The Staffordshire Bull
Terrier, whilst a robust and generally healthy breed, can suffer from
harmful and detrimental genetic diseases. Responsible breeders, with the
support of the ANKC and other breeders, are attempting to selectively breed
out these hereditary afflictions.
When purchasing a
Staffordshire Bull Terrier from registered breeders (unfortunately not all
breeders are registered with the ANKC, and generally refrain from health
testing breeding stock) do not be afraid to ask the breeder about their
stock, their breeding practices, nor be afraid to ask to see health
certificates.
L2-Hga
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.
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 L-2-HGA, nor
pass a
copy of the L-2-HGA 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
L-2-HGA. It will not develop L-2-HGA but will pass on the L-2-HGA gene
to 50% (on average) of its offspring.
AFFECTED:
the dog has two copies of the L-2-HGA
mutation and is affected with L-2-HGA. It will develop L-2-HGA 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.
Courtesy AHT
Hereditary Cataracts (also called Juvenile Cataracts)
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.
Courtesy AHT
Distichiasis
Sometimes
the condition is referred to as a double row of eyelashes, for extra hairs
arise from the edge of the eyelid to rub against the corneal surface. The
effects are variable and mild irritation to corneal ulceration will be seen.
Treatment is extremely difficult and invariably involves surgery to remove
the hair roots permanently. Plucking out the offending hairs is useful, but
requires the maximum cooperation of the patient!
Of course it
is followed by hair regrowth, and many surgical techniques have been
invented to remove the roots. Even then success is difficult to achieve, and
the dog may have to suffer this condition throughout its life. It is the
most common eye defect found in the Stafford in South Africa.
Entropian
Primarily an
inherited condition. It is due to an excess of eyelid tissue, or a small
eye, or both, the result being that a varying amount of hair-covered eyelid
can turn in to rub directly against the cornea or conjunctiva, or both.
It is usually
extremely painful, and the damage caused to the cornea can render the eye
blind. Most dogs are affected by six months of age and in some the signs of
the problem (excessive blinking and a wet face) may be seen within the first
month of life.
Occasionally
the condition is self-correcting as the puppy grows, but in the vast
majority of affect dogs surgery is necessary to turn the eyelid away from
the surface of the eye. Usually such surgery is successful, but it is much
better that, as with the other inherited eyelid defects, breeders try to
avoid producing this condition in their stock.
Ectropion
Primarily an
inherited condition, in which the lower eyelid droops away from the eyeball
to expose the third eyelid and the conjunctiva. Exposure of the delicate
mucous membrane causes conjunctivitis.
Correction is
possible by complicated surgery in which the eyelid is lifted and shortened.
Occasionally further surgery may be necessary to change completely the shape
of the eyelids.
Progressive Retinal Atrophy (PRA)
PRA is a term
used to describe a number of inherited retinal degenerations involving
several breeds. The group is broadly divided into two, generalized PRA and
central PRA. In the former, blindness at night time (nyctalopia) is an early
indication of the presence of the disease, but eventually the dog is
rendered totally blind.
Cataract is a
common secondary feature of the disease. In central PRA night blindness is
not a feature and though vision is several affected, the dog may not become
totally blind. In both groups of PRA there is degeneration of the
photoreceptors, but in the generalized form this degeneration is the
inherited defect, whereas in central PRA rod and cone degeneration follows
an inherited defect elsewhere in the retina.
Persistent Hyperplastic Primary Vitreous (PHPV)
This is a
congenital condition (present from birth) in which there is a developmental
defect in the normal regression of some of the intraocular structures of the
eye. PHPV can range from being very mild to severe abnormalities which may
lead to blindness.
The presence of
mild abnormalities are usually seen as small brown pigmented dots on the
posterior lens capsule. Previously the literature indicated that this was
always observed as a bilateral phenomenon but recently it has been stated
that affected dogs may show unilateral involvement, although this is less
common.
The present
knowledge of the mode of inheritance of this disease is thought to be an
autosomal irregular dominant with variable expression. Due to PHPV seldom
resulting in secondary cataracts in the Stafford, those that are mildly
afflicted will seldom show any form of visual impairment during the course
of their lives. Even those that are more severely afflicted, may be capable
of adapting by using peripheral to compensate.
Stafford
breeders should therefore not assume that the problem is absent simply
because they have not encountered blatant signs of visual impairment,
instead discerning breeders should ensure that all their Staffords are
tested through the National Eye Scheme.
Courtesy Stafford Mall
Hip
Dysplasia
Hip Dysplasia
is a terrible genetic disease because of the various degrees of arthritis
(also called degenerative joint disease, arthrosis, osteoarthrosis) it can
eventually produce, leading to pain and debilitation.
The very first step in the
development of arthritis is articular cartilage (the type of cartilage
lining the joint) damage due to the inherited bad biomechanics of an
abnormally developed hip joint. Traumatic articular fracture through the
joint surface is another way cartilage is damaged. With cartilage damage,
lots of degradative enzymes are released into the joint.
These enzymes degrade and
decrease the synthesis of important constituent molecules that form hyaline
cartilage called proteoglycans. This causes the cartilage to lose its
thickness and elasticity, which are important in absorbing mechanical loads
placed across the joint during movement. Eventually, more debris and enzymes
spill into the joint fluid and destroy molecules called glycosaminoglycan
and hyaluronate which are important precursors that form the cartilage
proteoglycans.
The joint's lubrication and
ability to block inflammatory cells are lost and the debris-tainted joint
fluid loses its ability to properly nourish the cartilage through impairment
of nutrient-waste exchange across the joint cartilage cells. The damage then
spreads to the synovial membrane lining the joint capsule and more
degradative enzymes and inflammatory cells stream into the joint.
Full thickness loss of
cartilage allows the synovial fluid to contact nerve endings in the
subchondral bone, resulting in pain. In an attempt to stabilize the joint to
decrease the pain, the animal's body produces new bone at the edges of the
joint surface, joint capsule, ligament and muscle attachments (bone spurs).
The joint capsule also eventually thickens and the joint's range of motion
decreases.
No one can predict when or
even if a dysplastic dog will start showing clinical signs of lameness due
to pain. There are multiple environmental factors such as caloric intake,
level of exercise, and weather that can affect the severity of clinical
signs and phenotypic expression (radiographic changes).
There is no rhyme or reason
to the severity of radiographic changes correlated with the clinical
findings. There are a number of dysplastic dogs with severe arthritis that
run, jump, and play as if nothing is wrong and some dogs with barely any
arthritic radiographic changes that are severely lame.
Courtesy OFA
