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L2-hga - L-2-hydroxyglutaric aciduria

   A neurometabolic disorder which is characterized by elevated levels of L-2-hydroxygutaric acid in urine, plasma and cerebrospinal fluid. L2-HGA affects the central nervous system with clinical signs usually becoming apparent between the ages of 6 months and 1 year but can sometimes appear later than this. The 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 responsible 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, meaning two copies of the defective gene (one inherited from each parent) must 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 are called "carriers" and show no symptoms but can pass the defective gene on to their offspring. When two “apparently” healthy carriers are mated, on an average 25% of their 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 been identified at the Animal Health Trust and using the information from their research the Animal Health Trust has developed a DNA test to detect 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. 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 most important to eliminate these carriers from the breeding population since they represent a hidden reservoir of the disease than can produce affected dogs at any time. 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 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 is Newton, a stafford that was taken to the vet for his strange behaviour after exercise and was subsequently diagnosed with L2-Hga

HC – Hereditary Cataracts

   Hereditary cataracts in the Staffordshire Bull Terrier has been recognised as an inherited condition since the late 1970’s. The type of cataract most prevalent in staffords is the "Juvenile Cataract". Affected dogs develop cataracts in both eyes at an early age. The condition is not congenital, many puppies appear normal at birth, so there is no way to know if the puppy you are buying is going to develop juvenile cataracts. Many dogs do not show signs until six months to two years of age. Some go even later with the cataracts forming five years later. Juvenile cataracts does not always lead to blindness. In many cases, the puppy or young dog still sees basic shapes, but they may be blurry. In some cases, the disease leads to glaucoma. The only way to eradicate juvenile cataracts in dogs, breeders should have both parents tested by a licensed veterinary ophthalmologist no more than a year before breeding. Not every breeder does this however, so you should ask for eye registry papers for both parents before agreeing to purchase a puppy. As with L2-hga, the gene for HC is the result of a mutation, or change to the structure of the gene responsible and is inherited from generation to generation.

PHPV – Persistent Hyperplastic Primary Vitreous

   This due to the retention of elements of the foetal vascular supply to the lens, the tunica vasculosis lentis. The lesions seen are variable amounts of fibrovascular plaque on the posterior lens capsule and possible posterior cortical cataract. The effect on sight can range from nothing to blindness. Removal of the diseased lens can be complicated by any vascular involvement. Persistent pupillary membrane is of the same origin, but this time remnant strands of the anterior part of the tunica vasculosis lentis remain attached to the iris and may occasionally interfere with sight as the result of associated lens or corneal opacities. Again, any effect on sight is variable, but cataract extraction is possible, whereas corneal opacity is not treatable.

Dr Keith Barnett - HC/PHPV in the SBT (extracts of notes from Staffordshire Bull Terrier Breed Council Meeting, 28th April, 2001

Persistent Hyperplastic Primary Vitreous (PHPV): Dr Barnett said that whilst a few cases of PHPV could be found in a number of dogs, inherited PHPV is found in only a few breeds, e.g. Doberman (particularly in the Netherlands where the breed was quite severely affected with PHPV) as well as Staffords. Unlike HC, which is not congenital (i.e. not present until around 3-4 weeks of age), PHPV is congenital (i.e. is present at birth). PHPV can be identified from as early as 2-3 weeks, although a more accurate diagnosis would be obtained at around 6-8 weeks of age. Although present at birth, PHPV is not progressive except in a few isolated cases, however it is very variable in its degree of severity and can affect both eyes. Dogs suffering from mild forms of PHPV can produce offspring that are severely affected.

   During questioning, Dr Barnett confirmed that both PHPV and HC could be diagnosed by the age of 12-18 months. He saw no requirement, therefore, to continue testing purely for PHPV/HC after that age if previous results had been clear. However, he did emphasise that eye tests are designed to look for all eye abnormalities that may be inherited, so it is beneficial to continue testing beyond 12-18 months to regularly check for these. He recommended testing up to any age, but particularly through the breeding cycle of the dog/bitch.

PPSC – Posterior Polar Subcapsular cataract 

   A small (often triangular) area at the back of the lens. It is usually static, has no significant effect on vision and in most cases does not worsen, however, in a small percentage of dogs diagnosed with this condition (less than 5%) it can progress.

   This type of cataract is found in other breeds, and usually remains as a small, punctate cataract. 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. It is advised that as this type of cataract can't be detected through litter screening (the mode of inheritance is not known) 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.

   It is detected by an eye test and can be seen in youngsters from about 12 months of age, although it is more often seen when they are a bit older. It is known to be genetic and believed to be inherited through an autosomal dominant gene, i.e. the progeny of a dog with post polar opacities has a 50/50 chance of inheriting the condition from its affected parent. It is therefore inadvisable to breed from a dog with this form of cataract.

   **When purchasing a puppy it is imperative that the parents are hereditarily clear of L2-hga and tested clear/unaffected under the BVA/KC/ISDS Eye Scheme. These results are printed on their Kennel Club registration papers as well as on the KC papers of the pup where the sire/dam are listed if they have already been received by the breeder, or, a certificate that the pup itself has been tested clear.**

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