Republican Sen. Johnny Isakson, the chairman of the Senate Veterans Affairs Committee and a longtime Georgia lawmaker, announced Wednesday that he will resign at the end of the year.

In a statement, he cited his battle with Parkinson’s disease.

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