DBE is not one mutation. Several different variants have been identified, mainly involving the PAX3 gene. They may produce a similar eye colour, but they are genetically different and they do not all have the same health findings.

What is DBE?

Dominant Blue Eyes, usually shortened to DBE, is not one single mutation. It is a general term used for several genetically different variants that can produce a similar phenotype, including blue or odd eyes and varying amounts of white.[1,2]

These variants are not all located in the same type of region of the PAX3 gene. Some affect coding regions, while others are non-coding; the DBE variants identified in Sphynx are non-coding.[1,2]

This distinction matters because describing a cat simply as “DBE” does not identify which variant it carries, and findings associated with one DBE variant should not automatically be applied to all of the others.

When two different DBE variants are inherited together (compound heterozygous), or a cat inherits two copies of the same variant (homozygous), the phenotype is typically more extreme, with cats being almost entirely or completely white.

DBE in Sphynx

For Sphynx, the variants relevant to the breed are DBE-Celestial (CEL) and DBE-Altai (ALT). Both involve the PAX3 gene.[1,2]

That distinction matters because simply saying that a cat has “DBE” tells us much less than knowing which variant is actually present.

What do we know about CEL and ALT?

The published research does not associate deafness with heterozygous CEL or ALT cats.[1–3] Problems have, however, been reported when two DBE alleles are combined. Deafness has been observed in cats carrying both variants of CEL and ALT or in homozygous ALT cats.[2]

This is an important difference.

One copy of CEL or ALT is not the same genetic situation as two DBE alleles, and the available evidence does not support treating them as though they carry the same risk.

This is also why genetic testing is so useful. Looking at the cat cannot tell us whether it carries CEL, ALT, another DBE variant or no DBE variant at all.

What about Waardenburg syndrome?

This is probably where the subject becomes unnecessarily confusing. Waardenburg syndrome is a human clinical disorder. It has not been established as a clinical diagnosis in cats.

Depending on the type, in human it can include hearing loss, pigmentation differences, blue or differently coloured eyes, dystopia canthorum and, in some forms, other developmental abnormalities.

PAX3 is one of the genes involved in human Waardenburg syndrome. But a variant affecting the same gene in another species does not automatically produce the same disorder.

KIT is a useful example. In cats, KIT variants produce familiar pigmentation phenotypes including dominant white and white spotting. In humans, pathogenic variants in the same gene can cause piebaldism, while other KIT variants are involved in cancers such as gastrointestinal stromal tumours.

The same applies to MC1R. In felids, MC1R variants can produce melanistic coat colour. In humans, MC1R is strongly associated with pigmentation and melanoma risk. A black cat is obviously not diagnosed with a human melanoma disorder simply because the same gene is involved.

MITF gives another close comparison. Variants affecting MITF produce pigmentation phenotypes across species, while in humans pathogenic MITF variants can cause syndromic disease and some variants are associated with melanoma susceptibility.

What matters is the specific variant, its functional effect, inheritance, species and resulting phenotype — not simply the name of the gene.

The same principle applies to PAX3. Finding a PAX3 variant in a cat does not, by itself, establish a diagnosis of human Waardenburg syndrome. What has been described in cats are PAX3-related phenotypes that share some features with human Waardenburg syndrome, sometimes referred to as Waardenburg-like.[1,2]

There is also an important historical point.

White deaf cats (KIT) were used as an animal model in research into human auditory-pigmentary abnormalities because their combination of pigmentation changes and congenital hearing impairment resembled features of the Waardenburg syndrome.[7] That is very similar to the reason the term “Waardenburg-like” has been used for the affected DBE-Re Maine Coons.[5]

But resemblance to a human syndrome is not the same as diagnosing every cat with a similar pigmentation phenotype with that syndrome.

What about DBE-Re?

DBE-Re is not the DBE variant relevant to the Sphynx lines discussed here, but it is useful because it shows why the variants should not be grouped together.

DBE-Re is a different PAX3 variant identified in Maine Coons. The original study found hearing impairment in affected heterozygous DBE-RE cats and described the phenotype as resembling human Waardenburg syndrome.[5]

Later evidence added an important qualification.

