RESUMO
Each neuron has 100-10000 connections (synapses) with other neural cells, therefore genome pathologies affecting a small proportion of brain cells are capable of causing dysfunction of the entire central nervous system (CNS). Recently, genome and chromosome instability has been uncovered in neurodegeneration (Alzheimer's disease, ataxia telangiectasia). Somatic tissue-specific mosaicism was observed in the brain of individuals with neuropsychiatric diseases including schizophrenia, autism, intellectual disability, and epilepsy. The study of genetic processes in neurons allows determination of a certain number of genetic pathways and candidate processes, modifications of which can cause impaired genome stability. Brain-specific somatic mutations generally occur at the earliest stages of development. Accordingly, genome variability and somatic mosaicism are expected to be mediated by cell cycle regulation, DNA repair, DNA replication, and programmed cell death in the brain. Endomitosis, endoreduplication, and abortive entrance to the cell cycle are also commonly observed in neurodegeneration. Brain-specific genome instability maybe a key element in the pathogenic cascade of neurodegeneration. Here we review the current state of knowledge concerning somatic genome variations in neurodegenerative and psychiatric diseases and analyze the causes and consequences of genomic instability in the CNS.
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Doença de Alzheimer , Doenças Neurodegenerativas , Doença de Alzheimer/genética , Encéfalo , Genoma , Instabilidade Genômica , Humanos , Doenças Neurodegenerativas/genéticaRESUMO
Recent genomic advances have exacerbated the problem of interpreting genome-wide association studies aimed at uncovering genetic basis of brain disorders. Despite of a plethora of data on candidate genes determining the susceptibility to neuropsychiatric diseases, no consensus is reached on their intrinsic contribution to the pathogenesis, and the influence of the environment on these genes is incompletely understood. Alternatively, single-cell analyses of the normal and diseased human brain have shown that somatic genome/epigenome variations (somatic mosaicism) do affect neuronal cell populations and are likely to mediate pathogenic processes associated with brain dysfunctions. Such (epi-)genomic changes are likely to arise from disturbances in genome maintenance and cell cycle regulation pathways as well as from environmental exposures. Therefore, one can suggest that, at least in a proportion of cases, inter- and intragenic variations (copy number variations (CNVs) or single nucleotide polymorphisms (SNPs)) associated with major brain disorders (i.e. schizophrenia, Alzheimer's disease, autism) lead to genetic dysregulation resulting in somatic genetic and epigenetic mosaicism. In addition, environmental influences on malfunctioning cellular machinery could trigger a cascade of abnormal processes producing genomic/chromosomal instability (i.e. brain-specific aneuploidy). Here, a brief analysis of a genome-wide association database has allowed us to support these speculations. Accordingly, an ontogenetic 2-/multiple-hit mechanism of brain diseases was hypothesized. Finally, we speculate that somatic cell genomics approach considering both genome-wide associations and somatic (epi-)genomic variations is likely to have bright perspectives for disease-oriented genome research.
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Encefalopatias/genética , Interação Gene-Ambiente , Estudo de Associação Genômica Ampla , Instabilidade Genômica , Doença de Alzheimer/genética , Transtorno Autístico/genética , Epigênese Genética , Predisposição Genética para Doença , Variação Genética , Humanos , Modelos Genéticos , Esquizofrenia/genética , Análise de Célula ÚnicaRESUMO
Ever increasing sophistication in the application of new analytical technology has revealed that our genomes are much more fluid than was contemplated only a few years ago. More specifically, this concerns interindividual variation in copy number (CNV) of structural chromosome aberrations, i.e. microdeletions and microduplications. It is important to recognize that in this context, we still lack basic knowledge on the impact of the CNV in normal cells from individual tissues, including that of whole chromosomes (aneuploidy). Here, we highlight this challenge by the example of the very first chromosome aberration identified in the human genome, i.e. an extra chromosome 21 (trisomy 21, T21), which is causative of Down syndrome (DS). We consider it likely that most, if not all, of us are T21 mosaics, i.e. everyone carries some cells with an extra chromosome 21, in some tissues. In other words, we may all have a touch of DS. We further propose that the occurrence of such tissue-specific T21 mosaicism may have important ramifications for the understanding of the pathogenesis, prognosis and treatment of medical problems shared between people with DS and those in the general non-DS population.
