Cognitive phenotype and biological mechanisms of Turner syndrome / 中华行为医学与脑科学杂志

Turner syndrome is a disease resulted from the complete or partial loss of an X chromosome, and the typical karyotype is 45, X. Patients with Turner syndrome are susceptible to many medical problems, including short stature, congenital agenesis of ovaries and cognitive function impairment. More specifically, recent studies reported that these patients’ brain structure and brain function are different with normal people, especially in the occipital area, the amygdala, the prefrontal cortex and temporal lobe.And they also show a particular pattern of cognitive impairment(including visuospatial ability, abstract reasoning and excutive function) and social impairment and an increased risk of specific neurodevelopmental disorders. Additionally, haploinsufficiency of escape genes, gonadal steroid deficiency and failure to express parentally imprinted genes may contribute to the differences in brain structure and brain function between these patients and normal people, causing cognitive and social impairment in patients with Turner syndrome. This study reviewed the alterations and biological mechanisms in brain structure, brain function and cognitive profile in patients with Turner syndrome.

Síndrome de Silver-Russell. Aspectos clínicos y etiopatológicos de una entidad ejemplo de impronta genómica / Silver-Russell syndrome. Clinical and etiopathological aspects of a model genomic imprinting entity

El síndrome de Silver-Russell se caracteriza por retraso del crecimiento intrauterino asimétrico, con circunferencia craneal normal, barbilla pequeña y puntiaguda, que proporciona un aspecto de rostro triangular. Puede, además, presentar asimetría corporal, entre otros. Tiene una incidencia mundial estimada de 1 en 30 000-100 000 nacimientos, aunque este número es, probablemente, subestimado. En alrededor del 60 % de los casos, se puede identificar una causa molecular y la principal es la hipometilación del alelo paterno en la región de control de impresión 1 localizado en 11p15.5-p15.4. Realizar el diagnóstico de esta entidad, excluir los diagnósticos diferenciales y conocer las correlaciones (epi)genotipo-fenotipo son necesarios para realizar el adecuado seguimiento, brindar las opciones terapéuticas disponibles y el oportuno asesoramiento genético familiar. El objetivo del presente artículo es mostrar el estado actual del síndrome de Silver-Russell, un ejemplo de trastorno de impronta genómica.

Silver-Russell syndrome is characterized by asymmetrical intrauterine growth retardation, with normal head circumference and small, pointed chin, which results in a triangular face. It can also include body asymmetry, among other characteristics. Its global incidence is estimated at 1 in 30 000-100 000 births, even though this figure may be underestimated. In approximately 60 % of cases, a molecular cause can be identified, and the main one is hypomethylation of the paternal allele at the imprinting control region 1 located at 11p15.5-p15.4. It is necessary to make the diagnosis of this entity, exclude differential diagnoses, and know (epi)genotype-phenotype correlations in order to ensure an adequate follow-up, provide available therapeutic options, and offer a timely family genetic counseling. The objective of this article is to describe the current status of the Silver-Russell syndrome, a model of genomic imprinting disorder.

Role of genomic imprinting in mammalian development

In mammals, DNA methyltransferases transfer a methyl group from S-adenosylmethionine to the 5 position ofcytosine in DNA. The product of this reaction, 5-methylcytosine (5mC), has many roles, particularly insuppressing transposable and repeat elements in DNA. Moreover, in many cellular systems, cell lineagespecification is accompanied by DNA demethylation at the promoters of genes expressed at high levels in thedifferentiated cells. However, since direct cleavage of the C-C bond connecting the methyl group to the 5position of cytosine is thermodynamically disfavoured, the question of whether DNA methylation wasreversible remained unclear for many decades. This puzzle was solved by our discovery of the TET (TenEleven Translocation) family of 5-methylcytosine oxidases, which use reduced iron, molecular oxygen and thetricarboxylic acid cycle metabolite 2-oxoglutarate (also known as a-ketoglutarate) to oxidise the methyl groupof 5mC to 5-hydroxymethylcytosine (5hmC) and beyond. TET-generated oxidised methylcytosines areintermediates in at least two pathways of DNA demethylation, which differ in their dependence on DNAreplication. In the decade since their discovery, TET enzymes have been shown to have important roles inembryonic development, cell lineage specification, neuronal function and cancer. We review these findings anddiscuss their implications here.

