For Judges

Phenotypic overlap

DBE lineages show a broad phenotypic spectrum, including one or two blue eyes, sectoral heterochromia and white expression ranging from minimal white, commonly registered as 09, to bicolour, harlequin, van or almost completely white phenotypes.

Extensive white may arise through different genetic circumstances. A cat carrying a PAX3-associated DBE variant together with a KIT dominant-white or white-spotting allele may present as white, bicolour, harlequin or van.

Extensive depigmentation has also been documented in particular PAX3 genotypes without a separately identified KIT white-spotting allele. White or almost-white phenotypes have been reported in homozygous DBE-ALT cats and in DBE-CEL/DBE-ALT compound heterozygotes.²

A high proportion of white therefore cannot, from appearance alone, be attributed to KIT-associated white spotting or used to confirm, exclude or classify a DBE genotype.

Eye colour, white markings and overall appearance should therefore not be interpreted as proof of genotype. Neither phenotype nor pedigree alone can confirm or exclude the presence of a DBE-associated variant.

Genetic confirmation

The only reliable method of confirming whether a cat carries a currently known DBE-associated variant is a validated, variant-specific genetic test.

However, a negative result for the currently characterised variants does not exclude a genetically unresolved DBE lineage, because the molecular cause of some DBE lines remains unknown.

The challenge of pedigree interpretation

Pedigrees document ancestry, not molecular genotype.

Where PAX3-associated DBE and KIT-associated white or white spotting have been combined within a breeding programme, pedigree analysis alone may be insufficient to determine which genetic mechanism is responsible for the observed phenotype.

Not all DBE variants are biologically identical

The term "DBE" refers to multiple genetically distinct variants.

Current scientific evidence demonstrates that these variants differ in:

• genomic location;

• variant type;

• predicted molecular consequences;

• phenotypic associations;

• and currently reported health outcomes.

To date, four PAX3-associated variants have been characterised: DBE-CEL, DBE-ALT, DBE-RE and DBE-AGO. These include two intronic variants with proposed regulatory effects and two protein-changing coding variants.¹ ² ³ ⁴

Reported hearing outcomes are not uniform across the variants:

• DBE-CEL has not been associated with deafness in the heterozygous cats studied to date.¹ ⁴

• DBE-ALT has not been associated with deafness in the heterozygous cats described in the current literature, although deafness has been reported in DBE-CEL/DBE-ALT compound heterozygotes and in one of the homozygous DBE-ALT cats reported to date.² ⁴

• DBE-RE has been associated with unilateral and bilateral sensorineural hearing impairment. However, additional heterozygous DBE-RE cats with normal bilateral hearing have also been documented, indicating that the hearing phenotype is not fully penetrant.³ ⁴

• Formal BAER data are not currently available for DBE-AGO.⁴

These variants should therefore be evaluated individually rather than treated as a single homogeneous condition. Scientific assessment should be based on the specific variant involved rather than on the assumption that all DBE variants have the same biological or clinical significance.

Appearance may raise a question, but only genetic testing can provide the answer.

White or White Spotting Does Not Exclude DBE

The presence of a white, bicolour, harlequin or van phenotype does not prove that blue or odd eyes are caused exclusively by KIT.

A cat may carry:

• a PAX3-associated DBE variant;

• KIT dominant white or white spotting;

• both a PAX3-associated DBE variant and a KIT allele;

• or another, currently unresolved genetic cause of blue eyes.

DBE and KIT-associated phenotypes can therefore overlap or occur together in the same cat. A high proportion of white must not automatically be interpreted as evidence that DBE is absent.

Pedigree information, colour registration and visual assessment cannot determine whether a cat carries a PAX3-associated DBE variant. They also cannot establish whether the blue-eye phenotype is caused by KIT, DBE or a combination of both.

Where a cat's DBE status is relevant to registration, breeding or show eligibility, an individual, variant-specific genetic result should be requested.

The presence of KIT does not prove the absence of DBE.

Show Classification and the Risk of Concealed DBE

Show classifications for blue-eyed and odd-eyed cats are generally based on visible eye colour and coat classification rather than on genetic testing. This creates an important limitation: where a show or registration system relies on appearance, a PAX3-associated DBE variant may go undetected when it occurs together with KIT-associated white or white spotting. A cat may appear — both visually and by registration — to be white, bicolour, harlequin or van, while still carrying a DBE variant.

Because show and registration classifications are assigned by appearance, they cannot on their own indicate which genetic mechanism underlies a cat's eye colour and coat. A white or white-spotted classification records how the cat looks, not whether a KIT or PAX3-associated DBE variant are present.

A white-spotted phenotype is therefore not a genetic exemption from transparency. Where the DBE status of a cat is relevant to show eligibility, genetic confirmation — not coat or eye-colour classification — is what establishes it.

For buyers, judges and breeders, the principle is simple:

A DBE-like appearance is not proof of DBE, and a KIT-like appearance is not proof of the absence of DBE.

For a detailed discussion of DBE and KIT combinations, breeder transparency and individual genetic confirmation, read:

DBE & KIT: Genetics, Breeding and Transparency →

Read more about the DBE variants —>

References

1. Abitbol M, Couronné A, Dufaure de Citres C, Gache V. A PAX3 insertion in the Celestial breed and certain feline breeding lines with dominant blue eyes. Animal Genetics. 2024;55(4):670–675. doi:10.1111/age.13433

2. Abitbol M, Dufaure de Citres C, Rudd Garces G, Lühken G, Lyons LA, Gache V. Different Founding Effects Underlie Dominant Blue Eyes (DBE) in the Domestic Cat. Animals. 2024;14(13):1845. doi:10.3390/ani14131845

3. Rudd Garces G, Farke D, Schmidt MJ, Letko A, Schirl K, Abitbol M, Leeb T, Lyons LA, Lühken G. PAX3 haploinsufficiency in Maine Coon cats with dominant blue eyes and hearing loss resembling the human Waardenburg syndrome. G3 Genes|Genomes|Genetics. 2024;14(9):jkae131. doi:10.1093/g3journal/jkae131

4. Abitbol M, Cloquell A, Kaczmarska A, Holmes K, Lühken G, Macaulay K. Dominant blue eyes in Maine Coon cats: New PAX3 variant and updated phenotypic data. Animal Genetics. 2025;56(3):e70020. doi:10.1111/age.70020