A substance that occurs naturally in cell membranes may fight symptoms of Parkinson's disease and help slow its progression, medical researchers said Tuesday.

A research team from Jefferson Medical College gave the substance GM1 ganglioside or a placebo to 45 patients with Parkinson's disease over a 16-week course.Many who received the drug saw improvement in symptoms such as rigidity and slowness of movement. Some who have been receiving GM1 treatment for at least two years have seen improvements continue.

"Some patients report significant improvement in the quality of their life, though others say improvements have been modest," said Dr. Jay Schneider, Jefferson professor of pathology, cell biology and anatomy and neurology.

Results of the research appeared in the June issue of the journal "Neurology".