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Huntingtons Disease Essay

  • Huntingtons Disease

    Huntingtons Disease

    Huntington's Background

    Huntington's disease is inherited as an autosomal dominant disease that gives rise to
    progressive, elective (localized) neural cell death associated with choreic movements
    (uncontrollable movements of the arms, legs, and face) and dementia. It is one of the
    more common inherited brain disorders. About 25,000 Americans have it and another
    60,000 or so will carry the defective gene and will develop the disorder as they age.
    Physical deterioration occurs over a period of 10 to 20 years, usually beginning in a
    person's 30's or 40's. The gene is dominant and thus does not skip generations.
    Having the gene means a 92 percent chance of getting the disease. The disease is
    associated with increases in the length of a CAG triplet repeat present in a gene
    called 'huntington' located on chromosome 4. The classic signs of Huntington disease
    are progressive chorea, rigidity, and dementia, frequently associated with seizures.

    Studies & Research

    Studies were done to determine if somatic mtDNA (mitochondria DNA) mutations might
    contribute to the neurodegeneration observed in Huntington's disease. Part of the
    research was to analyze cerebral deletion levels in the temporal and frontal lobes.
  • Research hypothesis: HD patients have significantly higher mtDNA deletionlevels than
    agematched controls in the frontal and temporal lobes of the cortex. To test the
    hypothesis, the amount of mtDNA deletion in 22 HD patients brains was examined by serial
    dilution-polymerase chain reaction (PCR) and compared the results with mtDNA deletion
    levels in 25 aged matched controls.
    Brain tissues from three cortical regions were taken during an autopsy (from the 22 HD
    symptomatic HD patients): frontal lobe, temporal lobe and occipital lobe, and putamen.
    Molecular analyses were performed on genomic DNA isolated from 200 mg of frozen brain
    regions as described above. The HD diagnosis was confirmed in patients by PCR amplification
    of the trinucleotide repeat in the IT 15 gene. One group was screened with primers that
    included polymorphism and the other was screened without the polymorphism.
    After heating the reaction to 94 degreesC for 4 minutes, 27 cycles of 1 minute at 94
    degreesC and 2 minutes at 67 degreesC, tests were performed. The PCR products were
    settled on 8% polyacrylamide gels. The mtDNA deletion levels were quantitated relative
    to the total mtDNA levels by the dilution-PCR method. When the percentage of the mtDNA
    deletion relative to total mtDNA was used as a marker of mtDNA damage, most regions of
    the brain accrued a very small amount of mtDNA damage before age 75. Cortical regions
    accrued 1 to 2% deletion levels between ages 80-90, and the putamen accrued up to 12%
    of this deletion after age 80. The study presented evidence that HD patients have much
    higher mtDNA deletionlevels than agematched controls in the frontal and temporal lobes
    of the cortex. Temporal lobe mtDNA deletion levels were 11 fold higher in HD patients
    than in controls, whereas the frontal lobe deletion levels were fivefold higher in HD

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