May-Hegglin Anomaly

May-Hegglin Anomaly (MHA) is a blood disorder that causes deficiency and abnormal shaping of the blood platelets which are important in the clotting process.

Key Signs

Platelet deficiency, Large platelets

Age of Onset

At birth

Present at birth


Autosomal Dominant

For autosomal dominant disorders, dogs with one or two copies of the disease variant are at risk of developing the condition. Inheriting two copies of the risk variant may make the risk higher or the condition more severe. They may produce puppies affected with the disorder if bred.

Likelihood of the Condition

Moderate likelihood

At risk dogs may show signs of this disease in their lifetime, although some will not develop the condition due to absence of additional risk factors.

What to Do

Here’s how to care for a dog with MHA

Partner with your veterinarian to make a plan regarding your dog’s well-being, including any insights provided through genetic testing. If your pet is at risk or is showing signs of this disorder, then the first step is to speak with your veterinarian.

For Veterinarians

Here’s what a vet needs to know about MHA

Platelets of affected dogs are bigger and their numbers are lower than usual. In addition, there are changes in neutrophils. The disease does not usually cause clinical signs, although bruising or bleeding tendencies may be noted during surgery. Human patients have been reported to develop renal disease, hearing problems, and cataracts, but these signs have not been observed in Pugs.

While this disorder is relatively mild, considerations for this disorder should be made before surgery, and any occurrence of excessive bleeding should be treated as appropriate.

For Breeders

Planning to breed a dog with this genetic variant?

There are many responsibilities to consider when breeding dogs. Regardless of test results it is important that your dog is in good general health and that you are in a position to care for the puppies if new responsible owners are not found. For first time or novice breeders, advice can be found at most kennel club websites.

This disease is autosomal dominant meaning that one copy of the mutation is needed for disease signs to occur. Use of dogs with one or two copies of the disease mutation for breeding is not recommended, as there is a risk that the resulting litter will contain affected puppies. For example if a dog with one copy of the MHA mutation is bred with a clear dog with no copies of the MHA mutation, about half of the puppies will have one copy and half will have no copies of the MHA mutation. Please note: It is possible that disease signs similar to the ones caused by the MHA mutation could develop due to a different genetic or clinical cause.

Technical Details

Gene MYH9
Variant G>A
Chromosome 10
Coordinate 28,120,346

All coordinates reference CanFam3.1

References & Credit

Credit to our scientific colleagues:

Flatland, B., Fry, M. M., Baek, S. J., Bahn, J. H., Leblanc, C. J., Dunlap, J. R., … Schleis, S. E. (2011). May-Hegglin anomaly in a dog. Veterinary Clinical Pathology, 40(2), 207–214. View the article