Cerebellar abiotrophy in the Arabian horse

Horse
CA-Foal

Cerebellar ataxia (CA) is a hereditary disease that has been demonstrated in Arabian Thoroughbreds and also affects horses of other Arabian breeds. Cases of cerebellar ataxia have also been described in Gotland ponies and Oldenburg Warmbloods.
The cause for the development of the disease symptoms is considered to be the death of the nerve cells (Purkinje cells) of the cerebellum. The cerebellum controls all movements, balance, coordination and fine motor skills. Horses affected by CA are conspicuous by varying degrees of disturbance in the sequence of movements in the head region and especially in the forelimbs. In severe cases, the first signs of CA can be seen shortly after birth. Usually, however, no or hardly noticeable changes are observed in CA-affected foals at birth and during the first months of life; only at about three months of age do the signs become increasingly obvious. In some cases, however, the disease is very protracted, so that the first symptoms do not appear until weaning from the mother, or in the young horse that begins training.

Genetic test
The Institute of Animal Breeding and Genetics has tested all samples received to date using the genetic test described by L. S. Brault et al. (2010, Genomics, USA) in the gene TOE1. The new test procedure now allows testing of horses of other Arabian breeds, Oldenburgers, Trakehners and other breeds. However, there are still cases of TOE1-positive animals (trait carriers) in this test procedure that do not show clinical symptoms. Our research aims to clarify these unclear cases and thus increase the test accuracy.

For further research into the genetic cause of the disease, it is important that as many available samples as possible are sent to our institute.
To perform the genetic test, please note the following instructions: Please fill out our submission form for the test for CA and attach a copy of the equine passport (pedigree).
In the instructions for performing the CA test, you will find all the information on sample collection and shipping of EDTA blood or hair root samples.

Instructions for performing the CA test

The CA test can be performed using hair root or EDTA blood samples.

Collection of hair root samples

  •     Tail hairs are most suitable.
  •     The sampling site should be as clean as possible.
  •     At least 80 hairs should be plucked out. It is important that the hairs are plucked and not combed out or cut off. Only on the plucked hairs are there still intact hair roots, which are needed for DNA isolation.
  •     Very long hairs should then be trimmed to fit into a clean envelope or other shipping container.
  •     It is best to wrap the rootless side of the hairs with scotch tape so that all hairs maintain the same orientation.
  •     If you are collecting hairs from multiple horses at the same time, please be sure to send each sample in a separate envelope or shipping container and do not mix hairs from different horses.
  •     Please label the envelope or shipping container with the horse's identity (name, life/breeding record number, date of collection) and fill out the associated information sheet completely.
  •     A copy of the horse's passport/breeding record should be included with the sample. For foals for which a document has not yet been issued, please include the appropriate documentation from the associated parents.
  •     The shipment should be made as soon as possible.
  •     If the test is not feasible due to insufficient quality of the samples, you will be informed immediately.

Collection of EDTA blood samples

  •     The collection of the blood should be as sterile as possible
  •     The sample tube must contain an anticoagulant, namely EDTA. It is very convenient to use EDTA-K monovettes.
  •     At least 5 ml of blood should be collected by the veterinarian.
  •     Please label the sample with the horse's identity and fill out the accompanying instruction sheet completely.
  •     Shipment should be made as soon as possible. In no case, however, on Friday or Saturday. In this case, please store the blood in the refrigerator (approx. 4o C) until Monday and only then send it.
  •     If the test is not feasible due to insufficient quality of the samples, you will be informed immediately.

Please send the samples to

Prof. Dr. Ottmar Distl

CA-Test

Institute for Animal Breeding and Genetics

Hanover University of Veterinary Medicine Foundation

Bünteweg 17p

30559 Hanover

Invoice
Invoicing is done immediately after receipt of the samples together with the confirmation of receipt to the pet owner.

In order for the test to be performed, the invoice amount must be paid in advance by bank transfer.

Costs for the CA-test per horse:

56,- € for hair roots

44,- € for EDTA blood samples

A discount of 5,- €/horse will be granted from 20 samples and from 40 samples from 10,- €/horse. An additional test for SCID costs 27,- €/horse regardless of the sample type.

Test results
On average, a period of about two to four weeks is required to perform the test. However, please note that the testing period may vary depending on the quality of the sample.
Results will be kept strictly confidential and will be provided in writing to the submitter.
For members of the VZAP who have expressly agreed to the transmission of the test results to the breeding association on the submission form, the result sheets will be sent to the association and the animal owner.
The test order includes a scientific utilization of the results. When using the data for scientific purposes, all information will be anonymized so that no conclusions can be drawn about the identity of the horse, the owner and the breeder.

Symptoms
The most common symptoms observed in CA, in varying degrees of severity, are.

  • uncontrolled movements (ataxia)
  • disturbance of head motor function; manifested by high-frequency jerking of the head at rest or when attempting to make a purposeful movement (intention tremor)
  • stiff or exaggerated gait from the shoulder
  • poor depth perception and general inability to judge space and distance (running into objects and other horses)
  • difficulty standing up, backing up, in tight turns

Affected horses are prone to accidents, tend to run into stationary objects, fall sideways when mounting, and often hit their heads, which can mistakenly lead to the impression that a severe head injury caused the ataxia. The affected horse has normal intelligence, clear vision, good appetite, and shows no muscle atrophy (muscle wasting).
Upon examination by the veterinarian, a cerebellar problem can be detected via neurological examination. However, a definitive diagnosis can only be made by histopathological evidence post mortem.
Regardless of the severity of the symptomatology, affected animals are often euthanized or kept as side horses because the risk to the rider is too high. In addition, there is a risk that the animal will severely injure itself via falls.

Inheritance
CA in horses is inherited in a monogenic autosomal recessive manner. In this mode of inheritance, the hereditary predisposition for the disease can be passed on "hidden" from healthy carrier animals (predisposition carriers) to the offspring.
The test procedure is designed to allow the breeder to avoid mating two trait carriers, thereby eliminating the 25% risk of producing trait carriers (diseased animals).

Results of the test are indicated as follows

  • N/N: with a very high probability anlage-free. The horse has no markers associated with the CA genomic region.
  • N /CA: very likely to be a carrier (1 copy of the CA allele). The horse has markers associated with the CA allele, is considered phenotypically normal and a carrier of the CA allele. In matings with anlage-free mating partners, there is a very high probability that no CA trait carriers will occur.
  • CA/CA: trait carrier (2 copies of the CA allele). The horse is very likely to develop CA or has already developed CA. However, there are also known cases that show no signs of the disease despite having a double copy of the CA allele. Which additional mechanisms play a role here is not yet clear at the present time.

Mating
The mating of two carriers can result in diseased offspring.

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