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Query: UMLS:C0025362 (mental retardation)
 15,878 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Down's syndrome (DS) is a genetic disorder involving an excess of chromosome 21 (trisomy 21) in approximately 96% of the cases and comprises approximately 15% of the population with mental retardation (Heller, 1969). In addition to the constitutional mental deficiencies associated with the syndrome many DS patients develop dementia associated with Alzheimer's disease (AD) in their later years of life (Thase et al., 1984). The genetic locus for Cu,Zn-superoxide dismutase (SOD1), a key enzyme in free radical metabolism, is located on chromosome 21, and the activity level of this enzyme is elevated by approximately 50% in a variety of cells of DS patients (see Kedziora and Bartosz, 1988; Sinet, 1982). Because alterations in free radical metabolism may be involved in neuronal death and may be associated with a number of pathological manifestations of DS, it is important to understand the role of free radical metabolism in cognitive impairments of DS, the topic discussed in this chapter.
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PMID:The role of alterations in free radical metabolism in mediating cognitive impairments in Down's syndrome. 145 May 86

Three Down syndrome patients for whom karyotypic analysis showed a "mirror" (reverse tandem) duplication of chromosome 21 were studied by phenotypic, cytogenetic, and molecular methods. On high-resolution R-banding analysis performed in two cases, the size of the fusion 21q22.3 band was apparently less than twice the size of the normal 21q22.3, suggesting a partial deletion of distal 21q. The evaluation of eight chromosome 21 single-copy sequences of the 21q22 region--namely, SOD1, D21S15, D21S42, CRYA1, PFKL, CD18, COL6A1, and S100B--by a slot blot method showed in all three cases a partial deletion of 21q22.3 and partial monosomy. The translocation breakpoints were different in each patient, and in two cases the rearranged chromosome was found to be asymmetrical. The molecular definition of the monosomy 21 in each patient was, respectively, COL6A1-S100B, CD18-S100B, and PFKL-S100B. DNA polymorphism analysis indicated in all cases a homozygosity of the duplicated material. The duplicated region was maternal in two patients and paternal in one patient. These data suggest that the reverse tandem chromosomes did not result from a telomeric fusion between chromosomes 21 but from a translocation between sister chromatids. The phenotypes of these patients did not differ significantly from that of individuals with full trisomy 21, except in one case with large ears with an unfolded helix. The fact that monosomy of distal 21q22.3 in these patients resulted in a phenotype very similar to Down syndrome suggests that the duplication of the genes located in this part of chromosome 21 is not necessary for the pathogenesis of the Down syndrome features observed in these patients, including most of the facial and hand features, muscular hypotonia, cardiopathy of the Fallot tetralogy type, and part of the mental retardation.
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PMID:No significant effect of monosomy for distal 21q22.3 on the Down syndrome phenotype in "mirror" duplications of chromosome 21. 146 8

Down syndrome (DS) is a major cause of congenital heart and gut disease and mental retardation. DS individuals also have characteristic facies, hands, and dermatoglyphics, in addition to abnormalities of the immune system, an increased risk of leukemia, and an Alzheimer-like dementia. Although their molecular basis is unknown, recent work on patients with DS and partial duplications of chromosome 21 has suggested small chromosomal regions located in band q22 that are likely to contain the genes for some of these features. We now extend these analyses to define molecular markers for the congenital heart disease, the duodenal stenosis, and an "overlap" region for the facial and some of the skeletal features. We report the clinical, cytogenetic, and molecular analysis of two patients. The first is DUP21JS, who carries both a partial duplication of chromosome 21, including the region 21q21.1-q22.13, or proximal q22.2, and DS features including duodenal stenosis. Using quantitative Southern blot dosage analysis and 15 DNA sequences unique to chromosome 21, we have defined the molecular extent of the duplication. This includes the region defined by DNA sequences for APP (amyloid precursor protein), SOD1 (CuZn superoxide dismutase), D21S47, SF57, D21S17, D21S55, D21S3, and D21S15 and excludes the regions defined by DNA sequences for D21S16, D21S46, D21S1, D21S19, BCE I (breast cancer estrogen-inducible gene), D21S39, and D21S44. Using similar techniques, we have also defined the region duplicated in the second case occurring in a family carrying a translocation associated with DS and congenital heart disease. This region includes DNA sequences for D21S55 and D21S3 and excludes DNA sequences for D21S47 and D21S17.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Down syndrome: molecular mapping of the congenital heart disease and duodenal stenosis. 153 Nov 66

