Dominant Blue Eyes

Everything About the Dominant Blue Eye (DBE) Gene

In this section, I would like to provide as much detailed information as possible about the Dominant Blue Eye (DBE) gene.
To understand it properly, it is helpful to first clarify an important question: How do the different eye colors in cats actually develop?

I am confident that many of your questions about the DBE gene will be answered after reading this section—so please take the time to read it carefully.

The Basis of Eye Color: Melanocytes

A cat’s eye color—just like its coat and skin color—is determined by melanocytes.
These cells produce the pigment melanin and transfer it to surrounding cells. The final eye color depends on the amount of melanin present in different parts of the eye, particularly in the front and back sections of the iris.

In cat embryos, there are around 34 pigment centers. From these centers, melanocytes migrate during development to the skin, coat, and retina.

However, pigmentation of the iris does not fully develop until after birth. This is why all kittens are initially born with blue eyes. Their final eye color usually develops between 4 and 12 months of age.

The blue eye color itself is not caused by pigment within the iris. Instead, it results from light reflection from pigments located in the back of the eye. The less pigment present there, the lighter the blue appears.

Eye Color and Inheritance

Although there are exceptions, eye color is generally considered to be inherited independently of coat color.

For example, the same blue eye color can occur in:

Point cats (cs/cs)
Dominant white cats (W-)
White-spotting carriers (S-)
Albinos (sasa)

White Coloring and Its Effects

In dominant white cats, a condition known as hypopigmentation occurs.
The W gene inhibits the migration of melanocytes, which results in a lack of pigment in the skin and iris.

Because light is scattered when pigment is missing, the eyes appear blue—even though strictly speaking this is not a true pigment color.

This light scattering is based on the same physical principle that makes the sky appear blue:
Tiny structures within the iris scatter light and cause it to appear blue.

However, the inhibition of pigment cells has additional consequences.
Melanocytes originate from the neural crest, just like certain hearing cells. Therefore, the W gene not only causes pigment deficiency but can also affect the development of the inner ear.

This may lead to partial or complete deafness, especially in cats with blue eyes and a high percentage of white coat color.

How Deafness Develops

At around 3–4 weeks of age, if melanocytes are absent or suppressed, degeneration of the blood supply in the inner ear may occur.

This leads to the death of the hair cells in the organ of Corti, which is the actual hearing organ.

The less pigment present in the eyes, the higher the risk of deafness.

Some blue-eyed cats also show an abnormal development or complete absence of the tapetum lucidum, a reflective layer in the eye that is important for vision in low light.

What Is the Tapetum Lucidum?

The tapetum lucidum is a reflective layer made of guanine crystals located behind the retina.
It reflects incoming light back onto the sensory cells, allowing cats to see even in very low light conditions—this is also why their eyes appear to “glow” in the dark.

This structure develops between the 2nd and 8th week of life.

If it fails to develop (as can happen in some blue-eyed cats), twilight or night vision may be reduced.

Theory of Eye Color and the Pigment Threshold

One theory suggests that there is a pigment threshold.

If the amount of pigment falls below this threshold, the eyes appear blue.
If it is above the threshold, the eyes develop another color such as green, copper, or yellow.

This rule does not apply to albinos, whose eye color follows different genetic mechanisms.

White Spotting (S Gene) and Eye Color

The S gene (responsible for bicolor, harlequin, or van patterns) partially prevents the migration of melanocytes, creating both white and pigmented areas in the coat.

Eye color then depends on whether the iris lies within a pigmented or non-pigmented area:

Pigmented area: normal eye color
Non-pigmented area: blue eyes

Therefore, logically speaking, all cats with white spotting can produce kittens with odd eyes or blue eyes.

However, why some breeding lines regularly produce such kittens while others never do has not yet been scientifically clarified.

Personal Theory

My personal theory is that there may be an as yet undiscovered recessive gene that influences the occurrence of blue or odd eyes.

This could explain why certain breeding lines produce offspring with these eye colors more frequently than others.

