Persistent hyperammonemia in two related Morgan weanlings.

The research focuses on two related Morgan foals that exhibited persistent hyperammonemia, which is unusually high levels of ammonia in the blood. Despite various diagnostic tests, no toxic, developmental, or infectious cause were found, leading to the hypothesis that the condition may have been a result of an inherited disorder similar to the human condition known as HHH syndrome.

Research Overview

The concerned research revolves around two related Morgan fillies or foals exhibiting troubling symptoms after their weaning phase. The key symptom noted was persistent hyperammonemia, a condition marked by unusually high levels of ammonia in the blood.

Diagnostic Tests

• Routine serum chemistries
• Complete Blood Count (CBC)
• Liver biopsy
• Hepatic ultrasonography
• Liver function test

Despite these diverse diagnostic evaluations, the tests did not indicate any toxic, developmental, or infectious cause behind the observed hyperammonemia.

Potential Causes

Following the inconclusive results from the various tests, the researchers needed to reconsider the possible causes of the condition. In the absence of environmental or infectious causes, they turned their attention to potential genetic factors.

HHH Syndrome

The researchers discovered abnormal serum amino acid and urine orotic acid concentrations, which led them to hypothesize that the foals could have a disorder similar to the human condition known as HHH syndrome. HHH syndrome, standing for Hyperornithinemia, Hyperammonemia, and Homocitrullinuria, is an inherited disorder that is usually caused by a defective mitochondrial transporter protein.

In HHH syndrome, a deficiency in ornithine, which is needed for complete urea synthesis, is observed. This deficiency indirectly causes increased levels of ammonia and ornithine in the blood, which could potentially explain the hyperammonemia observed in the two fillies.

This research opens up the potential for further investigation on the genetic factors that may influence the health of young horses, especially rare inherited disorders.