Since 2016, the dominant blue eyes (DBE) mutation has been bred into Maine Coon population in the Netherlands. This mutation first appeared in the Dutch male cat Rociri Elvis and has since spread worldwide. Maine Coons with this mutation are known for their deep colored blue eyes, broad nose bridge, widely spaced eyes that do not fit well into the eye sockets, and lack of white in their fur, which is impossible for Maine Coons with non-dominant blue eyes. These distinctive features have led breeders to suspect for years that cats with this DBE mutation have Waardenburg syndrome—a suspicion that has now finally been confirmed by science!
The term 'dominant' refers to the dominant inheritance pattern. A cat with this mutation has a 50% chance of passing this mutation (and thus the blue eyes) to its offspring.
Later dominant blue eyes has been purposely bred into the population by using the Altay/Topaz breed who were crossed with Maine Coon. These cats have a different mutation, but they both have dominant blue eyes. This line started wit Nikita'l Markiss.
Not part of the breed standard
Breeding with DBE has been controversial for years because it does not belong to the breed originally and is not part of the breed standard. Non-dominant blue eyes, associated with (partially or entirely) white fur, are part of the breed standard. Previously, it was impossible for Maine Coons with very little white to have blue eyes. As a result, no such trait was mentioned in the breed standard, which cannot anticipate all future mutations. Therefore, adjustments were needed (see image) to the breed standard to exclude the new mutation without affecting the non-dominant blue eyes, which have been part of the breed since its origin. Because no DNA test was available, a compromise was made by allowing DBE cats with a significant amount of white fur (at least bicolor with 25%-50% white). Later they have removed code 03 (bicolor) to be able to refuse DBE cats better from the registry and catshows. Now that a DNA test is available, DBE can be more easily excluded from the breed registry.
Correlation with deafness
Breeders who breed with dominant blue eyes (DBE) have always denied that there were any health problems associated with this trait. However, now that the mutation is widespread, these lines have also reached breeders who have been open about these issues. For example, a breeder in Germany finally raised the alarm. She reported that between 2020 and 2023, various kittens in her litters had died. She also observed signs of deafness in her kittens and adult Maine Coons with DBE. As a result, scientists picked up on this and conducted further research. They found the mutation leading to a defect in the PAX3 gene in blue-eyed cats. These cats all descend from the Dutch line, so they named this identified mutation DBE RE (stands for Dominant Blue Eyes - Rociri Elvis). These scientists investigated the cats with this mutation through DNA testing, blood tests, and BAER tests. This research revealed that all tested Maine Coons with the DBE RE mutation and blue eyes were unilaterally or bilaterally deaf. The Maine Coons from the same line with green eyes were fully hearing. This shocking finding prompted the researchers to also test other DBE mutations, such as the Altay/Topaz crosses with Maine Coons. Until now there is no evidence found that there is a relation with deafness for this mutation that is found in the Topaz lines (see source 5). The pathogenic PAX3 mutation was found only in the Rociri Elvis line and not in the Topaz crosses. However, Topaz crosses are not purebred Maine Coons, and these lines are not yet found in the Netherlands, unlike the Rociri Elvis line.
The PAX3 mutation is primarily associated with Waardenburg syndrome types 1 and 3 (WS1 and WS3) and is considered pathogenic. Based on previous knowledge of PAX3 variants in humans, mice, and horses, researchers believe that—in addition to the previously mentioned hearing loss—this mutation leads to the observed characteristics in Maine Coon cats:
Pigmentation abnormalities: This includes heterochromia (different colored eyes), a white forelock, and patchy loss of skin pigmentation.
Neurological abnormalities: Such as mental impairment, myelination defects, and ataxia (coordination disorder).
Skeletal abnormalities: Abnormalities in the bones of the face and skull.
Hirschsprung disease
This study also confirms suspicions that mating two DBE cats leads to dead kittens. This is especially dangerous in Maine Coons that do not have blue eyes but do carry the mutation (latently present DBE).
These symptoms arise from the abnormal development of neural crest cells, which are crucial for the formation of melanocytes (pigment-producing cells) and certain nerve tissues.
