Dalmatian Deafness, Extreme-White Spotting—and a New Risk Haplotype

By Caroline Coile

It’s long been known that dogs with the extreme-white color pattern, especially Dalmatians, have greater incidence of deafness. This deafness, called congenital sensorineural deafness, has been reported in up to 30% of Dalmatians. Extreme-white color patterning, which dog breeders know as Sw, causes a mostly white coat with few or no patches of color. The gene responsible for extreme white, called Melanocyte Inducing Transcription Factor (MITF), has been assumed by many to also cause deafness, with all extreme-white dogs in a breed equally at risk, but with random expression of deafness, somewhat similar to how spots are randomly expressed. Despite many attempts to uncover the genetic basis of this type of deafness, no DNA study has been able to positively identify a genetic cause—not even MITF.

Now a new AKC Canine Health Foundation-funded study has identified a “risk haplotype,” which is a combination of genes, near the MITF gene, that is associated with deafness in Dalmatians. Basically, all Dalmatians have the MITF extreme-white gene, but three possible haplotypes at another close-by location can then affect hearing. So extreme-white is a necessary but insufficient cause of deafness. Dalmatians with one of the three haplotypes were at greater risk of deafness than those with the other possible types.

Looking at Dalmatians from Australia, and validating with Dalmatians from the UK and US, these University of Sydney researchers found 62% of bilaterally deaf (deaf in both ears) dogs were homozygous (had two copies) for the “risk” haplotype, while 30% of bilaterally deaf and 45% of hearing dogs carried one copy of the risk haplotype.  Dalmatians that were homozygous for the risk haplotype were 10-times more likely to be deaf in both ears compared to those that carried one or no copies of the risk haplotype. They were also more likely to be deaf in one ear.

The relationship between risk haplotype is obviously not perfect. However, it gives more information than has ever been available before. Its incomplete penetrance could likely be due to interactions with genes that as yet are undiscovered locations. The researchers will continue to search for these.

They suggest a similar association may be found in other breeds with deafness associated with white, particularly white Boxers and Australian Cattle Dogs. The varying frequency of the haplotype from breed to breed could explain why deafness is more common in some extreme-white spotted breeds than in others.

The authors conclude: “We believe that results from this study open the door for genetic testing. In combination with currently applied selection criteria for breeding animals, selecting animals with the protective MITF haplotype will assist with reducing the number of deaf Dalmatians.”

Haase, B., Willet, C.E., Chew, T. et al. De-novo and genome-wide meta-analyses identify a risk haplotype for congenital sensorineural deafness in Dalmatian dogs. Sci Rep 12, 15439 (2022). https://doi.org/10.1038/s41598-022-19535-4

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Posted by Liz on Feb 25 2023. Filed under Current Articles, Featured, Health & Training. You can follow any responses to this entry through the RSS 2.0. Both comments and pings are currently closed.