The Secret of Dominant and Recessive Blue Eyes in Maine Coons

Maine Coon cats are one of the most beloved and recognizable breeds of cats. These gentle giants are known for their large size, upturned ears, and friendly personalities that have captured the hearts of cat lovers around the world. Of the many fascinating features of the Maine Coon, the color of their eyes, especially the blue eye color, is the most intriguing. But do you know the cruelty behind those eyes? We will explore the genetics behind the dominant and recessive blue eyes of Maine Coon cats.

What is DBE?

Dominant Blue Eyes (DBE) in Maine Coons were relatively rare in 2015. However, starting from 2020, some breeders began to breed DBE cats extensively due to the popular trend, making them no longer rare. This trait is usually associated with the presence of the white spotting gene (although there are DBE cats without white fur). Cats with this gene may have patches of white fur, and if the gene affects the area around the eyes during fetal development, it can result in blue eyes. This is because the white spotting gene inhibits the production of pigment in the iris, leading to blue eyes. In this case, the blue eye trait is dominant.

Over decades of research, scientists have discovered more than 10 different DBE mutations, indicating that DBE is not caused by a single gene mutation. In the Maine Coon population, there are likely more than three types of DBE mutations that occur naturally, and one type obtained through crossbreeding with other breeds (the only officially recognized DBE cat obtained through crossbreeding is from Blue Ridge Cattery).

The origin of Dominant Blue Eyes (DBE) in Maine Coon cats can be traced back to 2015. The first registered DBE Maine Coon in the breed database was Rociri Elvis, whose parents were AnversCoon Grenache and Famke of Keraysun. Rociri Elvis’s blue eyes were believed to be the result of a spontaneous mutation. Since then, the DBE gene has gradually spread among Maine Coons. It is estimated that around 60% of the DBE kittens can be traced back to this gene.

Subsequently, some breeders were "inspired" to cross Maine Coons with Topaz cats to get DBE Maine Coons, some breeders disclosed in their pedigrees that they were using Topaz cats for their crosses, and some breeders chose to forge pedigrees to cross Maine Coons.

What are the health effects of DBE on cats?

Different types of DBE (Dominant Blue Eyes) Maine Coons cannot be crossbred mainly due to genetic incompatibility. Different types of DBE genes may lead to chromosomal incompatibility, affecting cell division and gene expression, resulting in embryonic development failure. Additionally, different DBE types may cause gene conflicts during crossbreeding, leading to abnormal gene expression or the loss of essential genes. To avoid genetic defects and health issues, breeders typically avoid crossbreeding different types of DBE Maine Coons.

DBE Maine Coons may experience hearing loss or complete deafness. This is similar to Waardenburg syndrome in humans, where DBE cats and humans with Ws1 and Ws2 exhibit similar traits. This syndrome affects pigmentation and the auditory system, leading to facial features such as wide-set eyes, a broad nasal bridge, unibrow, and white hair. The DBE gene may also cause other genetic defects, such as developmental abnormalities and reduced pigmentation.

According to breeders cited in (1) literature, out of 8 litters, 3 stillborn kittens exhibited jaundice, abdominal distension, spasms, dehydration, and cranial abnormalities. Additionally, 2 kittens died a few months after birth. One had a cleft palate and was euthanized, while the other apparently died from an infection. The probability of such deformities is often much higher than that of normal mother cats giving birth to deformed kittens. The article also indicates that similar variants in homozygous rats have varying degrees of severity, including embryonic to perinatal death and malformations of the neural tube, spinal ganglia, heart, spine, hindbrain, and limb muscles.

Additionally, the facial features associated with DBE (Dominant Blue Eyes) can also be inherited by cats that do not have blue eyes. This means that even if a cat does not exhibit the blue eye trait, it may still inherit some of the associated genetic conditions. These conditions can include hearing loss, developmental abnormalities, and pigmentation issues. This could potentially have a significant impact on the genetic pool of the Maine Coon breed, leading to a substantial blow to the breed's genetic diversity.

Moreover, according to CFA and TICA breed standards, only white or bicolor Maine Coons should have blue or odd eyes. DBE Maine Coons do not meet these color standards. It’s important to understand that the breed standards for Maine Coons are established and modified based on ensuring the health of the breed.

TICA, The International Cat Association: Distance between the eyes is approximately one eye-width apart. Color: Any shade of green and/or gold. No relation to coat color. Blue and odd eyes accepted in only white and with white.