X-chromosome genetic association test incorporating X-chromosome inactivation and imprinting effects

Studies have shown that many complex diseases are sex-determined. When conducting genetic association studies on Xchromosome, there are two important epigenetic factors which should be considered simultaneously: X-chromosome inactivation and genomic imprinting. Currently, there have been several association tests accounting for the information on X-chromosome inactivation. However, these tests do not take the imprinting effects into account. In this paper, we propose a novel association test simultaneously incorporating X-chromosome inactivation and imprinting effects based on case–parent trios and control–parent trios for female offspring and case–control data for male offspring, denoted by MLRXCII. Extensive simulation studies are carried out to investigate the type I error rate and the test power of the proposed MLRXCII . Simulation results demonstrate that the proposed test controls the type I error rate well andis more powerful than the existing method when imprinting effects exist. The proposed MLRXCII test is valid and powerful in genetic association studies on X-chromosome for qualitative traits and thus is recommended in practice.

Alteration of Genomic Imprinting Status of Human Parthenogenetic Induced Pluripotent Stem Cells during Neural Lineage Differentiation

BACKGROUND AND OBJECTIVES: Genomic imprinting modulates growth and development in mammals and is associated with genetic disorders. Although uniparental embryonic stem cells have been used to study genomic imprinting, there is an ethical issue associated with the destruction of human embryos. In this study, to investigate the genomic imprinting status in human neurodevelopment, we used human uniparental induced pluripotent stem cells (iPSCs) that possessed only maternal alleles and differentiated into neural cell lineages. METHODS: Human somatic iPSCs (hSiPSCs) and human parthenogenetic iPSCs (hPgiPSCs) were differentiated into neural stem cells (NSCs) and named hSi-NSCs and hPgi-NSCs respectively. DNA methylation and gene expression of imprinted genes related neurodevelopment was analyzed during reprogramming and neural lineage differentiation. RESULTS: The DNA methylation and expression of imprinted genes were altered or maintained after differentiation into NSCs. The imprinting status in NSCs were maintained after terminal differentiation into neurons and astrocytes. In contrast, gene expression was differentially presented in a cell type-specific manner. CONCLUSIONS: This study suggests that genomic imprinting should be determined in each neural cell type because the genomic imprinting status can differ in a cell type-specific manner. In addition, the in vitro model established in this study would be useful for verifying the epigenetic alteration of imprinted genes which can be differentially changed during neurodevelopment in human and for screening novel imprinted genes related to neurodevelopment. Moreover, the confirmed genomic imprinting status could be used to find out an abnormal genomic imprinting status of imprinted genes related with neurogenetic disorders according to uniparental genotypes.

Genetic analysis of an adult with mosaicism of uniparental disomy 11p / 中华医学遗传学杂志

Objective@#To analyze the clinical phenotype and genomic abnormality of an adult featuring congenital heart defect and multiple developmental disorders.@*Methods@#The patient was subjected to conventional G-banding chromosomal karyotyping and single nucleotide polymorphism microarray (SNP-array) analysis.@*Results@#The patient showed a normal karyotype, while SNP-array revealed a 42.7 Mb mosaic uniparental disomy (UPD) in the 11p15.5p12 region ([hg19] chr11: 491 333 - 43 189 376).@*Conclusion@#The mosaicism of UPD of 11p15.5p12 region probably underlies the congenital heart defect and developmental disorders in the patient.

