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Cerebellar abiotrophy

Cerebellar abiotrophy (CA), also referred to as the cerebellar cortical abiotrophy (CCA), which is a genetic neurological disease in animals best known to affect certain breeds of horses and dogs. It develops when the neurons known as Purkinje cells, located in the cerebellum of the brain, begin to die off. These cells affect balance and coordination. They have a critical role to play in the brain. The Purkinje layer allows communication between the granular and molecular cortical layers in the cerebellum. Put simply, without Purkinje cells, an animal loses its sense of space and distance, making balance and coordination difficult.

Abiotrophy means the loss of a vital nutritive factor. The exact cause of cerebellar abiotrophy is not known, but it is thought to be due to an intrinsic metabolic defect.[1]

In most cases, the Purkinje neurons begin to die off shortly after the animal is born and the condition is noticeable when the animal is less than six months old, though sometimes the onset of symptoms is gradual and the animal is much older before the owner or caretaker notices a problem.

CA cannot be prevented, other than by selective breeding to avoid the gene, and it cannot be cured. In addition to dogs and horses, there also have been cases of cerebellar abiotrophy in Siamese and Domestic shorthair cats; in Angus, Polled Hereford, Charolais and Holstein Friesian cattle; Merino and Wiltshire sheep; and Yorkshire pigs.

Contents

Other terms used

The condition in Kerry Blue Terriers is sometimes called progressive neuronal abiotrophy (PNA). Other terms used to describe the condition in dogs include cerebellar cortical atrophy and postnatal cerebellar cortical degeneration.[2]

Cerebellar abiotrophy in horses was originally thought to be a form of cerebellar hypoplasia and was described as such in older research literature. However, it was discovered that in horses, the die-off of purkinje cells began after the animal was born, rather than occurring in utero. Cerebellar hypoplasia is particularly common in cats and has similar symptoms.

There are other diseases that lead to cerebellar degeneration, but the loss of Purkinje cells is a clear way to diagnose CA, and the combination of symptoms is sufficiently unique that CA can easily be distinguished from other conditions, even in a living animal.

Symptoms

File:AwkwardGait.jpg
A two-year-old Arabian horse with cerebellar abiotrophy, showing stiff awkward gait, and upper range of unnatural head bob. Though this horse has a relatively mild case, it cannot ever be ridden.
Symptoms of cerebellar abiotrophy include ataxia or lack of balance, an awkward wide-legged stance, a head tremor (intention tremor) (in dogs, body tremors also occur), hyperreactivity, lack of menace reflex, stiff or high-stepping gait, coarse or jerky head bob when in motion (or in very young animals, when attempting to nurse), apparent lack of awareness of where the feet are (sometimes standing or trying to walk with a foot knuckled over), poor depth perception, and a general inability to determine space and distance. The symptoms are, when taken as a group, fairly unique and not easily mimicked by other illnesses, though certain types of neurological injury and infection do need to be ruled out. Verifying the diagnosis in a laboratory setting is only possible by examining the brain post-mortem to determine if there has been a loss of Purkinje cells.

Most affected animals have normal intelligence and mildly affected animals can, in theory, live out a normal lifespan. However, affected animals are quite accident-prone, and for this reason many animals that develop CA, particularly horses, are euthanized for humane reasons. Horses may experience difficulty stepping up and over objects, run into fences, fall easily, and even if allowed to mature to full growth, are generally considered unsafe to ride. Dogs may need lifetime assistance with tasks such as climbing stairs.

In horses, the symptoms may worsen from the time of onset for six to 12 months, but if not severe enough to mandate euthansia, they stabilize over time. In some dog breeds, symptoms appear to progressively worsen, but research is not consistent on this point. There also is some evidence that affected animals partially compensate for the condition by cognitively learning alternative methods for moving or to determine distance, and thus appear to improve because they become less accident-prone.

Cerebellar abiotrophy in horses

Cerebellar abiotrophy (CA) is best known as a condition affecting Arabian horses. It has also been observed in the Miniature horse, the Gotland Pony, one Eriskay Pony, and possibly the Oldenburg. Most foals appear normal at birth, with symptoms noticeable at an average age of four months, though there have been cases where the condition is first seen shortly after birth and other cases where symptoms are first recognized in horses over one year of age.

In horses, CA is believed to be linked to an autosomal recessive gene. This means it is not sex-linked, and the allele has to be carried and passed on by both parents in order for an affected animal to be born. Horses that only carry one copy of the gene may pass it on to their offspring, but themselves are perfectly healthy—without symptoms of the disease. Because it is recessive, the allele for CA may pass through multiple generations before it is expressed.

CA is sometimes misdiagnosed. Though the symptoms are quite distinguishable from other neurological conditions, it has been confused with Wobbler's syndome, Equine Protozoal Myeloencephalitis (EPM), and injury-related problems such as a concussion.

An indirect DNA test which identifies markers associated with cerebellar abiotrophy is available.[3] Continued research is taking place at the Veterinary Genetics Laboratory at the [[UC Davis School of Veterinary Medicine. Researchers working on this problem include Dr. Cecilia Penedo, PhD, at UC Davis and her assistant Leah Brault. The late Dr. Ann Bowling also made significant contributions to the genetics research on CA.

