Civil rights activist Rev. Jesse Jackson has revealed that he has been diagnosed with Parkinson’s disease. A neurological disorder with no cure, Parkinson’s can cause tremors, stiffness and difficulty balancing, walking and coordinating movement.

“My family and I began to notice changes about three years ago,” Jackson wrote in a statement. “After a battery of tests, my physicians identified the issue as Parkinson’s disease, a disease that bested my father.”

Jackson added that “recognition of the effects of this disease on me has been painful.”

He also said he sees his diagnosis as “a signal that I must make lifestyle changes and dedicate myself to physical therapy in hopes of slowing the disease’s progression.”

Born in Greenville, S.C., the 76-year-old is a two-time Democratic presidential candidate. Highlights of his career include participating in civil rights demonstrations with the Rev. Martin Luther King Jr., negotiating successfully for the release of three US soldiers who had been held in Yugoslavia and receiving the Presidential Medal of Freedom from President Bill Clinton.

More recently, Jackson spoke out in 2014 about the shooting death of 18-year-old Ferguson, Mo., resident Michael Brown, which sparked protests and a national debate about race and police.

Parkinson’s disease is caused by the death of brain cells that contain dopamine, a neurotransmitter necessary for communication within the brain. Losing dopamine neurons is a normal part of aging, yet patients with Parkinson’s lose many more than usual, and the brain’s inability to compensate leads to symptoms.

Parkinson’s often starts with a small tremor in the hand or muscle stiffness and progresses over time. Usually, symptoms are worse on one side of the body. The obvious physical symptoms are the reason it is sometimes referred to as a “movement disorder,” yet other signs are also common: Patients can experience depression, sleep problems, anxiety, fatigue and constipation.

“I am far from alone,” Jackson said in his statement.

“I want to thank my family and friends who continue to care for me and support me,” he concluded. “I will need your prayers and graceful understanding as I undertake this new challenge.”