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  • 1
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract High resolution cytogenetics, microsatellite marker analyses, and fluorescence in situ hybridization were used to define Xq deletions encompassing the fragile X gene, FMR1, detected in individuals from two unrelated families. In Family 1, a 19-year-old male had facial features consistent with fragile X syndrome; however, his profound mental and growth retardation, small testes, and lover limb skeletal defects and contractures demonstrated a more severe phenotype, suggestive of a contiguous gene syndrome. A cytogenetic deletion including Xq26.3–q27.3 was observed in the proband, his phenotypically normal mother, and his learning-disabled non-dysmorphic sister. Methylation analyses at the FMR1 and androgen receptor loci indicated that the deleted X was inactive in 〉 95% of his mother’s white blood cells and 80–85% of the sister’s leukocytes. The proximal breakpoint for the deletion was approximately 10 Mb centromeric to FMR1, and the distal breakpoint mapped 1 Mb distal to FMR1. This deletion, encompassing ∼13 Mb of DNA, is the largest deletion including FMR1 reported to date. In the second family, a slightly smaller deletion was detected. A female with moderate to severe mental retardation, seizures, and hypothyroidism, had a de novo cytogenetic deletion extending from Xq26.3 to q27.3, which removed ∼12 Mb of DNA around the FMR1 gene. Cytogenetic and molecular data revealed that ∼50% of her white blood cells contained an active deleted X. These findings indicate that males with deletions including Xq26.3–q27.3 may exhibit a more severe phenotype than typical fragile X males, and females with similar deletions may have an abnormal phenotype if the deleted X remains active in a significant proportion of the cells. Thus, important genes for intellectual and neurological development, in addition to FMR1, may reside in Xq26.3–q27.3. One candidate gene in this region, SOX3, is thought to be involved in neuronal development and its loss may partly explain the more severe phenotypes of our patients.
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  • 2
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Linkage analysis of four polymorphic anonymous DNA markers from the Xp22 region was performed using families from the Centre d'Etude du Polymorphisme Humain. The loci DXS43 (pD2) and DXS16 (pXUT23) were found to be tightly linked ( $$\hat \theta $$ = 0.02 at $$\hat Z$$ = 14.96) and proximal to both DXS85 (782) and DXS143 (dic56). Multipoint linkage analysis suggests the order:
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  • 3
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Eleven families segregating for the X-linked recessive immune deficiency disorder, Wiskott-Aldrich syndrome (WAS), were studied by linkage analysis with an alpha satellite DNA probe, pBamX-7, which detects polymorphism at the X chromosome centromere, locus DXZ1, as well as three other polymorphic markers defining loci on the proximal short arm of the X chromosome. Linkage has been established between WAS and DXZ1 (ž (θ)=7.08 at θ=0.03) and WAS and the TIMP gene locus (ž (θ)=5.09 at θ=0.0). We have also confirmed close linkage between DXZ1 and two marker loci, DXS14 and DXS7, previously shown to be linked to the WAS locus. The probe pBamX-7 detected allelic variation in all females tested, reflecting the high frequency of polymorphism at the centromere. One WAS carrier revealed a recombination between WAS and both marker loci DXZ1 and DXS14, indicating that WAS does not map between these loci. In conjunction with previous data from genetic mapping studies of WAS, these results confirm the pericentromerix Xp localization of WAS and demonstrate the usefulness of alpha satelite DNA probes as tools for genetic prediction in WAS as well as other pericentric X-linked diseases.
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  • 4
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Three different long-arm X isochromosomes and an isodicentric X chromosome were examined by in situ hybridization with X-chromosome-specific α-satellite probes and by quantitation of Southern blots hybridized with proximal short-arm probes. Each chromosome had a unique pericentromeric structure. The isodicentric X chromosome was clearly dicentric, showing two distinct α-satellite hybridization signals and duplication of short-arm material. Two isochromosomes showed a larger than normal, bifid α-satellite signal and also had duplications of different extents of short-arm material. The third X isochromosome could not be distinguished from a classical long-arm isochromosome; it did not have a short-arm duplication and it had a single α-satellite signal. These data indicate that rearrangements responsible for X isochromosome formation can occur at numerous locations in the pericentromeric region and that some X isochromosomes may involve duplications of substantial portions of the short arm.
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  • 5
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary DNA encoding the human aminopeptidase N (EC 3.4.11.2) gene (PEPN) was first isolated using rat cDNA probes and then used in Southern analysis of DNA from mouse-human somatic cell hybrids to assign this gene to the long-arm region (q11-qter) of human chromosome 15. This human genomic DNA probe detects a frequent DraIII polymorphism that is a useful marker for human chromosome 15.
