About Maine Coons

The latest "fashionable" trend in Maine Coon colors is blue eyes with a normal coat color, called Dominant Blue Eyes (DBE). Cats with this eye color are called unique, exclusive, and rare.

Let's figure out what it is: an unusual feature or a complex mutation that can be accompanied by serious health problems.

Maine Coons are one of the most recognizable and popular breeds in the world. We love them for their good-natured character, impressive size, tufts on their ears, and expressive eyes. Despite the variety of colors, Maine coons in classic colors look as if they have just emerged from the snowy forests of Maine. Traditionally, the breed standard describes the eye color of the Maine Coon as an aboriginal cat, including all shades of green and yellow. Some coat colors, such as white or bicolor with a high white content, allow blue eyes.

Where do blue eyes come from?

Blue eyes can occur in cats for several reasons:

• The influence of the dominant white gene (W). In completely white cats and sometimes in bicolor cats with a high white content, there is no pigment in the iris of the eyes under the influence of the W gene. That's how blue eyes appear.
• The Colorpoint (cs) gene. It affects, among other things, the color of the iris. Breeds such as the Ragdoll, Siamese, and Neva Masquerade have blue eyes with varying color intensity.
• The Ojos Azules gene. This gene is practically absent in Maine Coons.
• Dominant blue eyes (DBE). Dominant blue eyes are most often associated with mutations in genes involved in the development of pigmentation. Mutations of the PAX3 gene have been found in some Maine Coon lines, but it is assumed that other genetic variants may exist.

So, if a cat has blue eyes and it is not white or colorpoint, this is due to a DBE mutation.

What is DBE in cats?

The Maine Coon is one of the oldest native breeds in North America. Historically, this breed has never had blue eyes with classic coloring (not white).

• Genetic studies have shown that DBE:
• Are inherited as a dominant trait (this means that one carrier of the mutation is enough for it to spread in the breeding line)
• Are transmitted to about half of the offspring
• In some cases, are associated with a mutation of the PAX3 gene.

The PAX3 gene and its similarity to Waardenburg syndrome.

The PAX3 gene is involved in the formation of:

1. Pigmentation of the skin and coat
2. Development of the nervous system
3. Development of auditory organs

Mutations in the PAX3 gene have been well studied in human medicine. They are associated with a disease known as Waardenburg Syndrome.

This syndrome is characterized by:

• blue eyes;
• congenital deafness;
• pigmentation disorders;
• facial features.

Other described risks include:

• developmental disorders of the skull;
• cleft palate;
• neurological disorders.

Also, some studies suggest that a homozygous combination of mutations may be incompatible with the normal development of the embryo and, with certain combinations of genes, causes the death of offspring in the womb. But these data require further research.

In separate studies, some blue-eyed cats have been found to have congenital deafness during BAER testing. However, the prevalence of this phenomenon among various DBE lines has not yet been definitively established.

Phenotypes and auditory function in the investigated Maine Coon cats. a) Individual exhibiting normal iris pigmentation (green eyes) and fully pigmented skin. b and c) WGS animals showing dominant blue eyes and minimal white spotting. The white spot on the bridge of the nose together with pink nasal planum and pink lips b) and the white stripe on the left side of the nose c) indicate a lack of facial skin melanocytes. To assess auditory function, BAER d–f) were recorded. The BAER comprises five distinctive waves corresponding to the transmission of auditory stimuli along the central hearing pathway. Repetitive auditory stimulation of both ears yields symmetrical waves in cats with normal hearing abilities a and d). A complete flat line or arbitrary “noise waves” indicate the absence of electrical activity transmission from the inner ear (cochlea) to the rest of the auditory pathway, leading to a diagnosis of sensorineural deafness. This condition may manifest unilaterally (right sensorineural deafness b and d) or bilaterally (bilateral sensorineural deafness c and f).

Several lines of Dominant blue eyes

Geneticists have discovered that blue eyes in Maine Coons are not associated with a single specific mutation.

Several independent lines of DBE are now known:

• Rociri Elvis
• Topaz
• Pillowtalk-Foreigner
• Nahal
• Agostino 

Each of them may have different variants of PAX3 mutations that arose independently of each other.

This means that the beautiful name "blue-eyed Maine Coon" may conceal not a single mutation, but a whole group of mutations united by a similar external manifestation.

Genetic laboratories have already developed tests that allow us to understand what type of mutation this blue-eyed Maine Coon has.

• Labogen test for PAX3:c.937C>T (Rociri Elvis line)
• Generatio / Laboklin - comprehensive PAX3 mutation test
• ZooGen - testing for various DBE variants

The origin of DBE in Maine Coons

The origin of DBE in Maine Coons raises many questions. Two main versions of the appearance of DBE in Maine Coons are considered:

1. Spontaneous mutation. Some lines (for example, in the Rociri Elvis line) of DBE could arise inside the breed by chance.
2. Hidden outcrosses. Crossbreeding with other breeds as part of experimental breeding programs.

