Huntingtons Disease

Huntington's Disease


Background


Huntington's disease is inherited as an autosomal dominant disease that gives

rise to progressive, elective (localized) neural cell death associated with

choleric 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 genetic 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 degrees C for 4 minutes, 27 cycles of 1 minute at 94 degreesC

and 2 minutes at 67 degrees C, 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

patients than in controls. There was no statistically significant difference in

the average mtDNA deletion levels between HD patients and controls in the

occipital lobe and the putamen. The increase in mtDNA deletion levels found in

HD frontal and temporal lobes suggests that HD patients have an increase mtDNA

somatic mutation rate. Could t
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