In 2025, six additional heterozygous DBE-Re cats from the same line underwent BAER testing and all six had normal bilateral hearing.[3]

So even with DBE-Re, where an association with deafness has been demonstrated, heterozygous DBE-Re does not automatically mean that the cat is deaf.

What do the data actually support for Sphynx?

For Sphynx, the relevant question is much simpler than the wider debate around DBE sometimes makes it appear.

The published evidence does not associate deafness with heterozygous CEL or ALT.[1–3]

A Waardenburg-like phenotype has not been demonstrated in heterozygous CEL or ALT Sphynx.[1–3]

Adverse outcomes have been reported when DBE alleles are combined, homozygous which is why knowing the genotype matters.[2]

And the appearance of a blue or odd eye alone cannot establish its genetic cause.

So there are two separate questions:

Which variant is present?

and

Can the cat hear normally?

A DNA test identifying the variant answers the first. A BAER test answers the second.

GCCF

GCCF has taken this distinction and put it into practice. DBE Sphynx cats can be registered, but this is not simply based on the breeder declaring that the cat has DBE. A genetic test identifying which DBE variant is present is required, together with a BAER hearing test. The DBE phenotype can then be recorded within the GCCF registration system using the appropriate GEMS coding.[8,9]

This is important because it creates a system in which DBE can be identified and monitored rather than guessed from appearance.

And cats meeting the requirements can still be shown.

This is very close to what the published research supports. The DBE variants are genetically different, their health findings are not identical, and the researchers recommend genetic testing of breeding cats and avoiding breeding combinations that could produce two DBE alleles.[2,3]

GCCF deserves particular recognition here because it is currently the major registry that has taken a science-based and gene-based approach to DBE and incorporated it into both registration and showing.

It has not treated all blue eyes as one problem and it has not treated all PAX3 variants as though they were biologically identical.

Instead, the variant is identified, hearing is checked and the information is recorded. That is what meaningful control of a genetic trait looks like.

TICA

TICA has taken a different approach. DBE can result in disqualification from the show ring, while TICA's own materials describe registration as remaining available.[10,11]

For Sphynx, that raises three separate questions.

The first is the scientific basis for the welfare restriction. Concerns surrounding DBE have included congenital sensory deficits and Waardenburg syndrome.[10,11] Yet published studies have not demonstrated deafness or a Waardenburg-like phenotype in heterozygous CEL or ALT Sphynx.[1–3]

The comparison with dominant white is difficult to ignore. KIT-associated W can also produce blue or odd eyes and has a well-documented association with congenital deafness and Waardenburg- like resemblance. Cornell University summarises reported deafness at approximately 17–22% in white cats without blue eyes, around 40% in white cats with one blue eye, and 65–85% in all-white cats with two blue eyes.[6] White deaf cats have also long been used as a feline model for auditory-pigmentary abnormalities resembling Waardenburg syndrome.[2,6] Yet solid white cats are specifically excepted from TICA Show Rule 216.12.12.[10]

For Sphynx, that exception is especially important. TICA's own Sphynx material states that eye colour is not important in the breed standard and that zero points are assigned to colour.[12] A solid white Sphynx with blue or odd eyes is therefore not disqualified by Rule 216.12.12, while a non-white Sphynx with the same visible blue or odd-eyed phenotype can be disqualified under the DBE rule.[10,12]

So if welfare is the reason for the restriction, the evidence creates an obvious inconsistency: heterozygous CEL and ALT Sphynx can be excluded for “welfare concerns” that have not been demonstrated in those variants, while solid white Sphynx with the same blue or odd-eyed appearance and a documented predisposition to congenital deafness remain eligible to compete.

The second question is what the show-ring restriction actually achieves for welfare. TICA permits DBE cats to be registered, but they can be excluded from showing.[10,11] The restriction therefore acts on exhibition rather than on the existence of the trait itself. If the concern is that DBE represents a welfare risk, it is reasonable to ask how preventing a registered cat from entering the show ring addresses that risk. A cat does not become more or less affected by a genetic welfare problem depending on whether it is exhibited.

