Persistent hyperammonemia in two related Morgan weanlings.
- Case Reports
- Journal Article
- Research Support
- U.S. Gov't
- P.H.S.
Summary
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.
Cite This Article
Publication
Researcher Affiliations
- Department of Food Animal and Equine Medicine, North Carolina State University, College of Veterinary Medicine, Raleigh, USA.
MeSH Terms
- Amino Acids / blood
- Ammonia / blood
- Animals
- Behavior, Animal / physiology
- Biopsy / methods
- Biopsy / veterinary
- Female
- Horse Diseases / blood
- Horse Diseases / diagnosis
- Horse Diseases / physiopathology
- Horses
- Liver / pathology
- Liver / physiopathology
- Liver Function Tests
- Metabolic Diseases / blood
- Metabolic Diseases / complications
- Metabolic Diseases / veterinary
- Nervous System Diseases / etiology
- Nervous System Diseases / physiopathology
- Nervous System Diseases / veterinary
- Ornithine / blood
- Weaning
Grant Funding
- R01-RR02599 / NCRR NIH HHS
Citations
This article has been cited 7 times.- Satué K, Miguel-Pastor L, Chicharro D, Gardón JC. Hepatic Enzyme Profile in Horses. Animals (Basel) 2022 Mar 29;12(7).
- Fielding CL, Magdesian KG, Mayer JR. Resolution of neurologic signs presumed to be associated with hyperammonemia in 2 endurance horses. Can Vet J 2020 Aug;61(8):860-864.
- Corley KTT. Metabolic disorders in foals. Equine Vet Educ 2012 Aug;24(8):392-395.
- Panza E, Martinelli D, Magini P, Dionisi Vici C, Seri M. Hereditary Spastic Paraplegia Is a Common Phenotypic Finding in ARG1 Deficiency, P5CS Deficiency and HHH Syndrome: Three Inborn Errors of Metabolism Caused by Alteration of an Interconnected Pathway of Glutamate and Urea Cycle Metabolism. Front Neurol 2019;10:131.
- Martinelli D, Diodato D, Ponzi E, Monné M, Boenzi S, Bertini E, Fiermonte G, Dionisi-Vici C. The hyperornithinemia-hyperammonemia-homocitrullinuria syndrome. Orphanet J Rare Dis 2015 Mar 11;10:29.
- Hisaeda K, LE NAT, Kadekaru S, Ono T, Hiasa Y, Ohzawa E, Hata A, Kutara K, Sugimoto K, Une Y, Iwata E, Kunieda T, Zhang C, Kitagawa H. Metabolic, pathological, and genetic analyses of foals neonatal foals that died in Noma horses. J Equine Sci 2025 Jun;36(2):55-65.
- Hisaeda K, Ono T, Kadekaru S, Hata A, Miyama TS, Kutara K, Sugimoto K, Hiasa Y, Ohzawa E, Kunieda T, Iwata E, Kitagawa H. Serum amino acid profiles in clinically normal Noma horses. J Equine Sci 2024;35(2):29-34.
