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

The analysis of the fine structure of the chromatids permits the identification of different regions on the long arm of chromosome 21. The preponderant role of the distal third of the long arm in the syndrome of trisomy 21 is now well established. Thus, trisomy of only band 21q22 results in a state identical to that caused by complete trisomy 21. If the trisomy involves only a part of band 21q22, the intensity of the symptoms is diminished, but the appearance of the patient is still reminiscent of Down's syndrome. Monosomy for band 21q22 results in a pathologic condition in which the morphological anomalies are the inverse of those observed in trisomic patients. This syndrome, as a "contre-type" to trisomy 21, is lethal. Trisomy of the proximal long arm region of chromosome 21 (21q21 leads to 21q22) is not associated with malformations but is accompanied by mental retardation. Monosomy of the same region results in a pathologic condition, which does not have features of the contre-type of trisomy 21.
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PMID:Structural variation of chromosome 21 and symptoms of Down's syndrome. 621 34

The typical neuropathological features of Alzheimer's disease, plaques and tangles, appear in virtually all patients with Down's Syndrome after the age of 40. Clinically, changes in cognitive performance and behavior appear to correlate with these neuropathological changes, although a satisfactory operational definition of dementia in a context of mental retardation is not available. It is unknown whether the cholinergic losses in the nucleus basalis, which are a feature of early onset Alzheimer's disease, also occur late in Down's syndrome. Two family studies have supported a greater than expected incidence of Down's cases among relatives of probands dying with Alzheimer-type dementia, but the association is not strong. It is noteworthy that in both studies, phenotypically normal carriers of the rare 15/21 translocation had severe early onset dementia, although this translocation is responsible for less than 0.4 per cent of Down's cases. An increased incidence of dementia among carriers of the more common 14/21 translocation has not been reported. In any case, it is proposed that a gene product originating from the long arm of chromosome 21 (21q) is necessary for Alzheimer-type pathology, since a segregating gene could not be responsible for the 100 per cent incidence of these changes among 21q trisomics.
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PMID:Down's syndrome and Alzheimer's dementia: defining an association. 624 13

Aneuploid chromosomal disorders may offer insight into the pathogenesis of certain common diseases. The birth defects and mental retardation that characterize Down's syndrome are well recognized. In addition, the altered chromosomal content that occurs in the syndrome apparently affects the prevalence of a variety of disorders, such as malignancy, endocrine dysfunction, infection, atherosclerosis, and premature aging. Because the single distinguishing factor in Down's syndrome is the presence of an excess of a part of chromosome 21, the genetic information contained in this chromosomal segment seems to be responsible for the disease manifestations. Techniques of somatic cell genetics and molecular biology allow mapping of human genes and study of their expression. With such methods it should be possible to understand Down's syndrome and other aneuploid disorders and to apply these considerations to other areas of medicine.
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PMID:Down's syndrome as a model disease. 646 5

Ring chromosome 21 is a very rare chromosomal abnormality known to cause a great variety of clinical findings. Persons with ring chromosome 21 can be intellectually and phenotypically normal, but this abnormality is found more often in persons with dysmorphic features, malformations and mental retardation. Ring chromosome 21 is also encountered as the only chromosomal abnormality in individuals with Down syndrome. We describe a four year old girl with ring chromosome 21 (karyotype 46,XX/46,XX,-21, +r(21)), who was examined in a department of child psychiatry because of delayed development. The child had serious speech and language problems, slightly dysmorphic features and bilateral hip-joint dysplasia.
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PMID:[Ring chromosome 21 as a cause of developmental disorder. A case report from the practice of child psychiatry]. 750 4

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

S100 beta, a calcium-binding brain protein, has been implicated in brain development and hippocampal neurophysiology including long-term potentiation. Its gene maps to chromosome 21, which is duplicated in Down syndrome. S100 beta levels are elevated in both Down syndrome and Alzheimer's disease, human neurodegenerative diseases associated with mental retardation and dementia. To investigate whether or not elevated S100 beta levels can cause brain dysfunctioning in mammals, transgenic mice carrying multiple copies of the human S100 beta gene were generated. Several independent lines of transgenic mice were compared to age-matched normal control mice of identical genetic background (CD1) by measuring their exploratory behaviors in novel situations. Transgenic mice exhibited a range of defects including female specific hyperactivity, lack of habituation to novelty and reduced T-maze spontaneous alternation rate. Although the neuroanatomical or physiological substrate of these abnormalities is unknown, they are similar to the behavioral manifestations of hippocampal dysfunction. The S100 beta mouse offers one of the first opportunities to investigate the relationship between over-expression of a human chromosome 21 gene product and abnormal behavior and brain functioning.
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PMID:Abnormal exploratory behavior in transgenic mice carrying multiple copies of the human gene for S100 beta. 770 19

