Congenital deafness in the dog has been reported in the literature (Braund, 1994; Erickson et al, 1977; Oliver et al, 1987; Hoerlein, 1978; deLahunta, 1983; Neer, 1990; Clark & Stainer, 1983) or observed by the author in at least 61 breeds (Table III). Because of the various possible acquired causes of congenital deafness, and in the absence of breeding studies, it cannot be stated that all or even most of these are inherited. Those breeds with the highest prevalence include Australian Cattle Dog, Australian Shepherd, Bull Terrier, Catahoula, Dalmatian, English Cocker Spaniel, English Setter, and West Highland White Terrier.
Studies of the prevalence of deafness in dogs are limited; published findings have ranged from 0.065% (260 cases out of 397,235 canine hospital visits, United States, Mulvihill & Hanson, 1979), to 0.025% (272 cases our of 1.1 million canine hospital visits, United States, Hayes et al., 1981), to 0.875% (12 cases out of 1,371 dogs reported in a survey of abnormalities in Australian purebred dogs, Johnston & Cox, 1970). However, these numbers reflect only bilateral deafness, since they predate the widespread availability of electrodiagnostic hearing testing instrumentation that enables detection of unilateral deafness (see below). These numbers are probably low by at least a factor of four. Hearing testing has been adopted and promoted by several dog breed organizations, most notably the Dalmatian Club of America, the Bull Terrier Club of America, and the English Setter Association of America. Similar European breed organizations have begun similar efforts. The prevalence in highly at-risk breeds for which data has been collected by the author and collaborators is shown in Table IV. These reported prevalence numbers may be low, since much of the data was collected at breed specialty dog shows, where deaf dogs and dogs not of show quality would have been excluded. Prevalence is highest in the Dalmatian, where 8.0% are bilaterally deaf and 21.8% are unilaterally deaf (Holliday et al., 1992; Strain et al., 1992). Prevalence in the Bull Terrier, English Setter, English Cocker Spaniel, and Australian Cattle Dog is one half to one third that of the Dalmatian. Unilateral or bilateral deafness has been reported to occur in 75% of all white Norwegian Dunkerhounds, but the prevalence in colored dogs is unknown (Foss, 1981). In Dappled Dachshunds, 54.6% are reported to be deaf, with 18.2% bilaterally deaf and 36.4% unilaterally deaf (Reetz et al., 1977).
Few cat breeds are noted for congenital deafness. Those reported with congenital deafness, or with potential for it, include all those carrying the dominant white (W) gene (Gebhardt et al, 1979; Table V) and perhaps the white spotting or piebald (S) gene (see below). Although cat owners in these breeds are familiar with the problem of deafness, little specific published information is available by breed. Several studies have examined deafness in mixed-breed white cats (Bosher & Hallpike, 1965; Mair, 1973; Bergsma & Brown, 1971; reviewed by Delack, 1984). Out of 256 white cats from these three studies, 12.1% were unilaterally deaf and 37.9% were bilaterally deaf, or a total of 50% were affected (Delack, 1984). When cats that were the offspring of two white parents were examined, the prevalence of deafness (unilateral or bilateral) ranged from 52% to 96%. When Mair (1973) and Bergsma & Brown (1971) examined the effect of blue eye color on deafness, they found, respectively, a prevalence of deafness (unilateral and bilateral combined) of 85% and 64.9% in cats with two blue eyes, 40% and 39.1% in cats with one blue eye, and 16.7% and 22% in cats with no blue eyes. The author is unaware of any study of deafness in cats by specific breed. Purebred white cats are said to have a lower prevalence of deafness than mixed-breed white cats (Pedersen, 1991), but supporting data are unavailable.