Blood tests determine Cardinals receiver John Brown has sickle-cell trait

The team believes Brown's hamstring issues were actually the result of his sickle-cell trait

The Arizona Cardinals have discovered the source of the leg pain John Brown has been experiencing for the better part of the last two seasons: The wide receiver has a sickle-cell trait, per the team's official website.

The Cardinals had previously believed that Brown was having hamstring issues, and had listed him on their injury report several times with information reflecting that. But when MRIs did not turn up anything in his hamstrings, the Cardinals looked elsewhere for causes and performed blood tests. Those tests revealed the sickle-cell trait.

The Cardinals have not ruled Brown out for Sunday's game against the Seattle Seahawks, but he did not practice Friday. "We're investigating how to help him," Cardinals coach Bruce Arians said, noting that Brown is "very happy he found out why his legs are hurting so bad."

Sickle-cell trait -- a trait abnormality that affects red blood cells -- is differentiated from sickle-cell disease because the person with sickle-cell trait inherits the trait from only one parent, rather than both. It is not curable, but it is treatable, and several athletes (including former NFL safety Ryan Clark, among others) have been able to continue having prominent and productive careers even after discovery of the trait.