GEORGIA - Sen. Johnny Isakson will retire at the end of the year.

Isakson, 74, is Georgia’s senior senator, serving since 2005. In 2016 he became the first Georgia Republican elected to a third term in the Senate, winning 54% of the vote.

Three years will remain on his term, and Gov. Brian P. Kemp will call a special election to fill it.

“After much prayer and consultation with my family and my doctors, I have made the very tough decision to leave the U.S. Senate at the end of this year,” Isakson said in a statement Wednesday morning.

Isakson said he told Kemp he intends to resign effective Dec. 31.

“I am leaving a job I love because my health challenges are taking their toll on me, my family and my staff,” Isakson said. “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.”