Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0025362 (mental retardation)
 15,878 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A decrease in the number and density of neurons is the most common phenotype in the brains of Down syndrome (DS) patients, causing mental retardation. Studies using primary cultured neurons from DS patients or from model mice have suggested that a defect in metabolism of reactive oxygen species, or diminished levels of glutathione, causes mitochondrial and caspase-mediated neuronal apoptosis in vitro. However, it is not well documented whether neuronal apoptosis also occurs in immature DS neurons, owing to the difficulty in isolating or identifying neuronal stem cells in human or mouse fetuses. Here we utilized an in vitro model system for neuronal differentiation, with mouse embryonic stem cells containing human chromosome 21 (TT2F/hChr.21) to examine the effect of an additional hChr.21 on the early phases of neurogenesis. The differentiation profile of TT2F/hChr.21 cells was essentially the same as those of parental TT2F ES cells. In differentiations of both TT2F and TT2F/hChr.21 cells, high level of apoptosis was observed in neuronal stem cells, but the rate of apoptosis in TT2F/hChr.21 cells was significantly higher than that of parental cells. These results suggest that quantitative changes in the level of apoptosis in DS neuronal stem cells may account for the reduction of neuronal number and density in the DS brain.
 ...
PMID:Elevated apoptosis in pre-mature neurons differentiated from mouse ES cells containing a single human chromosome 21. 1245 81

The DNA sequence of human chromosome 21 (HSA21) has opened the route for a systematic molecular characterization of all of its genes. Trisomy 21 is associated with Down's syndrome, the most common genetic cause of mental retardation in humans. The phenotype includes various organ dysmorphies, stereotypic craniofacial anomalies and brain malformations. Molecular analysis of congenital aneuploidies poses a particular challenge because the aneuploid region contains many protein-coding genes whose function is unknown. One essential step towards understanding their function is to analyse mRNA expression patterns at key stages of organism development. Seminal works in flies, frogs and mice showed that genes whose expression is restricted spatially and/or temporally are often linked with specific ontogenic processes. Here we describe expression profiles of mouse orthologues to HSA21 genes by a combination of large-scale mRNA in situ hybridization at critical stages of embryonic and brain development and in silico (computed) mining of expressed sequence tags. This chromosome-scale expression annotation associates many of the genes tested with a potential biological role and suggests candidates for the pathogenesis of Down's syndrome.
 ...
PMID:A gene expression map of human chromosome 21 orthologues in the mouse. 1251 4

Trisomy of human chromosome 21 is a major cause of mental retardation and other phenotypic abnormalities collectively known as Down syndrome. Down syndrome is associated with developmental failure followed by processes of neurodegeneration that are known to supervene later in life. Despite a widespread interest in Down syndrome, the cause of developmental failure is unclear. The brain of a child with Down syndrome develops differently from that of a normal one, although characteristic morphological differences have not been noted in prenatal life. On the other hand, a review of the existing literature indicates that there are a series of biochemical alterations occurring in fetal Down syndrome brain that could serve as substrate for morphological changes. We propose that these biochemical alterations represent and/or precede morphological changes. This review attempts to dissect these molecular changes and to explain how they may lead to mental retardation.
 ...
PMID:Molecular changes in fetal Down syndrome brain. 1260 15

Down syndrome (DS) is the most significant genetic disorder with mental retardation and is caused by trisomy 21. The phenotype of DS is thought to result from overexpression of a gene(s) located on the triplicated chromosome (region). An increasing body of evidence that challenge this "gene dosage effect" hypothesis, however, has been reported indicating that this hypothesis still remains to be elucidated. The availability of the complete sequence of genes on chromosome 21 could have an immediate impact on DS research, but no conclusions can be drawn from nucleic acid levels. This made us evaluate protein levels of six proteins, gene products, encoded on chromosome 21 (T-cell lymphoma invasion and metastasis inducing Tiam1 protein, holocarboxylase synthetase, human interferon-regulated resistance GTP-binding protein MxA, Pbx regulating protein 1, autoimmune regulator, and pericentrin) in fetal cortex from DS and controls at 18-19 weeks of gestational age using Western blot technique. None of the investigated proteins showed overexpression in DS compared to controls. Our present data showing unaltered expression of six proteins on chromosome 21 in fetal DS brain suggest that the existence of the trisomic state is not involved in abnormal development of fetal DS brain and that the gene dosage effect hypothesis is not sufficient to fully explain the DS phenotype. We are in the process of quantifying all gene products of chromosome 21 and our first results do not support the gene dosage hypothesis.
 ...
PMID:Protein levels of genes encoded on chromosome 21 in fetal Down syndrome brain: challenging the gene dosage effect hypothesis (Part I). 1262 42