Analysis of genetic defects in the 11p15.5 region in Russell-Silver syndrome / 临床儿科杂志

Objective To explore the pathogenesis of Russell-Silver syndrome (RSS). Methods Two milliliter peripheral blood samples were collected from 6 male patients aged 6 to 8 years with suspected RSS phenotype, the parents of 2 patients and 5 healthy boys. Mononuclear cells were isolated and genomic DNA was extracted. The methylation level of the H19 imprinting control region(ICR)1 on chromosome 11p15.5 was detected by pyrosequencing.The methylation status and the copy number variation in the corresponding region of one RSS patient with positive results by pyrosequencing were analysed by methylation-specific multiplex-ligation-dependent probe amplification assay (MS-MLPA). Results Pyrosequencing analysis revealed that the methylation rates on the 6 CpG targeting sites in H19 differentially methylated region(DMR)in the 6 RSS patients were about 11%~29%, which were significantly lower than those in their parents and normal controls (44%~59%). The MS-MLPA results of one patient with positive pyrosequencing showed that the methylation rates of 4 sites in H19-DMR were about 10%,which was obviously lower than the normal level.The methylation rates of the 4 sites in KCNQ1OT1 gene were about 50%, which was in the normal range. The copy number variations from all samples detected were in the normal range. Conclusion There is methylation aberration of H19-DMR in ICR1 in children with RSS.

Placental expression of CDKN1C imprinted gene and birth weight of appropriate and small for gestational age neonates / 中华围产医学杂志

Objective To investigate the relationship between the expression of imprinted gene CDKN1C in placenta and the birth weight of neonates.Methods Twenty-nine term small for gestational age (SGA) neonates admitted to Peking University Third Hospital from January 1,2014 to December 31,2014 were recruited,and 29 appropriate for gestational age (AGA) neonates with a difference of not more than one week in gestational age served as controls.Fresh placental tissue was collected and the expression of imprinted gene CDKN1C mRNA in the placenta were detected by real-time fluorescence quantitative-polymerase chain reaction,and its protein expression was estimated by Western-blot.Chi-square test,independent-sample t test,Pearson's correlation analysis were used for statistical analysis.Results The CDKN1C mRNA expression level in SGA was significantly higher than that in AGA (0.133± 0.059 vs 0.100±0.046,t=2.401,P=0.020),so was the CDKN1C protein expression (0.280±0.043 vs 0.190±0.041,t=8.410,P=0.000).The CDKN1C mRNA expression levels were negatively correlated with birth weight in both groups (SGA group,r=-0.587,P=0.001;AGA group,r=-0.569,P=0.001),and the correlation was slightly stronger in SGA (r2=0.344) than in AGA (r2=0.324).The CDKN1C protein expression levels of the two groups were negatively correlated with birth weight (SGA group,r=-0.579,P=0.001;AGA group,r=-0.497,P=0.006),the correlation being stronger in SGA group (r2=0.335) than in AGA group (r2=0.247).The CDKN1C mRNA and protein expression levels of the two groups were negatively correlated with birth weight for gender,especially in males [mRNA:r2=0.293(male)vs r2=0.185(female);protein:r2=0.730 (male) vs r2=0.601(female)].Neither CDKN1C mRNA nor protein expression level was correlated to the placenta weight (mRNA:SGA group,r=0.119,P=0.540;AGA group,r=-0.069,P=0.722;protein:SGA group,r=0.126,P=0.515;AGA group,r=-0.247,P=0.196).Conclusions The expressions of CDKN1C mRNA and protein may be related to birth weight of term SGA neonates,especially in male infants.

Mutações inativadoras no gene MKRN3 são causa de puberdade precoce central familial / Inactivating mutations in the MKRN3 gene are cause of familial central precocious puberty

