In autosomal recessive traits, such as PCD, carriers (Aa) "carry" the defective gene (a), but they also have a normal one (A), which allows them to be healthy. The checkerboard shows that there is - statistically - a 25% chance of having completely normal offspring, a 50% chance of having carriers, and a 25% chance of having affected dogs. The top of the pedigree above shows the first mating between two unrelated parents, one being a carrier and the other one normal. Remember that both of these parents look normal and do not show signs of disease (i.e. there was no way of knowing the mother was a carrier). If you were to do the "checkerboard" math again, you would see that a mating between AA and Aa would result in 50% AA and 50% Aa offspring. The second breeding in this pedigree was a carrier-brother X carrier-sister mating resulting in normal, carrier, and affected puppies. While the affected pups will be easy to recognize, the carrier and normal dogs cannot be distinguished just by looking at them. This is demonstrated in the drawing by the open symbols and the AA or Aa above each symbol. It is important to remember that when assessing risk analysis percentages that the influence of ancestors is cumulative.
Currently, there is no reasonable way to distinguish carriers from normal dogs, as they look the same. To eliminate PCD from the breeding population, a DNA-based test would be extremely valuable. At this time, the only way to know if potential parents are carriers is by having affected pups born (both parents are automatically carriers) or if a test mating was done by breeding the parent in question to a known carrier. If more than 11 normal pups are born, then the prospective parent is most likely not a carrier. However, this is a very crude method of "genetic testing". Currently, we are trying to find the gene for PCD and subsequently develop a DNA-based test for the disease. To perform these investigations, we are requesting blood samples from normal and affected dogs to extract DNA. Five - 10 ml of EDTA blood (purple top tube) should be sufficient. The blood may be sent on ice packs or at room temperature, but not frozen. Please include basic pedigree information (both registered and call (pet) names, gender, parents, and date of birth) and remit the signed consent form (available on the Study page
). The samples should be sent to the address below. Further information and updates on the PCD study can be found on the IW Foundation web site.
Treating PCD / Chronic Pneumonia
There are some dogs that require maintenance antibiotics all the time. These dogs may be kept on first generation cephalosporins or Clavamox for maintenance. Third generation cephalosporins, or azithromycin (Zithromax), are reserved for acute infections with clinical signs. Occasionally, resistance to some of these antibiotics develops, and it may be necessary to change to a combination of enrofloxicin (Baytril) and ampicillin. Doses should be determined by your veterinarian.
Dr Casal uses the following protocol in a university clinic setting:
- Cephalexin 22-30 mg/kg twice daily for dogs who have had chronic pneumonia until the next pneumonia occurs, then
- Zithromax 5-10 mg/kg. To prevent nausea from the Zithromax, the first day's dosage is 5mg/kg, then increase the dose to 10mg/kg from the second day on. Continue the high dosage amount of Zithromax until 5 days after the last clinical signs have disappeared.
- Therapy steam inhalation/coupage
Dr. Margret L Casal, med. vet, PhD, Dipl ECAR
Section of Medical Genetics, VHUP Room 4015
3900 Delancey Street, Philadelphia, PA 19104-6010
Further information and updates on research developments into this condition