Ring chromosome 21 is a rare chromosome anomaly often associated with mental retardation and dysmorphic features. Less commonly, the ring chromosome can be familial and associated with a normal phenotype. Phenotypically normal female carriers, however, are at increased risk of having children with Down syndrome, mosaic monosomy 21, and variable duplication or deletion of chromosome 21. Because of the relative mitotic and meiotic instability of ring chromosomes, abnormal cytogenetic findings encountered during prenatal diagnosis may not reflect the true genetic status of the fetus. This is a report of a phenotypically normal female carrier of a familial ring 21 chromosome. Prenatal diagnosis on her twin pregnancy revealed a mosaic 46,XX,r(21)(p13;q22) (77 per cent)/45,XX,-21 in one fetus and a normal male karyotype in the second. The pregnancy was carried to term. Both infants are completely normal, with a non-mosaic ring 21 karyotype from the lymphocytes of one twin. The diagnostic uncertainty and problematic genetic counselling related to fetal cytogenetic abnormalities are the subjects of this report.
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PMID:Prenatal diagnosis of familial ring 21 chromosome. 778 85

Unbalanced Robertsonian translocations are a significant cause of mental retardation and fetal wastage. The majority of homologous rearrangements of chromosome 21 in Down syndrome have been shown to be isochromosomes. Aside from chromosome 21, very little is known about other acrocentric homologous rearrangements. In this study, four cases of de novo secondary trisomy 13 are presented. FISH using alpha-satellite sequences, rDNA, and a pTRI-6 satellite I sequence specific to the short arm of chromosome 13 showed all four rearrangements to be dicentric and apparently devoid of ribosomal genes. Three of four rearrangements retained the pTRI-6 satellite I sequence. Case 1 was the exception, showing a deletion of this sequence in the rearrangement, although both parental chromosomes 13 had strong positive hybridization signals. Eleven microsatellite markers from chromosome 13 were also used to characterize the rearrangements. Of the four possible outcomes, one maternal Robertsonian translocation, two paternal isochromosomes, and one maternal isochromosome were observed. A double recombination was observed in the maternally derived rob(13q13q). No recombination events were detected in any isochromosome. The parental origins and molecular chromosomal structure of these cases are compared with previous studies of de novo acrocentric rearrangements.
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PMID:Molecular characterization of de novo secondary trisomy 13. 797 60

Phenotypic and molecular analysis of individuals with partial trisomy 21 can be used to determine which regions of chromosome 21 are involved in the pathogenesis of specific features of Down's Syndrome. Using dosage analysis of 27 sequences we defined, at the molecular level, the extent of the chromosome 21 duplication in ten individuals with partial trisomy 21. Phenotype-genotype correlations led to the definition of minimal regions, the duplications of which are linked to the expression of 23 clinical features of Down's Syndrome. The D21S55 region or Down's Syndrome Chromosome Region 1 (DCR1) (1/20 of the long arm), on 21q22.2-21q22.3 proximal, is involved in four cardinal features of the disease: mental retardation, growth retardation, muscular hypotonia and joint hyperlaxity, and in eight of the 18 more common morphological anomalies of the face, hands and feet. Overlapping the DCR1, the D21S55-MX1 region or DCR2 (1/10 of the long arm), spanning 21q21.2 down to the 1/4th proximal part of 21q22.3, is involved in the features defined by the DCR1 plus congenital heart defect and five additional morphological anomalies. Thus, our results indicate that duplication of a relatively small region of chromosome 21 plays a critical role in the pathogenesis of the Down's phenotype.
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PMID:Mapping of the Down syndrome phenotype on chromosome 21 at the molecular level. 799 86

Chromosomal abnormalities associated with bipolar disorder may help in the localisation of susceptibility genes for bipolar illness by pinpointing 'candidate' regions of the genome for further study using molecular genetic methods. We review descriptions of chromosomal abnormalities in association with bipolar and related affective disorders and evaluate their relevance for localising susceptibility genes for bipolar disorder, using standardised criteria. We found 28 reports. We identified four genomic regions of potential interest: 11q21-25; 15q11-13; chromosome 21;Xq28. It is important that clinicians are able to recognise patients who may have chromosome abnormalities which could help in the localisation of susceptibility genes for psychiatric disorders. We suggest referral for specialist investigation and karyotyping, to a psychiatric genetics research group, of any patient with functional psychosis and one or more of the following: (a) a strong family history of functional psychosis; (b) mental retardation; (c) another disease known to be caused by a single gene; or (d) congenital abnormalities.
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PMID:Chromosomal aberrations and bipolar affective disorder. 786 91


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