Assuntos
Cromossomos Humanos Par 21 , Síndrome de Down/genética , Mosaicismo , Variações do Número de Cópias de DNA , Síndrome de Down/epidemiologia , Síndrome de Down/etiologia , Genética Populacional , HumanosRESUMO
AIM: Long continuous stretches of homozygosity (LCSH) are regularly detected in studies using molecular karyotyping (SNP array). Despite this type of variation being able to provide meaningful data on the parents' kinship, uniparental disomy and chromosome rearrangements, LCSH are rarely considered as a possible epigenetic cause of neurodevelopmental disorders. Despite their direct relationship to imprinting, LCSH in imprinted loci have not been considered in terms of pathogenicity. The present work is aimed at studying LCSH in chromosomal regions containing imprinted genes previously associated with disease in children with idiopathic intellectual disability, autism, congenital malformations and/or epilepsy. MATERIAL AND METHODS: Five hundred and four patients with autism spectrum disorders and intellectual disability were examined. RESULTS: LCSH affecting imprinted loci associated with various diseases were identified in 40 (7.9%) individuals. Chromosomal region 7q21.3 was affected in twenty three cases, 15q11.2 in twelve, 11p15.5 in five, 7q32.2 in four. Four patients had 2 LCSH affecting imprinted loci. Besides one LCSH in 7q31.33q32.3 (~4 Mbp) region, all LCSH were 1-1.6 Mbp. Clinically, these cases resembled the corresponding imprinting diseases (e.g. Silver-Russell, Beckwith-Wiedemann, Prader-Willi, Angelman syndromes). Parental kinship was identified in 8 cases (1.59%), which were not affected by LCSH at imprinted loci. CONCLUSION: The present study shows that LCSH affecting chromosomal regions 7q21.3, 7q32.2, 11p15.5 and 15p11.2 occur in about 7.9% of children with intellectual disability, autism, congenital malformations and/or epilepsy. Consequently, this type of epigenetic mutations is obviously common in a group of children with neurodevelopmental disorders. LCSH less than 2.5-10 Mbp are usually ignored in molecular karyotyping (SNP array) studies and, therefore, an important epigenetic cause of intellectual disability, autism or epilepsy with high probability remains without attention.
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Síndrome de Angelman , Transtorno do Espectro Autista , Epigenômica , Deficiência Intelectual , Síndrome de Angelman/genética , Transtorno do Espectro Autista/genética , Criança , Humanos , Deficiência Intelectual/genética , Perda de HeterozigosidadeRESUMO
Isodicentric chromosomes are considered the most common structural abnormality of the human Y chromosome. Because of their instability during cell division, loss of an isodicentric Y seems mainly to lie at the origin of mosaicism in previously reported patients with a 45,X cell line. Here, we report on a similar case, which, however, turned out to be an example of dynamic mosaicism involving isodicentric chromosome Y and isochromosome Y after FISH with a set of chromosome Y-specific probes and multicolor banding. Cytogenetic analyses (GTG-, C-, and Q-banding) have shown three different cell lines: 45,X/46, X,idic(Y)(q12)/46,X,+mar. The application of molecular cytogenetic techniques established the presence of four cell lines: 45,X (48%), 46,X,idic(Y)(q11.23) (42%), 46,X,i(Y)(p10) (6%) and 47,X,idic(Y)(q11.23),+idic(Y)(q11.23) (4%). According to the available literature, this is the first case of dynamic mosaicism with up to four different cell lines involving loss, gain, and rearrangement of an idic(Y)(q11.23). The present report indicates that cases of mosaicism involving isodicentric and isochromosome Ys can be more dynamic in terms of somatic intercellular variability that probably has an underappreciated effect on the phenotype.
