Pelger-Huet Anomaly (PHA) causes abnormalities in blood cells called granulocytes. PHA may be mistaken for infection or early stage leukemia. PHA testing is advised in apparent infections lacking other signs or when there is a possibility of leukemia. It can also be a problem for breeders because it can result in reduced litter size.
The condition is inherited as an incomplete dominant. Dogs with only one gene are almost always healthy, but if bred to another carrying the mutation the pups that receive two copies of the PHA gene will be reabsorbed, stillborn or die shortly after birth. Occasionally a puppy will survive but have severe skeletal deformities and be susceptible to infection.
PHA is more a breeder’s problem than an owner’s as puppies with two copies of the PHA gene almost never survive. PHA may cause small litters or loss of newborns.
Litter sizes vary normally with the average for Aussies being around 7 pups. Whatever the number of embryos produced by a mating between two PHA-positive dogs, a quarter will not survive.
The PHA gene has not yet been found but PHA status of breeding dogs can be determined by examination of a blood smear by a veterinary pathologist. Most PHA carriers have minor anomalies in some of their blood cells. However, not every PHA carrier will exhibit these anomalies or the small sample viewed may not contain any abnormal cells. As with any type of blood test, false negative results are possible. Therefore any breeding dog with near relatives known to be PHA carriers should be tested. If a breeding dog has extremely variable litter sizes it may be a PHA carrier and should be screened.
Being PHA-positive is not a reason to remove a dog from breeding but it is advisable not to breed them to PHA-positive mates. That way it will not interfere with litter size. If a litter has a PHA-positive parent those buying puppies for potential breeding stock need to be advised.
A Special Note on PHA testing in the US and Canada:
Most if not all commercial veterinary labs will not do a PHA test. However, the test could be done by any board certified veterinary clinical pathologist. ASHGI recommends that you or your small animal vet contact the nearest veterinary teaching hospital to ask about PHA testing.