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  • 1
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary We have analyzed patient DNA samples in 77 unrelated Duchenne (DMD) and Becker (BMD) muscular dystrophy families, 73 of which were of French Canadian origin. We show that the frequency (68%) and distribution of deletions within the dystrophin gene was neither random nor unique in this population. We localized 33% of the deletions to the proximal portion of the dystrophin gene while 63% involved the exons spanning introns 43 through 55 with breakpoint clusters occurring within introns 44 and 50. Whether the dystrophin open reading frame (ORF) is maintained constrains the distribution of DMD/BMD deletions such that BMD deletions tend to be strikingly homogeneous. Finally, the conservation of the dystrophin ORF and the severity of the clinical phenotype were concordant in 95% of the DMD/BMD deletions documented by this work.
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  • 2
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Using human hypoxanthine-guanine phosphoribosyltransferase (HPRT) cDNA and an anonymous probe 36B-2, we examined the segregation of restriction fragment length polymorphism (RFLP) alleles with the Lesch-Nyhan phenotype in three affected families. Two families were informative. Five carriers of the mutation in one family and two potential carriers in the second were heterozygous for either one or both polymorphisms allowing for prenatal diagnosis. Southern blot patterns in patients from these three families indicated the absence of major structural alterations in the defective gene. Northern analysis using HPRT cDNA as a probe revealed no hybridizing RNA in one patient, whereas normal size mRNA was expressed at a very low level in the second and at a level comparable to normal in the third. These data are consistent with heterogeneity of Lesch-Nyhan genetic lesions resulting from point mutations or small DNA deletions or rearrangements, which may affect transcription, stability, or integrity of the HPRT message.
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  • 3
    ISSN: 1432-1203
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary We searched for DNA polymorphisms in seven amplified fragments of the dystrophin gene. Three fragments exhibited variable mobilities during nondenaturing strand-separating gel electrophoresis (SSGE). These variants were due to single base changes (three transversions and one transition). Three were intronic (upstream from exons 17, 15, and 48) and one was in exon 48. The frequencies of these sequence variants were determined in a sample of 54 normal X chromosomes of Caucasian origin. One of these DNA polymorphisms was observed in every 650 bp tested and the average heterozygosity was 0.05% per base pair (0.08% if exons were excluded). Such a detection density and the fact that single-strand conformational polymorphisms do not depend on the presence of any specific sequence makes them especially valuable as genetic markers. In the dystrophin locus this approach could allow simultaneous detection of frequent deletions.
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  • 4
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Biochemistry 19 (1980), S. 3799-3805 
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Biochemistry 21 (1982), S. 53-56 
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1573-7225
    Keywords: childhood leukemia ; developmental toxicity ; gene polymorphisms ; parental smoking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective: To evaluate the effect of parental smoking on childhood acute lymphoblastic leukemia and to determine if it is modified by child genetic polymorphisms. Methods: We carried out a case–control study in Québec, Canada, including 491 incident cases aged 0–9 years and as many healthy controls matched on age and sex. Each parent was interviewed separately with respect to smoking habits during and after pregnancy. In addition, we carried out a case-only substudy with 158 cases classified according to presence or absence of the alleles *2A, *2B, and *4 in the CYP1A1 gene. Results: There were small risk increases with maternal smoking during the later trimesters. Interaction odds ratios were increased (although often not significantly) for the CYP1A1*4 allele at high levels of maternal smoking in the last trimesters and at low level of paternal postnatal smoking, and decreased for the CYP1A1*2B allele. The latter appeared to confer a protective advantage at low levels for maternal prenatal smoking and at high levels for paternal postnatal smoking. Conclusions: Reported smoking habits showed no association with leukemia; risks for genetic polymorphisms lacked precision but indicated that the effect of parental smoking could be modified by variant alleles in the CYP1A1 gene.
