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Molecular pathogenesis of huntington's disease danilo a. Tagle head, molecular neurogenetics section, genetics and molecular biology branch, national human genome research institute, nih, bethesda, maryland 20892 usa huntington's disease (hd) is a progressive neurodegenerative disorder with a population frequency of 1 in 10,000 individuals. Clinical features of hd include chorea, cognitive deficit and psychiatric disturbances. Neuropathological hallmarks in hd patients consist of selective neurodegeneration of medium spiny neurons in caudate-putamen and pyramidal cells in cerebral cortex. The disease is inherited in an autosomal dominant fashion with age of onset primarily in middle age though it can range from early childhood to late adulthood (greater than 70 years of age). Juvenile-onset hd occurs in approximately 5% of the patients and is rapidly progressive presenting with rigidity, spasticity, and intellectual decline before age 20. Genetic anticipation is predominantly associated with male transmission, consequently 70% of juvenile cases inherit the disease from the paternal line. Hd was linked to the short arm of chromosome 4p16. 3 in 1983 and following a decade of intense positional cloning efforts, the hd gene was identified by an international consortium of researchers, the huntington's disease collaborative research group. The hd gene lacks homology to any previously characterized gene and consists of 67 exons spanning a genomic interval of 200 kb. It is ubiquitously expressed as two transcripts of 10. 3 and 13. 6 kb in length, differing in the utilization of the poly-a signal. It encodes a protein of 3144 amino acids with a molecular mass of 348 kda. The human sequence and its murine counterpart, hdh, show 91% sequence identity and homologous sequences have been identified in zebrafish, pufferfish and drosophila. The underlying mutation in hd consists of a trinucleotide repeat (cag)n expansion in the first exon of the gene. The cag repeat length is highly polymorphic in the population with repeat size ranging from 5-35 repeats in the alleles of normal individuals and from 26 to 121 in the affected alleles of hd patients. An inverse correlation is seen between cag repeat length and age of onset where adult-onset cases usually have an expansion from 40 to 59 repeats, whereas juvenile-onset cases have an expansion above 60 units. The cag repeat is translated into a long, uninterrupted stretch of glutamine residues in the gene product, huntingtin. buy cheap viagra buy viagra buy viagra online viagra for sale viagra online cheap viagra online buy viagra online http://nationalityinworldhistory.net/bsh-buying-generic-viagra-ap/ cheap viagra buy cheap viagra To date, eight such inherited neurological disorders have been identified to be caused by cag repeat expansion in their respective genes; hd, dentatorubral pallidoluysian atrophy (drpla), spinobulbar muscular atrophy (sbma), spinocerebellar ataxia types 1, 2, 3, 6 and 7 (.
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