HEREDITARY CATARACTS - HC
It is
known that HC is inherited by and automal recessive path (i.e. both
parents must be carriers of the defective gene to produce and affected
offspring). HC is a progressive condition and this means that although
a puppy is not born with cataracts they will start to develop at a
juvenile age. (maybe from 8 months onwards), and will progress until
the dog is totally blind. This condition is bilateral which means is
affects both eyes equally. Thanks to the tireless research by the
Animal Health Trust in Newmarket there is a now a DNA Test for SBT.
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.
http://www.psbtc.org.uk/
http://www.staffords.co.uk/