It took centuries for the slumped posture, trembling hands, poor balance, and cognitive impairments that characterize Parkinson’s disease (PD) to be recognized as manifestations of a single illness, distinct from other maladies of old age. It was a feat of methodical observation. But while the pace of scientific research has accelerated greatly, especially in recent years, it may still be many years before we understand what causes the disease.
In the last two centuries, researchers have shown that PD results from the relentless degeneration of specific neuronal populations in the substantia nigra, most notably those that produce dopamine, causing a deficiency that leads to motor abnormalities. The condition is usually partially treatable (mainly with dopamine-replacement therapy) for a few years after diagnosis. But this is generally followed by years of decline for which there is no effective therapy, culminating in premature death. Today, after Alzheimer’s disease, PD is the second ...