Assuntos
Aberrações Cromossômicas , Cromossomos Humanos Y , Genitália Masculina/anormalidades , Transtornos do Crescimento/genética , Mosaicismo , Humanos , Hibridização in Situ Fluorescente , Lactente , Cariotipagem , MasculinoRESUMO
Molecular cytogenetics is a promising field of biomedical research that has recently revolutionized our thinking on genome structure and behavior. This is in part due to discoveries of human genomic variations and their contribution to biodiversity and disease. Since these studies were primarily targeted at variation of the genome structure, it appears apposite to cover them by molecular cytogenomics. Human brain diseases, which encompass pathogenic conditions from severe neurodegenerative diseases and major psychiatric disorders to brain tumors, are a heavy burden for the patients and their relatives. It has been suggested that most of them, if not all, are of genetic nature and several recent studies have supported the hypothesis assuming them to be associated with genomic instabilities (i.e. single-gene mutations, gross and subtle chromosome imbalances, aneuploidy). The present review is focused on the intriguing relationship between genomic instability and human brain diseases. Looking through the data, we were able to conclude that both interindividual and intercellular genomic variations could be pathogenic representing, therefore, a possible mechanism for human brain malfunctioning. Nevertheless, there are still numerous gaps in our knowledge concerning the link between genomic variations and brain diseases, which, hopefully, will be filled by forthcoming studies. In this light, the present review considers perspectives of this dynamically developing field of neurogenetics and genomics.
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BACKGROUND: Autism is a common childhood neurodevelopmental disorder with a possible genetic background. About 5-10% of autism cases are associated with chromosomal abnormalities or monogenic disorders. However, the role of subtle genomic imbalances in autism has not been delineated. This study aimed to investigate a hypothesis suggesting autism to be associated with subtle genomic imbalances presenting as low-level chromosomal mosaicism. METHODS: We surveyed stochastic (background) aneuploidy in children with/without autism by interphase three-colour fluorescence in situ hybridisation. The rate of chromosome loss and gain involving six arbitrarily selected autosomes and the sex chromosomes was assessed in the peripheral blood cells of 60 unaffected children and 120 children with autism. RESULTS: Of 120 analysed boys with autism, 4 (3.3%) with rare structural chromosomal abnormalities (46,XY,t(1;6)(q42.1;q27); 46,XY,inv(2)(p11q13); 46,XY,der(6),ins(6;1)(q21;p13.3p22,1)pat; and 46,XY,r(22)(p11q13)) were excluded from further molecular cytogenetic analysis. Studying <420 000 cells in 60 controls and 116 children with idiopathic autism, we determined the mean frequency of stochastic aneuploidy in control and autism: (1) autosome loss 0.58% (95% CI 0.42 to 0.75%) and 0.60% (95% CI 0.37 to 0.83%), respectively, p = 0.83; (2) autosome gain 0.15% (95% CI 0.09 to 0.21%) and 0.22% (95% CI 0.14 to 0.30%), respectively, p = 0.39; and (3) chromosome X gain 1.11% (95% CI 0.90 to 1.31%) and 1.01% (95% CI 0.85 to 1.17%), respectively, p = 0.30. A frequency of mosaic aneuploidy greater the background level was found in 19 (16%) of 116 children with idiopathic autism, whereas outlier values were not found in controls (p = 0.0019). CONCLUSIONS: Our findings identify low-level aneuploidy as a new genetic risk factor for autism. Therefore, molecular cytogenetic analysis of somatic mosaicism is warranted in children with unexplained autism.
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Aneuploidia , Transtorno Autístico/genética , Mosaicismo , Células Cultivadas , Criança , Aberrações Cromossômicas , Mapeamento Cromossômico , Frequência do Gene , Humanos , Masculino , Síndrome de Rett/genética , Processos EstocásticosRESUMO
An approach towards construction of two-dimensional (2D) and three-dimensional (3D) profiles of interphase chromatin architecture by quantification of fluorescence in situ hybridization (FISH) signal intensity is proposed. The technique was applied for analysis of signal intensity and distribution within interphase nuclei of somatic cells in different human tissues. Whole genomic DNA, fraction of repeated DNA sequences (Cot 1) and cloned satellite DNA were used as probes for FISH. The 2D and 3D fluorescence intensity profiles were able to depict FISH signal associations and somatic chromosome pairing. Furthermore, it allowed the detection of replicating signal patterns, the assessment of hybridization efficiency, and comparative analysis of DNA content variation of specific heterochromatic chromosomal regions. The 3D fluorescence intensity profiles allowed the analysis of intensity gradient within the signal volume. An approach was found applicable for determination of assembly of different types of DNA sequences, including classical satellite and alphoid DNA, gene-rich (G-negative bands) and gene-poor (G-positive bands) chromosomal regions as well as for assessment of chromatin architecture and targeted DNA sequence distribution within interphase nuclei. We conclude the approach to be a powerful additional tool for analysis of interphase genome architecture and chromosome behavior in the nucleus of human somatic cells.
