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lieve, a recessive trait, each full sibling of an affected puppy has a 25% chance of being affected, a 50% chance of being a carrier and a 25% chance of being clear. We are unable to make definite statements about risks out- side of the initial litter itself because we do not know the frequency of the mutant allele in the population, or whether it is isolated to one or more subpopulations (lines). However, if the frequency of the mutant allele is low in the population, for half siblings, the risk is approximately halved


In order for this strategy to work effectively, breeders must openly share information about the incidence of TMT cardiomyopathy. Before breeding to a sire, you should be able to find out whether the disease has oc- curred in his immediate/close family. As a general rule, the more closely he is related to an affected dog, the more likely it is that he is a carrier. Until cardiomyopathy can be identified early, such as with a genetic test, it is important to remember that the complexity of breeding means cardiomyopathy is just one risk factor -one piece of the puzzle- to consider when making a decision about breeding. Our goal is to reduce the occurrence of cardiomyopathy without eliminating good breeding stock or causing the emergence of another abnormal trait through excessively rigid selection. This is a balance that can be achieved with more research.


Next Steps Further research is necessary to find the gene or genes for this trait, and the scientific community needs help from breeders. Since at this time TMT cardiomyopathy can only be diagnosed at necropsy, it is important that pups that die are examined to definitively determine whether they are affected with TMT cardiomyopathy. Blood or tissue samples from which DNA can be extracted are needed. Researchers at the University of Penn- sylvania have indicated that when 10 such samples are accumulated they may be able to begin looking for genetic markers at specific locations on the chromosomes, bringing us closer to finding the gene or genes influ- encing this trait. When genes are identified, it will be possible to test potential sires and dams to determine whether they are carriers.


Dr. Liz Hare is a statistical geneticist working on the understanding of complex traits in humans and dogs that are the result of interactions of many genetic and environmental factors. She has studied psychiatric illnesses including schizophrenia and bipolar disorder, working ability in explosives detector dogs, and litter size in dogs at the Univer- sity of Texas Health Science Center and Cornell University. Brandi Weaver holds a degree in Anthropology with a minor in biomedical sciences. She has performed pedigree work for psychiatric genetic grant research for over five years.


The American Manchester Terrier Club’s Health Committee can provide assistance in paying for necropsies through their innovative Breeder’s Challenge Fund. We recognize that necropsies can be expensive, how- ever the information and genetic material necropsies provide is priceless. That’s why we’re here to help you help our breed.


For more information or to access the Breeder’s Challenge Fund, please contact Kimberle Schiff, AMTC Health Chairperson (kimberle@oakwoodkennel.org) or Michelle Barlak, CMTC/AMTC Heart Study Chair (michelle@bleusprings.net) Users wishing to remain anonymous should direct inquiries to Dr. Shannon Martinson, Diagnostic Pathologist (smartinson@upei.ca)


34 BLACK & TAN | FALL 2010


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