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A high frequency of length polymorphisms in repeated sequences adjacent to Alu sequences
No full textWe describe a new class of DNA length polymorphism that is due to a variation in the number of tandem repeats associated with Alu sequences (Alu sequence-related polymorphisms). The polymerase chain reaction was used to selectively amplify a (TTA)(n) repeat identified in the 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase gene from genomic DNA of 41 human subjects, and the size of the amplified products was determined by gel electrophoresis. Seven alleles were found that differed in size by integrals of three nucleotides. The allele frequencies ranged from 1.5% to 52%, and the overall heterozygosity index was 62%. The polymorphic TTA repeat was located adjacent to a repetitive sequence of the Alu family. A homology search of human genomic DNA sequences for the trinucleotide TTA (at least five members in length) revealed tandem repeats in six other genes. Three of the six (TTA)(n) repeats were located adjacent to Alu sequences, and two of the three (in the genes for β-tubulin and interleukin-1α) were found to be polymorphic in length. Tandemly repetitive sequences found in association with Alu sequence may be frequent sites of length polymorphism that can be used as genetic markers for gene mapping or linkage analysis
TETRANUCLEOTIDE LENGTH POLYMORPHISM 5' OF THE ALPHA(2)-MACROGLOBULIN RECEPTOR (A2MR)/LDL RECEPTOR-RELATED PROTEIN (LRP) GENE
No full textN.A
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Molecular mechanisms of autosomal recessive hypercholesterolemia
No full textMutations in the phosphotyrosine-binding domain protein ARH cause autosomal recessive hypercholesterolemia (ARH), an inherited form of hypercholesterolemia due to a tissue-specific defect in the removal of low density lipoproteins (LDL) from the circulation. LDL uptake by the LDL receptor (LDLR) is markedly reduced in the liver but is normal or only moderately impaired in cultured fibroblasts of ARH patients. To define the molecular mechanism underlying ARH we examined ARH mRNA and protein in fibroblasts and lymphocytes from six probands with different ARH mutations. None of the probands had detectable full-length ARH protein in fibroblasts or lymphoblasts. Five probands were homozygous for mutations that introduced premature termination codons. No relationship was apparent between the site of the mutation in ARH and the amount of mRNA. The only mutation identified in the remaining proband was a SINE VNTR Alu (SVA) retroposon insertion in intron 1, which was associated with no detectable ARH mRNA. (125)I-LDL degradation was normal in ARH fibroblasts, as previously reported. In contrast, LDLR function was markedly reduced in ARH lymphoblasts, despite a 2-fold increase in LDL cell surface binding in these cells. These data indicate that all ARH mutations characterized to date preclude the synthesis of full-length ARH and that ARH is required for normal LDLR function in lymphocytes and hepatocytes, but not in fibroblasts. Residual LDLR function in cells that do not require ARH may explain why ARH patients have lower plasma LDL levels than do patients with homozygous familial hypercholesterolemia who have no functional LDLRs
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