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

Many human genetic diseases, including some cancers, are characterized by consistent chromosome abnormalities, such as deletions and translocations. Analyses of these mutations often prove crucial to the eventual cloning and characterization of the gene(s) responsible for the disease. Two methods for analyzing these chromosome abnormalities have been developed in recent years: somatic cell hybridization and pulsed field gel electrophoresis (PFGE). Somatic cell hybridization is a technique for segregating an aberrant chromosome from its normal homologue in a cell derived from an unrelated species, which is usually a rodent. Panels of such hybrids dividing a given chromosomal region into increasingly smaller units can be constructed and used specifically to map DNA probes into those units. PFGE can then be used to define precise physical distances between such an array of chromosome abnormalities. Demonstrations of these analytic techniques are presented, using as an example chromosomal abnormalities involving human chromosome band 11p13, the locus for the Wilms' tumor, aniridia, genitourinary abnormality, and mental retardation (WAGR) syndrome.
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PMID:Molecular analysis of chromosomal rearrangements using pulsed field gel electrophoresis and somatic cell hybrids. 166 Aug 7

The fragile X syndrome is the most common cause of familial mental retardation and is characterized by a fragile site at the end of the long arm of the X chromosome. The unusual genetics and cytogenetics of this X-linked condition make genetic counseling difficult. DNA studies were of limited value in genetic counseling, because the nearest polymorphic DNA loci had recombination fractions of 12% or more with the fragile X mutation, FRAXA. Five polymorphic loci have recently been described in this region of the X chromosome. The positions of these loci in relation to FRAXA were defined in a genetic linkage study of 112 affected families. The five loci--DXS369, DXS297, DXS296, IDS, and DXS304--had recombination fractions of 4% or less with FRAXA. The closest locus, DXS296, was distal to FRAXA and had a recombination fraction of 2%. The polymorphisms at these loci can be detected in DNA enzymatically digested with a limited number of restriction endonucleases. A strategy for DNA studies which is based on three restriction endonucleases and on five probes will detect one or more of these polymorphisms in 94% of women. This strategy greatly increases the utility of DNA studies in providing genetic advice to families with the fragile X syndrome.
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PMID:Genetic mapping of new DNA probes at Xq27 defines a strategy for DNA studies in the fragile X syndrome. 167 6

The fragile-X syndrome is the most frequent inherited form of mental retardation, with an incidence of 1 in 1,500 males. It is characterized by the presence of a fragile site at Xq27.3 induced in vitro by folate deprivation or by inhibitors of deoxynucleotide synthesis. Its mode of inheritance is unusual for an X-linked trait, with incomplete penetrance in both males and females. Some phenotypically normal males transmit the mutation to all their daughters who rarely express any symptoms, but penetrance is high in sons and daughters of these carrier women. Genetic and physical mapping of the Xq27-q28 region has confirmed that the disease locus is located at or very near the fragile site. Hypotheses proposed to account for the abnormalities in the inheritance of the disease include sequence rearrangements by meiotic recombination or a mutation that affects reactivation of an inactive X chromosome during differentiation of female germ cells. To detect such rearrangements, or methylation changes that may reflect a locally inactive X chromosome, we used pulsed-field gel analysis of DNA from fragile-X patients with probes close to the fragile-X locus. The probe Do33 (DXS465) detected abnormal patterns in fragile-X patients, but not in normal controls or in non-expressing male transmitters.
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PMID:Abnormal pattern detected in fragile-X patients by pulsed-field gel electrophoresis. 167 39

A mapping study was performed on a 3-generation Spanish family with X-linked syndromal mental retardation. Affected males have a typical facial appearance, ear malformations, abnormal growth of teeth, clinodactyly, dimpled skin at the lower back, and patellar luxation. In pneumoencephalography a marked subcortical cerebral atrophy was evident. In the linkage studies with polymorphic DNA markers, no recombination was found between the disease locus and the loci OTC and DXS148, both assigned to Xp21.1. One or more recombinants were observed between the disease locus and loci from the distal part of Xp and the pericentromeric region. Close linkage to loci of Xq has also been excluded. The analysis of multiple informative meioses suggests that the disease locus maps between DXS255 (Xp11.22) and DXS84 (Xp21.1) on Xp.
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PMID:Gene localization in a family with X-linked syndromal mental retardation (Prieto syndrome). 167 97

