It is estimated that at least 500,000 Americans are afflicted with Parkinson’s disease , which is a neurological disorder that results in the degeneration of the neurons (brain cells) that help control movement. This degeneration results in a shortage of a brain signaling chemical called dopamine. This deficiency of dopamine causes the movement disabilities characteristic of Parkinson’s disease.

People who have Parkinson’s disease experience trembling or shaking of their arms and legs. Other common symptoms include slow movement, the inability to transition normally from rest to activity, rigid limbs, a shuffling gait, and a stooped posture. In it’s most severe form, Parkinson’s disease results in a complete inability to perform voluntary movements.

There is no known cure for Parkinson’s disease, but medications are available that can replace the brain’s dopamine, easing symptoms. Medications may have dramatic benefits for some people, but these benefits tend to decrease with time and the medications are associated with a variety of complications. A new procedure, which involves implanting dopamine-producing tissue into the brains of people with Parkinson’s disease, is currently being investigated.

A study in the June 2004 issue of the Archives of Neurology found that implantations of dopamine-producing embryonic cells in people with Parkinson’s disease resulted in a modest—but significant—improvement in reaction time and movement time, both of which are markedly reduced with Parkinson’s disease.

About the Study

This study included 39 people with Parkinson’s disease (ages 35–76), who were randomly assigned to undergo embryonic cell implantation (20) or a placebo procedure (19). These individuals had relatively moderate Parkinson’s disease associated with some impairment of balance or walking.

Before the study began, and four and 12 months after the procedure, the researchers measured the participants’ reaction time and movement time. For these measurements, the participants were seated in front of a series of touch pads. A computer monitor instructed the participants to move their hands and feet from pad to pad. The device recorded their reaction times (RT, pre-movement brain processing) and movement times (MT, physiological movement) in response to the cues. The combination of RT plus MT measurements was used to quantify total motor performance.

The researchers used these data to analyze changes in RT and MT according to type of surgery (implant or placebo group), limb (hand or foot), and age (younger than 60 or 60 and older).

The Findings

The implant group experienced significantly less deterioration of motor function than the placebo group. This difference was mostly attributed to the deterioration in older placebo group participants, who experienced significantly worsened motor function at both four and 12 months. Motor function did not change significantly in younger participants of either group.

While, as a whole, the placebo group had significant deterioration in motor function at 12 months, the implant group showed slightly improved motor function at four and 12 months, but this finding did not reach statistical significance.

When the researchers analyzed data according to limb, they found that the implant group had significant improvement in foot motor function at four and 12 months. There was no significant change, however, in hand motor function. The placebo group experienced approximately equal deterioration in hand and foot motor function, with significant deterioration at four months.

While these results are compelling, it is important to note that the benefits noted in this study were modest, and the participants did not show any significant improvement in clinical outcome measures.

How Does This Affect You?

These findings suggest that embryonic cell implantation may potentially benefit people with Parkinson’s disease. While there was no significant clinical benefit in this study, the improvements in motor function cannot be ignored. Much previous research involving surgery for Parkinson’s disease has involved people with the severest forms of this disorder. This study is important because the participants had relatively mild impairment at the time of surgery.

It is likely that the participants will be followed over the next months and years to see if clinical benefit emerges. We know from previous studies that embryonic tissue survives for long periods—perhaps indefinitely—in people with Parkinson’s disease. This avenue of research is just emerging, and more studies will determine how tissue implants can benefit people with Parkinson’s disease and other neurological disorders.

This research comes in the wake of President Ronald Reagan’s death, which brought attention to the ongoing stem cell debate. Like stem cells, most embryonic cell implants are derived from products of legal abortions, which makes these procedures extremely controversial.

Another controversy surrounding these types of studies is placebo—or “sham”—procedures. In order to conduct a randomized, double-blinded trial (the gold standard in research), researchers must perform a “sham” procedure in participants on the placebo group. These “sham” procedures often pose the same risks as “real” procedures, especially in circumstances like this study, which involves a procedure involving the brain.

Beyond the controversy, the field of stem and embryonic cell transplantation is exciting to many researchers. An editorial that accompanies this study points out that the human genome was only first sequenced and analyzed in 2001, and “the era of genomic neurology has really just begun.”