(Part of the presentation to BCCA Board of Directors, October 1998
and Lay Summary of March 1999 Progress Report to AKC CHF)
As Malcolm Willis said about health databases (AKC Gazette, August 1996), "as breeders we cannot simply sit back and wait for harmful genes to be located. On the contrary, we have to take action. Perhaps the most important contribution we can make is to collect information about our dogs. . . All this information can serve as the raw material for figuring the Mendelian ratios used to assess the mode of inheritance of some defects. If they haven't already done so, parent clubs need to set up open databases for members to submit data on every bitch mated, every litter bred, listing consequences of matings and the fate of litters".
Tracking of health problems in Bearded Collies with the 1992 and 1996 health surveys has turned up some interesting facts. Among those facts, was a similar frequency of Addison's disease in the 1992 and the 1996 health surveys - 2.2% and 2.7% respectively. Another fact is that 30% of all deaths occurred before the age of 9 years. The leading causes of death in dogs less than 9 years were: autoimmune problems, cancer, kidney disease/failure, aggression, and infection. If we chose to follow a logical pathway, we need to begin work to identify which problems are preventable so as to reduce their occurrence in the future, thereby reducing early deaths.
Research Project on Addison's. The findings on Addison's disease in the 1996 health survey led to funding by The AKC Canine Health Foundation (CHF) of a research project, which is titled: "Identification and Inheritance of DNA Markers for Addison's Disease". The request was for a 2 year grant in the amount of $90,000. After review by the CHF scientific group, the project was funded for 1 year in the amount of $15,000 with the specific objective of "acquiring pedigrees with confirmed affected and unaffected status. Then consider molecular evaluation." Funding sources were the CHF for $11,000 and the BCCA for $4,000. CHF's financial support is indicative of their belief that the project is important to get underway, and a recognition that we will need to raise additional funds for this and other research projects in the future. Second year funding for the Addison's project depends on success in the first year. Success in the first year is measured by progress reports, with the first and most important due 6 months after startup.
The 6 month progress report lay summary from Dr. Wagner's report to CHF in March 1999 stated the following: "The goals for the current year of this study are (1) To collect pedigree information and blood samples from dogs that have confirmed Addison's disease, and from unaffected siblings, and (2) To confirm the utility of DNA markers for genetic mapping of genes involved in conferring Addison's disease. We have collected blood samples and pedigree information from over 90 Bearded Collies; this information indicates a recessive mode of inheritance of Addison's disease, however from the available data it is not clear how many different loci (genes) are involved in causing Addison's disease. In addition, we have demonstrated that molecular markers developed as part of the Dog Genome Project a the University of Oregon and the University of California, Berkeley, will work as markers for mapping genes related to Addison's disease within the Bearded Collie pedigrees. Progress made thus far has set the stage for a detailed genetic mapping effort in an attempt to identify DNA markers that are genetically linked to loci responsible for Addison's disease. Such DNA markers can then be used in routine tests for Addisonian alleles (genes) in the Bearded Collie." (Reproduced with permission from Debbie Lynch, Executive VP of AKC CHF, August 6, 1999).
Definitions of Terms Useful in Understanding Genetic Research.
Allele. One of the inherited forms of a particular gene or stretch of DNA. An animal carries two alleles for each gene, one from each parent.
Genetic Marker. A portion of DNA that appears in more than one form in a population, the variations of which can be detected in the lab and used to identify patterns of heredity.
Microsatellite. A genetic marker that depends upon a differing length of a specific repeating nucleotide pattern to detect differences between individuals. There are 4 nucleotides which make up DNA - C, A, G, T are the abbreviations for these nucleotides. For example, 10 vs. 12 CACACACACA repeats.
AFLP (amplified fragment length polymorphism). A genetic marker that detects slight changes in a DNA sequence, independent of the sequence. For example, GTCAACTCTT vs. GTCAACTtTT.
Allele Sharing Concept. Assuming that a genetic marker is linked to the gene causing the disease, two relatives with Addison's disease should share more of the linked marker alleles than is expected by chance. There is increased possibility of detection of a linked marker when comparisons can be made between grandparent-grandchild and/or discordant-sib trios (e.g., 1 affected, 2 normal; 2 affected, 1 normal). Thus, one can see how important it is to have 3 generation family information and DNA specimens. In fact, this is not easy to accomplish in Bearded Collie families due to the older age at which Addison's is often diagnosed, by which time the grandparents have died. As well, the oldest generations haven't been available because of some breeder's refusal to participate.
Linkage. The relationship between genetic markers and a disease gene(s). It is described in a unit of measure called the centiMorgan (cM). The lower the cM, the closer are the marker and gene, the less likely they are to separate during meiosis, and the better the prediction of genotype. Both microsatellite and AFLP marker techniques have resolution in the 5-10 cM range, giving a good likelihood of detecting a link in this study.
Significance of Characterizing DNA Markers. It a technique has a high level of resolution, it is possible to identify markers associated with a particular train even if a trait is polygenic (i.e., determined by more than a single gene). Once isolated and characterized, markers are relatively inexpensive, reliable, and can be used to identify potential carriers and affected individuals prior to maturity and breeding. That procedure allows breeders to test breeding stock, to make wise choices in breeding, and eventually to reduce the occurrence of a disease.
There are now genetic screening tests available for PRA (progressive retinal atrophy) in several breeds, copper toxicosis, cystinuria, and von Willebrands Disease. These genetic screening tests have come about because the individual breed clubs identified the health problem, raised money for research, identified researchers, and had the cooperation of their dog owners and breeders in obtaining pedigrees and specimens for the research!
Verification of Marker Linkage. It is planned that other breed pedigrees will be used to help confirm linkage of DNA marker(s) with a potential Addison's gene(s) which are identified in Bearded Collies. Among the other breeds interested in this project are the Leonbergers and Standard Poodles.