We report on a 10-year-old patient with the fragile X [fra(X)] syndrome and a 47,XXY karyotype. He had Martin-Bell syndrome, including typical craniofacial findings and mental retardation. The fra(X) was detected on both X chromosomes of the patient in 8% of the metaphases examined. DNA analysis using X-chromosome sequences from the pericentromeric region and from distal Xq suggests that the patient is homozygous at the fra(X) locus due to maternal nondisjunction during meiosis II.
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PMID:Origin of the supernumerary X chromosome in a patient with fragile X and Klinefelter syndrome. 167 17

Linkage of the gene responsible for an X-linked early onset parkinsonism disorder with mental retardation (McKusick 311510) to DNA probes that detect restriction fragment length polymorphisms is described. The disease gene is linked to the F8C gene, and to DNA probes detecting polymorphic loci DXS52, DXS15, DXS134, and DXS374 with maximum lod scores at theta = 0 of 5.08, 5.19, 5.00, 5.03, and 4.46, respectively. Multipoint linkage analysis gives a maximum multipoint lod score of 6.75 at the F8C gene. This places the disease gene in chromosomal region Xq27.3-qter.
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PMID:Waisman syndrome, a human X-linked recessive basal ganglia disorder with mental retardation: localization to Xq27.3-qter. 167 30

Cytogenetic analysis of a male infant referred for poor neurological development and failure to thrive showed a microdeletion of the X chromosome, his karyotype being 46,Y,del(X)(pter----q21.1:: q21.2----qter). His mother and grandmother were also found to carry the deletion. DNA probes were used to define the deletion molecularly and it was shown to span intervals 2 to 6 of Cremers et al, a portion of Xq that contains the TCD gene and genes whose absence is associated with deafness and mental retardation. RFLP analysis together with X inactivation studies using the probe M27 beta verified the carrier status of the female relatives and showed non-random X inactivation in the heterozygous females.
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PMID:Molecular and cytogenetic analysis of a familial microdeletion of Xq. 167 84

Fragile X syndrome, associated with the fragile X chromosome, is the most common cause of familial mental retardation. The condition is characterised by a heritable DNA sequence that consists of an abnormal number of CCG repeats, and which is unstable in both mitosis and meiosis. We suggest that such heritable unstable DNA sequences could be present in other parts of the genome and that these might explain a number of genetic events that are not well understood in terms of classic genetic mechanisms. Such poorly explained observations include anticipation, incomplete penetrance, variable expression, and possibly imprinting, variegation, and multifactorial inheritance.
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PMID:Hereditary unstable DNA: a new explanation for some old genetic questions? 167 19

Fragile X-linked mental retardation is an enigmatic inheritable syndrome in which severe mental retardation, a cytogenetically detectable fragile site at Xq27.3 (FraX) and a number of dysmorphic features are associated. Genetic analysis shows that the mode of inheritance is more complex than a straightforward X-linked recessive trait and probably involves a two-step process for which several models have been proposed. Early attempts at 'cloning the fragile site' provided several DNA segments lying in its general vicinity, and large scale DNA mapping methods were extensively applied in an effort to generate maps including this region. These efforts were complemented by more focussed methods such as microdissection; together these approaches have now provided a number of DNA segments within a 5 cM interval around FraX, and with the help of these new probes the site is indeed being cloned. Unravelling the nature of the sequence(s) responsible for the mental retardation syndrome will probably take some time, however.
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PMID:Fragile X-linked mental retardation and the difficulties of reverse genetics. 167 86

The origin of an extra marker chromosome in a patient with mental retardation and intractable epilepsy was ascertained by DNA analysis. Gene dose and restriction fragment length polymorphism (RFLP) studies of D15S9 proved that the patient was tetrasomic for the gene and that the extra chromosome was of maternal origin. On the basis of the molecular findings, further detailed GTG-banded chromosome analysis interpreted the marker chromosome as inv dup(15)(pter----q14::q14----pter). The clinical manifestations of the patient are consistent with those of the patients previously described.
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PMID:Identification of a marker chromosome as inv dup(15) by molecular analysis. 168 58


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