The fight of his life: boxing Great Muhammad Ali battles Parkinson's disease.

His feet moved with a dancer's grace, while his arms sent punches flying at lightning-fast speed. Throughout the 1960s and the mid1970s, Muhammad Ali's dynamic boxing style and larger-than-life personality mesmerized the world. "To win a fight you had to be able to move around the ring," says the three-time world heavyweight champion. "I moved so fast, I felt like I was floating."

In the late 1970s, Ali's signature ability to "float like a butterfly, and sting like a bee" in the boxing ring began deteriorating. The athlete began experiencing tremors, stiffness, and slow motion. In 1984, when the sports icon was just 42 years old, he was diagnosed with Parkinson's disease (PD).

This neurological (nervous-system-related) disease afflicts 6.5 million people worldwide, and its most marked characteristic is a progressive loss of motion control. As to what causes PD and why the boxing legend developed it, "in most individuals, we really don't know," says Robert A. Hauser, a neurologist at the University of South Florida. "Medications help fight the symptoms of the disease, but there is currently no cure."

Although PD is still largely a mystery, in the last 50 years, scientists have steadily made headway toward understanding the disease and developing new treatments for it.

DISEASE ORIGINS

The disease was named after a British doctor named James Parkinson. In 1817, Parkinson wrote an essay describing a small group of patients affected by a previously unidentified motion-impairing illness. His observations helped establish PD as a medical condition.

In the 1950s, scientists had a major breakthrough in PD research. That's when they first zeroed in on how a neurotransmitter, or chemical messenger, called dopamine relates to body motion--and subsequently, to PD (see Nuts & Bolts, p. 15).

The part of the brain responsible for initiating and regulating motion is called file basal ganglia. There, neurons, or nerve cells, produce dopamine. This chemical messenger transmits the brain's instructions for body movement to a complicated network of other nerve cells. When the nerve cells finally relay the brain's instructions to the muscles, the muscles contract or relax as directed to generate motion.

Scientists discovered that for some unknown reason, people with PD have a progressive and significant loss of the brain's dopamine-making neurons. "When you don't have enough dopamine, the body is not getting the signals to move correctly," says Hauser.

When a person loses approximately 50 percent of his or her dopamine-making neurons, the first symptoms of PD appear. These symptoms vary from person to person. Some people may notice tremors, while others may experience an uncoordinated ann.

When Ali was first diagnosed with PD, the symptoms were hardly noticeable. "He was still really energetic," recalls his daughter Rasheda. Today, after 20 years of dopamine loss, Ali's ability to initiate or maintain movement has declined. "It's a little bit more difficult for him now to say words or walk across the room," says Rasheda.

WHO GETS PARKINSON'S

Since PD is linked to the brain, could repeated blows to the head from boxing have caused Ali to develop the disease? "My doctors don't think so," he says.

At present, scientists can't predict who's at risk for PD. But they have noticed some possible trends: The average patient is diagnosed at 60 years of age, and two thirds of patients are male. When compared with the general public, PD patients tend to have had a higher exposure to agricultural pesticides and unfiltered well water.

In the last decade, scientists have also identified some mutations (abnormal changes) in genes, or units of hereditary material, that could cause PD. But scientists think that gene mutations account for only 5 to 10 percent of all PD cases. So having a relative with PD is far from a guarantee that the disease will be inherited by other members of the family.

"There may be a complex interaction between genes and environmental exposure," says Hauser. "There's so much that has yet to be figured out."

LEARNING TO COPE

Although no cure for PD has been found, "the disease can be well managed," says Laura Marsh, a psychiatrist who studies the brain and how it regulates behavior, at Johns Hopkins University in Maryland.

Today, one of the most common treatments for PD is a medicine called levodopa. When levodopa reaches the brain, dopamine-making neurons convert the chemical into dopamine to supplement the body's diminishing levels. During the early stages of PD when the patient still has a fair level of the neurons, "levodopa does a pretty good job of lessening the symptoms," says Hauser. But as the disease progresses, the medication wears off sooner and sooner, and patients become more dependent on it.

Many people with PD become frustrated because the disease's symptoms prevent them from doing things or communicating in ways that they normally would. For example, a loss of muscle control causes many PD patients to experience slow, garbled speech or be unable to show facial expressions. This could lead to miscommunication, and worse, generate misconceptions about people with FD. "Just because the person is slow to respond or does not seem to laugh at your jokes, it doesn't mean that he or she can no longer think or feel," says Marsh. "To ease communication and improve understanding, it's important for family members to be educated about the disease so that they can help in the best way possible."

