Evaluation of deafness in American Paint Horses by phenotype, brainstem auditory-evoked responses, and endothelin receptor B genotype.

OBJECTIVE

To evaluate deafness in American Paint Horses by phenotype, clinical findings, brainstem auditory-evoked responses (BAERs), and endothelin B receptor (EDNBR) genotype.

DESIGN

Case series and case-control studies.

ANIMALS

14 deaf American Paint Horses, 20 suspected-deaf American Paint Horses, and 13 nondeaf American Paint Horses and Pintos.

PROCEDURES

Horses were categorized on the basis of coat color pattern and eye color. Testing for the EDNBR gene mutation (associated with overo lethal white foal syndrome) and BAERs was performed. Additional clinical findings were obtained from medical records.

RESULTS

All 14 deaf horses had loss of all BAER waveforms consistent with complete deafness. Most horses had the splashed white or splashed white-frame blend coat pattern. Other patterns included frame overo and tovero. All of the deaf horses had extensive head and limb white markings, although the amount of white on the neck and trunk varied widely. All horses had at least 1 partially heterochromic iris, and most had 2 blue eyes. Ninety-one percent (31/34) of deaf and suspected-deaf horses had the EDNBR gene mutation. Deaf and suspected-deaf horses were used successfully for various performance events. All nondeaf horses had unremarkable BAER results.

CONCLUSIONS AND CLINICAL RELEVANCE

Veterinarians should be aware of deafness among American Paint Horses, particularly those with a splashed white or frame overo coat color pattern, blend of these patterns, or tovero pattern. Horses with extensive head and limb markings and those with blue eyes appeared to be at particular risk.