Huntington Disease
HD is the most common among those movement diseases collectively named choreas. The term “chorea” (meaning dance) was borrowed from the ancient Greek theatre to describe the slow, non-patterned involuntary movements, characteristic of the disease.
HD is an autosomal dominant disorder, caused by the expanded repetition of the trinucleotide CAG on the gene HTT (encoding for the protein huntingtin). The number of CAG repetitions is expanded in patients, with a larger repeat number correlating with an earlier age of disease onset (most commonly between 25 to 45 years).
The patients present with a triad of symptoms, which includes:
- movement disorders: the slow choretic movements rapidly progress to dystonias, rigidity, postural instability and, eventually, akinesia;
- cognitive decline: various degrees of intellectual impairment and memory loss will proceed to a frank dementia at the late stages of the disease;
- behavioral problems: while depression is the main complain among the patients, a small percentage can experience maniac episodes as well as obsessive-compulsive behaviors.
Thus far, the only available option to improve the quality of life and prevent the complications in HD patients is through symptomatic treatments. Unfortunately, addressing the hyperkinetic movements with tetrabenazine or controlling the psychotic episodes with risperidone do not actually change the progression of this neurodegenerative disease.