- 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.
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. Genetic testing can detect carriers. 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.
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.
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 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.
A DNA test which identifies markers associated with cerebellar abiotrophy is available. The test has been refined to identify the most likely mutations, and retesting of earlier samples based on an earlier indirect marker test developed by UCD, indicated a 97% accuracy rate for the old test relative to the newer version, with no false negatives. 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, and Leah Brault, PhD. 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. 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. 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.
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CA in horses
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- Hahn, Caroline (2006). "The wobbly horse: differential diagnoses". in Practice (UK) 28: 8–13.
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- Penedo, M. Cecilia T. and Leah Brault. "Progress Toward Identifying the Gene Responsible for Equine Cerebellar Abiotrophy (CA)." Genetics, Research Review, 2006, Center for Equine Health, University of California, Davis. Accessed November 6, 2011
- 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, Brett A. A Pedigree Analysis of Cerebellar Cortical Abiotrophy in the Arabian Horse. (Fourth-year seminar paper). Ithaca, NY: College of Veterinary Medicine, Cornell University, 1994.
- Sponseller, Max (1967). "Equine cerebellar hypoplasia and degeneration". Proceedings of the 13th annual convention of the American Association of Equine Practitioners. pp. 123–6.
- Waelchli RO, Ehrensperger F (November 1988). "Two related cases of cerebellar abnormality in equine fetuses associated with hydrops of fetal membranes". Vet. Rec. 123 (20): 513–4. doi:10.1136/vr.123.20.513. PMID 3206793. http://veterinaryrecord.bvapublications.com/cgi/content/full/123/20/513.
- WAHO. "GENETIC DISORDERS IN ARABIAN HORSES: CURRENT RESEARCH PROJECTS." World Arabian Horse Association, accessed online October 23, 2007
CA in dogs
- General information on genetics, breeding strategies, disease control and diversity. Mostly articles on dogs, but relevant to other species
CA in cats
- Barone G, Foureman P, deLahunta A (2002). "Adult-onset cerebellar cortical abiotrophy and retinal degeneration in a domestic shorthair cat". J Am Anim Hosp Assoc 38 (1): 51–4. PMID 11804315. http://www.jaaha.org/cgi/pmidlookup?view=long&pmid=11804315.
- A composite Site for information on Cerebellar Abiotrophy (CA)with CA Status List of Disclosed Horses.
- Information from the University of California-Davis on Cerebellar Abiotrophy in horses
- F.O.A.L., an organization dedicated to fighting lethal genetic conditions in Arabian horses.
- . The Dr. Van Haeringen Laboratorium bv, The Netherlands for CA testing in Europe. English and Dutch.
Video clips of equine CA cases
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Look at other dictionaries:
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