The third question is how TICA determines that the cat being disqualified is DBE at all.

Since DBE expression ranges from minimal white to high-grade white, it is visually indistinguishable from KIT-associated blue and odd eyes without DNA testing. In written correspondence, TICA Genetics Committee confirmed that DBE and KIT-associated blue eyes cannot reliably be distinguished by phenotype alone and that genetic testing is not required.[13]

That leaves a practical problem. Two Sphynx cats can have the same blue or odd-eyed appearance for different genetic reasons. If phenotype cannot reliably distinguish DBE from KIT-associated blue eyes and no genetic confirmation is required, what establishes that one particular cat should be disqualified as DBE?

This is also a question of fairness in competition. A disqualification should be based on a characteristic that can be established consistently. Where the rule depends on the genetic origin of a phenotype, but the genetic origin is neither visually distinguishable nor required to be tested, consistent application becomes difficult to demonstrate.

The contrast with GCCF is straightforward. GCCF requires genetic identification of DBE for registration and requires BAER hearing testing. The variant is therefore established rather than inferred from appearance.

Conclusion

For Sphynx, the central issue is not whether all DBE should simply be accepted or rejected. It is whether restrictions reflect the evidence for the specific variant and can be applied consistently and fairly.

For heterozygous CEL and ALT, the welfare outcomes cited in support of restriction have not been demonstrated in the published research.[1–3] At the same time, TICA permits registration, exempts solid white cats despite a documented association with congenital deafness, and does not require the genetic testing needed to distinguish DBE reliably from other causes of blue or odd eyes.[6,10,13]

A system based on genetic identification can distinguish between visually similar cats with different underlying variants. A system based on appearance alone cannot reliably do that.

Learn more about DBE here

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. 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:e70020. doi:10.1111/age.70020.

4. Giebel LB, Tripathi RK, King RA, Spritz RA. A tyrosinase gene missense mutation in temperature-sensitive type I oculocutaneous albinism. A human homologue to the Siamese cat and the Himalayan mouse.Journal of Clinical Investigation. 1991;87(3):1119–1122. doi:10.1172/JCI115075.

5. Rudd Garces G, Farke D, Schmidt MJ, et al. 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.

6. David VA, Menotti-Raymond M, Wallace AC, Roelke M, Kehler J, Leighty R, Eizirik E, Hannah SS, Nelson G, Schäffer AA, Connelly CJ, O’Brien SJ, Ryugo DK. Endogenous retrovirus insertion in the KIT oncogene determines white and white spotting in domestic cats.G3: Genes|Genomes|Genetics. 2014;4(10):1881–1891. doi:10.1534/g3.114.013425.

7. Brown KS, Bergsma DR, Barrow MV. Animal models of pigment and hearing abnormalities in man.Birth Defects Original Article Series. 1971;7(4):102–109. PMID:5173333.

8. Governing Council of the Cat Fancy (GCCF). Sphynx Registration Policy and DBE registration requirements.Governing Council of the Cat Fancy.

9. Governing Council of the Cat Fancy (GCCF). GEMS Code List: Dominant Blue Eyes (DBE), eye colour codes 68 and 69. Governing Council of the Cat Fancy.

10. The International Cat Association (TICA). Show Rules, Rule 216.12.12 – Dominant Blue Eyes. The International Cat Association.

11. The International Cat Association (TICA), Genetics Committee. Dominant Blue Eyes (DBE): Genetics Committee material.2025 Winter Meeting Appendix. The International Cat Association; 2025.

12. The International Cat Association (TICA). Sphynx Breed Standard. The International Cat Association.

13.Private correspondence between the TICA Genetics Committee and ICONICSX, 2026. Written clarification concerning the inability to reliably distinguish DBE from KIT-associated blue eyes by phenotype and the absence of a mandatory genetic-testing requirement. Correspondence held on file by ICONICSX; not publicly available.