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Haemophilia 'A' is a condition where the blood fails to clot
normally, due to a deficiency of Factor VIII. Though the disease has long been
known in man, it was described in dogs about 50 years ago. Most breeds are
affected to some degree, but we will concentrate on the GSD.
The symptoms
depend on the severity of the disease, and vary from lameness, swellings and
failure of the blood to clot in the normal time, to nothing visibly obvious in
mildly affected dogs. Severely affected dogs may bleed spontaneously into body
cavities, muscles or joints (so causing the swellings or lameness), whereas the
mildly affected ones may only become apparent after surgery or injury, when the
bleeding is difficult to stop. It is thought that the more severely affected
animals die early or are still born, so most cases surviving to maturity are
only mildly affected and are not so easily detected.
There are blood tests
that can be done to detect haemophiliacs, but because of the nature of the
inheritance of the disease, only the males can be declared clear. It is
inherited as a sex-linked recessive gene, which means it is carried on the 'x'
chromosome. The female has two of these, whereas the male has an 'x' and a 'y'.
This is where the problem in detection arises, as the male is either affected or
clear, depending on whether his 'x' chromosome carries the defective gene or
not, but the female has two 'x's, so three states exist. These are 'clear',
where neither chromosome carries the fault, 'carrier', where one 'x' has the
fault, but is hidden by the other normal 'x', and 'affected', where both 'x's
have the faulty gene. This is why the females are not tested, because it can
only show up whether she is affected or seemingly clear, when she may actually
be a carrier.
In theory, there are six possible types of
matings. |
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As can be seen from the table, a clear male mated to a clear
female will produce all clear progeny (barring any mutations). A clear male
mated to a carrier female will be expected to produce clear and affected sons,
and clear or carrier daughters. This is the most common way that haemophiliacs
are produced, as no-one knowingly uses affected males or females. If a male is
only mildly affected, and hasn't been tested clear, he may appear to be OK, but
as can be seen from examples 3 and 4, the problem can still be passed on to his
offspring.
The main source of haemophilia in the GSD seems to be from Canto
Von Der Wienerau, with his sons all being clear, and his daughters all being
carriers (mating no. 3). Although not tested, he died young in circumstances
that would suggest that he was a haemophiliac. Although his sire was clear, the
status of his mother was not known. All recent cases of the disease have been
traced back to Canto through his daughters, and the book, 'The German Shepherd
Dog A Genetic History of the Breed' by Malcolm Willis (used as reference for
this section) gives a list of dogs implicated as affected or producers of the
disease, as well as giving more in depth information about it.
The blood test
for the disease is inexpensive, and a list of dogs that are tested clear is
available from the National G.S.D. Breed Council (see 'Useful Links' page) |
