Huntington’s disease (HD) is a neurodegenerative dominant disorder caused by the expansions of polyglutamine in the gene encoding for Huntington’s protein. It is a developmental autosomal brain disorder that affects muscle coordination, emotional and personality problems. As well as subcortical dementia, further leading to cognitive decline this is all related with selective neuronal cell death mainly associated in the striatum and cortex (Scherzinger et al., 1997). HD causes emotional problems, uncontrolled movements and the loss of thinking ability. It can lead to disability and death from the illness. There are two forms of this disease: adult-onset and early-onset (juvenile).
Adult onset is by the far most common for HD; symptoms develop between the ages of mid 30s/40s, an individual will live an average of 20 years after symptoms and signs begin. Premature signs and symptoms are depression, involuntary movements, trouble learning new information, poor coordination; this can all progress very severely. The development of pre-disease symptoms into twitching or jerking is referred as Chorea. HD can be referred to Huntington Chorea. Although adult onset is more common disorder, juvenile form, defined by the onset of signs and symptoms before the age of 21 years, this occurs in about 7% of HD cases. (Nance, 2001) Juvenile onset has similar symptoms however the disease progresses more quickly compared to the adult onset form. Gente (1985) results showed findings by others, that the most juvenile-onset patients inherit the gene from their fathers and that the late-onset form is more frequently inherited from affected mothers.
HD occurs due to CAG/polyglutamine(polyQ) expansions, in the first exon of a gene encoding a large ~350 kDa protein(Scherzinger et al, 1997). Expansion of CAG repeats which code for polyglutamine; causes other neurodegenerative disorders. These include DentatoRubral and PallidoLuysian (DRPLA), which is similar to HD; and several forms of Spino-Cerebelluar Ataxia (SCA). The effects of neurodegenerative disorders are neuronal cell death of certain areas in the brain (Ross et al, 2002). Schezinger proposed that in Huntington the expanded glutamine repeats could function as polar zippers, hence joining protein molecules together. Therefore this could cause for specific neurons that result in neuronal loss in the Huntington protein.
In Huntington’s disease where there is an expansion of CAG repeats in the gene on a chromosome 4p16.3; a response will occur resulting in a benign disease only if it contains 36 repeats, at times the individual may be unaffected. Whereas a sequence with additional repeats, from 36 to 180 on the chromosome this will result in HD (Chen et al, 2002). Scherzinger declared that if it is from 36 to 180 repeats on HD chromosome then the individual will be affected. Longer polyglutamine tracts occur in juvenile-onset cases rather than in adult-onset cases (Panov et al, 2002). The additional...