Down syndrome (DS) is a major cause of mental retardation and heart disease. Although it is usually caused by the presence of an extra chromosome 21, a subset of the diagnostic features may be caused by the presence of only band 21q22. We now present evidence that significantly narrows the chromosomal region responsible for several of the phenotypic features of DS. We report a molecular and cytogenetic analysis of a three-generation family containing four individuals with clinical DS as manifested by the characteristic facial appearance, endocardial cushion defect, mental retardation, and probably dermatoglyphic changes. Autoradiograms of quantitative Southern blots of DNAs from two affected sisters, their carrier father, and a normal control were analyzed after hybridization with two to six unique DNA sequences regionally mapped on chromosome 21. These include cDNA probes for the genes for CuZn-superoxide dismutase (SOD1) mapping in 21q22.1 and for the amyloid precursor protein (APP) mapping in 21q11.2-21.05, in addition to six probes for single-copy sequences: D21S46 in 21q11.2-21.05, D21S47 and SF57 in 21q22.1-22.3, and D21S39, D21S42, and D21S43 in 21q22.3. All sequences located in 21q22.3 were present in three copies in the affected individuals, whereas those located proximal to this region were present in only two copies. In the carrier father, all DNA sequences were present in only two copies. Cytogenetic analysis of affected individuals employing R and G banding of prometaphase preparations combined with in situ hybridization revealed a translocation of the region from very distal 21q22.1 to 21qter to chromosome 4q. Except for a possible phenotypic contribution from the deletion of chromosome band 4q35, these data provide a molecular definition of the minimal region of chromosome 21 which, when duplicated, generates the facial features, heart defect, a component of the mental retardation, and probably several of the dermatoglyphic changes of DS. This region may include parts of bands 21q22.2 and 21q22.3, but it must exclude the genes S0D1 and APP and most of band 21q22.1, specifically the region defined by S0D1, SF57 and D21S47.
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PMID:Molecular definition of a region of chromosome 21 that causes features of the Down syndrome phenotype. 214 53

Down syndrome (DS) is a major cause of mental retardation and heart disease. Although it is usually caused by the presence of an extra chromosome 21, a subset of the diagnostic features may be caused by the presence of only band q22. Molecular and cytogenetic analysis of a family with 4 DS members has significantly narrowed the chromosomal region responsible for the DS phenotype: congenital heart disease, facial features, and possibly dermatoglyphics. Using high-resolution chromosome banding and in situ hybridization, we found the DS phenotype in the family is caused by a duplication of chromosome 21 material including a region of distal band q22.1 below the limit of cytogenetic resolution, in addition to bands q22.2-q22.3. By quantitative Southern blot analyses of DS members of the family, all random DNA sequences and expressed genes mapping in band q22.1 and proximal are found not to be duplicated. These include cDNA probes for the genes for superoxide dismutase (SOD1) mapping in 21q22.1 and for the amyloid precursor protein (APP) mapping in 21q21.05; D21S46 in 21q11.2-21.05; and D21S47 and SF57 in 21q22.1-q22.3. With one exception, DNA sequences mapping in band q22.3 are duplicated (D21S39, D21SD42, and D21S43). This analysis has now been extended to show that D21S17, previously mapped to band 21q22.3, is not duplicated. In conclusion, the genes SOD1 and APP have been excluded from a necessary role in generating the classical DS features, and the proximal border of the chromosomal region causing DS has been defined.
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PMID:Down syndrome: toward a molecular definition of the phenotype. 214 83

We compared the phenotypes, karyotypes, and molecular data for six cases of partial monosomy 21. Regions of chromosome 21, the deletion of which corresponds to particular features of monosomy 21, were thereby defined. Five such regions were identified for 21 features. Ten of the features could be assigned to the region flanked by genes APP and SOD1: six facial features, transverse palmar crease, arthrogryposis-like symptoms, hypertonia, and contribution to mental retardation. This region, covering the interface of bands 21q21-21q22.1, is 4.7-6.4 Mb long and contains the gene encoding the glutamate receptor subunit GluR5 (GRIK1).
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PMID:Molecular mapping of 21 features associated with partial monosomy 21: involvement of the APP-SOD1 region. 910 47