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Núcleo Celular/genética , Cromossomos Humanos/ultraestrutura , Genoma Humano , Interfase/genética , Encéfalo/citologia , Núcleo Celular/ultraestrutura , Células Cultivadas , Vilosidades Coriônicas/ultraestrutura , Aberrações Cromossômicas , Sondas de DNA , Feminino , Corantes Fluorescentes , Humanos , Hibridização in Situ Fluorescente , Linfócitos/citologia , Masculino , Hibridização de Ácido NucleicoRESUMO
According to WHO data, about 67 million people worldwide are affected by autism, and this number grows by 14% annually. Among the possible causes of autism are genetic modifications, organic lesions of the central nervous system, metabolic disorders, influence of viral and bacterial infections, chemical influence to the mother's body during pregnancy, etc. The conducted research shows that research papers published until today do not name any potential protein markers that meet the requirements of the basic parameters for evaluating the efficiency of disease diagnostics, in particular high sensitivity, specificity, and accuracy. Conducting proteomic research on a big scale in order to detect serologic markers of protein nature associated with development of autism spectrum disorders seems to be highly relevant.
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Transtorno do Espectro Autista/sangue , Transtorno do Espectro Autista/genética , Autoanticorpos/sangue , Biomarcadores/sangue , Citocinas/sangue , Humanos , Peptídeos/sangue , Serotonina/sangueRESUMO
We report on two unrelated cases of pericentric inversion 46,XY,inv(7)(p11q21.1) associated with distinct pattern of malformation including mental retardation, development delay, ectrodactyly, facial dismorphism, high arched palate. Additionally, one case was found to be characterized by mesodermal dysplasia. Cytogenetic analysis of the families indicated that one case was a paternally inherited inversion whereas another case was a maternally inherited one. Molecular cytogenetic studies have shown paternal inversion to have a breakpoint within centromeric heterochromatin being the cause of alphoid DNA loss. Maternal inversion was also associated with a breakpoint within centromeric heterochromatin as well as inverted euchromatic chromosome region flanked by two disrupted alphoid DNA blocks. Basing on molecular cytogenetic data we hypothesize the differences of clinical manifestations to be produced by a position effect due to localization of breakpoints within variable centromeric heterochromatin and, alternatively, due to differences in the location breakpoints, disrupteding different genes within region 7q21-q22. Our results reconfirm previous linkage analyses suggested 7q21-q22 as a locus of ectrodactily and propose inv (7)(p11q21.1) as a cause of recognizable pattern of malformations or a new chromosomal syndrome.
Assuntos
Inversão Cromossômica , Cromossomos Humanos Par 7/genética , Anormalidades Congênitas/genética , Impressão Genômica , Deficiência Intelectual/genética , Adolescente , Criança , Mapeamento Cromossômico , Cromossomos Humanos Par 7/ultraestrutura , DNA/análise , Genótipo , Humanos , Hibridização in Situ Fluorescente , Cariotipagem , Masculino , FenótipoRESUMO
We report on a case of chimerism and multiple abnormalities of chromosomes 21, Xand Yin spontaneous abortion specimen. To the best our knowledge the present case is the first documented chimera in a spontaneously aborted fetus. The application of interphase fluorescence in situ hybridization (FISH) using chromosome enumeration and site-specific DNA probes showed trisomy X in 92 nuclei (23 %), tetrasomy X in 100 nuclei (25 %), pentasomy of chromosome X in 40 nuclei (10 %), XXY in 36 nuclei (9 %), XXXXXXYY in 12 nuclei (3 %), XXXXXYYYYY in 8 nuclei (2 %), trisomy 21 and female chromosome complement in 40 nuclei (10 %), normal female chromosome complement in 72 nuclei (18 %) out of 400 nuclei scored. Our experience indicates that the frequency of chimerism coupled with multiple chromosome abnormalities should be no less than 1 : 400 among spontaneous abortions. The difficulties of chimerism identification in fetal tissues are discussed.
