Deafness
Congenital deafness in dogs can be caused by intrauterine infections, ototoxic drugs (like gentamicin), liver disorders, or other toxic exposures before or soon after birth
This condition can also be inherited.
Inherited deafness can be caused by a gene defect that is autosomal dominant, recessive, sex-linked, mitochondrial, or may involve multiple genes. It is usually impossible to determine the cause of congenital deafness unless a clear problem has been observed in the breed, or carefully planned breedings are performed.
Congenital deafness has been reported for approximately 85 breeds, with the list growing at a regular rate. This can happen in any breed but seems to appear more in those with white pigmentation.
Two pigmentation genes in particular are often associated with deafness in dogs: the merle gene (seen in the collie, Shetland Sheepdog, Dappled Dachshund, Harlequin Great Dane, American Foxhound, and Old English Sheepdog) and the piebald gene (Bull Terrier, Samoyed, Greyhound, Great Pyrenees, Sealyham Terrier, Beagle, Bulldog, Dalmatian, English Setter).Not all breeds with these genes have been affected.
The deafness usually develps in the first few weeks of age while the ear canal is still closed and usually results from the degeneration of part of the blood supply to the cochlea (the stria vascularis). The nerve cells of the cochlea subsequently die and permanent deafness results. The cause of the vascular degeneration is not known, but appears to be associated with the absence of pigment producing cells (melanocytes) in the blood vessels.
The prevalence of congenital deafness in different breeds is seldom known because of the limited number of studies.
In the Dalmatian, where the incidence is highest, 8% of all dogs in the US are bilaterally deaf and 22% are unilaterally deaf. In the English Setter, English Cocker Spaniel, Australian Cattle Dog, and Bull Terrier, where fewer numbers of dogs have been hearing tested, the incidence appears to be about one third to one half that of Dalmatians.
Recent studies have shown that deafness in Dobermans, which do not carry the merle or piebald genes, results from direct loss of cochlear hair cells without any effects on the stria vascularis. Vestibular (balance) system signs, including head tilt and circling, are seen, and the deafness is transmitted by a simple autosomal recessive mechanism. A similar pathology has been described for the Shropshire Terrier, a breed that may no longer be in existence.
The breeds that are known to be most affected with this are below. Please note that this does not mean in any way that all dogs of these breeds will be deaf. Reputable breeders check for this issue prior to breeding.