Huntington's disease was first discovered by Dr. George Huntington in 1872. He characterized it as a "chorea", which means "dance", because the people who had it tended to have an uncontrollable jerkiness and problems of cognitive and emotional control. To him these symptoms looked dance-like. Thus you may see it referred to with two names: Huntington's Chorea and Huntington's Disease. The illness is the same. Like Parkinson's disease, it is caused by a disruption of the basal ganglia, areas which help to control movement. In Huntington's disease, neurons in the striatum start to degenerate. Normally they provide an inhibitory influence on the control of movement, through a complex pathway containing other parts of the basal ganglia and the cortex. When they degenerate, this inhibitory influence goes away, causing inappropriate movement and actions (See diagram below) .
There are few treatments for Huntington's disease, so any help that stem cell treatment could provide is needed. In fact, neural stem cell grafts appear to be a very promising treatment for the disease. Researchers have tried several therapies using animals as test subjects. First, lesions (an area of damaged or frozen neurons) are made which resemble the destruction caused by Huntington's. Then cells are taken from embryonic areas that resemble the striatum, and grafted to the cite of the lesioned striatum (technical details about grafting).
For this treatment to be successful, the grafted neurons must send out axons to make the correct connection with the globus pallidus, as well as receive the correct input from the substantia nigra and cortex (see diagram below). In animal models it appears that the grafted cells are able to make these connections. Many develop into normal-looking striatal cells. With training, these animals are even able to relearn motor skills originally lost when the lesions were made. Thus, if the same treatment can be used for humans, people suffering from Huntington's Disease may be able to regain part or all of their normal motor skills (Bjorklund and Lindvall 2000 picture also).
Clinical trials on humans are still in the early stages, though it has been shown that grafts can establish themselves and survive in the striatum. Primate models of Huntington's disease are often used to study treatments. In these models, scientists will lesion the striatum in monkeys to simulate the effects of Parkinson's. When the fetal striatal grafts are connected to the lesioned area, they establish themselves normally and begin to receive and make connections with other brain areas. The monkeys also show improvements in the behavioral functions that were lost due to the lesions (Armstrong et al. 2000). There have not been as many studies done on humans as animals, but the evidence does look promising. In one study done to three patients, they all relieved striatal grafts of fetal stem cells. After this all of them showed increased performance, on cognitive tests. Hopefully this was due to the stem cells taking over the function of the lost striatum (Philpotta et al. 1996).
see the Huntington's disease web site in The Undergraduate Behavioral Neuroscience Resource Project.