogenous spleen ETS binding activities bound the methylated site effectively. Increased expression of the K18 gene in spleens of transgenic mice by use of an alternative, cryptic promoter 700 bp upstream of the enhancer resulted in modestly decreased methylation of the K18 ETS site and increased RNA expression. Expression in transgenic mice of a mutant K18 gene, which was still capable of activation by ETS factors but was no longer a substrate for DNA methylation of the ETS site, was fivefold higher in spleen and heart. However, expression in other organs such as liver and intestine was similar to that of the wild-type gene. This result suggests that DNA methylation of the K18 ETS site may be functionally important in the tissue-specific repression of the K18 gene. Epigenetic modification of the binding sites for some ETS transcription factors may result in a refractory transcriptional response even in the presence of necessary trans-acting activities.

Animals↗

PubMed2006

Epigenetic inactivation of tumor suppressor genes in serum of patients with cutaneous melanoma.

Small amounts of cell-free DNA circulate in both healthy and diseased human blood, while increased concentrations of DNA are present in the serum of cancer patients. Tumor-specific mutations or epigenetic modifications have predominantly been detected in tissue specimens. The purpose of this study was to investigate methylation of five different genes involved in tumor suppression and DNA repair (suppressors of cytokine signaling 1 and 2 (SOCS1, SOCS2)), Ras-association domain family protein 1A (RASSF1a), D-type p16(INK4a) cyclin-dependent kinase inhibitor (CDKN), and O6-methylguanine DNA-methyltransferase (MGMT)) in the serum of 100 patients using methylation-specific PCR. In all, 41 melanoma patients (stage I = 18; stage II = 10; stage III/IV = 13), 13 healthy controls without nevi, and 10 individuals with more than 15 nevi of >5 mm in size were investigated. For comparison, sera from patients with other skin tumors (nine basal cell cancers, five Kaposi's sarcoma), different metastasized cancers (five breast cancers, five colon cancers), and several chronic inflammatory diseases (n = 12) were also analyzed. In addition, we examined if methylation was involved in silencing transcription of these genes in 12 melanoma specimens. SOCS1, SOCS2, RASSF1a, CDKN2a, and MGMT were methylated in 75, 43, 64, 75, and 64% of melanoma samples, respectively. Of the 41 melanoma patients, 83% had one hypermethylated gene, while 66, 51, and 41% had two, three, or four hypermethylated genes, respectively. Also, 20% of these patients showed hypermethylation for all genes, while only 17% showed no methylation. Importantly, the methylation profile of the selected genes from melanoma patients was distinct from the other analyzed tumors. Transcription of SOCS1, SOCS2, CDKN2a, and RASSF1a genes was significantly reduced in fresh melanoma samples, while MGMT showed a 12-fold upregulation at the messenger ribonucleic acid level (P < 0.001). Our findings suggest that epigenetic silencing of the studied tumor suppressor genes is a common and probably important mechanism for melanoma formation. This convenient method using a simple blood sample may contribute to classification of melanoma and awaits clinical validation.

Adult↗

PubMed2004

Regulation of histone H3 lysine 9 methylation in oocytes and early pre-implantation embryos.

Epigenetic modifications of the genome, such as covalent modification of histone residues, ensure appropriate gene activation during pre-implantation development, and are probably involved in the asymmetric reprogramming of the parental genomes after fertilization. We investigated the methylation patterns of histone H3 at lysine 9 (H3/K9), and the regulatory mechanism involved in the asymmetric remodeling of parental genomes during early preimplantation development in mice. Immunocytochemistry with an antibody that specifically recognizes methylated H3/K9 showed a very weak or absent methylation signal in the male pronucleus, whereas a distinct methylation signal was detected in the female pronucleus. This asymmetric H3/K9 methylation pattern in the different parental genomes persisted until the two-cell stage. However, de novo methylation of H3/K9 occurred and the asymmetry was lost during the four-cell stage. The unmethylated male pronucleus underwent de novo methylation when it was transferred into enucleated GV- or MII-stage oocytes, which suggests that histone H3 methylase is active before fertilization, but not afterwards, and that the asymmetric methylation pattern is generated by this change in methylase activity in the cytoplasm after fertilization. Thus, histone H3 is methylated only in the maternal chromosomes, which are present in the oocytes before fertilization, and is not methylated in the paternal chromosomes, which are absent. The maintenance of asymmetric H3/K9 methylation patterns in early embryos is an active process that depends on protein synthesis and zygotic transcription, as de novo methylation in the male pronucleus occurred when either protein synthesis or gene expression was inhibited by cycloheximide or alpha-amanitin, respectively. In addition, corresponding de novo methylation of H3/K9 and DNA occurred when the male pronucleus was transferred to an enucleated GV oocyte. Our results suggest that H3/K9 methylation is an epigenetic marker of parental genome origin during early preimplantation development.