Down syndrome (DS) is the most common genetic cause of mental retardation. To explain the impact of extra chromosome 21 in the pathology of DS, gene dosage effect hypothesis has been proposed, but several investigators including our group have challenged this hypothesis. Although analysis of the sequence of chromosome 21 has been essentially completed, the molecular and biochemical mechanisms underlying the pathology are still unknown. We therefore investigated expression levels of six proteins encoded on chromosome 21 (HACS1, DYRK1A, alphaA-crystallin, FTCD, GARS-AIRS-GART, and CBS) in fetal cerebral cortex from DS and controls at 18-19 weeks of gestational age using Western blot analysis. Protein expression of HACS1 was significantly and remarkably decreased in DS, and the expression levels of five proteins were comparable between DS and controls suggesting that the gene dosage effect hypothesis is not sufficient to fully explain the DS phenotype. We are continuing to quantify proteins whose genes are encoded on chromosome 21 in order to provide a better understanding of the pathobiochemistry of DS at the protein level.
 ...
PMID:Protein levels of genes encoded on chromosome 21 in fetal Down syndrome brain: challenging the gene dosage effect hypothesis (Part II). 1262 43

Down syndrome (DS) is the most frequent genetic disorder with mental retardation and caused by trisomy 21. Although the gene dosage effect hypothesis has been proposed to explain the impact of extra chromosome 21 on the pathology of DS, a series of evidence that challenge this hypothesis has been reported. The availability of the complete sequences of genes on chromosome 21 serves now as starting point to find functional information of the gene products, but information on gene products is limited so far. We therefore evaluated expression levels of six proteins whose genes are encoded on chromosome 21 (synaptojanin-1, chromosome 21 open reading frame 2, oligomycin sensitivity confering protein, peptide 19, cystatin B and adenosine deaminase RNA-specific 2) in fetal cerebral cortex from DS and controls at 18-19 weeks of gestational age using Western blot analysis. Synaptojanin-1 and C21orf2 were increased in DS, but others were comparable between DS and controls, suggesting that the DS phenotype cannot be simply explained by gene dosage effects. We are systematically quantifying all proteins whose genes are encoded on chromosome 21 in order to provide a better understanding of the pathobiochemistry of DS at the protein level. These studies are of significance as they show for the first time protein levels that are carrying out specific function in human fetal brain with DS.
 ...
PMID:Protein levels of genes encoded on chromosome 21 in fetal Down syndrome brain: challenging the gene dosage effect hypothesis (Part III). 1262 44

Major advances have been made in annotation of sequences of the human genome, although elucidating the functions of these newly discovered genes remains to be a strong challenge. In an effort to give insight into how triplication of chromosome 21 leads to mental retardation in Down syndrome, we have constructed a two-dimensional protein map from control and Down syndrome fetal brain and identified hypothetical proteins with no known functions. Subsequent quantitative analysis of these proteins revealed no apparent change in expression of hypothetical proteins DKZp564P0562.1 (fragment), 16.6, 21.4, 39.5, and 40kDa as well as putative 55kDa protein between controls and Down syndrome fetuses. By contrast, hypothetical protein 28.5kDa was significantly elevated (P<0.05) in fetal Down syndrome. This finding offers an important clue that a hypothetical protein might be involved in the pathomechanisms of brain abnormality in Down syndrome.
 ...
PMID:Expression of hypothetical proteins in human fetal brain: increased expression of hypothetical protein 28.5kDa in Down syndrome, a clue for its tentative role. 1270 81

