Cerebellar abiotrophy

Cerebellar abiotrophy (CA), also referred to as cerebellar cortical abiotrophy (CCA), 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.

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 Siameses 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 en utero.

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
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, 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 gene has to be carried 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.

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.

There currently is no DNA test for CA in horses. However research is taking place at the Veterinary Genetics Laboratory at the UC Davis School of Veterinary Medicine, and at the Institute of Genetics at the University of Bern, Switzerland. Researchers working on this problem include Dr. Cecelia Penedo, PhD, at UC Davis; and Dr. Vinzenz Gerber and Dr. Tosso Leeb at University of Bern. The late Dr. Anne 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.

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.

CA in horses

 * AHA Equine Stress, Research and Education Committee. "Caution:Knowledge."  Modern Arabian Horse, August/September 2007, pp 100-105.  Hardcopy edition.  Online version at http://www.arabianhorses.org
 * Baird JD, Mackenzie CD. "Cerebellar hypoplasia and degeneration in part-Arab horses." Aust Vet J. 1974 Jan;50(1):25-8.
 * Beatty, Margaret T., Leipold, H.W., Cash, W., et al.' "Cerebellar Disease in Arabian Horses," Proceedings of the 21st annual convention of the American Association of Equine Practitioners, 1985, pp.241-255.
 * Bjïrck, G., Everz, K.E., Hansen, H.-J. and Henricson, B., 1973. "Congenital cerebellar ataxia in the Gotland pony breed." Zbl. Vet. Med. (A) 20:341-354.
 * Blanco A, et. al. "Purkinje cell apoptosis in arabian horses with cerebellar abiotrophy." J Vet Med A Physiol Pathol Clin Med. 2006 Aug;53(6):286-7.
 * "Cerebellar Abiotrophy," from "Changing Times," column, Journal of Equine Veterinary Science, Vol, 25 no. 10, October, 2005, p. 452.
 * DeBowes R.M., et. al. "Cerebellar abiotrophy." Vet Clin North Am Equine Pract. 1987 Aug;3(2):345-52.
 * de Lahunta, A. "Abiotrophy in domestic animals: a review." Can J Vet Res. 1990 January; 54(1): 65–76.
 * Fox, J., et. al. "Cerebello-Olivary and Lateral (Accessory) Cuneate Degeneration in a Juvenile American Miniature Horse." (2000)
 * Gerber H, Gaillard C, Fatzer R, Marti E, Pfistner B, Sustronck B, Ueltschi G, Meier HP, Herholz C, Straub R, Geissbuhler U, Gerber V. "Cerebellare Abiotrophie bei Vollblutaraber-Fohlen" (Cerebellar abiotrophy in pure-bred arabians) (German). Pferdeheilkunde 1995;11:423-43
 * Hahn, Caroline. "The wobbly horse: differential diagnoses" In Practice (UK), (2006) 28:8-13
 * MacKay, Robert. "Neurologic Disorders of Neonatal Foals." published in Vet. Clin. North Am. Equine Pract. 2005 Aug 21(2): 387-406, vii
 * Palmer, A.C., Blakemore, W.F., Cook, W.R., Platt, H. and Whitwell, K.E. "Cerebellar hypoplasia and degeneration in the young Arab horse: clinical and neuropathological features." Veterinary Record 93:62-66 (1973)
 * 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 January 13, 2007
 * Reich, Cindy. "Genetic Diseases: Breed Responsibly", Arabian Horse World, March, 2007: Volume 47 no. 6, pp. 277-279.
 * 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. "Equine cerebellar hypoplasia and degeneration." Proceedings of the 13th annual convention of the American Association of Equine Practitioners, 1967, p. 123-126
 * Waelchli, R.O. and F. Ehrensperger, "Two related cases of cerebellar abnormality in equine fetuses associated with hydrops of fetal membranes ", Veterinary College, University of Zurich, Switzerland. The Veterinary Record, Vol 123, Issue 20, 513-514 (1988)

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. "Adult-Onset Cerebellar Cortical Abiotrophy and Retinal Degeneration in a Domestic Shorthair Cat." J Am Anim Hosp Assoc. 2002 Jan-Feb;38(1):51-4.

External links to information on CA in Horses

 * Video of a foal with a mild case of Cerebellar Abiotrophy
 * 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.
 * Information from the University of Bern on Cerebellar Abiotrophy in horses (in English)
 * Information from the University of Bern on Cerebellar Abiotrophy in horses(German version)
 * Institute of Genetics at the University of Bern
 * Equine Clinic at the University of Bern

External links to information on CA in Dogs

 * Information on cerebellar abiotrophy in dogs
 * "Wobbly Scotties:" Information on CA in Scottish Terriers
 * Scottish Terrier Club of America information on CA