Are purebreds really more prone to genetic disease?

From ANIMAL PEOPLE, Jan/Feb 1994:

Purebred dogs may be increasingly susceptible
to genetic disease due to inbreeding, but one apparent
proof the Humane Society of the U.S. presented in the
September 1993 edition of its Shelter Sense newsletter
was not necessarily any such thing.
A special edition on “Purebreds and pet over-
population,” the issue featured articles by assistant editor
Julia Miller and HSUS vice president for farm animals
and bioethics Michael Fox, who backed the recent HSUS
call for a voluntary moratorium on dog and cat breeding
by linking the pursuit of breed standards to congenital
health problems. Illustrating their articles was a table
compiled by the Canine Genetic Disease Information
System at the University of Pennsylvania entitled
“Number of Genetic Disorders or Genetic Susceptibilities
to Disease Recognized in the Dog 1928-1988.”

The table showed that there were five recog-
nized genetic health problems in dogs in 1928; 13 in
1938; 24 in 1948; 55 in 1958; 114 in 1968; 221 in
1978; and 281 in 1988.
However, in the original context, the table did
not show that genetic problems are any more common in
dogs now than ever. All it actually purported to show
was the rapidly improving ability of veterinarians to diag-
nose and treat congenital conditions.
Asked by ANIMAL PEOPLE to explain the
use of the table, Fox responded, “Certainly there have
been improvements in veterinary diagnostics since 1928.
However, the rise in recognized disorders or susceptibili-
ties to disease correlates very closely with the rise in the
overpopulation of purebred dogs––especially during the
critical years 1968-1988, when the commercialism of
purebreds reached its zenith. This rise cannot be attrib-
uted simply to an exponential growth in veterinary
knowledge since 1968.”
Many geneticists would strenuously disagree.
The table began in 1928 because the preceding year,
1927, marked the birth of modern veterinary genetics
with the discovery that mutations can be induced, rather
than resulting strictly from chance. The doubling of the
number of congital diseases recognized in dogs between
1948 and 1958 coincided with the 1953 discovery of the
function of DNA, the 1955 synthesis of RNA, and an
explosion in the amount of genetic research done on dogs,
stimulated by concern over the genetic effects of nuclear
radiation. This epoch also coincided with the advent of
pound seizure, giving researchers free access to all the
dogs they could use. The next doubling, between 1958
and 1968, coincided with the peak use of dogs in
research. Then, in 1967, the synthesis of DNA touched
off the ongoing effort to identify the functions of specific
genes, with the object of eventually engineering healthier
and/or more useful plants and animals. The rate of recog-
nition of new genetic diseases in dogs finally slowed from
1978 to 1988––but as the common conditions were found,
the rest were ever less common and thus harder to find. It
may also be pertinent that between the abolition of pound
seizure in many locations and advances in alternatives to
animal-based research, the number of dogs used in bio-
medical research fell by 92% between 1964 and 1991.
Concluded Shelter Sense editor Geoffrey
Handy, “Our opinion is that the inbreeding, overbreed-
ing, and careless breeding of purebreds has in fact led to
additional genetic disorders that did not exist prior to
these practices.”
Maybe, but without comparative data on the
frequency of conditions, not just the number of condi-
tions known, the evidence is insufficient to say for sure.
––Merritt Clifton
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