Assuntos
Aborto Espontâneo/genética , Quimerismo , Cromossomos Humanos Par 21 , Cromossomos Humanos X , Cromossomos Humanos Y , Mosaicismo , Feto Abortado , Adulto , Sondas de DNA , Síndrome de Down/embriologia , Síndrome de Down/genética , Feminino , Humanos , Hibridização in Situ Fluorescente , GravidezRESUMO
AIM: Experimental verification of the hypothesis about the possible involvement of the mosaic genome variations (mosaic aneuploidy) in the pathogenesis of a number of mental illnesses, including schizophrenia and autism: a genetic study of the level of mosaic genome variations in cells of the brain autopsy tissues in healthy controls and schizophrenia. MATERIAL AND METHODS: Autopsy brain tissues of 15 unaffected controls and 15 patients with schizophrenia were analyzed by molecular cytogenetic methods to determine the frequency of chromosomal mutations (the mosaic aneuploidy) in neural human cells. The original collection of chromosome-enumeration DNA probes to autosomes 1, 9, 15, 16, 18 and the sex chromosomes X and Y was used for the interphase cytogenetic analysis of chromosomes in the cells of the brain. RESULTS AND CONCLUSION: The frequency of low-level aneuploidy per individual chromosome was 0.54% (median - 0.53%; 95% confidence interval (CI) CI - 0.41-1.13%) in controls and 1.66% (median - 1.55%; 95% CI -1.32-2.12%) in schizophrenia (p=0.000013). Thus, the three-fold increase in aneuploidy frequency in the brain in schizophrenia was detected. It is suggested that mosaic aneuploidy, as a significant biological marker of genomic instability, may lead to genеtic imbalance and abnormal functional activity of neural cells and neural networks in schizophrenia.
Assuntos
Aneuploidia , Encéfalo/patologia , Instabilidade Genômica , Mosaicismo , Esquizofrenia/genética , Autopsia , Estudos de Casos e Controles , Humanos , Hibridização in Situ Fluorescente , Neurônios , SoftwareRESUMO
AIM: To analyze structural variations in the genome in children with autism and intellectual disability. MATERIAL AND METHODS: Using high-resolution karyotyping (AffymetrixCytoScan HD Array) and original bioinformatic technology, 200 children with autism and intellectual disability were studied. RESULTS AND CONCLUSION: Data on structural variations in the genome in children with autism and intellectual disability are provided. Causative genomic pathology (chromosome abnormalities and copy number variations - CNV) was determined in 97 cases (48.5%). Based on these RESULTS: 24 candidate genes for autism with intellectual disability were selected. In 16 cases (8%), the chromosome mosaicism manifested as aneuploidy of whole autosomes and sex chromosomes (gonosomes) was identified. In 87 children (43.5%), there were genomic variations, which are characteristic of the so-called «grey zone¼ of genetic pathology in mental illnesses. Bioinformatic analysis showed that these genomic variations had a pleiotropic effect on the phenotype.
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Transtorno Autístico/genética , Aberrações Cromossômicas , Variações do Número de Cópias de DNA , Deficiência Intelectual/genética , Criança , Genoma Humano , Humanos , Cariotipagem , Fenótipo , Federação RussaRESUMO
The analysis of non-disjunction of chromosome 21 and alphoid DNA variation by using cytogenetic and molecular cytogenetic techniques (quantitative fluorescence in situ hybridization) in 74 nuclear families was performed. The establishment of possible correlation between alphoid DNA variation, parental age, environmental effects, and non-disjunction of chromosome 21 was made. The efficiency of techniques applied was found to be 92% (68 from 74 cases). Maternal non-disjunction wasfound in 58 cases (86%) and paternal non-disjunction - in 7 cases (10%). Post-zygotic mitotic non-disjunction was determined in 2 cases (3%) and one case was associated with Robertsonian translocation 46,XX,der(21;21)(q10;q10), +21. Maternal meiosis I errors were found in 43 cases (64%) and maternal meiosis II errors--in 15 cases (22%). Paternal meiosis I errors occurred in 2 cases (3%) and paternal meiosis I errors--in 5 cases (7%). The lack of the correlation between alphoid DNA variation and non-disjunction of chromosome 21 was established. Sociogenetic analysis revealed the association of intensive drug therapy of infectious diseases during the periconceptual period and maternal meiotic non-disjunction of chromosome 21. The correlation between non-disjunction of chromosome 21 and increased parental age as well as exposure to irradiation, alcohol, tobacco, mutagenic substances was not found. The possible relevance of data obtained to the subsequent studies of chromosome 21 non-disjunction is discussed.