Albinos, Eye Colors, and Their Genetic Basis in Cats

In true albinos—cats with red eyes—there is a complete absence of pigment in the eyes. The visible pinkish hue comes from the underlying blood vessels in the retina. Albinism is not just a color variation; it is a genetically caused functional disorder.

When a homozygous configuration of the c-gene (cc) is present, melanin production is completely blocked due to a biochemical inhibition. “Homozygous” in this context means that both chromosomes of a gene carry the same allele.

True (red-eyed) albinos are extremely rare. Much more common are blue-eyed heterozygous albinos with the gene combination caca.

Point Coloring (cscs) and Blue Eyes

Point-pattern cats (e.g., Siamese cats) carry the gene combination cscs, which is inseparably linked to blue eyes. These cats often show eye-related peculiarities. They have misrouted optic nerves: the stereoscopic image necessary for depth perception cannot be correctly processed because the signals from both eyes do not cross over to the opposite hemispheres of the brain as usual.

The result is double vision (diplopia). Some cats compensate by blocking one image, but this limits depth perception—a significant disadvantage for a predator. To counteract the image overlap, they often squint (strabismus), which can lead to permanent misalignment. Involuntary eye movements (nystagmus) may also occur. The same symptoms are observed in blue-eyed albinos.

Influence of Other Pigments

Eumelanin (black-brown pigment) and pheomelanin (reddish pigment) are thought to have no direct influence on eye melanin. However, an alternative theory suggests that high concentrations of eumelanin can result in hazel to dark brown eyes. Pheomelanin has been detected in the eyes of red, cream, tortoiseshell, and tabby cats—though how these pigments are regulated remains unclear.

Other Iris Color Phenomena

The iris consists of several layers, and differences in layer thickness and pigmentation can create complex color effects. For example, when deeper layers contain different pigments than the surface, a multicolored effect can appear—such as a greenish or yellow ring around the pupil. This is particularly common in young cats. In adults, uneven eye color is considered a disqualifying trait in breeding.

Pigment spots within the iris are also possible. Eyes that are completely different colors are referred to as complete heterochromia (Odd Eyes), while partial color changes in one eye are called partial heterochromia (mosaic or split eyes).

Breeding and Eye Colors

The eye color can be influenced through selective breeding. If a copper-eyed cat is paired with a blue-eyed cat, the offspring’s eye color depends on the intensity of the parents’ shades and the genes involved (e.g., cscs, caca, cc, W). Crossing green-eyed with blue-eyed cats also produces offspring with eye colors ranging between green and blue.

Problems can arise when crossing green-eyed cats with colorpoint cats (e.g., a Silver Persian with a blue-eyed colorpoint). Offspring often show “expressionless” eye colors. This occurs because the cscs gene responsible for blue mixes with pigment remnants from copper-colored ancestors, resulting in pale green or yellowish eyes—usually undesirable.

Modifying Genetic Factors—What Determines Eye Color in Detail?

Four main factors influence the final eye color:

a) Pigment depth in the iris structure:
The perceived color changes depending on how deep the pigment lies. Copper appears with pigment near the surface; beige and green with deeper pigment. If pigment-free tissue lies deep in the iris, the eyes appear light blue.

b) Pigment density (saturation):
Densely packed pigment cells produce more intense colors—e.g., deep amber or rich emerald green. Low density results in pastel tones or faint colors with visible underlying blood vessels.

c) Homogeneity of the pigment layer (color purity):
Uneven pigment distribution can cause unwanted mixed colors. The effect is similar to colored glass: different layers create complex color nuances.

d) Uniform distribution across the iris:
Irregular pigment distribution can produce rings or concentric circles around the pupil—a feature common in kittens but usually undesirable in adult cats.

Dominant Odd & Blue-Eye Gene

What Is Heterochromia (Odd Eyes)?

Heterochromia describes an uneven pigmentation of the iris caused by a deficiency or excess of melanin. There are two main types: complete heterochromia (e.g., one eye blue, the other copper) and partial heterochromia (iris divided into different colors). The complete form is most common in cats.

