Pelger-Huet Anomaly (PHA) is a hereditary canine health condition that causes an abnormality called “granulocytes” within the cells of the blood. PHA does not generally cause problems in dogs born with the condition, and so it is not considered to cause a particular threat to the dogs that have it; however, inheritance of Pelger-Huet Anomaly can cause spontaneous abortion in utero and problems in the surviving puppies, and ergo can be a risk to breeding stock.

Pelger-Huet Anomaly comes in two different forms, which are referred to as heterozygous and homozygous respectively. The heterozygous version is generally the more commonly diagnosed variant, as it is easy to identify by examination of the cell’s neutrophils; however, the homozygous variant may potentially be just as common, but underdiagnosed.

The heterozygous form of the condition is generally totally asymptomatic, and can only be identified by testing, whilst the homozygous version can, as mentioned, lead to spontaneous abortion of the affected puppies, and when pups with the condition do survive and are born, are unlikely to live for very long.

In dogs that carry the condition, Pelger-Huet Anomaly can lead to blood cell abnormalities called granulocytes, which are often mistaken in the first stages for leukaemia, and for this reason, testing for Pelger-Huet Anomaly often forms part of the differential diagnosis part of leukaemia diagnosis.

As a hereditary health condition, Pelger-Huet Anomaly has been identified as a potential risk to the Australian shepherd and the miniature American shepherd dog breeds, and as such, the UK breed clubs and organisations that advocate for these breeds strongly advise that pre-breeding health screening be carried out to identify the markers of the condition before a mating match is made.

In this article, we will look at Pelger-Huet Anomaly in more detail, including its mode of heredity, and how to get your own dog tested. Read on to learn more.

How is Pelger-Huet Anomaly passed from dog to dog?

Pelger-Huet Anomaly is a hereditary health condition, which means that it is not contagious, but is passed on through the breed line from parent dogs to their offspring.

The method of heredity for PHA is of the incomplete dominant form, which means that if only one of the two parent dogs of the litter carry the gene mutation responsible for the condition and so, pass it on to their litter, the litter will almost certainly be fine.

However, if both of the two parent dogs pass on a copy of the mutated gene that causes the condition, the litter will be compromised, and often, the entire litter will be spontaneously aborted and reabsorbed in utero. Litters that are successfully delivered will generally be smaller than normal, and the pups that result from such litters will invariably have a compromised immune system and skeletal deformities, both of which are usually fatal, or result in euthanasia.

What are the risks of the condition?

For the owners of adult dogs, Pelger-Huet Anomaly is not really a problem, because by virtue of the fact that the dog in question reached adulthood, they have not been affected by the condition.

However, for breeders of Australian shepherds or miniature American shepherds, the condition can be problematic, due to the potential for producing unviable litters.

What sort of dogs should be tested for the condition?

If you own an Australian shepherd or a miniature American shepherd that you intend to use for breeding, it is important to have your dog (and their potential mating match) tested for the condition before going ahead, in order to ensure the protection of the litter.

It is also worth noting that a litter born to one parent that has the markers of the condition will also inherit a copy of the mutated gene, and so will then be able to pass it on to their own offspring, if bred from.

How to get your dog tested

Whilst it is known that Pelger-Huet Anomaly is a hereditary health condition that is caused by a gene mutation, the precise gene responsible for the condition has not been identified, which means that the status of any given dog cannot be determined by a DNA test.

However, dogs that carry the condition tend to have cellular anomalies in their blood, which can be identified by examining a blood smear, something that is usually carried out by a specialist veterinary pathologist.

That said, even this method of testing is not 100% conclusive, because not all carriers will have blood abnormalities, meaning that there is a small risk of testing returning a false negative result.

Other indications of the condition within the two affected breed can lead to multiple failed pregnancies, a wide range of variation in the size of litters, and the birth of puppies affected by the condition.