Syndrome of High Gamma-Glutamyl Transferase in Racehorses.

Horses in racing and race training can develop high gamma-glutamyl transferase (GGT) syndrome (HGS), or increased GGT without overt evidence of primary liver disease. Current evidence points toward overtraining and a response to oxidative stress, but the etiology is incompletely understood. Evidence for an association of HGS with poor performance is mixed. Without a clear understanding of the etiology, the only evidence-based treatment option is rest or reduced training intensity. More research is needed to determine whether HGS is a physiologic adaptation, perhaps indicative of overtraining but not requiring direct intervention, versus a pathologic response that should be treated.