Demerrall Hungarian Vizsla's

 

 

Cerebellar ataxia is a rare neurological condition which has been identified in a small number of smooth-haired Hungarian Vizslas. Cerebellar ataxia affects gait and coordination from around two to three months of age and is an aggressive and progressive condition for which there is no treatment. Affected dogs are euthanased on welfare grounds at the advanced stages of the disease.

The genetic mutation responsible for this condition was discovered by researchers at the Kennel Club Genetic Centre at the Animal Health Trust in early 2016.

How common is the disease?

This condition in the Hungarian Vizsla is quite rare but it is crucial to identify any possible carriers in order to prevent any more puppies being born with this horrible neurological disease, and to stop it becoming a bigger problem in future lines. The carrier rate for this condition is estimated at approximately 1 in every 100 smooth-haired Vizsla however, as this is an emerging disease, it is not possible to say which lines may carry the mutation, so DNA testing is highly recommended to get this condition under control in the Vizsla.

How was the mutation identified?

In order to find the mutation responsible, the AHT used whole genome sequencing technology to study all 2.4 billion letters of DNA from just one affected Vizsla. This is the same technology at the heart of the AHT’s Give a Dog a Genome project to create the UK’s largest canine genome bank, to benefit all future inherited disease research at the AHT. The discovery of this mutation demonstrates the effectiveness of this technique. 

 

Traditionally, a genetic investigation into a disease of this nature would require DNA samples from at least twelve affected dogs and the same number of healthy control dogs from the same breed. Now, advanced genome sequencing technology and the use of state-of-the-art computer analysis allows every letter of DNA from a single affected dog to be interrogated and compared to a bank of genome sequences of healthy dogs from different breeds, in order to find the change in DNA responsible for a specific inherited disease. This approach allowed the genetics of cerebellar ataxia in the Hungarian Vizsla to be investigated straight away, without collecting additional DNA samples.

The causal mutation was quickly identified as a single letter change in the 2.4 billion letter DNA code. Once this mutation had been pinpointed, it was confirmed by screening healthy Hungarian Vizsla DNA samples. Only the Hungarian Vizslas with cerebellar ataxia had two copies of the genetic mutation needed to cause the disease. Following further tests to validate the discovery, the DNA test was promptly launched.

How is the disease inherited?

The disorder shows an autosomal recessive mode of inheritance, which means that two copies of the defective gene (one inherited from each parent) have to be present for a dog to be affected by the disease.

Individuals with one copy of the defective gene and one copy of the normal gene, called carriers, show no signs of disease but can pass the defective gene onto their offspring. When two carriers are crossed, 25% (on average) of the offspring will be affected by the disease, 25% will be clear and the remaining 50% will themselves be carriers.

After DNA testing the results will be defined as follows:

CLEAR: The dog has two copies of the normal gene and will not develop cerebellar ataxia, or pass a copy of the gene to any of its offspring. 

CARRIER: The dog has one copy of the normal gene and one copy of the mutant gene that causes cerebellar ataxia.  It will not develop cerebellar ataxia but will pass on the cerebellar ataxia gene to 50% (on average) of its offspring. 

AFFECTED: The dog has two copies of the cerebellar ataxia mutation and is affected with the disease. 

Carriers can still be bred to clear dogs. On average, 50% of such a litter will be clear and 50% carriers; there can be no affected dogs produced from such a mating. Pups which will be used for breeding can themselves be DNA tested to determine whether they are clear or carrier of cerebellar ataxia.