The main cause is an uneven distribution of melanin in the iris. This phenomenon occurs in various animal species—especially in cats, dogs, horses, and humans.

In cats, heterochromia usually manifests as one blue eye and one differently colored eye (e.g., green, yellow, or copper). It is often seen in cats with white fur patches or completely white coats—particularly in breeds such as Turkish Angora and Turkish Van.

Important: Heterochromia does not affect a cat’s vision or overall health. It is not a disease, but a genetic color variation. In some cases, however, it can be associated with unilateral deafness—especially in white cats.

Heterochromia can be congenital (hereditary) or acquired. Acquired heterochromia may result from injury, illness, or medical treatments. If a cat’s eye color suddenly changes, a veterinarian should be consulted.

In hereditary heterochromia, the final eye color usually appears only a few weeks after birth, as all kittens are initially born with blue eyes.

Heterochromia also occurs in other breeds such as British Shorthair, British Longhair, or Persian cats. In these lines, it is usually inherited recessively, meaning cats without visible Odd Eyes can carry the gene and pass it to offspring—sometimes only after several generations. Odd-eyed kittens in these lines are rare, often appearing only in color patterns such as Van or Harlequin. Breeding such cats intentionally requires careful planning and patience.

Dominant Blue Eyes (DBE): A New Genetic Mutation

Today, some cats inherit blue or differently colored eyes in a dominant pattern. The responsible gene is known as DBE (Dominant Blue Eyes), a mutation in the PAX3 gene.

DBE can produce minimal white spotting as well as blue-eyed and odd-eyed offspring. If a DBE cat is paired with a non-DBE cat, about 50% of the kittens may inherit the DBE gene and show its traits in their phenotype.

This mutation is also known in humans, where it can be inherited dominantly or recessively. Whether the same applies to cats is not yet clear. Therefore, offspring from DBE lines without visible blue or odd eyes should not be bred further.

Important breeding note: Combining DBE with existing white spotting genes can slightly increase the risk of deafness or even malformations. Breeding with DBE should therefore be done with extreme caution.

Experiences from Our Cattery

Our cattery is now in its second generation, and since 2016 we have been working specifically with various DBE lines. During this time, we gained valuable experience—including some painful lessons. Unfortunately, we also faced deaf and even stillborn kittens before fully understanding the genetic connections.

Responsible Breeding vs. Uncontrolled Reproduction

A breeder’s role is to preserve and improve a breed responsibly. Using DBE indiscriminately in British Shorthair or Longhair cats without proper knowledge can result in deafness, stillbirths, or malformations in the offspring. This is not breeding—it is irresponsible reproduction.

Breeding clubs that allow this or fail to create clear regulations are not acting in the best interest of animal welfare or responsible breeding.

DBE must be marked in the pedigree!

Diversity of DBE Mutations and Their Manifestations

It is likely that genetic mutations responsible for blue or odd eyes have arisen independently in different parts of the world. There may be multiple genetically distinct mutations, each with its own characteristics. A well-known example is the Ojos Azules breed, in which a separate mutation causes blue eyes.

Each genetic variant can affect genotype and phenotype differently. Expression is variable, meaning that even if a kitten inherits the DBE gene, it may not necessarily show blue or odd eyes.

Possible Appearances in Heterozygous DBE Cats

(Cross between a DBE cat and a non-DBE cat)

Blue-eyed or odd-eyed cats without visible white spotting
(note: at least a few white whiskers are usually present)
Blue-eyed or odd-eyed cats with minimal white markings
Odd-eyed cats with sectoral iris coloration (splitted or mosaic eyes), with little or no white in the coat
Cats with seemingly green or yellow eyes that reveal a latent red reflex under flash photography (“red pupils”)—possible hidden DBE
Cats with amber, green, or yellow eyes, with or without visible white markings

Why Breeding Cats with Extensive White Spotting (Bicolor, Harlequin, Van) Should Be Avoided

Cats with strong white spotting wear a “white coat” that can completely cover the subtle white markings typical of the DBE gene. This can lead to the false assumption that the cat does not has the DBE gene.