A maioria dos casos de puberdade precoce central (PPC) em meninas permanece idiopática. A hipótese de uma causa genética vem se fortalecendo após a descoberta de alguns genes associados a este fenótipo, sobretudo aqueles implicados com o sistema kisspeptina (KISS1 e KISS1R). Entretanto, apenas casos isolados de PPC foram relacionados à mutação na kisspeptina ou em seu receptor. Até recentemente, a maioria dos estudos genéticos em PPC buscava genes candidatos selecionados com base em modelos animais, análise genética de pacientes com hipogonadismo hipogonadotrófico, ou ainda, nos estudos de associação ampla do genoma. Neste trabalho, foi utilizado o sequenciamento exômico global, uma metodologia mais moderna de sequenciamento, para identificar variantes associadas ao fenótipo de PPC. Trinta e seis indivíduos com a forma de PPC familial (19 famílias) e 213 casos aparentemente esporádicos foram inicialmente selecionados. A forma familial foi definida pela presença de mais de um membro afetado na família. DNA genômico foi extraído dos leucócitos do sangue periférico de todos os pacientes. O estudo de sequenciamento exômico global realizado pela técnica ILLUMINA, em 40 membros de 15 famílias com PPC, identificou mutações inativadoras em um único gene, MKRN3, em cinco dessas famílias. Pesquisa de mutação no MKRN3 realizada por sequenciamento direto em duas famílias adicionais (quatro pacientes) identificou duas novas variantes nesse gene. O MKRN3 é um gene de um único éxon, localizado no cromossomo 15 em uma região crítica para a síndrome de Prader Willi. O gene MKRN3 sofre imprinting materno, sendo expresso apenas pelo alelo paterno. A descoberta de mutações em pacientes com PPC familial despertou o interesse para a pesquisa de mutações nesse gene em 213 pacientes com PPC aparentemente esporádica por meio de reação em cadeia de polimerase seguida de purificação enzimática e sequenciamento automático direto (Sanger). Três novas mutações e duas...

Most cases of central precocious puberty (CPP) in girls remain idiopathic. The hypothesis of a genetic cause has been strengthened after the discovery of some genes associated with this phenotype, particularly those involved with the kisspeptin system (KISS1 and KISS1R). However, genetic defects in KISS1 and its receptor are rare and have been identified in only a few patients with CPP.over the past years. To date, most genetic studies in CPP was based mainly on a candidate gene approach, including genes selected in animal studies, human models of patients with hypogonadotropic hypogonadism or in genome wide association studies. In the present study, we used whole exome sequencing, a more advanced method of sequencing, to identify variants associated with CPP. Thirty-six patients with the familial form of CPP (19 families) and 213 apparently sporadic cases were initially selected. The familial form was defined by the presence of more than one member affected in the family. Genomic DNA was extracted from peripheral blood leukocytes in all patients. Whole exome sequencing performed by ILLUMINA technique in 40 members of 15 families with CPP, identified inactivating mutations in a single gene, MKRN3, in five out of these families. Analysis of MKRN3 mutations performed by automatic sequencing in two additional families (four patients) identified two novel mutations. MKRN3 is an introless gene located on chromosome 15, in the Prader Willi syndrome critical region, and it is expressed only by the paternal allele due to the maternal imprinting. Following the initial findings, we searched for MKRN3 mutations in 213 patients with apparently sporadic CPP using polymerase chain reaction followed by direct enzymatic purification and automated sequencing (Sanger). Three new mutations and two previously reported, including four frameshifts and one missense variant was identified in six unrelated girls with CPP. All variants were not described in...

Perfil clínico de una cohorte de pacientes con síndrome de Silver-Russell atendidos en el Hospital Infantil de México Federico Gómez de 1998 a 2012 / Clinical profile of a cohort of Silver-Russell syndrome patients followed at the Hospital Infantil de México Federico Gómez from 1998 to 2012

Introducción: El síndrome de Silver-Russell presenta restricción del crecimiento intrauterino y posnatal, macrocefalia relativa y asimetría, entre otras características. Es causado por mecanismos genéticos y epigenéticos en el cromosoma 11p15.5 en el 40% de los casos y por disomía uniparental materna del cromosoma 7 en el 10%. Métodos: Se identificaron los pacientes con diagnóstico de síndrome de Silver-Russell del Hospital Infantil de México Federico Gómez atendidos de 1998 a 2012; se reevaluaron 20 pacientes según los criterios clínicos internacionales, y se confirmó el diagnóstico en nueve sujetos. Resultados: Todos los pacientes presentaron restricción del crecimiento intrauterino y talla baja, ambos criterios diagnósticos mayores. La macrocefalia relativa estuvo presente en el 78% y la asimetría corporal solo en el 33%. Otras características, como la acidosis tubular renal, estuvieron presentes en más del 50%. Conclusiones: El diagnóstico del síndrome de Silver-Russell es complejo, por lo que contar con criterios clínicos adecuados es fundamental. Dado que la talla baja es la principal solicitud de atención médica en este síndrome, es relevante establecer diagnósticos diferenciales y valorar el crecimiento y desarrollo de todos los pacientes para identificar a aquellos en quienes la talla baja forma parte de una entidad sindrómica y que serían candidatos para realizar estudios moleculares. Este abordaje tendrá implicaciones para su manejo, pronóstico y asesoramiento genético.

