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What is HC and L2-HGA

 Inherited Disease in the Staffordshire Bull Terrier

As with other breeds of dog the Staffordshire bull terrier suffers from its fair share of inherited disease. The AHT has been researching the genetic basis of two such diseases over the last few years, Hereditary Cataract (HC) and L-2-Hydroxyglutaric Aciduria (L-2-HGA) and is pleased to announce the development of DNA Diagnostic Tests for both these conditions are now available at the AHT.

L-2-Hydroxyglutaric aciduria

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-hydroxyglutarate is normally metabolised to a-ketoglutarate but in affected dogs it is not, and builds up in the body with devastating results. 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 behavior.

Hereditary Cataract

Hereditary cataract in the Staffordshire bull terrier was first reported in the United Kingdom in 1976. The condition is not congenital, so puppies are born with normal eyes, but cataracts begin to appear at a few weeks to months in age, progressing to total cataracts by 2 to 3 years of age. This cataract is always bilateral, symmetrical in the two eyes, and progressive until total with resultant blindness.

Autosomal Recessive Disease

Both HC and L-2-HGA are autosomal recessive conditions. This type of disease is caused by a mutation within a single gene located on one of the 38 pairs of autosomes. Mutations causing recessive diseases can be small (for example a single incorrect nucleotide, or the insertion or deletion of a small number of nucleotides) or large (such as the deletion of a large number of nucleotides). Because the mutations are within genes located on the autosomes both males and females suffer from the disease with equal frequency.
A dog has to have a mutation in each copy of the gene (i.e. the copy on each of its chromosomes) before it will actually develop symptoms of the disease. This is known as being homozygous for the disease allele. If it has one mutated copy of the gene and one normal copy it will be a carrier of the disease but will never actually develop symptoms. It can, however, pass the mutation onto future generations. For a dog to be affected with an autosomal recessive disease, both its parents have to be either carriers or affected. If two carriers are mated together on average one in four of their offspring will be affected, one in four will be genetically clear and half will be carriers.

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.

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.