However: even minimal white markings, such as a few white whiskers, may indicate that a kitten has the DBE gene—even without obvious white patches.

Breeding cats with patterns such as Bicolor, Harlequin, or Van can therefore make it difficult or impossible to reliably identify DBE cats—and also increases the risk of health problems in the offspring.

Example:

Important Notes on Interpreting White Markings and Other Traits in DBE Cats

It is important to emphasize that small white spots or white whiskers are not necessarily an indicator of the DBE gene. In many cases, these are harmless color variations that can occur genetically independent of DBE. Such minor color variations are somewhat more common in Chocolate and Cinnamon cats.

Similarly, white whiskers are not a definitive or reliable sign of DBE—they can also appear randomly.

DBE and Facial Structure

Different variants of the DBE gene can also subtly influence a cat’s facial features. This trait is observable, but its expression varies—like all other phenotypic traits associated with DBE—from barely noticeable to clearly pronounced.

For this reason, breeders often compare the DBE mutation to Waardenburg syndrome in humans, which shows similar phenotypic variability, particularly regarding pigmentation and facial structure.

Observations in DBE Kittens

In my own DBE breeding line, the presence of the DBE gene can already be recognized shortly after birth. Notably, DBE kittens often show slightly altered fur in the region between the eyes and the nose:

The hairs are slightly longer and denser than in non-DBE cats.

This subtle feature can serve as an additional clue for experienced breeders to identify potential DBE inheritance—but it is not, of course, definitive on its own.

DBE – Telecanthus / Apparent Missing Tear Duct

Recently, there have been claims that DBE cats lack a tear duct or have “altered eye anatomy.”

I would like to share an observation with photo comparison.

Note: This concerns only one DBE gene among many. I do not speak for all DBE genes and have not had experience with every DBE variant in the world.

The photos were taken of two 8-week-old kittens while they were half-asleep. Both were very relaxed and not subjected to any pain. Using thumb and forefinger, I gently moved the upper and lower eyelids. The photos were not taken from exactly the same position/angle, so minor differences are possible.

Comparison: DBE vs. Non-DBE

(same litter of the Lykanthera® breed & same litter BRI/experimental DBE line)

The images show the medial canthus (inner corner of the eye):

In the DBE male, the area between the eye and nose often appears “softer” or fuller.
In the non-DBE male, the eyelid edge is more clearly visible.

Important:
The lacrimal punctum (tear duct opening) is present in both cats.
There is no indication of a missing tear duct.

What Explains the Difference?

It is not an anatomical defect, but most likely longer/softer fur in the infraorbital area.

In DBE cats, this area often grows longer, finer hair, which can partially cover the inner eye corner. This can make the tear duct appear:

smaller
obscured
or “absent”

This is purely an optical effect, not a structural absence.

Developmental Biology Background

Genes associated with DBE (neural-crest related, e.g., PAX3-related pathways) influence not only pigmentation but also:

Skin development
Hair follicle type
Hair growth cycle

Transitional zones in the face—where eye, nose, tear duct, and fur boundaries meet—are particularly sensitive.

Key Takeaways

DBE cats*¹ do have a tear duct.
There is no telecanthus (altered eye spacing).
The appearance is due to fur structure, not missing anatomy.

The fact that adult DBE cats (e.g., a mother with blue eyes and a father with odd eyes from another litter) consistently show longer fur in this area clearly indicates a stable genetic phenotype—not a disease or malformation.

Conclusion

What is often interpreted as a “missing tear duct” is actually the result of a combination of genetics, development, and fur growth.

It is a clear example of how small genetic differences can strongly affect appearance without being pathological.

Additional note: DBE cats are more light-sensitive than non-DBE cats, which can cause varying tear production.

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*¹ DBE Igor Line

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DBE and Telecanthus: Morphological Features in Cats

Cats carrying the DBE gene sometimes exhibit a form of what is known as telecanthus.