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  • 8
    ISSN: 1432-1432
    Keywords: Primate Alu ; Rodent B1 ; 7SL RNA ; 4.5S RNA ; BC200 RNA ; Evolution of RNA folding ; Retroposition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Primate and rodent genomes are populated with hundreds of thousands copies of Alu and B1 elements dispersed by retroposition, i.e., by genomic reintegration of their reverse transcribed RNAs. These, as well as primate BC200 and rodent 4.5S RNAs, are ancestrally related to the terminal portions of 7SL RNA sequence. The secondary structure of 7SL RNA (an integral component of the signal recognition particle) is conserved from prokaryotes to distant eukaryotic species. Yet only in primates and rodents did this molecule give rise to retroposing Alu and B1 RNAs and to apparently functional BC200 and 4.5S RNAs. To understand this transition and the underlying molecular events, we examined, by comparative analysis, the evolution of RNA structure in this family of molecules derived from 7SL RNA. RNA sequences of different simian (mostly human) and prosimian Alu subfamilies as well as rodent B1 repeats were derived from their genomic consensus sequences taken from the literature and our unpublished results (prosimian and New World Monkey). RNA secondary structures were determined by enzymatic studies (new data on 4.5S RNA are presented) and/or energy minimization analyses followed by phylogenetic comparison. Although, with the exception of 4.5S RNA, all 7SL-derived RNA species maintain the cruciform structure of their progenitor, the details of 7SL RNA folding domains are modified to a different extent in various RNA groups. Novel motifs found in retropositionally active RNAs are conserved among Alu and B1 subfamilies in different genomes. In RNAs that do not proliferate by retroposition these motifs are modified further. This indicates structural adaptation of 7SL-like RNA molecules to novel functions, presumably mediated by specific interactions with proteins; these functions were either useful for the host or served the selfish propagation of RNA templates within the host genome.
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  • 9
    ISSN: 1432-1432
    Keywords: Key words: Short interspersed sequence elements (SINES) — Retroposition — Alu evolution — Alu RNA folding — Primate lineages — Prosimians — Genomic repeats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. To get insight into the early evolution of the primate Alu elements, we characterized sequences of these repeats from the Malagasy prosimians, lemurs (Lemuridae) and sifakas (Indriidae), as well as from galagos (Lorisidae). These sequences were compared with the oldest Alu species known from the human genome: dimeric Alu J and S and free Alu monomers. Our analysis indicates that about 60 Myr ago, before the prosimian divergence, free left and right monomers formed an Alu heterodimer connected by a 19-nucleotide-long A-rich linker. The resulting elements successfully propagated in diverging primate lineages until about ∼20 Myr ago, conserving similar sequence features and essentially the same Alu RNA secondary structure. We suggest that until that time the same ``retropositional niche'', molecular machinery making possible the proliferation by retroposition, constrained the evolution of Alu elements in extant primate species. These constraints became subsequently relaxed. In the Malagasy prosimians the dimeric Alu continued to amplify after acquiring a 34- to 36-nucleotide extension of their linker segment, whereas in the galago genome the ``retropositional niche'' was occupied by novel short elements.
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  • 10
    ISSN: 1432-1432
    Keywords: Key words: Human evolution — DNA polymorphisms — Dystrophin locus — Population size — Neutral evolution — Mutation rate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Neutral DNA polymorphisms from an 8-kb segment of the dystrophin gene, previously ascertained in a worldwide sample (n= 250 chromosomes), were used to characterize the population ancestral to the present-day human groups. The ancestral state of each polymorphic site was determined by comparing human variants with their orthologous sites in the great apes. The ``age before fixation'' of the underlying mutations was estimated from the frequencies of the new alleles and analyzed in the context of these polymorphisms' distribution among 13 populations from Africa, Europe, Asia, New Guinea, and the Americas (n= 860 chromosomes in total). Seventeen polymorphisms older tan 100,000–200,000 years, which contributed ∼90% to the overall nucleotide diversity, were common to all human groups. Polymorphisms endemic to human groups or continentally restricted were younger than 100,000–200,000 years. Africans (six populations) with 13 such sites stood out from the rest of the world (seven populations), where only 2 population-specific variants were observed. The similarity of the frequencies of the old polymorphisms in Africans and non-Africans suggested a similar profile of genetic variability in the population before the modern human's divergence. This ancestral population was characterized by an effective size of about 10,000 as estimated from the nucleotide diversity; this size may describe the number of breeding individuals over a long time during the Middle Pleistocene or reflect a speciation bottleneck from an initially larger population at the end of this period.
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