CFA, Cat Fanciers Association: Eye color can be shades of green, gold, green-gold or copper. White cats and all cats with white may have blue or odd eyes.

What are recessive blue eyes?

Recessive blue eyes in cats are primarily associated with the OCA2 gene, and these cats typically have more than 50% white markings, although low-white variants can also occur. Other genes may also contribute to this trait. Generally, these blue eyes do not affect the cat’s health and welfare. However, the main drawback of this gene is its low heritability. In most cases, cats with recessive blue eyes cannot pass this trait on to their offspring, making the occurrence of recessive blue eyes largely a matter of chance or specific pairings of breeding cats. Recessive blue Eyes are also allowed to show them at cat shows.

This unpredictability is why many "breeders" prefer to breed Dominant Blue Eye (DBE) cats. While recessive blue eyes do not carry any disease genes, But DBE has a 50% chance of being inherited, compared to recessive blue eyes, which have no guaranteed way of being passed on.

Pretty boy from Calicats cattery with CFA's National Winner title

For experienced breeders, most Dominant Blue Eye (DBE) cats can be easily identified by their unique appearance. However, for most people, distinguishing between Dominant Blue Eyes and Recessive Blue Eyes can still be challenging. Generally, two main factors can help differentiate them: the degree and location of white markings, and facial structure.

Degree and Location of White Markings: Recessive Blue Eye cats typically have more than 50% white markings, although cats with fewer white markings are occasionally seen, but this is very rare. If a cat has no white markings or only minimal white on its paws, it is likely a Dominant Blue Eye (DBE). DBE cats have irregular white markings that do not follow a specific pattern and may not be concentrated on the limbs. In contrast, normal white-marked cats usually have all-white limbs. The image below shows the difference between a normal low-white Recessive Blue Eye cat and a low-white or non-white DBE cat.

Facial Structure:Dominant Blue Eyes (DBE): DBE cats have distinctive facial features, including small eyes, wide-set eyes, and a low, broad nose. The image below also illustrates this difference well.

Research on Dominant Blue Eyes (DBE) in cats by scientists and breeders is still superficial, and data remains insufficient. Breeders continue to propagate these cats without publishing information or monitoring the outcomes. The exact cause of DBE is unclear, and the potential problems it may cause are even less understood. DBE is not a gene that was originally introduced into the Maine Coon breed. It can pass on traits and diseases that are not typical of Maine Coons, gradually contaminating the breed’s gene pool. This is why mainstream associations have banned it.

We cannot prevent people from breeding DBE cats or damaging the breed’s gene pool. However, we can understand the potential issues DBE may cause. If you are an experienced breeder who understands Maine Coons and is already working with DBE, you should actively collaborate with experts to research and share any problems encountered during breeding.

If you can, warn new breeders around you, or if you are a new breeder yourself, please avoid working with DBE cats, especially if you are unfamiliar with DBE and are simply attracted to their appearance.

If possible, consider breeding a healthy DBE gene as a new breed. This approach would prevent contamination of the Maine Coon gene pool. Similar to polydactyl cats, if the gene is found to cause no issues, it can be considered for breeding and showcasing as a new breed.

For pet lovers, purchasing cats that meet breed standards helps maintain the breed’s integrity and supports breeders who follow ethical guidelines. If you are particularly fond of blue eyes, make sure to buy from ethical breeders. They should conduct echocardiograms, hip dysplasia tests, DNA tests, hearing tests, and any other necessary tests for DBE breeding cats and kittens.

In the past decade, many new trends have emerged in Maine Coons. It is difficult to distinguish what is harmful, what is beneficial, what is native, and what is introduced. Breeders and pet lovers should not chase trends. Instead, they should adhere to the rules of feline associations and avoid the risk of cat illnesses.

Ultimately, health should take precedence over everything else. This is the essence of ethical breeding.

Sources:

1.https://academic.oup.com/g3journal/article/14/9/jkae131/7692872?login=false

2.http://messybeast.com/DBE-maine-coon.htm

3.http://messybeast.com/blue-eye-breeds.htm

Disclaimer

We will not be publishing the names of any DBE catteries as this may impact people.

Thanks to all the breeders who were willing to provide photos.

Special thanks to the Chinese cattery Blue Obsidian Cattery for helping me with dbe teaching and messybeast.com for research on DBE.