What is PHPV?
​
PHPV stands for "Persistent Hyperplastic Primary Vitreous". It describes an abnormal proliferation of the vascular (blood vessel) supply to the posterior region of the lens. This abnormal process occurs during development, while the pup is still in the dam’s uterus. What are the signs of PHPV and when can it be diagnosed? The exact signs vary from individual to individual but always involve some form of opacity of the posterior lens capsule. In more extensive cases, there may be abnormal blood vessels in the posterior region of the eye, bleeding within the eye and cataract. Both eyes are usually affected.
​
PHPV can usually be diagnosed in puppies at 6-8 weeks of age. It should be noted, however, that very minor cases of PHPV may very occasionally be missed at this age and so the results of litter examination should be seen as preliminary and routine eye examination should be repeated prior to intended breeding. PHPV itself is not progressive as it is a congenital condition. However, dogs with PHPV are at risk of developing secondary complications in the future such as progressive cataracts, bleeding within the eye and retinal detachment.
​
PHPV is significant because it can cause blindness – usually as a result of cataract formation. Cataract surgery may be possible in some cases but dogs with PHPV tend to have more serious complications after surgery such as retinal detachment. Thus, PHPV is best regarded as a condition to be avoided by selective breeding though elimination of affected individuals from the breeding population.
​
Under the BVA/KC/ISDS scheme, dogs are either classed as ‘affected’ or ‘unaffected’ – there is no grading system. This is in contrast to the European (ECVO) scheme which grades PHPV based on a system originally proposed for the Doberman.
​
PHPV is considered inherited in the Staffordshire Bull Terrier although the precise mode of inheritance is unknown. Further work is needed to fully understand the genetics of this disease and a project, with this purpose, is ongoing at the Animal Health Trust.
HEREDITARY CATARACTS 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.
​
Samples submitted should be cheek swabs ( a non-invasive sampling method). Sampling kits are obtainable from the Animal Health Trust webshop www.ahtdnatesting.co.uk/canine_tests. Further information can be obtained by emailing dnatesting@aht.org.uk