Scientists Gabriela Rudd Garces, Daniela Farke, Martin J. Schmidt, Anna Letko, Katja Schirl, Marie Abitbol, Tosso Leeb, Leslie A. Lyons and Gesine Lühken identified the mutation in the DNA through this research. This now allows for testing of Maine Coons to determine whether they carry the PAX3 mutation. This information can serve as evidence for cat organisations that issue pedigrees to ensure that the Maine Coon does not have this mutation. It can also be important for breeders to know whether this mutation is latently present.
Breeding recommendations
Thanks to this new scientific study, it is now clear what the breeding recommendations should be. Here they are:
Due to the correlation with deafness, it is recommended not to breed cats with the PAX3 mutation. For now this recommendation is only for the DBE-RE mutation (started with Rociri Elvis).
To avoid embryonic or fetal lethargy, it is advised not to mate two Maine Coon cats with DBE. This recommendation is for all DBE mutations.
According to Dutch, Belgian, and German animal protection laws (and probably other European countries that have similar animal welfare laws), breeding animals with defective organ systems is prohibited, which includes deafness. Therefore, it is recommended to test the DNA for the PAX3 mutation in all DBE cats to exclude those with the mutation from breeding.
What can cat associations do?
Breed associations should respect the animal welfare legislation by not issuing pedigrees for cats with the DBE RE mutation (PAX3). A DNA test or BAER test can serve as proof.
For the Topaz lines, pedigrees should not be issued at all as these are not purebred Maine Coons but crosses. These crosses are not yet found in the Netherlands.
What can breeders do?
Breeders should thoroughly check their lines to ensure there is no DBE RE mutation present. This can be done easily via the PawPeds Maine Coon database, where you can check whether Rociri Elvis is one of the ancestors. Another check in this database is to look for ancestors with the EMS code 68 (Dominant blue eyes) or 69 (Dominant odd eyes). Before purchasing a kitten, check whether the breeder uses this mutation. In PawPeds, you can search by EMS code to see a list of all breeders who have bred a kitten with DBE. Unfortunately this list is not complete. Do you know more DBE Maine Coons that should have the correct EMS code 68 or 69, let the MCO database maintainers of PawPeds know.
Note that not all cats with this mutation have blue eyes; the mutation can also be latent in cats with green or yellow eyes. A DNA test can confirm that your cat does not carry this mutation from its ancestors.
Breeders can also submit proposals to their cat associations to prevent further spread of DBE in the breed register. For instance, by requiring the eye color to be reported or mandating a DNA test and/or BAER test.
If you already have these cats in your breeding program, it is advisable to conduct a BAER test and a DNA test and make these available for further scientific research. Following the breeding recommendations above will help prevent health problems. If you still want to breed these cats against all regulations, consider advocating for a new experimental breed under a different name. DBE does not belong to the Maine Coon breed.
What can cat enthusiasts do?
Cat enthusiasts should avoid buying Maine Coon kittens with blue eyes unless they are non-dominant blue eyes. Maine Coons with non-dominant blue eyes who have a high amount of white are not likely to be deaf and are not involved in any breeding that will create a certain amount of deaf cats. Dominant white cats with non-dominant blue eyes could be a second alternative. They have a small chance of producing white, deaf kittens. The difference is that these cats need to undertake a Baer test to be proven fully hearing, otherwise their offspring cannot get a pedigree by many cat organisations in Europe. You can also ask the breeder for a BAER test to make sure your kitten is fully hearing before buying it.
Enthusiasts play a crucial role in creating demand for these blue-eyed Maine Coons. If no one buys them, the interest in breeding these cats will disappear.
If you already have a blue-eyed Maine Coon and no BAER test has been done, consider having it tested. Reliable test addresses in The Netherlands and Belgium are listed on the RMC website. You can also raise awareness among other enthusiasts about these issues by sharing your experiences.
What can judges do at cat shows?
Judges at cat shows should disqualify these cats as they do not meet the breed standard. Awarding titles and prizes to these cats would send a very negative message to the cat fancy community. Additionally, awarding a prize or title to a DBE cat would damage the reputation of breeders in general. Prizing such mutations would fuel animal welfare organizations to lobby for more strict legislation or bans through authorities.
Sources:
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