The commercial factor

When an unusual mutation becomes fashionable, the market reacts very quickly. Many people want to own a unique and unusual Maine Coon, the cost of which can be several times higher than usual. The high price and "exclusivity" of the rarity creates a strong commercial incentive for breeding such cats.

However, the problem is that scientific research on these mutations is still ongoing, and their effects on health have not yet been fully understood. And it turns out that a gene that could potentially be associated with developmental problems is beginning to spread in the breed faster than scientific research has time to assess its effects.

Why are Dominant blue eyes considered a problem for the Maine Coon breed

Most felinological organizations don't recognize cats with DBE, considering such a gene undesirable for the Maine Coons.

Some feline organizations are discussing a mandatory DNA test for PAX3 mutations for Maine coons with blue eyes.

Proponents of DBE often argue that felinological organizations are pursuing a policy of double standards by banning DBE and allowing white blue-eyed cats, which also have a risk of having deaf offspring. But the fact is that the Dominant White (W) gene, unlike DBE lines and mutations in the PAX3 gene, has long been studied and included in the Maine Coon standard. To eliminate the risk of having deaf offspring, breeders avoid crossing white cats with blue eyes, as they are most at risk of deafness (recall that the W gene sometimes affects pigmentation and causes impaired development of the inner ear). In addition, auditory brainstem response tests (BAER test) have been developed and successfully applied to ensure that the cat has good hearing.

The BAER test (Brainstem Auditory Evoked Response) is the gold standard for hearing assessment in cats.

• Testing is performed from the age of 6 weeks
• Detects unilateral and bilateral deafness
• According to recent studies, up to 30-40% of tested cats from the Rociri Elvis line show hearing impairments.
• Thus, the comparison of white cats with blue eyes and DBE is not entirely correct.

In turn, the problem of DBE goes beyond just genetics and concerns the ethics of breeding.

• Is it acceptable to breed Maine Coons with a mutation that is potentially associated with diseases?
• Can a commercial interest justify the risk to animals?
• Is changing the standard Maine Coon phenotype a threat to the breed?

Many breeders agree that breeding Maine Coons with DBE can lead to the erosion of the breed type and the accumulation of genetic problems and adhere to the principle

Health and Maine Coon type are more important than a rare external feature.

After all, the main purpose of breeding is to preserve the health and breed type of the Maine Coon, and not to create commercially attractive variations.

To summarize.

Dominant blue eyes in Maine Coons are a complex and controversial phenomenon at the intersection of genetics, breeding, and breeder ethics.

To date, it is known that:

• Some DBE lines are caused by mutations in the PAX3 gene
• The trait is inherited in an autosomal dominant manner.
• There are several independent mutations causing the DBE phenotype.
• Some DBE lines may be associated with health risks, including deafness and other abnormalities.

Let's keep in mind that the dominant blue eyes of Maine Coons are not just a rare eye color. This is a genetic mutation, some of which are associated with changes in the PAX3 gene and potential health risks.

Responsible breeding is primarily aimed at the health, type and genetic stability of the breed. These are the goals that should underpin the work of Maine Coon breeders.

Therefore, many experts and Maine Coon breeders are of the opinion that the spread of DBE in the breed should be carried out with extreme caution or not supported at all until science provides definitive answers about the safety of this mutation.

In conclusion, let's briefly analyze a few myths about dominant blue eyes in Maine Coons.

Blue eyes of Maine Coons: myths and reality

Myth 1. Blue eyes are just a beautiful color.

Fact. In Maine Coons, blue eyes are most often associated with genetic mutations that affect the development of pigment and, sometimes, the development of the nervous system and hearing. It is associated with symptoms similar to Waardenburg syndrome.

Myth 2. Blue-eyed cats are all deaf.

Fact. Deafness does not occur in all blue-eyed cats, but they have a higher risk of developing it. A BAER test is used to test hearing.

Myth 3. Blue eyes are a naturally rare feature of the Maine Coon breed.

Fact. The standards of felinological systems describe blue eyes only for white cats or cats with a high white content. For classic coat colors of Maine Coon, blue eyes appeared as a result of spontaneous mutations and hidden outcrosses with other breeds.

Myth 4. The brighter and richer the eye color, the more valuable and expensive it is.

Fact. The pursuit of 'brightness' encourages the crossing of two carriers of the mutation, which dramatically increases the risk of deafness, birth defects and intrauterine death of kittens.

Myth 5. Blue eyes do not affect cat's health. 

Fact. In some lines of dominant blue eyes associated with PAX3 mutations, the following have been described: hearing problems, developmental disorders, and mortality in kittens. Geneticists continue to actively study the nature of dominant blue eyes.

Myth 6. All blue-eyed Maine Coons are the same. 

Fact. There are several independent lines of dominant blue eyes. They are caused by different mutations in the PAX3 gene or other genes and carry different health risks.

Sources:

Different Founding Effects Underlie Dominant Blue Eyes (DBE) in the Domestic Cat - PubMed

Dominant blue eyes in Maine Coon cats: New PAX3 variant and updated phenotypic data

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