ls—in this area of the brain is dopamine, which is deficient in people who have Parkinson’s. The cause of this deficiency is not known, but research suggests that several factors may reinforce each other to produce Parkinson’s disease. There may be a genetic predisposition for some forms of the disease—between 15 and 20 percent of people with Parkinson’s are closely related to an individual who displays the disease’s characteristic symptoms. In 1996 scientists identified a gene associated with a rare form of Parkinson’s disease. Genetic predisposition may be limited only to rare forms of the disease, however. A 1999 study found that the most common form of Parkinson’s disease is not inherited, suggesting that exposure to certain environmental agents may be a primary cause. Although the identity of these agents remains unknown, candidates include harmful pesticides or toxins in food; and free radicals, which are unstable molecules that may contribute to neuron damage by reacting with other molecules—especially metallic elements such as iron—in the basic chemical process known as oxidation. Introduction of the drug L-dopa, or levodopa, in the mid-1960s led to the relief of Parkinson’s symptoms in many people with the disease. L-dopa stimulates the production of dopamine in surviving neurons in the substantia nigra. L-dopa becomes less effective over time in relieving symptoms, at which point a substitute drug such as pergolide or bromocriptine may be prescribed. In 1997 the drugs pramipexole (sold under the brand name Mirapex) and ropinirole, (brand name Requip) were approved by the Food and Drug Administration (FDA) for use in the treatment of Parkinson’s disease. These drugs appear to have fewer side effects than some of the older medicines. Other drugs that affect the action of central nervous system neurotransmitters have proven useful in relieving tremors. Brain ...
