Syndrome of High Gamma-Glutamyl Transferase in Racehorses.

Overview

• This study discusses the occurrence of high gamma-glutamyl transferase (GGT) syndrome (HGS) in racehorses, characterized by elevated GGT levels without clear liver disease.
• It explores current theories about its cause, its potential impact on racehorse performance, and highlights the need for further research to guide treatment strategies.

Background on High Gamma-Glutamyl Transferase Syndrome (HGS) in Racehorses

• HGS is defined by an elevated level of the enzyme gamma-glutamyl transferase (GGT) found in the blood of racehorses.
• Unlike typical liver diseases where GGT is increased due to liver damage, horses with HGS show high GGT without obvious signs of primary liver disease.
• This makes HGS a unique syndrome whose underlying causes are not fully understood.

Current Understanding of Etiology

• One leading hypothesis is that HGS is related to overtraining in racehorses.
• Increased GGT may be a response to oxidative stress caused by intense and prolonged exercise.
• Oxidative stress involves the accumulation of free radicals which can impact cellular functions, potentially elevating GGT as a protective or stress-related marker.
• Other causes or contributing factors to the elevated GGT have not been clearly identified, underscoring the complexity of the syndrome.

Association with Performance

• Research so far offers mixed evidence about whether HGS negatively affects a horse’s racing performance.
• Some studies suggest a correlation between high GGT levels and poorer performance, while others find no clear relationship.
• This inconsistency limits the ability to use GGT levels as a straightforward predictor or diagnostic marker for performance issues.

Treatment and Management

• Due to incomplete understanding of the syndrome’s cause, treatment options remain limited.
• Currently, the only evidence-based approach involves rest or reducing the intensity of training to allow recovery.
• No pharmaceutical or specific intervention treatments have been established as effective for HGS at this time.
• Decisions about treatment are often empirical and guided by clinical judgment and monitoring of GGT levels and performance.

Implications and Future Research Needs

• The key open question is whether HGS represents a normal physiological adaptation to training stress or a harmful pathological condition.
• If HGS is an adaptive response, it might not require treatment beyond normal management adjustments.
• If it is pathologic, more aggressive interventions may be needed to prevent long-term damage or performance decline.
• Future research should focus on:
  • Clarifying the biological mechanisms that cause elevated GGT in racehorses
  • Determining the impact of HGS on overall health and racing outcomes
  • Identifying potential biomarkers or diagnostic criteria for monitoring HGS
  • Developing targeted treatments or preventative strategies