Animals↗

PubMed1998

Genetic and epigenetic alterations of the cyclin-dependent kinase inhibitors p15INK4b and p16INK4a in human thyroid carcinoma cell lines and primary thyroid carcinomas.

BACKGROUND: D-type cyclins, in association with the cyclin-dependent kinases CDK4 and CDK6, promote progression through the G1 phase of the cell cycle. CDK activity is modulated by inhibitors such as p15INK4b and p16INK4a. Loss of function of p15INK4b and p16INK4a (multiple tumor suppressor-I and CDK4 inhibitor) determines impairment in the control of the cell cycle and contributes to the transformation of several cell types. METHODS: The authors examined 20 thyroid neoplasms (12 papillary carcinomas and 8 follicular adenomas) and 4 human thyroid carcinoma cell lines for gene mutations and epigenetic modifications of the p15INK4b and p16INK4a genes by Southern blot analysis, single strand conformation polymorphism, and a polymerase chain reaction-based methylation assay. RESULTS: Abnormalities of p16 were found in the four cell lines studied. In follicular carcinoma (WRO) cells, both the p15 and p16 genes were homozygously deleted. Undifferentiated carcinoma (FRO) cells had a nonsense point mutation at codon 72 (CGA-TGA, Arg-Stop) of p16, whereas the poorly differentiated papillary carcinoma (NPA) line harbored a point mutation at the exon 1-intron 1 boundary that altered the donor splicing site and caused an aberrantly spliced form of p16INK4a. Furthermore, p16 allelic loss was evident in the DNA of both FRO and NPA cells. Finally, p16 expression was absent in the ARO cell line, likely due to a de novo methylation of exon 1 of p16INK4a. Regarding the primary thyroid tumors, a missense point mutation at codon 91 was found in 1 of 12 papillary thyroid carcinomas (GCC-GTC, Ala-Val). No mutations were found in follicular adenomas. However, in 6 of 20 primary tumors there was hypermethylation at exon 1 of p16. CONCLUSIONS: The high prevalence of p15 and p16 mutations in the cell lines described suggests involvement of these genes in immortalization in vitro. The p16 defects may have preexisted in a small subclone of the primary tumor that were selected for in vitro. Alternatively, p16 mutations may have arisen de novo during cell culture. Mutations of p15INK4b and p16INK4a do not appear to be critical events in the development of follicular adenomas or papillary carcinomas. However, de novo methylation of the 5' CpG island of p16 is common in primary tumors, indicating that the function of this gene may be lost as an epigenetic event during disease progression.

Adenoma↗

PubMed2025

DNA methylation and machine learning: challenges and perspective toward enhanced clinical diagnostics.

DNA methylation is an epigenetic modification that regulates gene expression by adding methyl groups to DNA, affecting cellular function and disease development. Machine learning, a subset of artificial intelligence, analyzes large datasets to identify patterns and make predictions. Over the past two decades, advances in bioinformatics technologies for arrays and sequencing have generated vast amounts of data, leading to the widespread adoption of machine learning methods for analyzing complex biological information for medical problems. This review explores recent advancements in DNA methylation studies that leverage emerging machine learning techniques for more precise, comprehensive, and rapid patient diagnostics based on DNA methylation markers. We present a general workflow for researchers, from clinical research questions to result interpretation and monitoring. Additionally, we showcase successful examples in diagnosing cancer, neurodevelopmental disorders, and multifactorial diseases. Some of these studies have led to the development of diagnostic platforms that have entered the global healthcare market, highlighting the promising future of this field.

Humans↗

PubMed2025

Altered mitochondrial DNA methylation in blood in individuals with mild cognitive impairment.

