Pelger-Huet Anomaly is an inherited condition in which certain blood cells are mutated, specifically the neutrophils and eosinophils, which are white blood cells actively involved in the immune system. The disease is passed through a dominant gene, which makes it critical that affected animals not be bred.
Pelger-Huet anomaly causes the nuclei within leukocyte cells to be abnormally shaped into two distinct patterns, heterozygotes (which make the cell appear shaped like a pair of eyeglasses or a dumbbell), and homozygotes (cells which have a single abnormal nuclei and other structures that are clumped together). These mutated cells circulate within the blood, causing an immune deficiency and predisposing the animal to inflammation and bacterial infections. In cats, for example, the anomaly is often a precursor to the development of feline leukemia. Under microscopic examination, in fact, these cells are structurally very similar to leukemia cells, and extensive testing must be performed in order to distinguish between the two.
The anomaly is rare, but has been reported in several dog breeds, most notably Basenjis and Foxhounds. When it's present in a homozygous form, many puppies die in utero. Pups that do survive birth usually have skeletal deformities, developmental delays and seizures, and do not survive long enough to be weaned. Dogs with a heterozygous form of the disease usually are unaffected, with a normal immune system, but if bred they often pass along the more deadly form of the syndrome to their offspring.
The parents and siblings of affected dogs usually carry the anomaly as well, although there will be no obvious physical signs. In some cases, PH anomaly has been found in connection with another genetic disease called chondrodysplasia, which causes the cartilage between joints to become deformed and the affected animal's legs to become crippled. The connection between these two disorders is not yet well understood.
Pelger-Huet anomaly is diagnosed through tests of the blood and bone marrow which identify affected cells. In dogs with this condition the cells mutate, making the animal susceptible to leukemia or a pre-leukemia condition. If the dog has been treated with sulfa drugs, this mutation is even more likely. However, PH anomaly is not proven as a direct cause of any known disease, so no treatment is recommended. Instead it's recommended that these dogs not be bred and that their parents and siblings also not be bred, in order to prevent the genetic defect from being passed on to a new generation.