Scientists announced Thursday what may be the most important breakthrough for Parkinson's disease in more than 30 years: They have discovered a gene that causes the disease.

``The finding opens completely new horizons in understanding the disease and interpreting the biology of the illness,'' says Miheal Polymeropoulos of the National Human Genome Research Institute at the National Institutes of Health.

However, the gene still is significant because it quite likely plays a role in most Parkinson's cases. Polymeropoulos, lead author of the report in today's Science, says there could be a variety of defects in the gene that leads to Parkinson's.