What Is Telecanthus?

Telecanthus (also called dystopia canthorum) refers to an increased distance between the inner corners of the eyes (medial canthi), while the distance between the pupils remains unchanged. This is clearly different from hypertelorism, in which the entire eye spacing—including the pupil distance—is enlarged.

Telecanthus is considered a minor developmental variant, a so-called “telekante.” These are morphological features without functional limitations. Unlike malformations, they do not have significant medical or cosmetic consequences.

Common Misunderstandings and Observations

Contrary to some breeders’ assumptions, telecanthus is not a problem of the nasal bridge.

The nasal bridge of cats with this trait is not sunken, flattened, or deformed—it is anatomically completely normal.

Additionally, both the literature and our experience show that telecanthus often diminishes with age. It is most noticeable in the first days of life, especially immediately after the eyes open. Later, it usually disappears completely or leaves only very subtle signs, such as a slightly asymmetric upper eyelid—a finding that can also occur in cats without DBE.

Limits of Diagnosis Based on External Features

Not all DBE variants can be reliably identified by external features such as facial structure. In certain lines or mutations, this may be possible—but in many cases, it is not reliable.

For example, the DBE gene in the legendary Ojos Azules cats was associated with pronounced skull changes and shortened tails. These health issues ultimately led to the discontinuation of breeding for this line.

Genetic Diversity and Current Research

So far, six distinct DBE mutations have been officially identified. These can already be detected through genetic testing, for example via Petgeno.

However, there are many additional DBE variants for which no specific genetic tests currently exist.

These mutations may be located on different chromosomes and in various genes, including:

PAX3
MITF
EDNRB
and others

Similar or related mutations are also found in humans, mice, dogs, ferrets, horses, and other animals.

In humans, for instance, a mutation in the PAX3 gene is known as Waardenburg syndrome—a condition associated with pigment changes, telecanthus, and sometimes hearing impairments.

Genetics: Different Perceptions in Humans and Animals

Interestingly, many genetic mutations that are harmless or breed-typical in pets are classified as syndromes or diseases in humans.

Examples include:

Albinism (TYR gene)
- Humans: oculocutaneous albinism, increased skin cancer risk
- Cats: results only in point coloration (e.g., Siamese)
KIT gene
- Humans: piebaldism, involved in oncogenesis
- Cats: simple white spotting (e.g., Bicolor, Harlequin, Van)
ASIP gene
- Humans: metabolic disorders, obesity
- Cats: zonal coat patterns (e.g., Ticked or Shaded)

Conclusion

Research on the DBE gene is still in its early stages. While individual mutations have already been identified, the full spectrum of genetic variants and their effects is far from fully understood. This is why responsible breeding is essential—based on experience, careful observation, and scientific guidance.

The DBE Gene and Its Significance in Azul Cats

The so-called DBE gene (Dominant Blue Eyes) is a genetic mutation that causes the dominant inheritance of blue or odd-eyed eyes in cats (one blue eye and one differently colored eye). A cat with the DBE gene can be bred with any cat that does not carry this gene—about half of the offspring will usually inherit the gene and display the corresponding eye traits in their phenotype.

Important: The presence of the DBE gene should not automatically be equated with a genetic disorder, such as Waardenburg syndrome. To date, no confirmed connection has been found between the DBE gene and harmful malformations.

Latent DBE Cats

Some cats carry the DBE gene without showing visible blue or odd eyes—these are called latent DBE cats. These cats may have green, yellow, or amber eyes but still carry the gene. Their offspring can still develop blue or odd eyes, especially when bred with cats visibly showing DBE.

Note: The term “DBE carrier” can be misleading. With a dominant gene, a cat cannot simply be a carrier. A cat either has the gene—visible or latent—or does not.

Breeding Rules for DBE Cats

Breeding DBE cats requires strict rules:

Two DBE cats must NOT be bred together, as this can produce homozygous offspring with an increased risk of deafness.
DBE cats may only be bred with cats without white spotting.
Cats with white spotting (Bicolor, Van, Harlequin) should be excluded from DBE breeding.

