Familial narcolepsy in the Lipizzaner horse: a report of three fillies born to the same sire.

This study examines three Lipizzaner horses that displayed signs of narcolepsy, a sleep disorder typically characterized by excessive daytime sleepiness, hallucinations, and in some cases, sudden losses of muscle strength. Despite familial ties and showing symptoms since an early age, the horses’ conditions seemed to improve over time and their cerebrospinal fluid appeared normal.

Study Overview

• The researchers observed three half-sibling Lipizzaner horses that exhibited symptoms of narcolepsy.
• Signs such as excessive sleepiness, swaying, stumbling, and bouts of unsteadiness displayed by these horses were present early in their lives.
• The clinical symptoms have lessened over time for two out of the three affected horses, otherwise, symptoms increase upon exiting their stables.

Testing and Evaluation

• A physostigmine test, which is used to diagnose disorders causing muscle weakness, was performed on all three horses.
• Two of the horses returned positive results, confirming the presence of a muscle-related disorder, possibly narcolepsy.
• The third horse’s results were not clear due to its continual sleepiness.

Cerebrospinal Fluid Test

• The level of Hypocretin-1, a neurotransmitter linked to narcolepsy, in the cerebrospinal fluid of the horses was measured.
• These levels were found to be normal in all three horses.

Familial History

• The sire, or father, of these three affected horses has had 19 other offspring that did not display any clinical signs of sleep disorders.
• The dams, or mothers, of these three horses also gave birth to healthy foals indicating that the disorder may not be a result of genetic inheritance.

Conclusion

• Based on the physostigmine test results, the horses’ symptoms, and the lacking presence of sleep disorders in their extended family, the researchers concluded that the three Lipizzaner horses are most likely affected by a familial form of equine narcolepsy.