HEREDITARY CATARACT IN STAFFORDSHIRE BULL TERRIER
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
L-2-HGA (L-2-hydroxyglutaric aciduria) IN STAFFORDSHIRE BULL TERRIERS
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-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 behaviour.
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 this disease but can also detect those dogs which are carriers, displaying no symptoms of the disease but able to produce affected pups. Carriers could not be detected by the tests previously available, which involved either a blood or urine test detecting elevated levels of L-2-hydroxyglutarate or magnetic resonance imaging. 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 L-2-HGA, nor pass a copy of the L-2-HGA 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 L-2-HGA. It will not develop L-2-HGA but will pass on the L-2-HGA gene to 50% (on average) of its offspring.
AFFECTED: the dog has two copies of the L-2-HGA mutation and is affected with L-2-HGA. It will develop L-2-HGA 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 HC 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
PHPV – PERSITENT HYPERPLASTIC PRIMARY VITREOUS
The mode of inheritance of PHPV is not so clear, but it is known that it is a congenital condition (present at birth) and that it is not progressive. This means that if a puppy is born with PHPV it can be detected by ophthalmic screening from 6 weeks of age and if it is affected, whatever the condition of the problem at that stage it will not change throughout the dogs life.
Either of the above conditions can be operated on, but it is a serious operation and can be traumatic and very expensive. It is not always covered by insurance due to the hereditary nature.
Even though the genetic test is now available for Hereditary Cataracts it is still important to screen for PHPV.
Here are details of Eye testing clinic closest to you...BVA_eye_panelists.pdf
PPSC – POSTERIOR POLAR SUBCAPSULAR CATARACT.
This type of cataracts is found in other breeds, particularly the Labrador and Golden Retriever.
It usually remains as a small, punctuate cataract and doesn’t usually lead to sight problems in these two breeds. It has been placed on schedule 3 of the BVA/KC/ISDS Eye Scheme because a number of Staffords that have been through the Scheme have been found to have this type of cataract. This type of cataract cannot be detected through litter screening. The mode of inheritance is unknown and has a variable age of onset.
BREEDING STOCK SHOULD BE TESTED ANNUALLY TO DETERMINE THAT THE DOG IS CERTIFIED CLEAR AT THE TIME OF MATING.
DNA PROFILING IDENTIFICATION
The DNA profile is the ultimate in individual identification and offers a 'tamper-proof' means of identity. The profile need only be produced once and the DNA sample used to produce it can be stored as a permanent DNA record throughout the dog's life. Identification could be essential in a number of instances. For example, the availability of a profile could be used to identify an animal that may have been lost or stolen, and subsequently recovered. The profile could also be used to check the authenticity of a DNA sample being used to screen for the presence of disease-causing genes. Many such tests are being developed and it would be invaluable to be able to verify that the correct dog's DNA is being tested for the presence of the deleterious gene. Repeating the DNA profile on the same sample of DNA being used to carry out the gene test would be straightforward and prove conclusively that the correct animal is being tested.
Please note: DNA profiles are not instantaneous, so it is worthwhile microchipping your dog in addition. They also do not give information on the disease status.
Parentage/pedigree analysis
Provided that the DNA profiles of both parents are available, pups in a litter can be profiled and their profiles checked with their parents' profile to verify that the correct parents have been registered.
DNA profiling kit request - KC DNA profiling service
DNA profiling costs £25 per dog, and this amount is payable on ordering a profiling kit. Once ordered, a kit will be sent to you together with instructions on how to get a sample from your dog (by rubbing loose cheek cells onto a swab). Once you have taken the sample, you will need to return the kit, in the envelope provided, to the laboratory. Once a DNA profile has successfully been completed, you will receive a DNA Profiling Certificate and your dog's KC records will be updated accordingly.
THE PROOF OF THE PUPPY IS IN ITS PROFILE
A more detailed explanation of the process of DNA profiling - by Dr Jeff Sampson.
Buried within the DNA of each and every individual is a special DNA signature that can be used to uniquely identify that individual. DNA profiling is the name given to the technique that has been developed to reveal this DNA signature. Initially, DNA-based approaches to identifying individuals were pioneered in humans, but the same technology has easily been transposed to the dog. Nowadays, special sequences found in DNA called microsatellites are used to build up this DNA signature. Microsatellites have become the system of choice for DNA profiling and genetic testing in humans. The US Armed Forces, FBI, Scotland Yard, The Royal Canadian Mounted Police and multiple forensic laboratories use microsatellites for their forensic, paternity and individual identification tests. The reasons that have made them come to the fore in humans are the very reasons that currently make them the system of choice for dogs.
The technique essentially involves preparing a DNA sample from an individual dog. For this we need to obtain some tissue from the dog in order to prepare the DNA. The ideal source of material would be a blood sample which will permit us to isolate DNA from the white cells; this however requires a vet to take the sample of blood before passing it onto the laboratory for testing. Less invasive techniques which don't require veterinary intervention have therefore been sought to make the procedure more convenient. One alternative source of tissue are the cells that can be easily removed from the inside of a dog's cheek, called buccal cells.
In this case all that is required is to gently rub a small plastic brush against the inside of the cheek to remove the buccal cells. The brush, containing the cells can then be returned to the laboratory for analysis. DNA can be made from both tissue sources, although considerably less DNA is provided by the buccal cells because they are considerably fewer in number.
Once isolated, the DNA can then be treated to reveal the individual-specific DNA signature. Several laboratories throughout the world have been using this technique successfully for a number of years. Many of you will have read in the dog press of the American Kennel Club's pilot study on DNA profiling which has recently been concluded.
What can DNA profiling offer? Well, as I have explained, the DNA signature that is revealed can uniquely identify an individual dog. However, the profile is not just a means of identification because it also carries within it information on the parents of the dog. This is because a puppy inherits half of its DNA from its mother and the remaining half from its father. This essentially means that half of the components that make up the profile are maternal in origin and the other half paternal. So it is in these two areas that profiling has impact: individual identification and parentage verification
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