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Cromossomos Humanos Par 21 , Doenças Transmissíveis/tratamento farmacológico , DNA/genética , Síndrome de Down/genética , Variação Genética , Não Disjunção Genética , Análise Citogenética , DNA/análise , Feminino , Humanos , Hibridização in Situ Fluorescente , Masculino , Meiose , Mitose , TrissomiaRESUMO
OBJECTIVE: Microduplications of the long arm of the X chromosome including the MECP2 gene are relatively common causes of neurodevelopmental disorders in males. Authors analyzed clinical presentations of this disease in children. MATERIAL AND METHODS: Authors performed a clinical and genetic analysis of four cases using contemporary cytogenetic, molecular cytogenetic studies (FISH, array CGH) and X chromosome inactivation analysis. RESULTS AND CONCLUSION: We described somatic, neurologic and mental symptoms of the patients. The genetic imbalance impact on the patients' phenotype, necessity of comprehensive family studies for correct genetic diagnosis and effective genetic counseling in cases of microduplications of the long arm of the X chromosome including the MECP2 gene are discussed.
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Duplicação Cromossômica , Cromossomos Humanos X/genética , Proteína 2 de Ligação a Metil-CpG/genética , Aberrações dos Cromossomos Sexuais , Transtornos dos Cromossomos Sexuais , Pré-Escolar , Aconselhamento Genético , Testes Genéticos , Humanos , Hibridização in Situ Fluorescente , Masculino , Transtornos dos Cromossomos Sexuais/diagnóstico , Transtornos dos Cromossomos Sexuais/genética , Transtornos dos Cromossomos Sexuais/fisiopatologia , Síndrome , Inativação do Cromossomo XRESUMO
Fluorescence in situ hybridization (FISH) of DNA-DNA or DNA-RNA using post-mortem brain samples is one approach to study low-level chromosomal aneuploidy and selective expression of specific genes in the brain of patients with neuropsychiatric diseases. We have performed a pilot molecular-cytogenetic analysis of post-mortem brain of schizophrenic patients. Multicolor FISH on two post-mortem brain samples of normal individuals and six schizophrenic individuals (area 10 of cortex) was applied. A set of DNA probes for FISH included: (i) centromeric alphoid DNA probes for chromosomes 7, 8, 13 and 21, 18, X and Y; (ii) classical satellite DNA probes for chromosomes 1 and 16; and (iii) region-specific DNA probes for chromosomes 13, 21 and 22. A statistically significant level of aneuploidy (up to 0.5-4% of neurons) involving chromosomes X and 18 was detected in two post-mortem brains of patients with schizophrenia. These results indicate that low-level chromosomal aneuploidy could be involved in the pathogenesis of schizophrenia. FISH could be applied to extended studies of chromosomal aneuploidy, abnormal patterns of chromosomal organization and functional gene expression in situ in the neurons of the brain in different psychiatric and neurodevelopmental diseases. Schizophrenia and Rett syndrome might be considered as psychiatric diseases of special interest for molecular-cytogenetic analysis as both of them could be associated with mutations in genes involving regulation of neurodevelopmental processes in the brain.
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Aneuploidia , Encéfalo/metabolismo , Análise Mutacional de DNA/métodos , Hibridização in Situ Fluorescente/métodos , Mutação/genética , Esquizofrenia/genética , Esquizofrenia/patologia , Adulto , Idoso , Encéfalo/patologia , Encéfalo/fisiopatologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Projetos Piloto , Mudanças Depois da Morte , Aberrações dos Cromossomos Sexuais , Cromossomos Sexuais/genética , Fatores SexuaisRESUMO
We have developed an approach to differentiate homologous X chromosomes in metaphase chromosomes and interphase nuclei by a fluorescence in situ hybridization (FISH) technique with chromosome X-specific alpha-satellite DNA probe. FISH analysis of metaphase chromosomes in a cohort of 33 girls with Rett syndrome (RTT) allowed us to detect eight girls with structurally different X chromosomes, one X chromosome with a large and another one with a small centromeric heterochromatin (so-called chromosomal heteromorphism). Step-wise application of differential replication staining and the FISH technique to identify the inactivation status of paternal and maternal chromosome X in RTT girls was applied. Skewed X inactivation in seven RTT girls with preferential inactivation of one X chromosome over the other X chromosome was detected in 62-93% of cells. Therefore, non-random or skewed X inactivation with variable penetrance in blood cells could take place in RTT.
