By Dr Tom Miller, Scientific Secretary.

Recent studies repoted in Nature Medicine by Dr Kendall and colleagues at the University of Cambridge, United Kingdom, have contributed to the question of whether transplants of embryonic tissue into cerebral sites can be to restore motor neurone function in HD.
    Motor neurones are the nerve cells that control the voluntary movement of muscles. Upper motor neurones are in the part of the brain responsible for body and limb movement; lower motor neurones are located in the spinal cord and specific areas of the brain. Functions under their control include swallowing, chewing, tongue movements and facial muscle control.

HD is characterised by the progressive degeneration of neurological tissue that give rise to irregular and involuntary movements. The medical term for these symptons is "chorea" ( pronounced Ko-re-ah ). People affected by chorea may undergo personality changes and have impaired cognitive ( ie. memory and logical thought ) functions.

The symptons usually appear at about 30 to 50 years of age but occasionally are noticed in childhood or as late as 70. Currently there is no treatment capable of modifying the inevitable progression.

A great deal of research has gone into defining the genetic mutation associated with HD with attention being concentrated on a protein called "huntingtin". It has been suggested that a mutant of the huntingtin protein might be responsible for the dysfunction and death of striatal neurones in sufferers; the striatal neurones appear to be sensitive to the mutant protein.

Increasing knowledge of the disease mechanism will hopefully hasten the introduction of appropriate treatments but while these events are unfolding, an alternative approach, namely cell replacement therapy through intracererbral tissue transplantation, is being considered. The concept behind the grafting of embryonic striatal cells is that these cells will produce normal protein after being grafted into the site of the failing neurones and restore motor function to normal.

The conditions for survival of the graft have been worked out for laboratory situations and the researchers have extended the work to an animal model of HD. As predicted, the embryonic grafts survived for up to 12 months and became integrated to the host brain. Encouraginly the transplant reversed some symptons. The most effective grafts were located at a precise site in the brain and this data provided new information as to the importance of accurate graft placement if functional recovery is to occur.

The outcome of these experiments has been encouraging enough to begin clinical studies involving the transplantation of human striatal embryonic cells. A safety report relating to the transplant procedure recently has been published by an American team , but deciding when to commence a clinical trial always raises ethical questions.

The debate is between the two ethical positions that these situations generate - whether the technique has been worked up sufficiently to offer a real chance of improvement to patients or, conversely, whether it is ethical to withhold a new therapy if there is a possibility of benefit to a person with an incurable disease. In the first instance the topic requires informed discussion between researchers and clinicians and, once a consensus has been reached by these two groups, extension of the debate into the area of ethical committees and public comment. Irrespective of the ethical outcome, the scientific community can regard with some satisfaction the fact that there is now the possibility of a successful treatment where no hope existed before for people with HD.