Background: Patients with Silver-Russell syndrome suffer from severe intrauterine and postnatal growth retardation, relative macrocephaly and body asymmetry, among other characteristics. It is caused by several genetic and epigenetic mechanisms in 11p15.5 in 40% of the cases and maternal uniparental disomy of chromosome 7 in 10%. Methods: Twenty patients with a diagnosis of Silver-Russell syndrome who were seen at the HIMFG from 1998 to 2012, were evaluated according to international clinical criteria confirming the diagnosis in nine of the subjects. Results: All patients showed intrauterine and postnatal growth retardation and short stature, both considered as major criteria of Silver-Russell syndrome. Relative macrocephaly was present in 78% of the patients and asymmetry in 33%. Other characteristics such as renal tubular acidosis were present > 50% of the cases. Conclusions: The clinical diagnosis of Silver-Russell syndrome is complex. Short stature is the main reason for seeking medical attention and is helpful in the identification of a differential diagnosis. This situation underlines the importance of growth and development evaluation of all patients and particularly in those with short stature to identify those cases that may require molecular studies, with implications in management, prognosis and genetic counseling.

Regulation and Function of the Peg3 Imprinted Domain

A subset of mammalian genes differ functionally between two alleles due to genomic imprinting, and seven such genes (Peg3, Usp29, APeg3, Zfp264, Zim1, Zim2, Zim3) are localized within the 500-kb genomic interval of the human and mouse genomes, constituting the Peg3 imprinted domain. This Peg3 domain shares several features with the other imprinted domains, including an evolutionarily conserved domain structure, along with transcriptional co-regulation through shared cis regulatory elements, as well as functional roles in controlling fetal growth rates and maternal-caring behaviors. The Peg3 domain also displays some unique features, including YY1-mediated regulation of transcription and imprinting; conversion and adaptation of several protein-coding members as ncRNA genes during evolution; and its close connection to human cancers through the potential tumor suppressor functions of Peg3 and Usp29. In this review, we summarize and discuss these features of the Peg3 domain.

No influence of parental origin of intact X chromosome and/or Y chromosome sequences on three-year height response to growth hormone therapy in Turner syndrome

PURPOSE: Whether parental origin of the intact X chromosome and/or the presence of Y chromosome sequences (Yseq) play a role in three-year height response to growth hormone (GH) were investigated. METHODS: Paternal (Xp) or maternal (Xm) origin of X chromosome was assessed by microsatellite marker analysis and the presence of hidden Yseq was analyzed. The first-, second-, and third-year GH response was measured as a change in height z-score (Z_Ht) in Turner syndrome (TS) patients with 45,Xp (n=10), 45,Xm (n=15), and 45,X/46,X,+mar(Y) (Xm_Yseq) (n=8). RESULTS: The mean baseline Z_Ht did not differ according to Xp or Xm origin, however the mean baseline Z_Ht was higher in the Xm_Yseq group than in Xm group, after adjusting for bone age delay and midparental Z_Ht (P=0.04). There was no difference in the height response to GH between the 3 groups. The height response to GH decreased progressively each year (P<0.001), such that the third-year increase in Z_Ht was not significant. This third-year decrease in treatment response was unaffected by Xp, Xm, and Xm_Yseq groups. Increasing GH dosage from the second to third-year of treatment positively correlated with the increase in Z_Ht (P=0.017). CONCLUSION: There was no evidence of X-linked imprinted genes and/or Yseq affecting height response to 3 years of GH therapy. Increasing GH dosages may help attenuate the decrease in third-year GH response in TS patients with 45,X and/or 46,X/+mar(Y).

