WASHINGTON — Heavy metal rocker Ozzy Osbourne died this week at 76, just weeks after his farewell show and about five years after announcing he had Parkinson’s disease.

Here’s what to know about the disease:

Parkinson’s is a neurologic disease that robs people of control over their movements. It typically starts with tremors and is characterized by slow movement, a shuffling gait, stiff limbs, balance problems and slurred speech.

About 1 million Americans are living with Parkinson’s, and 10 million people worldwide, the Parkinson’s Foundation. estimates. It usually appears after age 60, although sometimes it can develop before age 50.

The exact cause isn’t known, but Parkinson’s develops when cells that produce one of the brain’s chemical messengers, called dopamine, begin to deteriorate and die.

Dopamine transports signals to parts of the brain that control movement. Parkinson’s symptoms appear after enough dopamine-producing cells die that there’s too little of this neurotransmitter in the brain.

According to the foundation, most experts believe genetic and environmental factors are behind the disease. Dozens of gene mutations linked to Parkinson’s have been discovered and genetics account for 10% to 15% of all cases. Other factors suspected of increasing the risk include head injuries, exposure to pesticides and herbicides and where you live.

There is no cure but there are treatments, including medications that affect dopamine levels and a surgically implanted tremor-blocking device. Patients also can benefit from physical and occupational therapy.

Symptoms worsen over time, usually slowly. The severity of symptoms and how quickly they progress varies widely between patients. In advanced cases, people may be unable to walk or care for themselves. They also can suffer from depression as well as memory and thinking problems.

While Parkinson’s itself isn’t considered fatal, people can die from complications of the disease, including lung problems as muscle weakness impedes the ability to cough and to swallow.

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