Virginia senior defensive end Cam Johnson, who led the team last season in sacks and tackles for a loss, has sickle cell trait, Cavaliers Coach Mike London said Monday.

According to London, Johnson (Gonzaga) has known he’s had the trait for “at least a couple years,” and London was informed of the development when he returned to Virginia in 2010.

People with sickle cell trait carry a defective gene that affects blood hemoglobin and can cause mild anemia under stressful conditions such as high-level exercise.

London said he believes there is a correlation between Johnson having sickle cell trait and the player’s dramatically varying degrees of energy on the field. There were times last season when Johnson would be dominant for several plays and then become a non-factor.

“Now it’s the management of him,” London said. “If he’s not an eight-plays-in-a-row, every-down guy, then manage the three or four plays that he plays. Get him out, get him rested and then get him back in there.”

Johnson’s frame (6-foot-4, 265 lbs.) and production seemingly would suggest he could have game-changing impact. London said Monday that if you were to create a highlight video of Johnson’s best plays, it would elicit oohs and ahs.

“He can be that type of guy,” London said, “but he’s got to want to be that type of guy play after play.”

This has been the consistent knock on Johnson during his Virginia career. On first and second down, he frequently creates havoc for opposing offenses. But sometimes on third down when the Cavaliers need a big rush – the type they know Johnson is capable of bringing – he does not oblige.

“He has a chance to be as good as he wants to be,” London said. “He’s not an every down player right now, in my estimation. He’s a guy that plays every down, but to be an every-down difference-maker, he’s got to raise it up another notch. He can be a good player and a dominant player when he wants to, but you’ve got to want to all the time.”