One of Ali's symptoms is slurred speech. His family has learned to incorporate nonverbal methods to express emotions. "My children love to draw, and my dad loves to draw," says Rasheda. "So they would start exchanging pictures with one another."

Although PD has caused his body to slow down, Muhammad Ali's knockout attitude is still soaring. As a lifelong advocate for peace and justice, he continues to promote his cause. "All of us are born with the potential for greatness," he says. "Focus on what you can do and what you can be--not what you can't do or what you can't be."

Nuts & Bolts

The nervous system processes information and also directs the body on how to respond. Follow the steps below to see how the brain instructs an arm to move.

1 BRAIN

Inside the motor-controlling region, the basal ganglia, is the substantia nigra. This region contains neurons, or nerve cells, that make dopamine--a chemical messenger that transmits the brain's instructions for movement.

2 NEURONS

The message travels as nerve impulses through a threadlike axon, heading toward a synapse (space between neurons).

3 DOPAMINE

Receptors on another neuron receive the impulses. Stringy dendrites carry the message toward the neuron's cell body. The impulses continue traveling in this manner from one neuron to another.

4 MUSCLES

When impulses finally reach the muscles, the muscles contract or relax as directed to move the arm.

DID YOU KNOW?

* Deep Brain Stimulation, a surgical procedure, is sometimes used to help reduce the symptoms of Parkinson's disease (PD). For this procedure, doctors insert a wire into a targeted area in the patient's brain. The wire is then attached to an electronic device that is surgically embedded into the patient's chest. The battery-operated device sends electric currents to the brain. The currents help regulate neuron activity, leading to a reduction in certain PD symptoms, such as tremors.

* Muhammad Ali was born Cassius Marcellus Clay, Jr., on January 17, 1942, in Louisville, Kentucky. He took the name "Muhammad Ali," on March 6, 1964, when he accepted the teachings of the Nation of Islam.

CRITICAL THINKING:

* What are some ways to help a person with Parkinson's cope with the disease?

CROSS-CURRICULAR CONNECTIONS:

HISTORY: Research to write a biographical essay about Dr. James Parkinson and his contributions to science.

RESOURCES

* For more information about Parkinson's disease, be sure to check out the Web site for the Parkinson's Disease Foundation: www.pdf.org/

* Teens can learn more about Muhammad Ali by reading The Greatest: Muhammad Ali, by Walter Dean Myers, Scholastic, 2001.

CHECK FOR UNDERSTANDING

DIRECTIONS: On a separate piece of paper, answer the following questions in complete sentences.

1. What is the most marked characteristic of Parkinson's disease (PD)?

2. What is dopamine, and how does it relate to body movement?

3. How is dopamine level related to PD?

4. Although scientists can't predict who's at risk for PD, they have noticed some possible trends. Describe the trends.

5. How does the medicine levodopa work to help treat people with PD?

ANSWERS

The Fight of His Life

1. The most marked characteristic of Parkinson's disease (PD) is a progressive loss of motion control.

2. The part of the brain responsible for initiating and regulating motion is called the basal ganglia. There, neurons produce dopamine. This chemical messenger transmits the brain's instructions for body movement to a complicated network of other nerve cells. When the nerve cells finally relate the brain's instructions to the muscles, the muscles contract or relax as directed to generate motion.

3. Scientists discovered that for some unknown reason, people with PD have a progressive and significant loss of dopamine-making neurons. Without enough dopamine, the body does not receive the signals to move correctly. When a person loses approximately 50 percent of his or her dopamine-making neurons, the first symptoms of PD appear. These symptoms vary from person to person. Some people may begin with tremors, while others may experience an uncoordinated arm.

4. Scientists have noticed that the average PD patient is diagnosed at 60 years of age, and two-thirds of patients are male. When compared with the general public, PD patients tend to have had a higher exposure to agricultural pesticides and unfiltered well water. Scientists have also identified some mutations in genes that could cause PD. But gene mutations account for only 5 to 10 percent of all PD cases. Scientists suspect there is a complex interaction between genes and environmental exposure.

5. When levodopa reaches the brain, dopamine-making neurons convert the chemical into dopamine to supplement the body's diminishing levels. During the early stages of PD when the patient still has a fair Level of the neurons, levodopa does a pretty good job of lessening the symptoms. But as the disease progresses, the medication wears off sooner and sooner, and patients become more dependent on it.