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WASHINGTON (Reuters) - Republican Senator Johnny Isakson of Georgia said on Wednesday he will leave the Senate at the end of 2019, citing his struggles with Parkinson’s disease and other medical issues.

“My Parkinson’s has been progressing, and I am continuing physical therapy to recover from a fall in July. In addition, this week I had surgery to remove a growth on my kidney,” Isakson said in a statement.

“With the mounting health challenges I am facing, I have concluded that I will not be able to do the job over the long term in the manner the citizens of Georgia deserve,” Isakson added.

He said he would return to Washington Sept. 9 when Congress reconvenes after a summer recess, and resign effective Dec. 31.

Isakson, 74, chairs the Senate Veterans Committee and the Select Ethics Committee. The Senate currently has a majority of 53 Republicans with 45 Democrats and two independents that align with Democrats.

Georgia Governor Brian Kemp, also a Republican, will appoint Isakson’s replacement. To retain the seat that person will have to run in 2020, the next statewide election in Georgia, and again in 2022, after which the winner would serve a full six-year term.

The state’s other senator, Republican David Perdue, is up for re-election in 2020.

Isakson had won re-election in 2016 with 54% of the vote. He was the first Republican in Georgia to be elected to a third, six-year term in the Senate, his office said. He was diagnosed with Parkinson’s disease in 2013.

Democrats had been hoping to convince Stacey Abrams, who ran unsuccessfully for Georgia governor last year, to seek a U.S. Senate seat next year. She declined to challenge Perdue and issued a statement on Twitter on Wednesday saying that she would not seek Isakson’s seat.