Sen. Johnny Isakson (R-Ga.) in November 2014. Isakson has Parkinson's disease, but says the condition won't alter his decision to seek reelection in 2016 or his ability to serve if he wins a new term. (David Goldman/AP)

Sen. Johnny Isakson (R-Ga.) said Wednesday that he has been diagnosed with Parkinson's disease, a progressive disorder of the nervous system.

Isakson, 70, is in his second term and said his diagnosis will not keep him from seeking reelection in 2016. Roughly 1 million Americans have some form of Parkinson's disease, including notable figures such as boxer Muhammad Ali and actor Michael J. Fox. In Isakson's case, the disease is in its mild, early stages.

"My diagnosis has not impacted my ability to represent the state of Georgia in the U.S. Senate," Isakson said in a statement. "I am busier and have more responsibility today than ever before in my political career, and I couldn’t be happier about that. I remain devoted to public service, to my state and to my constituents. I am eager to take my record of results to the voters of Georgia as I run for reelection in 2016.”

Isakson's office also released a statement from his neurologist, Thomas M. Holmes, who said he first diagnosed Isakson as having Parkinson’s in August 2013.

Currently, Holmes said, Isakson is in Stage 1.5 on a five-stage scale of progress, which he said is "indicative of his mild symptoms of Parkinson's disease." Holmes said he has prescribed medication, a daily exercise routine and "a rigorous physical therapy regimen" to treat his symptoms.

Parkinson's disease generally affects a person's physical abilities -- most commonly seen in limb tremors, limb rigidity and an overall slowdown in movement -- though metal acuity can be increasingly impaired in the later stages of the disease.

Isakson said he first sought medical attention for his symptoms in 2012 for arm stiffness. Today, he said, his primary symptoms are continued stiffness in his left arm and a "slowed, shuffling gait."

“While I am facing this health challenge head on, I have wrestled with whether to disclose it publicly," he said. "I recently shared the news with my three grown children and my senior staff a couple of months ago. Their support, along with the steadfast support of my wife, Dianne, helped me to take this step today. In the end, I decided I should handle my personal health challenge with the same transparency that I have championed throughout my career."

Said Holmes, "I believe he is fully capable of continuing to perform his duties as a U.S. senator, and I believe he is fully capable of running for reelection and serving for another term."

In the Senate, Isakson is considered a mainstream conservative who is a reliable ally of Senate Majority Leader Mitch McConnell. He chairs both the Committee on Veterans Affairs and the Senate Ethics Committee.

Said McConnell said in a statement: "No one works harder than Johnny Isakson, who is the only Senator who is chairing two committees in the Senate. This diagnosis will not slow him down one bit."

Isakson is a real estate businessman who served in the Georgia House of Representatives from 1977 to 1991, in the Georgia Senate from 1993 through 1997, and in the U.S. House from 1999 to 2005. He replaced Zell Miller, the incumbent conservative Democrat, after Miller decided not to contest the 2004 U.S. Senate race.

No significant opposition from either major party has yet emerged in Isakson's reelection race.

CORRECTION, 3:45 P.M.: This post originally said Isakson defeated Zell Miller in 2004. Miller, in fact, decided not to seek election in 2004; Isakson defeated Democratic nominee Denise Majette.