The study of genomic divergence between humans and primates may provide insight into the origins of human beings and the genetic basis of unique human traits and diseases. Chromosome 21 is the smallest chromosome in the human genome, and some of its regions have been implicated in mental retardation and other diseases. In this study, we sequenced the coding and regulatory regions of 127 known genes on human chromosome 21 in DNA samples from human and chimpanzees and a part of the corresponding genes from orangutan, gorilla, and macaque. Overall, 3,003 nucleotide differences between human and chimpanzee were identified over approximately 400 kb. The differences in coding, promoter, and exon-intron junction regions were 0.51 +/- 0.02%, 0.88 +/- 0.03%, and 0.85 +/- 0.02%, respectively, much lower than the previously reported 1.23% in genomic regions, which suggests the presence of purifying selection. Significant variation in substitution rate among genes was observed by comparing the divergence between human and chimpanzee. Furthermore, by implementing a bioinformatics-based approach, we showed that the identification of genetic variants specific to the human lineage might lead to an understanding of the mechanisms that are attributable to the phenotypes that unique to humans, by changing the structure and/or dosage of the proteins expressed. A phylogenetic analysis unambiguously confirms the conclusion that chimpanzees were our closest relatives to the exclusion of other primates and the relative divergence of the Homo-Pan and that of (Homo-Pan)-Gorilla are 4.93 million years and 7.26 million years, respectively.
 ...
PMID:Divergence of the genes on human chromosome 21 between human and other hominoids and variation of substitution rates among transcription units. 1282 12

Down syndrome (DS) is the most frequent genetic disorder with mental retardation and caused by trisomy 21. Although the molecular mechanisms of the various phenotypes of DS could be due to overexpression of gene(s) on chromosome 21, several groups have challenged this gene dosage effect hypothesis. The near completion of the sequencing of human chromosome 21 provides unprecedented opportunities to understand the molecular pathology of DS, however, functional information on gene products is limited so far. We therefore evaluated the levels of six proteins whose genes are encoded on chromosome 21 (trefoil factor 1, trefoil factor 2, trefoil factor 3, coxsackie virus and adenovirus receptor, carbonyl reductase 1 and interferon- alpha receptor) in fetal cerebral cortex from DS and controls at the early second trimester using Western blot analysis. None of the investigated proteins showed overexpression in DS compared to controls suggesting that these proteins are not involved in abnormal development of fetal DS brain and that DS phenotype can not be simply explained by the gene dosage effect hypothesis. We are systematically quantifying all proteins whose genes are encoded on chromosome 21 and these studies may provide a better understanding of genotype-phenotype correlation in DS.
 ...
PMID:Protein levels of genes encoded on chromosome 21 in fetal Down syndrome brain: Challenging the gene dosage effect hypothesis (Part IV). 1283 57

Mental retardation in Down's syndrome, human trisomy 21, is characterized by developmental delays, language and memory deficits and other cognitive abnormalities. Neurophysiological and functional information is needed to understand the mechanisms of mental retardation in Down's syndrome. The trisomy mouse models provide windows into the molecular and developmental effects associated with abnormal chromosome numbers. The distal segment of mouse chromosome 16 is homologous to nearly the entire long arm of human chromosome 21. Therefore, mice with full or segmental trisomy 16 (Ts65Dn) are considered reliable animal models of Down's syndrome. Ts65Dn mice demonstrate impaired learning in spatial tests and abnormalities in hippocampal synaptic plasticity. We hypothesize that the physiological impairments in the Ts65Dn mouse hippocampus can model the suboptimal brain function occuring at various levels of Down's syndrome brain hierarchy, starting at a single neuron, and then affecting simple and complex neuronal networks. Once these elements create the gross brain structure, their dysfunctional activity cannot be overcome by extensive plasticity and redundancy, and therefore, at the end of the maturation period the mind inside this brain remains deficient and delayed in its capabilities. The complicated interactions that govern this aberrant developmental process cannot be rescued through existing compensatory mechanisms. In summary, overexpression of genes from chromosome 21 shifts biological homeostasis in the Down's syndrome brain to a new less functional state.
 ...
PMID:Understanding mental retardation in Down's syndrome using trisomy 16 mouse models. 1293 90


<< Previous 1 2 3 4 5 6 7 8 9 10