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Inherited Disease in the Staffordshire Bull Terrier
As with other breeds of dog the Staffordshire bull terrier suffers from its fair share of inherited disease. The AHT has been researching the genetic basis of two such diseases over the last few years, Hereditary Cataract (HC) and L-2-Hydroxyglutaric Aciduria (L-2-HGA) and is pleased to announce the development of DNA Diagnostic Tests for both these conditions are now available at the AHT.
L-2-Hydroxyglutaric aciduria
L-2-HGA (L-2-hydroxyglutaric aciduria) in Staffordshire Bull Terriers is a neurometabolic disorder characterised by elevated levels of L-2-hydroxyglutaric acid in urine, plasma and cerebrospinal fluid. L-2-hydroxyglutarate is normally metabolised to á-ketoglutarate but in affected dogs it is not, and builds up in the body with devastating results. L-2-HGA affects the central nervous system, with clinical signs usually apparent between 6 months and one year (although they can appear later). Symptoms include epileptic seizures, "wobbly" gait, tremors, muscle stiffness as a result of exercise or excitement and altered behavior.
Hereditary Cataract
Hereditary cataract in the Staffordshire bull terrier was first reported in the United Kingdom in 1976. The condition is not congenital, so puppies are born with normal eyes, but cataracts begin to appear at a few weeks to months in age, progressing to total cataracts by 2 to 3 years of age. This cataract is always bilateral, symmetrical in the two eyes, and progressive until total with resultant blindness.
Autosomal Recessive Disease
Both HC and L-2-HGA are autosomal recessive conditions. This type of disease is caused by a mutation within a single gene located on one of the 38 pairs of autosomes. Mutations causing recessive diseases can be small (for example a single incorrect nucleotide, or the insertion or deletion of a small number of nucleotides) or large (such as the deletion of a large number of nucleotides). Because the mutations are within genes located on the autosomes both males and females suffer from the disease with equal frequency.
A dog has to have a mutation in each copy of the gene (i.e. the copy on each of its chromosomes) before it will actually develop symptoms of the disease. This is known as being homozygous for the disease allele. If it has one mutated copy of the gene and one normal copy it will be a carrier of the disease but will never actually develop symptoms. It can, however, pass the mutation onto future generations. For a dog to be affected with an autosomal recessive disease, both its parents have to be either carriers or affected. If two carriers are mated together on average one in four of their offspring will be affected, one in four will be genetically clear and half will be carriers.
DNA Diagnostic Tests
After several years of research into the genetic basis of these two inherited conditions the AHT is pleased to announce the identification of the mutations that cause both diseases. The research was made possible by funding from the Kennel Club Health Foundation Fund, the American Kennel Club Canine Health Foundation, the Staffordshire Bull Terrier Breed Council and PetSavers. DNA samples from affected dogs and their close relatives were donated by Staffordshire Bull terrier owners and breeders and the AHT is sincerely grateful to all those who donated samples from their dogs.
How Breeders Can Benefit From the DNA Diagnostic Tests
Owners can now submit a DNA sample from any dog for testing and find out whether the dog is clear, a carrier or affected with either, or both, HC and L-2-HGA. The owner will receive a certificate that states whether the dog is Clear, Carrier or Affected, with the following explanations:
CLEAR: the dog has 2 copies of the normal gene and will neither develop HC / L-2-HGA, nor pass a copy of the HC / L-2-HGA mutation to any of its offspring.
CARRIER: the dog has one copy of the normal gene and one copy of the mutant gene that causes HC / L-2-HGA. It will not develop HC / L-2-HGA but will pass on the HC / L-2-HGA mutation to 50% (on average) of its offspring.
AFFECTED: the dog has two copies of the HC / L-2-HGA mutation and is affected with HC / L-2-HGAand will develop HC / L-2-HGA during its lifetime.
Samples should be sent with a completed DNA Testing Form and a cheque for £60-00 (inc VAT) per sample for Hereditary Cataract or L-2-HGA testing alone, or £100-00 (inc VAT) per sample for Hereditary Cataract and L-2-HGA DNA testing together, to Genetic Services, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU.
DNA testing forms can be downloaded from the web site (http://www.aht.org.uk).
DNA testing forms can also be obtained by contacting Vikki Lett 08700 50 91 44 ext 1223 or via e-mail to vikki.lett@aht.org.uk.
Blood samples which have already been tested for L-2-HGA can also be tested for Hereditary Cataracts - please provide a completed DNA Testing Form quoting the Sample Number from the L-2-HGA certificate, with a cheque for £60-00 inc VAT. DNA testing forms can also be obtained by contacting Vikki Lett 01638 750659 ext 1223 or via e-mail to vikki.lett@aht.org.uk.
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