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Análise Mutacional de DNA/métodos , Mecanismo Genético de Compensação de Dose , Hibridização in Situ Fluorescente/métodos , Mutação/genética , Síndrome de Rett/genética , Cromossomo X/genética , Adolescente , Criança , Pré-Escolar , Feminino , Humanos , Lactente , Recém-Nascido , Linfócitos/citologia , Síndrome de Rett/sangueRESUMO
We examined 30 patients with a presumptive diagnosis of Prader-Willi and Angelman syndromes. In four patients, 15q11.2-q13 deletions were identified by cytogenetic techniques. The FISH method was used to study eight patients, in five of them microdeletions were also confirmed. High-resolution comparative genomic hybridization (CGH) and comparative genomic hybridization using DNA microarrays (array CGH) allowed to find 15q11.2-q13 deletions in five patients. These cases demonstrate the need for high-resolution post-genomic technologies (array CGH - molecular karyotyping) in the combination with classical cytogenetic and molecular cytogenetic techniques.
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Síndrome de Angelman/diagnóstico , Deleção Cromossômica , Cromossomos Humanos Par 15/genética , Testes Genéticos/métodos , Síndrome de Prader-Willi/diagnóstico , Síndrome de Angelman/genética , Hibridização Genômica Comparativa , Humanos , Recém-Nascido , Masculino , Síndrome de Prader-Willi/genéticaRESUMO
It is hard to imagine that all the cells of the human organism (about 10(14)) share identical genome. Moreover, the number of mitoses (about 10(16)) required for the organism's development and maturation during ontogeny suggests that at least a proportion of them could be abnormal leading, thereby, to large-scale genomic alterations in somatic cells. Experimental data do demonstrate such genomic variations to exist and to be involved in human development and interindividual genetic variability in health and disease. However, since current genomic technologies are mainly based on methods, which analyze genomes from a large pool of cells, intercellular or somatic genome variations are significantly less appreciated in modern bioscience. Here, a review of somatic genome variations occurring at all levels of genome organization (i.e. DNA sequence, subchromosomal and chromosomal) in health and disease is presented. Looking through the available literature, it was possible to show that the somatic cell genome is extremely variable. Additionally, being mainly associated with chromosome or genome instability (most commonly manifesting as aneuploidy), somatic genome variations are involved in pathogenesis of numerous human diseases. The latter mainly concerns diseases of the brain (i.e. autism, schizophrenia, Alzheimer's disease) and immune system (autoimmune diseases), chromosomal and some monogenic syndromes, cancers, infertility and prenatal mortality. Taking into account data on somatic genome variations and chromosome instability, it becomes possible to show that related processes can underlie non-malignant pathology such as (neuro)degeneration or other local tissue dysfunctions. Together, we suggest that detection and characterization of somatic genome behavior and variations can provide new opportunities for human genome research and genetics.
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The human genome demonstrates variable levels of instability during ontogeny. Achieving the highest rate during early prenatal development, it decreases significantly throughout following ontogenetic stages. A failure to decrease or a spontaneous increase of genomic instability can promote infertility, pregnancy losses, chromosomal and genomic diseases, cancer, immunodeficiency, or brain diseases depending on developmental stage at which it occurs. Paradoxically, late ontogeny is associated with increase of genomic instability that is considered a probable mechanism for human aging. The latter is even more appreciable in human diseases associated with pathological or accelerated aging (i.e. Alzheimer's disease and ataxia-telangiectasia). These observations resulted in a hypothesis suggesting that somatic genomic variations throughout ontogeny are determinants of cellular vitality in health and disease including intrauterine development, postnatal life and aging. The most devastative effect of somatic genome variations is observed when it manifests as chromosome instability or aneuploidy, which has been repeatedly noted to produce pathologic conditions and to mediate developmental regulatory and aging processes. However, no commonly accepted concepts on the role of chromosome/genome instability in determination of human health span and life span are available. Here, a review of these ontogenetic variations is given to propose a new "dynamic genome" model for pathological and natural genomic changes throughout life that mimic those of phylogenetic diversity.