The Molecular Nature of Very Small Embryonic-Like Stem Cells in Adult Tissues

Pluripotent stem cells (PSCs) have been considered as the most important cells in regenerative medicine as they are able to differentiate into all types of cells in the human body. PSCs have been established from several sources of embryo tissue or by reprogramming of terminally differentiated adult tissue by transduction of so-called Yamanaka factors (Oct4, Sox2, Klf4, and cMyc). Interestingly, accumulating evidence has demonstrated the residence of PSCs in adult tissue and with the ability to differentiate into multiple types of tissue-committed stem cells (TCSCs). We also recently demonstrated that a population of pluripotent Oct4(+) SSEA-1(+)Sca-1(+)Lin-CD45(-) very small embryonic-like stem cells (VSELs) resides in the adult murine bone marrow (BM) and in other murine tissue. These very small (~3-6 microm) cells express pluripotent markers such as Oct4, Nanog, and SSEA-1. VSELs could be specified into several tissue-residing TCSCs in response to tissue/organ injury, and thus suggesting that these cells have a physiological role in the rejuvenation of a pool of TCSCs under steady-state conditions. In this review article, we discuss the molecular nature of the rare population of VSELs which have a crucial role in regulating the pluripotency, proliferation, differentiation, and aging of these cells.

Transcriptional Profiles of Imprinted Genes in Human Embryonic Stem Cells During In vitro Differentiation

BACKGROUND AND OBJECTIVES: Genomic imprinting is an inheritance phenomenon by which a subset of genes are expressed from one allele of two homologous chromosomes in a parent of origin-specific manner. Even though fine-tuned regulation of genomic imprinting process is essential for normal development, no other means are available to study genomic imprinting in human during embryonic development. In relation with this bottleneck, differentiation of human embryonic stem cells (hESCs) into specialized lineages may be considered as an alternative to mimic human development. METHODS AND RESULTS: In this study, hESCs were differentiated into three lineage cell types to analyze temporal and spatial expression of imprinted genes. Of 19 imprinted genes examined, 15 imprinted genes showed similar transcriptional level among two hESC lines and two human induced pluripotent stem cell (hiPSC) lines. Expressional patterns of most imprinted genes were varied in progenitors and fully differentiated cells which were derived from hESCs. Also, no consistence was observed in the expression pattern of imprinted genes within an imprinting domain during in vitro differentiation of hESCs into three lineage cell types. CONCLUSIONS: Transcriptional expression of imprinted genes is regulated in a cell type-specific manner in hESCs during in vitro differentiation.

Placental hydroxymethylation vs methylation at the imprinting control region 2 on chromosome 11p15.5

In addition to methylated cytosines (5-mCs), hydroxymethylcytosines (5-hmCs) are present in CpG dinucleotide-enriched regions and some transcription regulator binding sites. Unlike methylation, hydroxymethylation does not result in silencing of gene expression, and the most commonly used methods to study methylation, such as techniques based on restriction enzymatic digestion and/or bisulfite modification, are unable to distinguish between them. Genomic imprinting is a process of gene regulation where only one member of an allelic pair is expressed depending on the parental origin. Chromosome 11p15.5 has an imprinting control region (ICR2) that includes a differentially methylated region (KvDMR1) that guarantees parent-specific gene expression. The objective of the present study was to determine the presence of 5-hmC at the KvDMR1 in human placentas. We analyzed 16 third-trimester normal human placentas (chorionic villi). We compared two different methods based on real-time PCR after enzymatic digestion. The first method distinguished methylation from hydroxymethylation, while the other method did not. Unlike other methylation studies, subtle variations of methylation in ICRs could represent a drastic deregulation of the expression of imprinted genes, leading to important phenotypic consequences, and the presence of hydroxymethylation could interfere with the results of many studies. We observed agreement between the results of both methods, indicating the absence of hydroxymethylation at the KvDMR1 in third-trimester placentas. To the best of our knowledge, this is the first study describing the investigation of hydroxymethylation in human placenta using a genomic imprinting model.

