Hearing loss has been demonstrated in many mammalian species and can be divided into conductive and sensorineural forms depending on the structure affected.
Conductive deafness is characterized by a disturbance in sound conduction and results from a defect in the external auditory canal and the middle ear (chronic otitis externa/media or tumors).
For the sensorineural form, on the other hand, the cause is a disturbance in the reception and transmission of sound waves in the inner ear. This occurs as a result of degeneration of the sensory cells in the inner ear. The cause may be congenital (congenital) or acquired (ototoxic drugs, otitis interna, old age dustiness).
In dogs, over 54 breeds are described with this congenital (inherited) sensorineural form.
The inner ear consists of the so-called cochlea.
This cochlea is lined with hair cells that are moved by sound transmission and thus can transmit acoustic signals to the cochlear nerve and brain to enable hearing. The development and maintenance of these hair cells involves a complex mechanism in which melanocytes (pigment cells) play an important role. If this mechanism is disturbed, degeneration and destruction of the inner ear structures occurs, which manifests itself in unilateral or bilateral deafness in the puppy at about 8 weeks of age.
Deafness is clearly diagnosed by the BAER test (brainstem auditory evoked potential). In this test, auditory signals are transmitted through the eardrum and hair cells to the cochlear nerve to be detected as brain waves.
Melanocytes are also involved in the dark pigmentation of coat color. The discovery that white dogs are much more frequently affected by sensorineural deafness confirms the suspicion that melanocytes are involved in the development of deafness.
The Dalmatian shows the highest incidence of deafness of all dog breeds.
Again, a correlation between degree of pigmentation and deafness is evident, as dogs with blue eyes are more frequently affected by deafness, while dogs with so-called plates (patches) are much less likely to suffer hearing loss.
Although heritability has been demonstrated in the Dalmatian, it has not yet been possible to find a deafness-causing gene.
Thanks to the Dalmatian clubs, which want to fight this problem, it was possible to constantly increase the level of knowledge. So today we assume that several genes are involved in the expression of deafness. However, it is still necessary to obtain blood samples, especially from deaf Dalmatians, as this is the only way to further clarify the mode of inheritance and to develop a genetic test. If possible, samples should be taken from the parents and all littermates of an affected animal. Please always send the blood samples with pedigree and BAER test result.
At any time we are also interested in samples from congenitally deaf dogs of any breed, especially if they have a white coat color.