Sensory neuropathy in the border collie
About the disease
Sensory neuropathy (SN) is a severe neurological disease caused by the degeneration of sensory and, to a lesser extent, motor nerve cells. The onset of the disease in affected Border Collies is from 2 to 7 months of age and signs include knuckling of the feet, self-mutilation wounds (caused by excessive chewing or licking due to the lack of feeling in the limbs) and a progressive incoordination of gait (ataxia). A progressive loss of sensation occurs in all limbs. Urinary incontinence and regurgitation can occur in the later stages of the disease. Prognosis is poor, with no effective treatment available. As quality of life is severely affected, dogs with SN are euthanised on welfare grounds usually before two years of age.
We are delighted to report that the mutation causing SN in the Border Collie has been identified at the Kennel Club Genetics Centre at the Animal Health Trust (AHT) and a DNA test was launched in April 2015. The test costs £48 and is available to order from the AHT's DNA Testing Webshop.
Scientists at the AHT have been researching the genetic basis of this disease in the Border Collie since two affected dogs were diagnosed by neurologists in the AHT’s Small Animal Centre, providing DNA samples to begin a genetic investigation. A third DNA sample was provided from the University of Glasgow.
The three samples were compared to the DNA of 170 Border Collies whose DNA has been submitted to the AHT from owners to aid its epilepsy research in the Border Collie. This extensive bank of DNA was crucial in enabling the AHT to identify which chromosome contained the genetic mutation for SN as quickly as possible. Once this was identified the chromosome was sequenced to find the faulty gene responsible for SN.
How common is the disease?
Sensory neuropathy is a rare disease, but cases have been reported in several countries worldwide. In collaboration with the University of Glasgow and University of Missouri we have tested DNA from a total of eleven dogs suffering from SN, all of which were confirmed to have two copies of the mutation identified by scientists at the AHT. A summary of results is shown below
Country of origin No of cases identified
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 SN, or pass a copy of the SN 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 SN. It will not develop SN but will pass on the SN gene to 50% (on average) of its offspring.
AFFECTED: The dog has two copies of the SN mutation and is affected with SN.
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 SN.
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