Windt im Wald Farm
Geauga County, Northeast
Ohio
since 1995
CID:
THE PARADIGM
HAS
SHIFTED
COPYRIGHT 1997 By
MICHAEL BOWLING
used by permission of Michael Bowling
Author's note: This
piece illustrates the vitality of a new communications medium for
it grew primarily out of Internet discussions of the subject. Special
thanks to Mary Anne Grimmell who planted the seed of "putting into
laymen's language" the potential uses and misuses of the new CID
test, along with the positive impact it will have on breeding farms,
large and small, and who assisted in reviewing the story in draft.
Everything you know about CID has to
be re-examined in the light of a single new fact. It is now
possible to know where the CID gene is. This changes the shape
of our world. No CID foals ever need be produced again.
CID: PROGENY
TESTING
Remember that progeny
testing was previously the only way
to know whether an Arabian horse had
the CID gene. One could wait, and hope
the gene did not turn up by accident;
or one could make a systematic effort,
and breed a stallion to known carrier
mares, as one prominent breeder did
with an imported horse a few years ago.
(I am not aware that any other stallion
was formally progeny tested, though
there may have been one or two that
I missed. Obviously if any horse had
been so tested, and turned up negative,
it would have been trumpeted from the
housetops. Even at the highest estimates
of CID gene frequency, most horses are
expected to be negative; this implies
that few were tested.)
To achieve 95% confidence
of knowing an individual Arabian did
not have the gene, one would have to
see a) 11 healthy offspring from known
carrier mates; or b) healthy inbred
offspring from 22 of the tested animals's
own offspring. That awkward gender-free
sentence is the only one I am going
to have to write, since obviously no
mare could ever be rigorously progeny
tested to be CID-free, and also have
a breeding career as such. Most Arabian
stallions would end up siring more offspring
in their progeny testing phase than
they did in their breeding careers.
(Note that breeding a prospective sire
to 22 of his own daughters would have
the advantage, over the 11 offspring
from carrier mares, of potentially turning
up any lethal or seriously deleterious
gene(s), not just CID. Note also that
it is 11 offspring from known carriers--which
could include several offspring from
any one carrier--but it is offspring
from 22 different daughters.) That testing,
to that level of confidence, has been
prohibitively expensive -- this is plain
from the fact that essentially no one
did it. And it would generate a whole
crowd of young horses that needed to
be somewhere, after the testing was
done, whether the results were positive
or negative.
CID can be openly discussed,
because acknowledging one individual has the
gene will no longer cast a pall over a whole
breeding program or line of breeding. Individual
horses can be tested and their individual status
can be known; matings can be planned accordingly;
guilt by association, and the notion of contagious
genes, can finally be laid to rest. The rumor
mill will have to find something else to grind.
Statements of the form "Our neighbor's daughter's
boyfriend's cousin knew someone who bred a mare
to that horse and had a CID foal" will no longer
carry any weight (not that they should ever
have done, but the climate of ideas will change,
and the impossibility of proving a negative
will no longer apply). The delusion that CID
is the only lethal gene of concern in Arabian
breeding can be put out of its misery as well,
and the substantive discussion of other problems,
and the search for other gene tests, can begin
-- inspired by the success with this difficult
and challenging problem. The paradigm has shifted.
New ways of thinking will be required.
A.
What are the drawbacks
to CID (or any lethal defect) without a gene
test? I submit, the following:
1) Foals
die.
2) Breeders
suffer major emotional and financial hardship.
3) Potential
newcomers are put off becoming involved
with the breed: at best they cannot be sure
their new horses are not carriers, and they
are at some risk of having known, but unadmitted,
carriers foisted off on them.
B.
What becomes of those
drawbacks, given a carrier test? They all go
away:
1) No
foals need die, because no one need unknowingly
cross together two horses with the gene.
2) Breeders
can test their stock and know how to avoid
the problem.
3) Potential
buyers can test their prospects and
know where they stand. The paradigm
shifts, and new ways of thinking are
required.
For the frequency of a gene in a breed
to be reduced, it is not necessary to remove from breeding all
individuals possessing it. Such animals need only sire or produce
fewer offspring than they would have done under random mating
(if their status had not been known, in other words). That is
almost certainly what will happen once this gene test is in
widespread operation, and the gene's frequency in the breed
will gradually decrease. The benefits of the test therefore
can be obtained without gelding all gene-positive colts, or
denying registration to all gene-positives, or any other such
scheme; therefore to do so would be an injustice. It would be
applying the test to punish "a moral flaw," rather than as a
tool to manage "a gene" for the benefit of the breed. Genes
do not have moral or ethical content; questions of right and
wrong arise in the way humans deal with their knowledge.
Every individual of every species carries
genetic defects, and CID is not the only lethal operating in the
Arabian breed. Acknowledging the existence of a problem, and developing
a rational means to deal with it, is the opposite of denying that
it is a serious one. All the drawbacks of CID arose out of the fact
that we could not tell where the gene was. Now we can. Vicki Hearne's
Adam's Task, a book of long essays on animal training, describes
human-animal interaction as a form of language. One of Hearne's
recurring themes is "the stories we know" about animals, or about
the ways humans interact with animals, or the way animals interact
with humans (she refers to animals as "knowing stories" too). Her
position is that we can operate only in terms of the stories we
tell ourselves, because that is the practical form our knowledge
takes.
