Huntington´s disease characterized by chorea because of voluntary body movement such as random movement which is uncontrollable, this due to a gene mutation.The Huntingtin protein (HTT) codes by Huntingtin gene (HTT) in all human, the section of this gene called “trinucleotide repeat“ ( Francis O Walker,2007) and differentiate from person to another by the length which varies. A dishonorable gen may produce if the repeat in a fine gene because of dynamic mutation which rise the repeat count, and mutates form of a protein is produced known as mutant Huntingtin protein when the length of the repeated part reaches into a specific threshold. The various work of this protein causes the symptoms of the disease. The mutation of (HTT) allele in a human cause the disease.
The (HTT) gene find on chromosome 4 and contain “a sequence of three DNA bases cytosine-adenine-guanine (CAG) called trinucleotide repeat“ (Francis O Walker,2007) these three letters code the amino acid glutamine and the sequence of this amino acid produce a series of glutamine called a´´ polyglutamine tract (or polyQ tract), and the repeated part of the gene(polyQ region) “ (Masahisa Katsuno, et al,2008).Individuals have less than 36 repeated glutamine in the repeated part of the gene, this leads to output “cytoplasmic protein Huntingtin“ (Francis O Walker,2007). Increase or decrease of this chain of glutamine produces a protein which has various property, this various form, called mutant huntingtin (mHTT), which rise the degeneration rate of specific types of neurons in the brain.
The nerve cell affected by this gene mutation such as the cerebral cortex it functions is thinking and action, and basal ganglia its function is movement, motor control, emotion, and behavior. When that area of the brain affected cause some changes such as uncontrollable movement of the body, emotional and mental change. (Francis O Walker,2007) and (Wikipedia).The early symptoms of Huntington´s disease are the change of personalities like humor, physical change, unstable walk and uncommon behavior ( Adam MP, et al, 1998). Early symptoms are related to the work of “ the striatum and its cortical connections“ ((Francis O Walker,2007)and(Wikipedia) which involve in body movement, emotion, and behavior.