BACKGROUND: Previous studies reported that altered mitochondrial methylation in Alzheimer's disease (AD), however, whether epigenetic modifications in mitochondrial genomes contribute to preclinical AD remains unclear. This study aimed to investigate mitochondrial methylation changes in individuals with cognitive decline. RESEARCH DESIGN AND METHODS: We examined whole mitochondrial genome methylation in 50 individuals with mild cognitive impairment (MCI) and 50 individuals without MCI, using bisulfite amplicon sequencing, assessing methylation at 366 Cytosine-guanine oligodeoxynucleotide (CpG) sites. RESULTS: We found the overall methylation level of mitochondrial DNA (mtDNA) in each subject was relatively low, ranging from 0% to 15%. Global methylation was significantly higher in individuals with cognitive decline compared to controls (3.86% vs. 3.46%, p = 0.037), with 34 differentially methylated CpG sites identified. Methylation differences (MD) between cognitive decline individuals and controls were 22.93 ± 5.60% at chrM6465 (Q = 0.013), 12.55 ± 3.02% at chrM9612 (Q = 0.013), 11.45 ± 3.88% at chrM11762 (Q = 0.159) and 11.03 ± 3.88% at chrM11766 (Q = 0.172), respectively, while the level of MD at chrM15812 was -13.11 ± 4.31% (Q = 0.159) after Benjamini-Hochberg FDR adjusted. Furthermore, Methylation at specific sites were significantly correlated with Mini-Mental State Examination scores, distinguishing individuals with cognitive decline from controls. CONCLUSIONS: Our study provides an mtDNA methylation map and suggests a role for these sites in preclinical AD pathogenesis.

Humans↗

PubMed2024

A methylation risk score for chronic kidney disease: a HyperGEN study.

Chronic kidney disease (CKD) impacts about 1 in 7 adults in the United States, but African Americans (AAs) carry a disproportionately higher burden of disease. Epigenetic modifications, such as DNA methylation at cytosine-phosphate-guanine (CpG) sites, have been linked to kidney function and may have clinical utility in predicting the risk of CKD. Given the dynamic relationship between the epigenome, environment, and disease, AAs may be especially sensitive to environment-driven methylation alterations. Moreover, risk models incorporating CpG methylation have been shown to predict disease across multiple racial groups. In this study, we developed a methylation risk score (MRS) for CKD in cohorts of AAs. We selected nine CpG sites that were previously reported to be associated with estimated glomerular filtration rate (eGFR) in epigenome-wide association studies to construct a MRS in the Hypertension Genetic Epidemiology Network (HyperGEN). In logistic mixed models, the MRS was significantly associated with prevalent CKD and was robust to multiple sensitivity analyses, including CKD risk factors. There was modest replication in validation cohorts. In summary, we demonstrated that an eGFR-based CpG score is an independent predictor of prevalent CKD, suggesting that MRS should be further investigated for clinical utility in evaluating CKD risk and progression.

Humans↗

PubMed2024

Epigenetic footprints: Investigating placental DNA methylation in the context of prenatal exposure to phenols and phthalates.

BACKGROUND: Endocrine disrupting compounds (EDCs) such as phthalates and phenols can affect placental functioning and fetal health, potentially via epigenetic modifications. We investigated the associations between pregnancy exposure to synthetic phenols and phthalates estimated from repeated urine sampling and genome wide placental DNA methylation. METHODS: The study is based on 387 women with placental DNA methylation assessed with Infinium MethylationEPIC arrays and with 7 phenols, 13 phthalates, and two non-phthalate plasticizer metabolites measured in pools of urine samples collected twice during pregnancy. We conducted an exploratory analysis on individual CpGs (EWAS) and differentially methylated regions (DMRs) as well as a candidate analysis focusing on 20 previously identified CpGs. Sex-stratified analyses were also performed. RESULTS: In the exploratory analysis, when both sexes were studied together no association was observed in the EWAS. In the sex-stratified analysis, 114 individual CpGs (68 in males, 46 in females) were differentially methylated, encompassing 74 genes (36 for males and 38 for females). We additionally identified 28 DMRs in the entire cohort, 40 for females and 42 for males. Associations were mostly positive (for DMRs: 93% positive associations in the entire cohort, 60% in the sex-stratified analysis), with the exception of several associations for bisphenols and DINCH metabolites that were negative. Biomarkers associated with most DMRs were parabens, DEHP, and DiNP metabolite concentrations. Some DMRs encompassed imprinted genes including APC (associated with parabens and DiNP metabolites), GNAS (bisphenols), ZIM2;PEG3;MIMT1 (parabens, monoethyl phthalate), and SGCE;PEG10 (parabens, DINCH metabolites). Terms related to adiposity, lipid and glucose metabolism, and cardiovascular function were among the enriched phenotypes associated with differentially methylated CpGs. The candidate analysis identified one CpG mapping to imprinted LGALS8 gene, negatively associated with ethylparaben. CONCLUSIONS: By combining improved exposure assessment and extensive placental epigenome coverage, we identified several novel genes associated with the exposure, possibly in a sex-specific manner.

Humans↗

PubMed1996

Mosaic methylation of Xist gene before chromosome inactivation in undifferentiated female mouse embryonic stem and embryonic germ cells.

