Tetrabenazine cuts down involuntary movements in Huntington's disease

Feb 17 2006

The medication tetrabenazine cut down involuntary movement in patients with Huntington's disease on average by about 25 percent, with many patients experiencing a greater improvement, according to a study in the February 14 issue of the journal Neurology.

Overall, patients who received the medication were six times as likely to be considered by their doctors to have improved considerably, compared to participants who received a placebo.

Dr. Kathleen M. Shannon, neurologist and Huntington's disease specialist at the Huntington's Disease Society of America Center of Excellence at Rush University Medical Center, led the Rush study. Rush was one of 16 sites to participate in the randomized, controlled study which involved 84 patients.

Tetrabenazin is available in Europe and Canada - but not the United States, but is currently being reviewed by the U.S. Food and Drug Administration. If approved, the medication would be the first authorized by the agency expressly for the treatment of Huntington's disease, which affects about 30,000 people in the United States.

"Huntington's disease is an inherited brain disorder that causes patients to experience uncontrollable jerky movements (chorea), as well as changes in personality, behavior, thinking and memory. There are no FDA-approved treatments for the chorea. Anti-psychotic drugs like haloperidol (Haldol) are commonly used to suppress chorea, but they cause many different side effects. This study shows that tetrabenazine can decrease chorea, and the drug is well-tolerated by most research subjects," said Shannon.

Tetrabenazine was originally developed in the 1950s to treat psychosis, but was quickly pushed aside by more effective medications. But doctors in the United Kingdom found it to be effective to treat the excessive involuntary movements of Huntington's, and it is approved for use in several nations. In the United States, tetrabenazine is designated as an "orphan drug" by the FDA since it's targeted to a disease directly affecting fewer than 200,000 people in the nation.

The symptom that tetrabenazine treats - involuntary, writhing movements of the limbs, face, and sometimes the entire body - is the hallmark symptom of Huntington's disease, an inherited neurodegenerative disorder that worsens as brain cells known as medium spiny neurons are killed off by a mutant protein.

The disease brings with it an array of other difficulties as well, including cognitive problems, changes in personality, and psychiatric problems like depression. As many as one-quarter of patients with the disease attempt suicide, and many suffer from progressive cognitive decline.

Unlike Alzheimer's disease, where patients usually lose their memory and insight into their disease at some point, most Huntington's patients understand exactly what is happening to them throughout most of their illness.

The disease usually strikes people in their 30s and 40s, though some patients are affected as early as childhood, while others aren't affected until their older years. Virtually everyone with the disease had a parent with the disease, and children of a person with Huntington's have a 50-percent chance of inheriting the disease.

Thirteen years ago the gene that causes the disease was identified by scientists, and now a simple blood test can tell people whether they will develop the disease or not. But since there is no way known to prevent the disease or slow its progression, and for other reasons as well, many patients decline the test, instead waiting to see if they develop symptoms like the ones they witnessed in a parent.

Patients usually live for 15 to 20 years after the onset of symptoms.

"Tetrabenazine does not help all the features of Huntington's disease, and other medications are commonly needed to improve mood and behavior. For those Huntington's disease patients whose function is impaired by chorea, however, tetrabenazine can help activities of daily living, and improve functional capacity," Shannon said.

"If the drug is approved, physicians will need to work carefully with patients and caregivers to find the appropriate dose. Side effects were seen in about 25% of subjects in the study. The most common side effect was sleepiness, but restlessness, slowed movement and depression were also seen in some subjects. Suicide is common in Huntington's disease, and one subject committed suicide during the study. Patients will also need close supervision so that suicide can be prevented."