Waardenburg syndrome in humans is a pigment-related deafness syndrome consisting of hypopigmentation in the hair, blue eyes, deafness, and minor facial structural abnormalities; two subtypes of Waardenburg syndrome are recognized. The defective gene for type 1 Waardenburg syndrome, known as PAX3, has recently been located on the long arm of chromosome 2 (Foy et al., 1990; Baldwin et al., 1992), providing the possibility for diagnoses through DNA blood testing. Unfortunately, blood from deaf Dalmatians did not test as abnormal in one assay (Milunksy, A., personal communication, 1994). This may be the result of a difference in chromosomes, since dogs have 39 pairs of chromosomes compared to the 23 pairs in humans. Efforts are currently underway to isolate the normal canine PAX3 gene, clone it, and develop DNA testing procedures to determine if the same gene is responsible for pigmentation-related deafness in dogs. More recently, the defective gene for the human type 2 Waardenburg syndrome, named MITF, has been localized to the short arm of chromosome 3 (Tassabehji et al, 1994). DNA is being isolated from deaf dogs in our laboratory and stored for future work in this area.
In the absence of a reliable blood test to identify carriers of deafness genes in dogs, efforts are currently underway to establish a hearing registry in the United States, whereby dogs certified to have normal bilateral hearing would be registered to enable breeders to reliably select mates for their own animals to minimize the production of deaf offspring.
The author thanks Bruce L. Tedford for assistance in data compilation and analysis, and to the many individuals who provided dog breed hearing testing data. Supported by NIH grant 1R15DC01128-01, the American Kennel Club, Schering-Plough Animal Health, and the Dalmatian Club of America.