Epigenetic modification is implicated in the choice of the X chromosome to be inactivated in the mouse. In order to gain more insight into the nature of such modification, we carried out a series of experiments using undifferentiated mouse cell lines as a model system. Not only the paternally derived X (XP) chromosome, but the maternally derived one (XM) was inactivated in the outer layer of the balloon-like cystic embryoid body probably corresponding to the yolk sac endoderm of the post-implantation embryo in which XP is preferentially inactivated. Hence, it is likely that the imprint responsible for the nonrandom XP inactivation in early mouse development has been erased or masked in female ES cells. CpG sites in the 5' region of the Xist gene were partially methylated in female ES and EG and parthenogenetic ES cell lines as in the female somatic cell in which the silent Xist allele on the active X is fully methylated, whereas the expressed allele on the inactive X is completely unmethylated. In the case of undifferentiated ES cells, however, methylation was not differential between two Xist alleles. This observation was supported by the demonstration that single-cell clones derived from female ES cell lines were not characterized by either allele specific Xist methylation or nonrandom X inactivation upon cell differentiation. Apparently these findings are at variance with the view that Xist expression and X inactivation are controlled by preemptive methylation in undifferentiated ES cells and probably in epiblast.

Alleles↗

PubMed2000

The role of DNA hypermethylation in human neoplasia.

Cancer development and progression is dictated by a series of alterations in genes such as oncogenes, tumor suppressor genes, DNA repair genes, and others. DNA methylation is an epigenetic modification that is profoundly altered in most cancers. Recently, hypermethylation of CpG-rich areas located in the promoter of genes (CpG islands) has been shown to be commonly implicated in silencing tumor suppressor genes in cancer. By cloning and characterizing a large number of such CpG islands hypermethylated in colon cancer, we found that two processes explain most of these events. Age-related CpG island methylation in a subset of cells in normal tissues, followed by intensification of methylation in cancer cells explains the majority of hypermethylation events in colon cancer and may provide a mechanistic link between aging and cancer formation. Most of the other CpG islands methylated in colon cancer can be explained by a newly described phenotype, the CpG island methylator phenotype (CIMP) which results in multiple methylation events in a subset of cancers. CIMP accounts for the majority of sporadic colon cancers characterized by microsatellite instability, as well as most tumors with k-ras mutations. Understanding further the factors that lead to, and modulate, aberrant methylation in cancer may provide novel avenues for prevention and treatment of this disease.

Cell Transformation, Neoplastic↗

PubMed2000

Failure to establish linkage on the X chromosome in 301 families with schizophrenia or schizoaffective disorder.

The hypothesis that a gene for susceptibility to psychosis (specifically in the X-Y homologous class) is located on the sex chromosomes has been proposed. Such a gene would account for the excess of sex chromosome anomalous males and females in populations of patients with psychosis, a tendency towards concordance by sex within families, and sex differences associated with psychosis and its underlying brain pathology. In earlier studies we observed small positive LOD scores in Xp11, and in a more recent and larger cohort of 178 sibling pairs, a peak multipoint nonparametric LOD score of 1. 55 at the locus DXS8032 in Xq21. The present study with a new set of markers extended the cohort to 301 ill sibling pairs and their parents. Despite the increase in sample size, the LOD score did not increase. A peak NPL of 1.55 was observed at the locus DXS1068 in proximal Xp, a region remote from the previous report. Separating families into those who were more likely to have X chromosome inheritance (maternal with no male to male transmission) did not yield stronger findings. In spite of the evidence that psychosis is related to a sex-dependent dimension of cerebral asymmetry, it is concluded that no consistent linkage of schizophrenia to the X chromosome can be demonstrated. In the context of the general failure of replication of linkage in psychosis, the possibility that the genetic predisposition to psychosis is contributed to by epigenetic modification rather than variations in the nucleotide sequence has to be considered.

Chromosome Mapping↗

PubMed2006

Epigenetics and chronic lymphocytic leukemia.

The DNA methylation level in patients with chronic lymphocytic leukemia is generally lower than healthy individuals. Although DNA methylation is globally decreased, regional hypermethylation of gene promoters leads to gene silencing. Many of these genes have tumor suppressor phenotypes. Unlike mutations or deletions, hypermethylation is potentially reversible after inhibition with DNA methylation modulators. Myelodysplastic syndrome has been a model disease in which treatment of patients results in demethylation of specific genes. The story in patients with chronic lymphocytic leukemia is slowly unraveling as epigenetic modifications likely also play an important role. Ongoing clinical trials correlating clinical response to gene expression after treatment with DNA methylation inhibitors will ultimately allow us to better risk stratify and predict the subgroup of patients who will benefit from treatment with this class of drugs.

DNA Methylation↗