Congenital macrothrombocytopenia is characterized by oversized platelets, also called macroplatelets, and an abnormally low number of platelets. Macroplatelets function normally and the affected dogs do not exhibit any health problems due to either the size or the lower platelet count. Macrothrombocytopenia is not associated with spontaneous bleeding.

While this disorder is relatively mild, it is important not to mistake macrothrombocytopenia for other more severe conditions characterized by low platelet counts.

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 condition is autosomal recessive meaning that two copies of the mutation are needed for signs to occur. However signs of this condition are very mild, and are unlikely to affect a dog's wellbeing. Breeding a carrier dog with a clear dog will not produce any puppies with clnical signs of this condition. About half of the puppies will have one copy (carriers) and half will have no copies of the Macrothrombocytopenia mutation. Breeding a dog with two copies of the Macrothrombocytopenia mutation with a clear dog will produce a litter containing all carriers. Please note: It is possible that signs similar to the ones caused by the Macrothrombocytopenia mutation could develop due to a different genetic or clinical cause.