The recent discoveries in the past few years in the field of genetics have allowed scientists to formulate clinical tests which diagnose the existence of a disorder before the onset of symptoms. New technologies allow researchers to be able to extract DNA and or RNA from an individuals blood sample and determine the existence of mutated genes in the DNA, an aid in diagnosing specific types of disease. The most positive effect of these discoveries will be an understanding of the biochemical mechanism of the disorder which will hopefully lead to a cure.

One disease that has been recently studied is Huntington's Disease. It was named after Dr. George Huntington, who described the disorder in patients in East Hampton, Long Island in 1872. He identified the symptoms of the disease, and also noted the inheritablity of it. The disease would become apparent in a victims fourth decade of life, where uncontrolled movement of individual joints would be noticed by patients. These uncontrolled movements would grow until the whole body was affected. Interestingly, these symptoms would cease only when the patient was asleep. As the disease progresses, many other neurological problems would present themselves. Patients usually die within 15 to 20 years after the first symptoms of Huntington's disease are discovered.

Through linkage studies, the location of the Huntington's Disease (HD) gene was mapped to chromosome 4p16.3 in 1983. The mutation is caused by an unstable CAG repeat region in exon 1of the gene. The HD gene differs from the normal gene in the number of CAG repeats occurring in this region. A normal individual will have up to 34 copies of this sequence, while the HD gene will have 37 or more copies. The length of the CAG repeats in the HD gene has been associated with the onset of the disease, with longer repeats associated with younger age of onset. The cases of juvenile onset HD show much longer regions of CAG repeats than in individuals with the onset of symptoms in the fourth decade of life.

By discovering the gene for HD, scientists were able to determine the protein product and how it differed from the normal protein. Due to increased length of the CAG region, the HD gene contains a large glutamine repeat region near the N-terminal of the protein. At this point scientists do not understand the function of the protein, but with more research will hopefully come more understanding and a cure.