Huntington’s Disease (HD) is a brain disorder that affects a person’s ability to think, talk, and to move. This disease effects basal ganglia which controls movement, emotion and cognitive ability of a person. HD is caused by a mutation in a gene on p arm of the chromosome 4. The function of huntingtin protein is to direct the delivery of small packages (vesicles containing important molecules) to the outside of the cell.
Normally, the coding region of this gene contains the DNA sequence “CAG” repeated again and again. The number of times this triplet is repeated varies from person to person, ranging from 10 to 26 times. People with HD have an abnormally high number of these CAG triplets, approximately 40 or more. This likely disrupts the function of the gene’s protein product, but how the expansion of the CAG repeat causes disease is unknown. Somehow the brain cells of HD patients accumulate clumps of protein that become toxic, resulting in cell death. Some patients lose more than 25% of their brain cells before they die.