The first time many of us heard of Parkinson's disease was when Michael J Fox announced he had the condition, back in 1999.
More recent sufferers include Billy Connolly and, as revealed on Thursday, the late comedian Robin Williams, who took his own life on Monday.
Like diabetes, there is no cure for Parkinson's, and scientists do not know what exactly causes the disease.
Around 127,000 people in the UK have Parkinson's disease, and it is caused by a loss of brain cells that produce a chemical messenger called dopamine.
Symptoms tend to get worse the longer a person has the disease because it is a progressive neurological disorder. It differs from case to case but often include a tremor or fine shake while the person is at rest, rigidity of muscles, slowness of movement and unsteady balance.
• Tremor (shaking)
• Slowness of movement
• Rigidity (stiffness)
• Physical and other symptoms of Parkinson's
• Bladder and bowel problems
• Eye problems
• Falls and dizziness
• Restless legs syndrome
• Skin, scalp and sweating problems
• Sleep problems
• Speech and communication problems
• Swallowing problems
• Hallucinations and delusions
• Memory problems
Source: Parkinson's UK
Other possible symptoms can include memory loss and earlier this year, Connolly admitted he had started to forget his lines during performances.
The NHS website advises: "The average age for the symptoms to start is around 60; although around 1 in 20 cases first develop in people aged under 50. Men are one-and-half times more likely to get Parkinson’s disease than women."
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Parkinson's UK say that it can make everyday tasks like getting dressed or using a computer and phone difficult and "frustrating". They add: "On top of symptoms affecting movement, people with Parkinson’s often experience problems such as tiredness, pain, depression and constipation, which impact their day-to-day lives."
Symptoms can be controlled using a combination of drugs, therapies and occasionally surgery, but often more care and support may be needed as they progress.
Steve Ford, Chief Executive at Parkinson's UK, said diagnosis can be a "positive" experience for people.
He said: "Often people when they are diagnosed with Parkinson's will say 'Now I realise I've probably had it for several years'. They might have been living with a tremor in their fingers or a stiffness which is why diagnosis can be a positive and they can start treatment for a tremor or slowness of movement.
"It is important to say that the treatment can deal with some of the symptoms but not the underlying causes and Parkinson's is a progressive illness so as you go on more of the cells in the brain die and it gets worse although the rate at which it gets worse differs in individuals."
Mr Ford said patients can also be helped with physiotherapy sessions and speech and language therapy to help them deal with the symptoms.
The NHS also advises that: "Due to the advancements in treatment, people with Parkinson’s disease now often have a normal or near-normal life expectancy."
Actor Bob Hoskins announced his retirement last year after being diagnosed with the disease.
The disease was identified by - and named after - Dr James Parkinson who wrote An Essay On The Shaking Palsy in 1817 which established it as a recognised medical condition.
Fox, known for his roles in "Spin City" and the "Back to the Future" trilogy, was diagnosed with Parkinson's disease at age 30 in 1991, according to his foundation's website. However, he didn't share his condition publicly until 1998, and he officially retired from "Spin City" in 2000. That same year, Fox launched The Michael J. Fox Foundation for Parkinson's Research, which is dedicated to raising awareness and funding.
The boxing champion first started experiencing symptoms of Parkinson's shortly after he retired from the sport in 1981, but The Guardian reported that he wasn't officially diagnosed until 1984. By that time, he was already experiencing symptoms of tremors, slow movement and slurred speech, according to The Guardian. The Associated Press reported that today, Ali, now 70, is largely left unable to speak, save for several whispers in the mornings. "The Parkinson's has affected him a lot, one of [the] things he has is a lot of difficulty speaking," Dr. Abraham Lieberman, director of the Muhammad Ali Parkinson Center in Phoenix, told the Associated Press. "But he's never downbeat about it ... He's a tremendous inspiration to everyone."
The former U.S. Attorney General -- and the first woman to hold that position -- announced her diagnosis of Parkinson's in 1995, the New York Times reported. The first sign for her was uncontrollable shaking of her left hand. "Her hand shook like mad, but she pointed out that her brain wasn't shaking," Reno's sister, Maggy Hurchalla, said at the opening of the University of Florida Center for Movement Disorders and Neurorestoration last year, according to a statement. Reno told the American Academy of Neurology's Neurology Now in 2006 that even though the tremors associated with her condition have become worse throughout the years, they have been mainly in her left hand.
While the Chinese Communist leader's cause of death in 1976 is not 100 percent confirmed, Mao was believed to have suffered from Parkinson's disease, the New York Times reported.
Kerr, who had roles in "The King & I," "From Here to Eternity" and "An Affair to Remember," passed away from Parkinson's at age 86 in 2007, People magazine reported. TCM reported that the actress was diagnosed with the condition in 1994, and had to use a wheelchair.
The iconic country music singer and Rock and Roll Hall of Fame inductee publicly announced his diagnosis in 1997, CNN reported. At the time, his condition spurred cancellations of book promotions and concert tours. Cash ultimately died from diabetes complications in 2003 at age 71, USA Today reported.
Reverend Billy Graham publicly announced that he had Parkinson's in 1992 at age 73, CBC News reported. His spokesman said at the time that "Evangelist Billy Graham has known for about three years that he is in the early stages of Parkinson's disease," the Philadelphia Daily News reported. "It was diagnosed during a routine checkup at the Mayo Clinic. His early manifestations were a mild tremor that causes difficulty in handwriting and some difficulty in gait and in descending steps without a rail. Both symptoms improved significantly with a modest amount of medication." Today, Graham also suffers from macular degeneration and hearing loss, and was most recently hospitalized because of pneumonia, the Charlotte Observer reported.
If you've been affected by the issues in this article, please call the Samaritans on 08457 90 90 90.
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