Epigenética: regulação da expressão gênica em nível transcricional e suas implicações / Epigenetics: gene expression regulation at transcriptional level and its implications

A epigenética compreende um conjunto de mecanismos que promovem a regulação da expressão gênica a nível transcricional através de modificações químicas no DNA e na cromatina, como metilação, acetilação e fosforilação, que resultam na conseqüente mudança fenotípica do indivíduo sem, no entanto, ocorrer nenhuma alteração na seqüência do DNA. Essas modificações químicas no DNA são constantemente feitas e desfeitas durante toda a vida do indivíduo, exceto para marcações químicas constitutivas que são herdadas geneticamente, visto que freqüentemente os indivíduos entram em contato com agentes promotores desses fenômenos durante a vida. Alterações nos padrões epigenéticos promovendo a expressão aberrante ou o silenciamento de determinados genes podem aparecer em organismos com idade avançada, e em uma ampla variedade de eventos e patologias como no câncer, na inativação do cromossomo X, no imprinting genômico, e em diversas síndromes de ordem neurológica e de prejuízo no desenvolvimento motor. Desse modo, busca-se atualmente o desenvolvimento de drogas que possuem a capacidade de reverter as marcações químicas alteradas em regiões específicas do genoma relacionadas a determinadas doenças. Uma maior compreensão desse universo da epigenética associada com suas implicações aos estados fisiológicos normais e patológicos mostra-se como uma grande promessa nessa era molecular, para o desenvolvimento de ferramentas profiláticas, diagnósticas e terapêuticas de uma ampla variedade de doenças.

Epigenetics includes several mechanisms that promote the gene expression regulation at transcriptional level through chemical changes in DNA and chromatin, such as methylation, acetylation and phosphorylation, resulting in phenotypic change without no changes occur in the DNA sequence. These DNA chemical changes are constantly made and unmade throughout the individual life, except for constitutive chemical markings that are genetically inherited, because often people are in contact with agents that promote these phenomens during their lifes. Changes in epigenetic patterns promoting aberrant expression or gene silencing may appear in aged organisms, and in a wide variety of events and conditions such as cancer, X chromosome inactivation in genomic imprinting, and in various neurological and motor development syndromes. Thus, seek currently drugs development that have the ability to reverse altered chemical markings in specific regions of the genome related to certain diseases. A greater understanding of the epigenetic universe associated with its implications to normal physiological and pathological states, it is a great promise in molecular era to development of prophylactic, diagnostic and therapeutic tools of a wide variety of diseases.

The Expression of IGF2 in Mouse Embryonic Stem Cells to Differentiate into Islet-Like Cells / 天津医药

Objective To observe the effects of insulin-like growth factor-2 (IGF2) in the course of mouse embryon-ic stem cells induced to differentiate into islet-like cells. Methods Mouse ES cells were induced to differentiate into islet-like cells in vitro. The expression of islet specific markers was tested by RT-PCR and immunofluorescence assay. RT-PCR/RFLP was used to test the imprinted genes IGF2 parental expression in cells at different stages. Results Islet specific mark-ers were expressed in differentiated cells, such as insulin, glucagon and C-peptide. PCR-RFLP showed that imprinted genes IGF2 derived from embryonic stem cells were biallelic expression and loss of imprinting. Conclusion Gene imprinting sta-tus of IGF2 was changed in differentiated cells in vitro.

Genetic syndromes associated with overgrowth in childhood

Overgrowth syndromes comprise a diverse group of conditions with unique clinical, behavioral and molecular genetic features. While considerable overlap in presentation sometimes exists, advances in identification of the precise etiology of specific overgrowth disorders continue to improve clinicians' ability to make an accurate diagnosis. Among them, this paper introduces two classic genetic overgrowth syndromes: Sotos syndrome and Beckwith-Wiedemann syndrome. Historically, the diagnosis was based entirely on clinical findings. However, it is now understood that Sotos syndrome is caused by a variety of molecular genetic alterations resulting in haploinsufficiency of the NSD1 gene at chromosome 5q35 and that Beckwith-Wiedemann syndrome is caused by heterogeneous abnormalities in the imprinting of a number of growth regulatory genes within chromosome 11p15 in the majority of cases. Interestingly, the 11p15 imprinting region is also associated with Russell-Silver syndrome which is a typical growth retardation syndrome. Opposite epigenetic alterations in 11p15 result in opposite clinical features shown in Beckwith-Wiedemann syndrome and Russell-Silver syndrome. Although the exact functions of the causing genes have not yet been completely understood, these overgrowth syndromes can be good models to clarify the complex basis of human growth and help to develop better-directed therapies in the future.

