[pyrnet] GDC Newsletter - Dr. Jerold Bell interview

[Kshoffman@aol.com]

Below is the entire interview/article I spoke of recently (with Dr. Jerold 
Bell) that addresses issues relative to genetic disease and breed control 
plans in dogs.  It was published in a recent GDC Newsletter.  This Summer 
2000 issue also includes an interview/article with Linda Weisser entitled 
"Putting the Breed Before the Dog". To download entire "GDC Exchange" 
newsletters in PDF format (both Summer 2000 issue and Winter 2000 issue) go 
to the following URL:

http://www.vetmed.ucdavis.edu/gdc/maininfo.htm#exchange
____________________________

From the GDC Exchange
Summer 2000

[begin quoted material]

INTERVIEW
JEROLD S. BELL, DVM

Dr. Jerold Bell is a clinical assistant professor and director of the 
Clinical Veterinary Genetics Course at the Tufts University School of 
Veterinary Medicine. He is a veterinary genetic counselor, and is involved 
nationally with a number of genetic disease control programs in various 
breeds of dogs. Dr. Bell practices small animal medicine at Freshwater 
Veterinary Hospital in Enfield, CT. He and his wife breed Gordon Setters.

GDC EXCHANGE: From your perspective as a veterinarian and genetic counselor, 
how serious is canine genetic disease?

Dr. Jerold Bell: There is no simple answer as to where we stand now with 
genetic disease. Some breeds have serious problems with one or more genetic 
disorders, and others have more minor problems. Every breed and every 
disorder in the breed is different, based on the frequency of affected 
individuals and carriers in the population and on the seriousness of the 
disorder itself. All breeds have several disorders to try to deal with, and 
there are no simple formulas or fixes that apply across the board. We have 
learned, for example, that focusing our efforts on controlling just one 
defective gene can have the unanticipated effect of increasing the frequency 
of another defective gene in the breed. Each breed group has to look at the 
overall picture and design a program that will work best.

What is your concern about breeders focusing on the elimination of a single 
defective gene?

If we are selecting against one gene out of the estimated 100,000 genes in 
the canine genome without considering what desirable genes we may also be 
selecting against, we are doing a disservice to the breed. If breeders 
eliminate most of the carriers of a particular defective gene they can be 
eliminating entire families along with their desirable genes. When tests for 
carriers exist, we advise breeding carrier individuals to non-carrier 
individuals in many cases so that we don't lose the good genes in that 
breeding program. But then the next critical step is replacing carrier 
parents with normal testing offspring. We need to select against carrier 
offspring, and to select individuals whom we know are not carrying the gene 
and have the positive characteristics we want to preserve in the breed. A 
major problem is that it is almost never just one trait you are selecting for 
or against. There may be a couple of other genetic disorders you want to 
control--maybe hip dysplasia, or a problem in certain families in the breed 
with epilepsy. And that is just the negative selection pressure you want to 
apply. You also need to put positive pressure on traits like conformation, 
behavior, personality, or performance characteristics like hunting or 
coursing. The more things that you want to select for, the smaller the group 
that you are selecting among becomes. And eliminating the families of 
carriers entirely can profoundly reduce genetic diversity in your breed.

What are the key principles or tools that breeders can work with?

With the exception of genetic tests, for many years we've actually had most 
of the tools we need to control genetic disorders, but I don't feel we have 
gotten the word out to breeders on how to use them. They are relatively 
simple tools--diagnostic tests such as radiographs or blood tests to tell us 
whether a dog is affected or not; test matings to try to identify carriers, 
open disclosure of information so we know which dogs are affected and which 
are not, and genetic pedigree analysis and relative risk assessment. In many 
instances these are the tools we have to use even now when we don't know a 
mode of inheritance, or don't have genetic or other tests for an apparent 
carrier. One of the most important things we do is to try to understand the 
epidemiology of a defective gene. How old is that gene in the population? How 
far back does it go? Does it have a wide-spread pedigree base? Do all 
affecteds trace back many, many generations to where that gene originated, 
and so does the entire breed then have a high liability factor for carrying 
that gene? A breed health survey is extremely important as a first step in 
starting a program for controlling a genetic disorder. The AKC Canine Health 
Foundation has worked on standardizing breed health surveys to help breed 
clubs get valid information about the whole breed, identifying the most 
common problems. The breed has to be open about which dogs are affected and 
which are not. Having an open registry is absolutely essential, whether it is 
run by the breed, a genetics researcher or by an outside organization like 
GDC. For example, if we know that a disorder is produced by an autosomal 
recessive gene, then we know that both parents of the affected dog are 
carriers. We know that full siblings of carrier parents have a 50 percent 
chance of being carriers. And we know that offspring of carriers have a 50 
percent chance of being carriers bred to dogs with a known background, we can 
actually calculate the relative risk of producing carrier offspring. The 
bottom line is that we don't want to multiply the carrier frequency in the 
gene pool. Many people might say, "Well, I am producing carriers, but I know 
I can breed to normals and not produce an affected, so I don't care.”  We 
don't want to replace carrier parents with three or four carrier offspring, 
thereby increasing the frequency of the gene in the population.

So the real bottleneck in controlling genetic disease is people's attitudes 
rather than the technology?

Yes. No one really wants to breed carriers, or produce affected dogs, or 
propagate a genetic defect. But everyone is doing it, whether we know it or 
not. Some detrimental genes are in every litter. The major reason people are 
afraid to be open is that they don't want to be attacked; they don't want to 
be blamed. People have to recognize that breeders did not create defective 
genes. We need to put emotions and accusations behind us and deal with the 
problem of control. When we start to do genetic counseling with a breed 
group, we say, "OK, we all need to work together for the betterment of the 
breed you love. We need to have everybody willing to talk to each other. We 
need for people to be open about which dogs are and are not affected. For the 
vast majority of genetic disorders, maintaining open registries such as those 
at GDC is the only way we can get the selection potential we need to control 
those diseases. If we are dealing with polygenic disorders, or single gene 
disorders that we don't have extremely accurate tests for, we need to have 
pedigree breadth and depth. We need to look at the close relatives of a dog 
(the siblings, half-siblings, parents and their siblings) like GDC does with 
their KinReports. You need to know not just who is normal, but who is 
affected, who are the carriers, and be able to utilize that information in 
making breeding decisions.

FURTHER READING

Control of Canine Genetic Diseases; George A. Padgett, DVM, Howell
Book House, New York, 1998

Genetics of the Dog; Malcom B. Willis, Howell Book House, New York,
1989

Genetics for Dog Breeders; R. Robinson, Pergamon Press, Oxford Eng-land,
1990

Introduction to Veterinary Genetics; F. W. Nicholas, Oxford University Press
ISBN 0-19-854292-5, 1996

Genetic counseling for cat and dog owners and breeders--managing the
emotional impact; K. J. Fowler et al., Am. Vet. Med. Assoc. V.216#4:498-
501 (2000)

[end quoted material]
______________________

Kelley Hoffman
kshoffman@aol.com