Chondrodysplasia, An Overview and Current Approach to Breeding Management
In the late 1960’s a condition known as “dwarfism” (aka Chondrodysplasia, or ChD) was identified as an autosomal recessive condition in the Alaskan Malamute, with an apparent high incidence in certain lines.
Chondrodysplasia is a genetically-determined skeletal disorder that occurs primarily in the purebred Alaskan Malamute. The chondrodysplastic Malamute displays in varying degrees the following phenotypic characteristics.
1) Excessively shortened front limbs with various degrees of bowing and deformity, especially the radius and ulna
2) A topline that slopes from the pelvis down to the withers
Some chondrodysplastic Malamutes display a severe degree of deformity while others display almost no visible characteristics. This condition is only able to be diagnosed/confirmed by examination of x-rays of the lower front limb (distal ulna) at an early age (prior to growth plate closure). Looking at physical attributes of the dog, such as limb deformity or short stature does not confirm or refute a case of ChD since several other conditions can result in the same physical appearance and a mildly affected dog may show no outward physical abnormalities.
As a result, the AMCA introduced what was, at that time, a cutting edge, ground-breaking program to try to eliminate the condition from the breed. With this knowledge, experts in radiology, genetics and the breed came together to provide a workable system that would reduce the incidence of carriers and, they hoped, eliminate the condition in the Alaskan Malamute.
This program was based on test-breeding dogs and calculating a theoretical (mathematical) probability that a dog was not a carrier based on the number of puppies produced when an individual was bred to an affected dog or a carrier, providing that all puppies produced were screened by x-ray at 6 to 8 weeks of age and that none of the pups were affected by the condition. The cut-off point, based on pure practicality, where a dog was considered “OK/approved to breed” was at a probability of 6.25% mathematical risk of being a carrier.
This program was very successful in reducing the incidence of carriers (and the “bad gene”) in the breed from quite prevalent in certain lines to rather rare in the population as a whole. It has resulted in bringing the overall probability within the population down to under 6.25% overall. After many generations of breeding low probability dogs, today there is no selection pressure on “certified” dogs to reduce this any further. Based upon information provided by Dr. Jerold S. Bell, DVM, at
Tufts University, it was also determined that many of the probabilities assigned to modern day dogs were based upon historical numbers so many generations removed that they did not represent an accurate reflection of risk. It is also apparent from the results of survey to Alaskan Malamute breeders worldwide that the incidence of this condition is very low in the Malamute population and the certification program therefore no longer helped to reduce the risk of producing an affected dog in the general population.
It is important to realize that even test-bred dogs carry SOME risk, it was known from the start by those that set up the original program that some carriers would slip through due to the theoretical nature of the calculation and the practical aspects of finding a compromise cut-off that allowed the breed to still exist.
It is important to realize that even test-bred dogs carry SOME risk
Thus, we have carriers in the current breeding population, albeit at very low levels. It was the confirmation of a dwarf being produced from certified parents that created the impetus to revisit the program and the formation of a working group to propose alternative methods of addressing this genetic disease.
Based on information received from the eminent geneticist Professor Jerold S Bell DVM at Tufts University, a review of programs/methods used to control autosomal recessive genes by other dog clubs (and even other conditions in Alaskan Malamutes outside of the US), and a world-wide survey of Malamute owners and breeders, it was recommended that AMCA change the approach to handling this genetic disease. These recommendations are predicated on the very low incidence of the condition in the breed as a whole, the lack of significant morbidity or suffering of affected dogs and the sincere wish/hope that the members of AMCA can develop and foster an open, respectful and mutually beneficial understanding between all breeders and owners that works in the best interests of the breed in the long-term.
The recommendations of the working group were brought to a membership vote, with the result a majority vote to approve these. As a result, the following changes have been implemented:
1) The previously mandated ChD certification program (test-breeding and certification) and the CCC were permanently retired.
2) The breeder’s Code of Ethics was changed to reflect the recommendations of the working group/AMCA policy (breeders are no longer required to have Chd certification on breeding stock as this option no longer exists)
3) AMCA will establish an open database of confirmed carriers and affected dogs. (**Note**this is still in development. However, only four currently living dogs in open breeding are confirmed to be carriers as of May, 2014. Living carriers resulting from old test-breeding are not included in this list as they will not be used for future breeding.).
a) A confirmed carrier means a dog that has produced one or more confirmed (by expert x-ray analysis) affected dog(s)
b) The database is intended to be prospective but can include any confirmed carriers/affected dogs identified under the conditions in parts d) and e) below.
c) The database will be made available to both members and non-members of AMCA.
d) Dogs included in the database must be identified/submitted by the owner or breeder of record to be accepted
e) The diagnosis must be confirmed by radiograph and a written report by a Board-certified (or equivalent expert*) Veterinary Radiologist
f) The database shall include the registered name, breed registry used (e.g. AKC) and registration number, date of birth, and gender of each confirmed carrier/affected dog;
g) Database information (carrier/affected-status of a dog) shall be considered public information and may be included in pedigree programs, such as that produced by AMAL
4) AMCA now focuses on providing recommendations, guidelines and
education to help breeders, including (but not limited to) the
following:
a) AMCA provides clear information on x-ray screening to detect/confirm affected dogs and makes the following recommendations with respect to screening “high risk” litters:
i) X-ray one carpus (wrist), one view, at between 6 and 12 weeks of age
ii) Submit x-rays to OFA, or other Board-certified (or equivalent expert*) Veterinary Radiologist for evaluation
iii) The following puppies are considered “high risk” and should be examined to gain maximum information:
(1) Offspring of known carriers
(2) Offspring of siblings to known/confirmed affected dogs
(3) All puppies in a litter (provided they are not older than 16 weeks) with at least one confirmed affected puppy
b) AMCA provides updated and ongoing educational materials/opportunities for owners and breeders including support to help breeders & owners understand genetic disease, genetic principles of breeding, and to remove the fear/stigma of producing an affected dog (with any genetic disease, not just ChD)
i) Provide educational seminars, web-based learning and/or published articles in the newsletter to keep members informed about the latest knowledge and understanding of genetic diseases and their control ii) Encourage openness & collaboration amongst breeders
and owners
Please note that the Alaskan Malamute Club of America is working actively with Dr. Hannes Lohi and the American Kennel Club Canine Health Foundation to develop a genetic test for Chondrodysplasia. Information about the status of this research and how you can help can be found HERE. *** DNA of any affected dogs or their known carrier arents is needed to help contribute to this research project.***