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.
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.
Persistent Hyperplastic Primary Vitreous (PHPV) in Staffordshire Bull Terriers
Persistent Hyperplastic Primary Vitreous (PHPV) is an inherited condition whereby the embryonic blood vessels within the eye develop and persist abnormally after birth. It is believed to have an incomplete autosomal dominant mode of inheritance. This means that affected dogs usually have at least one affected parent, and will pass the condition on to at least half of their offspring, even if bred with another dog that is unaffected. However, because the condition possibly displays ‘incomplete penetrance’ dogs may carry the mutation but be clinically unaffected. For the same reason genetically affected cases may not be detectable by eye examination or may only be mildly affected. No genetic test exists for this condition yet. It is reported in Staffords and Dobermann Pinschers and has been suggested in Standard Schnauzers. Sporadic cases in other breeds have occurred, in fact, the disease was first recorded in a Greyhound in 1969. The blood vessels are in the back of the eye from the optic nerve to the back of the lens and frequently cause cataract. A plaque of fibrous tissue, sometimes with pigment, is seen on the back of the lens. This is sometimes accompanied by bleeding into the back of the eye or into the lens. The disease can be graded (1-6) based on severity Surgery to operate on these cataracts is more difficult than normal cataract surgery and complications such as bleeds in the eye and retinal detachment can occur. In one study in Dobermann Pinschers, only 50% of surgical cases were successful. These days, with more sophisticated techniques the success rate is better, but this surgery is still not straightforward. This information was kindly sent to me by Animal Health - Thank you
