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 mutation. Several genetically different variants can produce the same general appearance: one blue eye, two blue eyes, or sometimes only part of an eye being blue. They do not all have the same genetic origin and, importantly, they do not all have the same health findings.[1,2]

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 and has never been diagnosed in any cat breed.

Depending on the type, 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.

A Waardenburg-like phenotype has been reported in a DBE-Re Maine Coon line in which blue eyes and hearing impairment occurred together.[5] That finding is relevant to DBE-Re. It has not been demonstrated in heterozygous CEL or ALT Sphynx.[1–3]

There is also an important historical point.

White deaf cats 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 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 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.

That makes it even more difficult to justify transferring the findings from DBE-Re Maine Coons onto heterozygous CEL or ALT Sphynx.

White cats, white spotting and blue eyes

DBE is also not the only genetic route to blue or odd eyes in cats. The KIT locus is particularly important here.

Two KIT-associated alleles are already well established in domestic cats: dominant white (W) and white spotting (ws).[2,6]

Both can be associated with blue or odd eyes. But again, they do not have identical health findings.

Published research associates congenital deafness with the dominant white W allele, while no deleterious phenotype has been described for the KIT white-spotting ws allele itself.[2,6]

This is another example of why phenotype alone is not enough. A blue eye can occur with DBE, dominant white (KIT), white spotting (KIT) and points cats (TYR).

And those genetic situations do not carry identical evidence of risk.

This distinction matters particularly when discussing Sphynx, because blue or odd eyes can have more than one genetic explanation.

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, 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 cats can be registered and shown, 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.[10,11]

For Sphynx, this is particularly unusual because the breed does not have one required eye colour. Eye shape, size and placement form part of the breed standard, while the presence of a blue or odd eye is not by itself incompatible with the Sphynx standard.[12]

The stated reasoning surrounding the DBE restriction has included concerns about congenital sensory deficits and Waardenburg syndrome.[10,11]

The problem is that these concerns do not match the published findings for heterozygous CEL and ALT.

Neither deafness nor a Waardenburg-like phenotype has been demonstrated in heterozygous CEL or ALT Sphynx.[1–3]

There is also another problem which is particularly relevant to this breed. TICA does not require a genetic test to establish which variant is actually present.

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 creates a fairly obvious difficulty.

If DBE cannot reliably be distinguished from KIT-associated blue eyes by appearance, and DNA testing is not required, then the genetic cause of the blue eye has not actually been established.

This becomes even more difficult to explain when dominant white and white spotting are considered.

KIT-associated W and ws can both produce blue or odd eyes.[2,6] Dominant white has a documented association with congenital deafness, while no deleterious phenotype has been described for white spotting itself.[2,6]

And yet solid white cats are specifically excepted from TICA Show Rule 216.12.12.[10] For Sphynx, therefore, the difference between the two approaches is quite clear.

GCCF requires the DBE variant to be genetically identified and requires BAER hearing testing.

TICA does not require genetic confirmation, despite acknowledging that DBE cannot reliably be distinguished from KIT-associated blue eyes by phenotype alone.[13]

That is not a small technical difference. One system establishes what genetic variant is actually present and checks the health outcome that is being discussed. The other can exclude the trait from the show ring without first establishing either of those things.

Conclusion

For Sphynx, the available evidence does not support treating every blue or odd eye as the same genetic or health issue.

Heterozygous CEL and ALT have not been associated with deafness in the published research, and a Waardenburg-like phenotype has not been demonstrated in heterozygous CEL or ALT Sphynx.[1–3]

Different results have been reported when DBE alleles are combined and with other DBE variants such as DBE-Re.[2,3,5]

KIT adds another layer again. Dominant white and white spotting can also produce blue or odd eyes, but even those two alleles do not have identical health findings.[2,6]

The common feature is the appearance of the eye. The biology behind it can be completely different. For that reason, appearance alone is a poor substitute for testing.

If the concern is the genetic variant, identify the variant. If the concern is hearing, test hearing.

GCCF has already shown that this can be incorporated into a registration and showing system without either ignoring DBE or treating every DBE cat as inherently unhealthy.

For Sphynx, that is the approach most consistent with the evidence currently available.

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.