Bicolor Cats and the Recessive Blue-Eye Gene

Breeding with bicolor cats is generally safe as long as they are not used for further breeding. Otherwise, there is a risk of confusion between the dominant DBE gene and the recessive blue-eye gene, which is common in British Shorthair/Longhair breeds. Breeders who want to specifically work with white spotting and blue/odd eyes should consider the recessive gene, where breeding two carriers is allowed.

Caution: In certain DBE lines, such as the Nanotigr line (DBE-Oliver gene), crossing with bicolor or recessive blue-eye carriers has been linked to sudden death in kittens or even adults. While no direct causal link is proven, caution is advised.

Determining Eye Color in Kittens

DBE kittens often show their future eye color early:

Blue eyes: pupils reflect red under flash photography.
Odd eyes: often only one eye shows the red reflex.
Latent kittens: initially show red reflex but later develop yellow, green, or amber eyes.
Mosaic eyes (also sectoral heterochromia or “splitted eyes”) can be partly blue and partly another color—these eyes do not always reflect red.

Homozygous DBE Cats

Homozygous means the cat has two identical alleles for a trait.

Homozygous DBE cats are always blue-eyed, never odd-eyed.
They result from breeding two DBE cats with minimal or no visible white.
Homozygous cats pass the gene to almost 100% of their offspring, theoretically increasing the success rate for blue-eyed kittens.

Caution: Homozygosity can increase the risk of deafness. For this reason, breeding two blue-eyed DBE cats together is strictly prohibited.

However, not all homozygous DBE cats are deaf—some breeders report completely healthy cats. Further research is needed to fully understand these phenomena.

Conclusion

The DBE gene offers fascinating possibilities for breeding cats with unique eye colors. At the same time, responsible handling of this gene requires thorough knowledge of genetics, clear breeding rules, and openness to new scientific insights. Misunderstandings—such as equating DBE with Waardenburg syndrome—should be avoided until reliable data supports such claims.

Latent DBE Cats

As previously mentioned, the DBE gene is known to have variable expression. This means that even if a kitten inherits the gene, it does not necessarily result in blue or odd-eyed eyes.

What Does “Latent” Gene Expression Mean?

Latency (from the Latin latens, “hidden”) describes a gene or trait that is present in the background without being visibly expressed. In other words, the gene is genetically present but does not manifest externally, or only partially.

Among breeders, there is disagreement about when a DBE cat—or Lykanthera cat—can be considered “latent.”

Some believe that only DBE cats whose eyes flash reddish in light should be classified as latent.
Others consider any cat with yellow or green eyes, descended from DBE cats, to be latent, while “red-eyed” animals (with reflective eye backgrounds) are considered strongly expressed.

Important Note

The DBE gene is not simply a blue-eye gene. It is a dominant gene for minimal white spotting, which under certain circumstances can lead to blue or odd eyes.

All latent DBE cats show at least white vibrissae (whiskers). Larger white markings or red-reflecting pupils are not present in all cases. These traits are often misinterpreted or intentionally used to market cats as DBE carriers—sometimes at very high prices. In many cases, these are simply color variations.

Breeding Recommendation

To be safe, breeders should only breed cats that are clearly blue-eyed or odd-eyed. All other potential DBE cats—especially those without clear external traits—should be neutered to prevent unwanted inheritance.

Common Breeder Question

"Can I breed a blue-eyed DBE cat with a cat carrying latent DBE, or is there a risk of deaf kittens?"

Answer:
Yes, there is a risk. In such a pairing, there is a 25% chance of homozygous offspring (i.e., kittens with two DBE alleles). These homozygous DBE cats may be deaf.

If only one parent carries the DBE gene, the risk of deafness is zero.

Clear Breeding Rule

Never breed two DBE cats together.
This rule protects the animals and must be strictly followed.

Copying is prohibited.

More information to follow.

Updated on: February 20, 2026