Impronta Genómica y Desarrollo Embrionario / Genomic Imprinting and Embryonic Development

En los organismos diploides, cada gen autosómico está representado por dos copias, o alelos, heredados de cada progenitor al momento de la fecundación. Para la gran mayoría de los genes la expresión ocurre desde ambos alelos de manera simultánea. Sin embargo, un número reducido de genes (menos del 1%) es afectado por un proceso de impronta genómica. Este proceso determina que la expresión del gen sea dependiente del origen parental, es decir, se comporte de manera distinta si su origen es materno o paterno. La metilación del ADN es una de las modificaciones epigenéticas mejor estudiadas y su participación resulta esencial durante el establecimiento de la impronta genómica. Si bien los patrones de metilación a nivel genómico son estables y heredables, existen al menos dos períodos del desarrollo embrionario de mamíferos durante los cuales los patrones de metilación globales son borrados y re-establecidos. Estos dos períodos del desarrollo coinciden con el borrado y establecimiento de la impronta genómica específica de cada individuo. Desde el punto de vista funcional, la mayoría de los genes sometidos a impronta cumplen roles en el control del crecimiento y desarrollo embrionario y placentario. Alteraciones en el patrón de expresión de ellos han sido relacionados a patologías tales como el Síndrome de Algelman y el Síndrome de Prader-Willi, entre otros.

In diploid organisms, autosomal genes are composed of two copies, or alleles, inherited from both parents at fertilization. For the vast majority of autosomal genes, expression occurs from both alleles simultaneously. However, a small proportion (<1%) of genes are imprinted, meaning that their expression depends on the parental origin . DNA methylation is one of the most known epigenetic modifications and its function is critical for the establishment of imprinting. The global pattern of genomic methylation is stable and inheritable, however, it is erased and re-established in a sex-depended manner at two critical periods of embryonic development. Functionally, the majority of imprinted genes play roles in the control of embryonic and placental growth and development. Alterations in imprinted genes have been correlated with several pathologies including the Angelman and Prader-Willi syndromes.

El tumor de Wilms. Un paradigma de heterogeneidad genética: a paradigm of genetic heterogeneity / Wilm's toumor

El Tumor de Wilms constituye el más frecuente de los cánceres renales pediátricos, aparece antes de los 5 años de edad y con igual frecuencia en ambos sexos. El gen causante de la enfermedad está localizado en 11p13, se extiende unas 50 kb con 10 exones y sus alteraciones pueden ser tanto genéticas como epigenéticas. Por diferentes mecanismos se originan al menos 24 productos con funciones diversas. Existen otras regiones cromosómicas, cuyas alteraciones pueden dar lugar a la aparición del tumor. En este sentido, el Tumor de Wilms es un ejemplo sobresaliente de heterogeneidad genética. El presente trabajo hace un análisis de los fundamentos moleculares de la enfermedad y presenta a modo de ilustración una breve reseña de los principales síndromes hereditarios con predisposición a presentar este tumor.

Wilm's tumor is the most frequent cancer of the kidney in childhood with onset before five year old. WT gene was mapped in 11p13 and span 50 kb with 10 exons. WT modifications would be either genetics or epigenetics. The gene code for at least 24 isoforms of protein products. Other chromosomes loci whose alterations may be cause of disease have been identified, so Wilm's tumor is a remarkable paradigm of genetic heterogeneity. In this paper an analysis of the molecular basis of the disease is presented and, also, a brief references on main hereditary syndromes which include Wilm's tumor.