Robbie Roper, the star quarterback from Roswell who died unexpectedly Dec. 22, suffered from elevated blood ammonia levels caused by a genetic condition called urea cycle disorders (UCD), Roper’s father, James, told USA Today in an article published Wednesday.

The father said he did not publicly discuss his son’s cause of death sooner because he “wanted him remembered as a perfect kid.”

“I just didn’t want anybody thinking that he had some abnormality when they thought about him,” James Roper said.

According to the Mayo Clinic, UCD is a group of genetic disorders that can disrupt the urea cycle, which lead to the accumulation of ammonia and a toxic response to the nervous system. Roper’s condition was diagnosed after he became ill.

The Roper family’s attorney, Patrick Moore, told the newspaper that the disorder can be set off by certain medications or situations related to a surgical procedure, including the use of anesthesia. The article said Roper had shoulder surgery Dec. 14.

Roper, who stood 6 feet, 4 inches, was a senior who began the season without scholarship offers but was beginning to get opportunities after a breakout season. He passed for 3,010 yards and 37 touchdowns while leading Roswell to a 10-3 finish and a top-10 final ranking in Class 7A.

Before his death, Roper was voted by his region’s coaches as the Region 5-7A offensive player of the year. The Atlanta Journal-Constitution named him the North Fulton offensive player of the year.