I have been asked to answer the question, "So what might be some
of our options if the marker for any of the diseases [ARVC, DM, RD]
turns out *not* to be a simple recessive? I understand how a recessive
gene works but what if we are faced with autosomal dominant as Dr. Meurs
suspects for BCM /ARVC?"
Theresa Garton has dealt with this quite effectively but let me put
the following further points to you:
- ARVC/CM is said to show an autosomal dominant inheritance.
- Accepting this is true, there are going to be homozygotes.
Do these survive; die in utero; or what? We have no idea.
- This dominant gene is said to show poor penetrance. This
means that a proportion of dogs that carry the gene – with the
potential to be affected – may never show any ill effects.
They appear normal. And these may be (and almost certainly
will be) the majority class.
The conclusion from the above is that not only have you (possibly)
homozygotes to deal with, which may be the most severely affected
(earliest onset, highest VPCs etc); not only will you have expressing
heterozygotes (high VPCs, liable to develop the disease) to deal with;
but you will have all the seemingly normal heterozygotes. The
latter are critical, because although they may live normal lives, they
will still pass the gene on to 50% of their offspring and these will
show disease effects at the full range of ages.
With the gene identified, all of these genetic classes would be
revealed. If the gene frequency is low then, as Theresa said, the
problem would be easy to deal with. Just don't breed from those
dogs that carry the gene. But if, as seems likely from all the
correspondence on these lists, the gene frequency is high and a large
proportion of the breed is involved there will be many difficult
decisions and compromises. Otherwise, huge sections of the breed
could be wiped out.
All this may be a bit academic at this time because finding the gene,
or genes may be a long way away but it would help a lot if the
frequency/incidence of the disease was known. Are there any
estimates? This is something that could be done now.
Bruce Cattanach
Email: bcattanach@steynmere.freeserve.co.uk
Part 1
