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Description
Cataracts are a
clouding of lens of the eye caused by a  breakdown
of tissue in the eye. This generally results in an inability to
see clearly,
and can cause total blindness. In canines, cataracts are often familial;
this type is known as Hereditary Cataracts. A mutation in the HSF4
gene causes this type of cataracts in several breeds of dogs. In
this case, the dog is typically affected bilaterally, in that both
eyes are affected by the cataracts. The cataracts associated with
HSF4 also occur in the posterior region of the lens. They usually
begin small and grow progressively, though the speed of growth is
highly variable. Some cataracts will grow so slowly that the dog's
vision remains relatively clear, while others will grow such that
the dog will quickly go blind. Corrective surgery is possible, though
it is costly and is not always effective.
One HSF4 mutation causes the recessive form of Hereditary Cataracts
in Boston Terriers, Staffordshire Bull Terriers, and French Bulldogs.
Because it is recessive, a dog must have two copies of this mutation
to experience this form of cataracts. This mutation is only responsible
for early-onset hereditary cataracts, which typically occur between
12 months and 3 years of age in Staffordshires, and between 2-3
years in Boston Terriers. Boston Terriers can also be afflicted
by late-onset hereditary cataracts; however, the HSF4 gene mutation
is not responsible for that particular form of cataracts. The causative
gene for Late-onset Hereditary Cataracts in Boston Terriers has
not been determined at this time.
A separate mutation of
the HSF4 gene is responsible for  Hereditary
Cataracts in Australian Shepherds. This mutation affects Aussies
differently, in that the disease is dominant, but not completely
penetrant. This means that only one copy of the mutation is necessary
to predispose a dog to the disease, however, incomplete penetrance
means that a dog that has this mutation will not always develop
HC. Research suggests that the mutation makes a dog 12 times more
likely to develop posterior bilateral cataracts at some point in
their lifetime. It is likely that a secondary gene interaction occurs
in the small percentage of dogs possessing the HC mutation but do
not develop cataracts, however, this interaction is not yet know.
It should also be noted that not all cataracts are hereditary. Cataracts
can also be caused by old age or injury. Also, cataracts that occur
in different regions of the lens can also be familial, however,
are not attributed to this gene mutation.
HC
Testing
Animal
Genetics offers DNA testing and detection of the gene mutation responsible
for certain forms of Hereditary Cataracts in Australian Shepherds,
Boston Terriers, French Bulldogs and Staffordshire Bull Terriers.
Breeds Affected
Australian
Shepherds
Boston Terriers
French Bulldogs
Staffordshire Bull Terriers
Cost
$45.00
US per sample
Sample Collection
Collect
sample using buccal swabs provided by Animal Genetics. Ensure that
the dog has not eaten within a few hours of sample collection. Any
food particles can inhibit the test. Rub each of the swabs along
the inside of the dog's mouth for 10-15 seconds, and allow the swabs
to dry thoroughly. Label the provided envelope with the dog's name,
and place the swab inside it. Download and complete a submission
form for each sample and send along with payment to Animal Genetics
for testing.
Results
Results
are given using the following symbolic notation:
Staffordshire
Bull Terriers, French Bulldogs, Boston Terrier:
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HC/HC
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AFFECTED:
The dog carries two copies of the mutant gene and is homozygous
for Hereditary Cataracts. The dog is affected by HSF4-Hereditary
Cataracts, and will always pass on a copy of the mutated gene
to its offspring. |
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n/HC
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CARRIER:
Both the normal and mutant copies of the gene detected. Dog
is a carrier for Hereditary Cataracts, and can pass on a copy
of the defective gene to any offspring. |
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n/n
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CLEAR:
Dog tested negative for the Hereditary Cataract gene mutation,
and will not pass on the defective gene to its offspring. |
Australian Shepherds:
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HC/HC
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AFFECTED:
The dog carries two copies of the mutant gene and is homozygous
for the HSF4-HC gene mutation. The dog is extremely likely to
develop cataracts over his lifetime, and will always pass on
the mutation to any offspring. |
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n/HC
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AFFECTED:
Both the normal and mutant copies of the gene detected. Dog
is heterozygous for the HSF4-HC gene mutation. The dog is extremely
likely to develop cataracts over his lifetime, and can pass
a copy of the mutation to any offspring. |
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n/n
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CLEAR:
Dog tested negative for the Hereditary Cataract gene mutation,
and will not pass on the defective gene to its offspring. |
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