HC, PHPV & L2 Hydroxyglutaric Aciduria
Eye Conditions HC & PHPV
For many years now the breed has been aware of two hereditary eye conditions, HC (Hereditary Cataract) and PHPV (Persistent Hyperplastic Primary Vitroeus)
It is known that HC is inherited by an autosomal recessive path (i.e. that both parents must be carriers of the defective gene to produce affected offspring). HC is a progressive condition and this means that although the puppy is not born with cataracts they will start to develop at a juvenile stage (maybe from 8 months onwards) and will progress until the dog is totally blind. The condition is bi-lateral, meaning that it will affect both eyes equally
The mode of inheritance for 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 dog's life
Either condition can be operated on but it is a serious operation, obviously quite traumatic and expensive. It is not always covered by pet insurance due to the hereditary nature
NEUROLOGICAL CONDITION - L2-HGA (L2 hydroxyglutaric aciduria)
In the past few years a number of Staffords have been diagnosed with a metabolic disorder; its clinical title is L-2 hydroxyglutaric aciduria or L-2 HGA. This condition has manifested itself in varied ways with dogs exhibiting behaviour changes and dementia (staring at walls, getting stuck under tables and in corners, loss of obedience and house training), anxiety states, having full blown seizures, as well as exercise intolerance, ataxia (unsteady gait), tremors and muscular stiffness. Dogs from differing bloodlines have been found to be sufferers and the number of affected dogs diagnosed has risen
Anyone who hasn't had their dogs tested but want now to take the opportunity for testing can download the appropriate form or by contacting Vikki for forms
The cost of the testing is £63 for an indevidual test per dog or £105 for the combined L2-HGA & HC tests plus what the vet charges you to take and send the blood to the AHT
Understanding Recessive Genes
Recessive genes are responsible for many aspects in dogs, such as the production of blue or liver coats, and most do not affect the dog's physical well-being. A few however do cause health problems. Two have been described in Staffords – hereditary cataract (HC), causing blindness in young dogs, and L-2-Hydroxyglutaric Aciduria (L-2-HGA), a metabolic condition that affects the brain, causing seizures that may be misdiagnosed as epilepsy
All dogs have two copies of every one of their thousands of genes with the exception of those on the sex chromosomes in the case of males. One copy of each comes from the sire and the other from the dam. The copies of each gene may not be identical but each will be at the exact same position on the appropriate chromosome. Differences between pairs of genes, mutations, are the result of little biochemical errors occurring somewhere in the replication process between generations
With recessive genes the ‘original' variant, let's call it ‘X', produces the ‘normal' effect as long as one copy of ‘X' is present. If a mutation has occurred at some point, resulting in a recessive variant, ‘x', then the normal effect will be produced as long as it is paired with ‘X'. ‘X' is thus considered to be dominant to ‘x', or putting it another way ‘x' is recessive to ‘X'. X/X will naturally produce the normal effect but if x/x is produced then the resultant effect may be totally different
With both HC and L-2-HGA three gene combinations are possible as you will have realised already
1. X/X – the dog is clinically unaffected and is not a carrier of the condition, as it does not possess ‘x', and thus cannot pass it to its off-spring
2. X/x – the dog is clinically unaffected but is a carrier as it possesses ‘x' which, on average, it will pass on to half its progeny
3. x/x – the dog is affected with the appropriate condition and were it used for breeding it must pass the defective ‘x' gene to all its progeny
The aim of any control measures must be simply to prevent any clinically affected animals being born and eventually to eliminate the defective ‘x' from the breeding population. With the development of laboratory tests for the recessive genes that cause the two conditions (tests for L-2-HGA are already available) the first step must be not to breed two carriers together – ensuring both sire and dam are tested prior to mating should guarantee this. Previously the only way of knowing a dog is a carrier is when it has produced affected off-spring. With careful selection, breeders, who have lines affected with either condition should be able to get rid of the defective genes within two or three generations while hopefully maintaining the quality of stock they desire