Huntington's Disease Case Study

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Previous studies have established that the gene responsible for Huntington’s disease (HD) is located in chromosome 4 – labeled as 4p16.3. Early symptoms of the disease include chorea or involuntary movements, loss of balance, as well as cerebral atrophy1. Although the disease has a late onset, juvenile form of the disease is also probable. The disease is manifested in children and teenagers and is characterized by transmission from an affected father (paternal transmission effect), unusually large repeat size of nucleotides, and rigidity and seizure disorder2. The neuropathology of the disease shows selective loss of neurons that is most severe in caudate and putamen. Despite heavy research, the treatment to effectively delay or prevent the …show more content…
It was established that the HD chromosomes of this kindred were paternally transmitted to seven children. Three normal chromosomes present in the three out of seven offspring produced a PCR product in the normal size range. The DNA of all the affected individuals, except for the two, showed PCR product of a different size. This indicated the instability of the HD chromosome trinucleotide repeat. Further evidences supported the latter. The PCR product in one of the offspring’s DNA was slightly smaller than the father’s. The PCR products of the four offspring were progressively larger. One of the offspring had DNA possessing (CAG)n repeat that was too long – estimated to contain 100 copies. This child had a juvenile onset of HD at the age of 2 years. The other offspring had the onset at the age of 26, 25, 14, and 11 years. The father had the onset at the age of 40 years. This highly suggested the rough correlation between the age at the onset of HD and the length of the trinucleotide repeat. The second sibship from the Venezuelan family in which both parents were HD heterozygotes were tested. PCR analysis revealed that several of the offspring were heterozygotes. Each parent’s DNA contained one allele in the normal range. The PCR products of the DNA in both parents and children were much larger than the normal size and also showed extensive variation in mean size. …show more content…
They examined two pedigrees from families with sporadic cases of HD. PCR analysis of the HD chromosomes of these families revealed that some of the offspring produced PCR product containing approximately 36 copies which was at the extreme high end of the normal range. The trinucleotide repeat had also undergone sequential expansions to approximately 44 to 46 copies. Similar results were obtained in the second family where the new HD mutant had chromosomes containing expanded repeat. The results suggested that the ultimate HD chromosome displayed the marker haplotype of 1/3 of all HD chromosome which may be predisposed to undergoing repeat

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