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  • 6
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary We have investigated the organization and genomic distribution of sequences homologous to p82H, a cloned human alpha satellite sequence purported, based on previous in situ hybridization experiments, to exist at the centromere of each human chromosome. We report here that, using Southern blotting analysis under conditions of high stringency, p82H hybridizes solely to a low-copy or single-copy alphoid domain located at or near the centromeric region of human chromosome 14. In contrast, conditions of reduced hybridization stringency permit extensive cross-hybridization with nonidentical, chromosome-specific alpha satellite subsets found elsewhere in the human genome. Thus, the previously described ubiquity of “82H” human centromeric sequences reflects the existence of diverse alpha satellite subsets located at the centromeric region of each human chromosome.
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  • 7
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary A sensitive, reliable, and easily performed procedure is described for the prenatal and postnatal detection of inborn errors of propionate, methylmalonate, and cobalamin metabolism using cultured amniotic cells and skin fibroblasts. With this assay, control fibroblast lines incorporated a mean of 6.89 nanoatoms 14C/mg protein from [1-14C]propionate into trichloroacetic acid (TCA)-precipitable cell material in 10h. Twenty-five mutant fibroblast lines from patients with propionicacidemia or one of the methylmalonicacidemias fixed 0.04 to 0.93 nanoatoms 14C/mg. Considerable variation was observed, both among and within discrete mutant classes, with respect to the residual amount of propionate pathway activity, possibly reflecting further molecular heterogeneity in these disorders. We applied this procedure to cultured amniotic cells from controls and 4 midtrimester pregnancies at risk for methylmalonicacidemia and diagnosed one fetus with a methylmalonyl CoA apomutase defect and 3 fetuses which were unaffected.
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  • 8
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The pericentromeric region of human chromosomes is composed of diverse classes of repetitive DNAs, which provide a rich source of genetic variability. Here, we describe two novel centromeric polymorphisms associated with a subset of alpha satellite repetitive DNA, D11Z1, which is specific for human chromosome 11. Segregation and inheritance of the polymorphisms are demonstrated and their relative frequencies are determined. These polymorphisms may be useful genetic tools for distinguishing between individual chromosome 11 centromeres. In addition, these polymorphisms may be applied to the development of a centromerebased genetic linkage map of chromosome 11. Molecular models for the generation of these polymorphisms are discussed.
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  • 9
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. The centromeric regions of human and primate chromosomes are characterized by diverged subsets of tandemly repeated α-satellite DNA. Comparison of the α-satellites on known homologous chromosomes in human and chimpanzee provides insight into the very rapid evolution of satellite DNA sequences and the mechanisms that shape complex genomes. By using oligonucleotide primers specific for a conserved region of human α-satellite DNA, we have amplified a chromosome-specific α-satellite subset from the chimpanzee genome by the polymerase chain reaction. Fluorescence in situ hybridization showed that clones pαPTR4N and pαPTR4H are homologous to sequences at the centromere of the chimpanzee chromosome 4. This α-satellite subset is organized as a series of pentameric (higher-order) repeats, operationally defined by digestion of genomic DNA with HaeIII, MboI, RsaI, SstI, and XbaI. The lengths of four independent centromeric arrays measured by pulsed-field gel electrophoresis varied between 800 and 3,500 kb (mean = 1,850 kb, SD = 1,000 kb). Nucleotide sequence analysis demonstrated that chimpanzee chromosome 4 α-satellite is most closely related to the suprachromosomal subfamily II, which is evolutionarily different from the subfamily I to which the α-satellite on the homologous human chromosome 5 belongs. This implies that the human-chimpanzee sequence divergence has not arisen from a common ancestral α-satellite repeat(s) but instead represents concerted evolution of distinct repeats on homologous chromosomes.
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  • 10
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The human alpha satellite DNA family, like many highly repeated satellite DNAs in eukaryotic genomes, is organized in distinct chromosome-specific subsets. As part of investigations into the molecular and evolutionary basis for the chromosome-specific nature of such subsets, we report the isolation and characterization of alpha satellite sequences specific for human chromosome 3. This subset is characterized by a predominant tandemly arranged ∼2.9 kb higher-order repeat unit which, in turn, consists of 17 tandem diverged monomer repeat units of ∼171 bp. Nucleotide sequence analysis reveals that the chromosome 3 higher-order repeat units are comprised, at least in part, of diverged dimeric (∼ 340 bp) sub-repeats and that this divergence accounts for the chromosome-specific behavior of this subset. Pulsed-field gel electrophoresis demonstrates that the chromosome 3 higher-order repeat units are localized in large domains, at least 1000 kb in length. Familial restriction fragment length polymorphisms associated with the satellite subset can be detected by pulsed field gel electrophoresis and may facilitate molecular analysis of interchromosomal variation.
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