Huntington disease is normally diagnosed in the clinic on the basis of motor performance (onset of chorea). Several other tests may also be performed and measured using the unified Huntington's disease rating scale in order to obtain an overall assessment of disease progression. As HD is an adult-onset disorder, individuals are generally between 35 and 50 years of age when onset of the motor symptoms occur. However, while rare, juvenile cases have been described. Subsequent to the clinical motor diagnosis, DNA testing is done to conclusively determine that it is HD. The DNA test measures the number of CAG repeats present in the HD gene and determines if it falls in the normal or expanded (HD) range. As there is an inverse correlation between CAG size and age of onset, for those individuals that have HD in the family but do not have symptoms, they can elect to have the HD gene test to determine if they will develop HD in the future.

Gene Silencing

This is a pathological process that involves dysfunction of glutamate receptors, in particular N-Methyl-D-aspartic acid (NMDA) receptors. Excitotoxins bind to these receptors and can cause excitotoxic stress due to high levels of calcium ions entering the cell, protease activation and eventual cell death.

Excitotoxic neuropathological changes are observed in Huntington disease and are considered to be an early event in the pathogenesis of this disease. Efforts are ongoing to screen drug libraries in order to identify inhibitors of excitotoxic stress. Once the compounds have been identified they are then tested in HD mouse models in order to determine if protection and amelioration of the symptoms is observed and to identify compounds that may prove beneficial in human clinical trials.