Down syndrome (trisomy 21) is a genetic disease with developmental brain abnormalities resulting in early mental retardation and precocious, age dependent Alzheimer-type neurodegeneration. We tried to discuss the role of neurodevelopmental abnormalities in connection with aberrant expression of genes on chromosome 21 including amyloid precursor protein (APP), CuZn superoxide dismutase (SOD1) and glial-derived S100 beta protein for neurodegeneration in DS. In this model, alterations in developmental pathways due to aberrant gene expression can impair cellular homeostasis and predispose to neurodegeneration of certain brain regions and types of nerve cells, involving cholinergic, serotonergic and catecholaminergic transmission, by shifting balance toward a pro-apoptotic state.
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PMID:The brain in Down syndrome. 1177 48

Down syndrome (DS) is the most common chromosomal abnormality associated with early mental retardation and neurological abnormalities followed by precocious age dependent Alzheimer-type neurode generation later in life. Knowledge of the pathological mechanisms involved in DS is far from complete, but overexpression of genes residing in chromosome 21 was considered to be the central point for the DS phenotype. In this regard, beta amyloid precursor protein (APP), CuZn superoxide dismutase (SOD1) and S100beta have been implicated in causing apoptosis, a mechanism thought to be responsible for neuronal loss in DS, in one way or another. The gene dosage hypothesis has been challenged, however, and dysregulation of expression of genes located on other chromosomes has been described, which may well be secondary to chromosomal imbalance or a direct consequence of the disease process. The present review focuses on the protein expression profile in DS and we postulate that abnormalities in the coordinated expression, as well as interaction of proteins may be responsible for the neuropathology of DS. A series of candidate proteins are discussed that may be directly causing or reflecting the DS phenotype, in particular the brain abnormalities in DS.
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PMID:Protein expression in Down syndrome brain. 1185 95

Down Syndrome (DS), one of the major genetic causes of mental retardation, is characterized by disrupted corticogenesis produced, in part, by an abnormal layering of neurons in cortical laminas II and III. Because defects in the normal migration of neurons during corticogenesis can result in delayed cortical radial expansion and abnormalities in cortical layering, we have examined neuronal migration in murine trisomy 16 (Ts16), a mouse model for DS. Using an in vitro assay for chemotaxis, our data demonstrate that the number of acutely dissociated Ts16 cortical neurons migrating in response to glutamate or N-methyl-D-aspartate (NMDA), known chemotactic factors, was decreased compared to normal littermates, suggesting a defect in NMDA receptor- (NMDAR-) mediated events. Ts16 neurons did not lack NMDAR since expression of mRNA and protein for NMDAR subunits was observed in Ts16 cells. However, the number of cells that generated an observable current in response to NMDA was decreased compared to normal littermates. Similar to DS, Ts16 CNS demonstrated an inherent oxidative stress likely caused by the triplication of genes such as SOD1. To determine if the abnormal redox state was a factor in the failure of NMDAR-mediated migration in Ts16, we treated Ts16 neurons with either n-acetyl cysteine (NAC) or dithiothrietol (DTT), known antioxidants. The reduction in NMDAR-mediated migration observed in Ts16 neurons was returned to normal littermate values by NAC or DTT. Our data indicate that oxidative stress may play a key role in the abnormal glutamate-mediated responses during cortical development in the Ts16 mouse and may have an impact on neuronal migration at critical stages.
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PMID:Redox regulation of neuronal migration in a Down Syndrome model. 1295 49

Trisomy 21 or Down syndrome (DS) is the most common genetic birth defect associated with mental retardation. The over-expression of genes on chromosome 21, including SOD1 (Cu/Zn superoxide dismutase) and APP (amyloid-beta precursor protein) is believed to underlie the increased oxidative stress and neurodegeneration commonly described in DS. However, a segmental trisomy 16 mouse model for DS, Ts1Cje, has a subset of triplicated human chromosome 21 gene orthologs that exclude APP and SOD1. Here, we report that Ts1Cje brain shows decreases of mitochondrial membrane potential and ATP production, increases of reactive oxygen species, hyperphosphorylation of tau without NFT formation, increase of GSK3beta and JNK/SAPK activities and unaltered AbetaPP metabolism. Our findings suggest that genes on the trisomic Ts1Cje segment other than APP and SOD1 can cause oxidative stress, mitochondrial dysfunction and hyperphosphorylation of tau, all of which may play critical roles in the pathogenesis of mental retardation in DS.
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PMID:Mitochondrial dysfunction and tau hyperphosphorylation in Ts1Cje, a mouse model for Down syndrome. 1689 9


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