Much work remains to be done to identify deafness genes in domestic animals so that DNA testing can be used to inform breeding decisions that limit the trait’s prevalence, an expert in the field says.
George Strain, in a review on the genetics of deafness in domestic animals published in the journal Frontiers in Veterinary Science, said although deafness can be acquired throughout an animal’s life from a variety of causes, hereditary deafness, especially congenital hereditary deafness, was a significant problem in several species.
Hereditary deafness in many species and breeds was associated with genes for white pigmentation, he noted, including horses.
Strain, who is professor of veterinary physiology, pharmacology and toxicology at Louisiana State University, said few genes responsible for deafness have been identified in animals, but progress has been made in identifying genes responsible for the associated pigmentation phenotypes.
Across species, the genes identified with deafness or white pigmentation patterns include MITF, PMEL, KIT, EDNRB, CDH23, TYR, and TRPM1 in dogs, cats, horses, cows, pigs, sheep, ferrets, mink, camelids, and rabbits.
Multiple causative genes are present in some species, he noted.
“Significant work remains in many cases to identify specific chromosomal deafness genes so that DNA testing can be used to identify carriers of the mutated genes and thereby reduce deafness prevalence,” he said.
Strain noted that the greatest number of hereditary deafness forms had been identified in dogs, followed by cats, horses, and a few other species.
“Although many of these deafness disorders are associated with pigmentation traits, none have been designated as syndromic since the pigmentation effects are not necessarily considered to be a phenotype abnormality or disease, and diseases of other tissues and systems are not present.”
Discussing equids, Strain said deafness has long been recognized to occur in horses with great amounts of white pigment and blue eyes, especially among Appaloosa, American Paint, piebald, skewbald, Pinto, and Clydesdale breeds and color patterns, suggesting similarity to pigmentation-associated patterns in dogs and cats.
He traversed a number of mutations linked to white pigmentation and deafness in horses.
Several studies also discussed white pigmentation gene mutations, he said, but auditory findings were not reported, so associations with deafness have not been excluded.
White pigmentation in horses but without reported hearing loss has also been shown to result from mutations in the MITF, PAX3 and KIT genes.
In summary, he said despite progress, much work remained in identifying unequivocal gene mutations that can be shown to directly cause deafness in domestic species.
“In animals that are bred and raised for show and where a mandated phenotype is strongly associated with deafness, such as a white coat and absence of a patch in the dalmatian, progress in reducing deafness prevalence will by necessity be slow, but will be facilitated by the availability of a DNA marker that can guide breeding decisions.”
The genetics of deafness in domestic animals
George M. Strain
Front. Vet. Sci., 08 September 2015 http://dx.doi.org/10.3389/fvets.2015.00029