Parkinson's Disease: A Movement Disorder, and a Mystery of the Brain
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This is SCIENCE IN THE NEWS in VOA Special English. I'm Barbara Klein. And I'm Bob Doughty. Today we tell about the latest research and treatments for Parkinson's disease.
Parkinson's is a disease of the central nervous system. It is a progressive disorder. It gets worse over time. The disease affects a small area of cells in the middle of the brain. This area is called the substantia nigra. The cells slowly lose their ability to produce a chemical called dopamine.
The decrease in the amount of dopamine can result in one or more general signs of Parkinson's disease. These include shaking of the hands, arms and legs. They also include difficulty moving or keeping balanced while walking or standing. Also, there may be emotional changes, like feeling depressed or worried. The symptoms of Parkinson's differ from person to person. They also differ in their intensity.
The disease is named after James Parkinson. He was a British doctor who first described this condition in eighteen seventeen. Doctor Parkinson did not know what caused it. During the nineteen sixties, medical researchers discovered changes in the brains of people with the disease. These discoveries led to medicines to treat the effects of the disease. There is no cure for Parkinson's and no way to prevent it. And doctors still are not sure about the cause.
Parkinson's affects more than four million people around the world. It affects more than one million people in North America. Most are older adults.
Most patients have what is called idiopathic Parkinson's disease. Idiopathic means the cause is unknown. People who develop the disease often want to link it to something they can identify. This might be a medical operation or extreme emotional tension.
Yet many doctors reject this idea of a direct link to Parkinson's. They point to other people who have similar experiences and do not develop the disease.
Still, doctors say it is possible that such events might cause symptoms of Parkinson's to appear earlier than they would have.
Studies have found a link between the disease and some chemical products. Last year, an American study showed such a link between Parkinson's and pesticides, like those used for killing insects. The study compared three hundred nineteen Parkinson's patients to more than two hundred family members.
Two years ago, a European study showed a link between pesticide use and Parkinson's. This study also found that serious head injuries also increased a person's risk. Scientists at Aberdeen University in Scotland collected information about more than nine hundred people with Parkinson's or similar conditions. They compared this group to almost two thousand people without the disorder. All the people were asked about their use of pesticides, chemical fluids and metals like iron. The researchers also collected information about family history of the disease and head injuries.
Farm workers and others who said they often used pesticides had a forty-one percent greater risk of Parkinson's than other people. The disease was also two and one-half times more common among people who had been knocked unconscious more than once in their lives. These people temporarily lost consciousness after suffering a blow to the head.
Another area of study is family genetics. There are examples of members of a family having the disease. The National Institutes of Health in the United States says about fifteen percent of people with Parkinson's have a family history of the disease. But most cases involve people with no such family history.
A few years ago, researchers completed what they called the first large map to show genetic links with Parkinson's disease. The map identifies changes in genes that may increase the risk in some people.
Recently, a gene-testing company announced plans for a large genetic study of Parkinson's patients. The company, 23andme, was the idea of Ann Wojcicki.
She is the wife of Sergey Brin, who helped create the Internet search engine Google. He has a gene that increases his risk of developing Parkinson's. His mother has the disease. The company is working with two not-for-profit groups. They hope to collect DNA from ten thousand Parkinson's patients. The goal is to search for common genes that may cause the disease.
There is no cure for Parkinson's disease. But improved treatments to ease the effects of the disease make it possible for many patients to live almost normal lives. People who have lost their ability to do many things are sometimes able to regain some of these abilities with treatment.
The most commonly used drug is levodopa. The National Institutes of Health says levodopa is a chemical found naturally in plants and animals. When it reaches the brain, levodopa is changed into dopamine, the chemical that is lacking in people with the disease.
Levodopa helps ease the symptoms of Parkinson's. But it does not prevent more changes in the brain that are caused by the disease. Long-term use can produce unwanted effects in some people. These side effects include feeling sick to the stomach.
To prevent this from happening, levodopa can be combined with other substances, like carbidopa. The National Institutes of Health says carbidopa delays the changes in levodopa until it reaches the brain.
Other drugs used to treat Parkinson's disease act like dopamine. They produce reactions in the nerve cells in the brain. They can be given alone or in combination with levodopa. Many of the possible side effects are similar to those linked with the use of levodopa. They include sleepiness, feeling sick or having bad dreams.
An operation called deep-brain stimulation also is used to treat Parkinson's disease. Doctors place small electrical devices deep in the brain. The devices are connected to a piece of equipment called a pulse generator.
Deep brain stimulation can reduce the need for levodopa and other drugs. It also helps to reduce symptoms such as shaking and slowness of movement. Recently, a report in Science magazine showed how deep-brain stimulation works. It found that the treatment affects neural wires called axons.
The researchers were from Stanford University in California. They used light-sensitive molecules to turn on and off nerve cells in the deep brain structure of mice. Nothing happened when they turned on the light in cells in an area of the brain called the subthalamic nucleus. But bursts of electricity on the axons improved movement in the animals.
A separate study found that a less invasive treatment might reduce the symptoms of Parkinson's. It showed that a treatment called dorsal column stimulation could re-establish movement in rodents with Parkinson's-like problems. In the study, researchers fired bursts of electricity at the animals' spinal cords. Romulo Fuentes of Duke University in North Carolina led the researchers. He noted that doctors already use spinal cord stimulation in people to help reduce long-lasting pain.
Scientists are also exploring other experimental treatments. In March, President Obama ended restrictions on the use of federal money for research using human embryonic stem cells. Stem cells from very early embryos are able to grow into any tissue in the body. Scientists say such cells might be able to cure or treat diseases like Parkinson's. But opponents say stem cell experiments are wrong because human embryos are destroyed. They say this is just like destroying a human life.
American actor Michael J. Fox has had Parkinson's disease for eighteen years. But unlike most patients, he got the disease as a young man. He is forty-seven now and has many symptoms of the disease. But Fox still acts on television, writes books and is an activist for Parkinson's. The Michael J. Fox Foundation has raised more than one hundred forty-two million dollars to fund research for better treatments. Michael J. Fox says he is sure that a cure for Parkinson's disease will be found in the future.
This SCIENCE IN THE NEWS was written by George Grow. Our producer was Brianna Blake. I'm Barbara Klein. And I'm Bob Doughty. Transcripts, MP3s and podcasts of our programs are at voaspecialenglish.com. Join us again next week for more news about science in Special English on the Voice of America.