CID: COMBINED
IMMUNODEFIENCY
The genetic immuno-deficiencies
are a complex set of conditions; since the early
1950s close to 20 different syndromes have been
reported in humans and examples have been recorded
in a few other species. The first indications
of what came to be recognized as severe combined
immunodeficiency (SCID) of Arabian foals were
clinical reports out of Australia in the 1960s,
and the syndrome was described in the U.S. in
1973. Its inheritance as a simple autosomal
recessive was established by 1977. The disease
can be tentatively diagnosed from a blood sample
of a young foal. A white blood cell (lymphocyte)
count of less than 1000 per mm3 (vs 2500-3000
for a healthy foal) and lack of IgM (immunoglobulin
M) are presumptive evidence of SCID; confirmation
is by post-mortem showing underdeveloped thymus
and lymph nodes. Lacking immune capacity, such
foals will succumb before 5 months of age of
massive infections.
With
the SCID gene test:
Sick
Arabian foals of untested parents can be
tested for the presence of the SCID gene
in double dose, which will provide rapid
and definite distinction between foals which
are candidates for major supportive efforts
and those which are not.
Mare
owners considering outside stallions for
prospective matings can ask to see evidence
of SCID gene status, and make informed breeding
decisions.
Within
a breeding program, excellent individuals
which happen to possess the SCID gene may
be bred so as to retain their good qualities
and yet avoid producing affected foals,
and gradually reduce the gene's frequency.
It should
be emphasized that SCID is a recessive genetic
defect; no evidence has ever been found
for any defect or weakness in heterozygous
animals.
This notion has wide applications.
For many years Arabian breeders told themselves the
story that the Arabian, as "the oldest and purest
breed of horse," must by that nature be free of
lethal defects. Many of them even extended this story
to say that, if a lethal gene ever appeared, it must
be the result of a pedigree flaw (not in the sense of
introducing a gene from outside, but of somehow "causing"
defects by violating the breed's metaphysical purity).
I recently commented to someone that Arabian horses
have been held to be immune to the laws of biology;
their genetic problems are viewed as the effects of
past moral transgressions (this is a prominent theme
in 19th century nature philosophy, and in early 20th
century racism). The story of population genetics now
tells us that lethal genes, like other genes, are part
of a breed's and a species's history. Every individual
of every species is now held to carry some lethal or
highly deleterious gene(s) in hidden form. The longer
a species has been under domestication, with matings
controlled by humans and limited by studbook breed definitions,
the more such genes will have a chance to arrive at
substantial frequencies, and therefore to become unhidden
through homozygous expression. In other words, the story
that many Arabian breeders tell themselves, which amounts
to saying that CID was a temporary aberration and if
we can only get rid of that gene we will be "safe" again,
is mis- (or dis-) information. There are candidate lethals
described in the genetics or veterinary literature,
some of which are better established than others (in
terms of mode of inheritance, or the simple fact of
being inherited; some are at present merely suspicious,
since they appear to be recurring and breed-specific.).
The success of the CID story
is that the gene now can become unhidden without killing
foals. Our constructive response now is not to obsess
over CID, which has been made harmless. It is to look
for modes of inheritance, and for gene tests, which
will put the other problems in the same position. People
have been breeding blind with regard to CID for decades
(its recessive nature has been known for over 20 years,
never mind how long it existed before being defined).
Now that situation has changed. With a gene test, CID
is going to become a matter of fact. It will not be
a whispers-behind- the-hand subject as it has been for
so long. Some discussions of this topic seem to assume
that the way things are (attitudes and assumptions,
the stories we tell ourselves) are going to remain the
way they are right now, forever. They will not. The
paradigm has shifted. New ways of thinking are not only
required, they are inevitable.
Selected References:
McGuire, T.C. and M.J. Poppie.
1973. Hypogammaglobulinemia and thymic hypoplasia in horses:
A primary combined immunodeficiency disorder. Infection and
Immunity 8: 272-277.
Poppie, M.J. and T.C. McGuire.
1977. Combined Immunodeficiency in foals of Arabian breeding:
evaluation of mode of inheritance and estimation of prevalence
of affected foals and carrier mares and stallions. J. Amer.
Vet. Med. Assoc. 170: 31-33.
Shin, E.K., L.E. Perryman
and K. Meek. 1997. A Kinase-Negative Mutation of DNA-PK (subscript
CS) in Equine SCID Results in Defective Coding and Signal Joint
Formation. J. Immunol. 158 (8): 3565-3569.
Studdert, M.J. 1978. Primary,
Severe, Combined Immunodeficiency Disease of Arabian Foals.
Austr. Vet. J. 54: 411-417.
Wiler, R., R. Leber, B.B.
Moore, L.F. Van Dyk, L.E.Perryman and K. Meek. 1995. Equine
severe combined immunodeficiency: A defect in V(D)J recombination
and DNA-dependant protein kinase activity. Proc. Nat. Acad.
Sci. US 92: 11485-11489.