Cerebellar abiotrophy in dogs

CA has been seen in the Australian Kelpie, Gordon Setter, Border Collie, Labrador Retriever, Airedale, English Pointer, Scottish Terrier, Kerry Blue Terrier, Miniature Schnauzer, and other dog breeds. Time of onset varies. In a few breeds, such as the Beagle, Rough Collie, and Miniature Poodle, Purkinje cells begin to die off at or shortly before birth, and pups are born with symptoms or develop symptoms by three to four weeks of age.[4] Most breeds prone to the condition, such as the Kerry Blue Terrier, Border Collie, Australian Kelpie, and Labrador Retriever, begin showing symptoms between six and sixteen weeks of age.[4] In a very few breeds, such as the American Staffordshire Terrier, Old English Sheepdog, Brittany Spaniel, and Gordon Setter, symptoms do not appear until adulthood or even middle age.[5]

In dogs, CA is also usually an autosomal recessive gene, but in a few breeds, such as the English Pointer, the gene is sex-linked.

Footnotes

  1. Sandy J, Slocombe R, Mitten R, Jedwab D (2002). "Cerebellar abiotrophy in a family of Border Collie dogs". Vet. Pathol. 39 (6): 736–8. doi:10.1354/vp.39-6-736. PMID 12450206. 
  2. Aitken, Sarah "Listing of Inherited Disorders in Animals; Disorder: Cerebellar abiotrophy" University of Sydney. Web site accessed March 26, 2007
  3. Johnson, Robert S. "Test Allows Arabian Breeders to Scan for Inherited Neurologic Disorder" The Horse online edition, September 23 2008, Article # 12746. Accessed September 23, 2008
  4. 4.0 4.1 Berry M, Blas-Machado U (2003). "Cerebellar abiotrophy in a miniature schnauzer". Can. Vet. J. 44 (8): 657–9. PMID 13677598. 
  5. Buijtels J, Kroeze E, Voorhout G, Schellens C, van Nes J (2006). "[Cerebellar cortical degeneration in an American Staffordshire terrier]". Tijdschrift voor diergeneeskunde 131 (14-15): 518–22. PMID 16916197. 


Bibliography

  • deLahunta, Alexander; deLahunta, Alexander (1983). Veterinary Neuroanatomy and Clinical Neurology (2nd ed.). Philadelphia: Saunders. ISBN 0-7216-3029-4. 
  • deLahunta, Alexander; Summers, Brian Alan; Cummings, John Thomas (1995). Veterinary neuropathology. St. Louis: Mosby. ISBN 0-8016-5063-1. 


CA in horses

  • Adams, Ragan (M.A., D.V.M.); Mayhew, Ian G. (B.V.Sc., Ph.D.) (April 1985). "Neurologic Diseases". Veterinary Clinics of North America: Equine Practice 1 (1): 209–234. 
  • Beatty, Margaret T., Leipold, H.W., Cash, W., et al. (1985). "Cerebellar Disease in Arabian Horses". Proceedings of the 21st annual convention of the American Association of Equine Practitioners. pp. 241–55. 
  • Beech, Jill (1976). "Cerebellar Hypoplasia". Proceedings of the Twenty-Second Annual Convention of the American Association of Equine Practitioners (Dallas, Texas): 77–78. 
  • Björck G, Everz KE, Hansen HJ, Henricson B (May 1973). "Congenital cerebellar ataxia in the gotland pony breed". Zentralbl Veterinarmed A 20 (4): 341–54. PMID 4199630. 
  • DeBowes RM, Leipold HW, Turner-Beatty M (August 1987). "Cerebellar abiotrophy". Vet. Clin. North Am. Equine Pract. 3 (2): 345–52. PMID 3497695. 
  • Gerber H, Gaillard C, Fatzer R, Marti E, Pfistner B, Sustronck B, Ueltschi G, Meier HP, Herholz C, Straub R, Geissbuhler U, Gerber V (1995). "Cerebellar abiotrophy in pure-bred arabians" (in German). Pferdeheilkunde 11: 423–43. ISSN 0177-7726. 
  • Hahn, Caroline (2006). "The wobbly horse: differential diagnoses". in Practice (UK) 28: 8–13. 
  • Palmer AC, Blakemore WF, Cook WR, Platt H, Whitwell KE (July 1973). "Cerebellar hypoplasia and degeneration in the young Arab horse: clinical and neuropathological features". Vet. Rec. 93 (3): 62–6. PMID 4748678. 
  • Reich, Cindy (March 2007). "Genetic Diseases: Breed Responsibly". Arabian Horse World 47 (6): 277–9. 
  • Reich, Cindy (January 2009). "Cerebellar Abiotrophy: Carrier Status Announced". Arabian Horse World: 438–9. 
  • Sponseller, Max (1967). "Equine cerebellar hypoplasia and degeneration". Proceedings of the 13th annual convention of the American Association of Equine Practitioners. pp. 123–6. 

CA in dogs

CA in cats

External links to information on CA in Horses

Video clips of equine CA cases

External links to information on CA in Dogs

Video clips of canine CA cases



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