Hereditary Cataract in Staffordshire Bull Terriers
Hereditary Cataract in Staffordshire Bull Terriers has been recognised as an inherited condition since the late 1970’s. Affected dogs develop cataracts in both eyes at an early age. The condition is not congenital, so the lenses are normal at birth but cataracts appear at a few weeks to months in age, progressing to total cataract (and resulting blindness) by 2 to 3 years of age.
The mutation, or change to the structure of the gene, probably occurred spontaneously in a single dog but once in the population has been inherited from generation to generation like any other gene. The disorder shows an autosomal recessive mode of inheritance: 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 symptoms but can pass the defective gene onto their offspring. When two apparently healthy 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
The mutation responsible for the disease has recently been identified at the Animal Health Trust. Using the information from this research, we have developed a DNA test for the disease. This test not only diagnoses dogs affected with the disease but can also detect those dogs which are carriers, displaying no symptoms of the disease but able to produce affected pups. Under most circumstances, there will be a much greater number of carriers than affected animals in a population. It is important to eliminate such carriers from a breeding population since they represent a hidden reservoir of the disease that can produce affected dogs at any time.
The test is available now and information on submitting samples is given below.
Breeders will be sent results identifying their dog as belonging to one of three categories:
CLEAR: the dog has 2 copies of the normal gene and will neither develop Hereditary Cataract, nor pass a copy of the Hereditary Cataract 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 Hereditary Cataract. It will not develop Hereditary Cataract but will pass on the Hereditary Cataract gene to 50% (on average) of its offspring.
AFFECTED: the dog has two copies of the Hereditary Cataract mutation and is affected with Hereditary Cataract. It will develop Hereditary Cataract at some stage during its lifetime, assuming it lives to an appropriate age.
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 affecteds 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.
This test requires 3mls of whole blood in EDTA tube or cheek swab samples (swab kits available free of charge from the address below or e-mail swab.request@aht.org.uk can be sent. Samples should be sent together with a completed DNA Testing form and payment of £67* inc VAT for each sample to Genetic Services, Animal Health Trust, Lanwades Park, Kentford, Newmarket, Suffolk CB8 7UU.
*if DNA testing for L-2-HGA is requested at the same time both tests together can be done at a discounted rate of £112 inc VAT.
L-2-hydroxyglutaric aciduria (L2HGA) and Hereditary Cataracts (HC) - DNA Testing for Staffordshire Bull Terriers
With immediate effect - please note the following change to the blood sample requirements for the above tests
Any blood samples for animals from outside the European Union (except Australia and New Zealand) must be 8-10 mls EDTA blood.
Samples from Australia should continue to be sent via Curtin Medical School.
Samples from New Zealand should continue to be sent via Gribbles Veterinary Pathology
Any queries, please contact dnatesting@aht.org.uk or telephone 0044 8700 509144
DNA Testing forms can be downloaded by clicking here.
Enquiries should be made to Symone Ingram telephone +44 (0) 1638 555621 or fax +44 (0) 1638 555643 or via e-mail to dnatesting@aht.org.uk.
