Hearing & Eye Color
Though not intuitively obvious, coat color, pigment
production and hearing are linked together in a way not yet completely
understood. However, there are countless examples in mammals where coat
color is associated with a hearing disorder and the Dalmatian is often cited as
the definitive example.
Since the mid 1990's we have been engaged in several
investigations on the inheritance of hearing loss in Dalmatians. And all
of this work began with the help of Dr. Candace Sousa, veterinarian practicing
in the Sacramento area. That first bit of work resulted in a report
published in the journal Mammalian Genome (1996, Volume 7, pages
650-653). If you would like to read the abstract for that paper - just click
here for abstract. Put briefly, this research was able to demonstrate
several key points. First, hearing
loss in the Dalmatian is inherited, and that breeders, should they choose to
select against hearing loss, can make significant progress in lowering the
prevalence of the disease. Eye
color and the presence or absence of a color patch at birth were also
significant contributors to the risk for hearing loss.
Specifically, we found that blue-eyed dogs (even dogs with
just one blue eye) had a higher risk
of hearing loss. In addition, dogs
born with a color patch have a significantly lower
risk of suffering from hearing loss. The
following table is taken from this first bit of research presented in Mammalian
Genome. Here is a table of the
predicted probability of hearing status (normal, unilateral deaf, bilateral
deaf) for puppies born without a patch, classified by the eye color of the puppy
and the hearing status of their parents. The
complementary table – for puppies born with a patch – can be found
here.
After that article, and the discovery that dogs with blue eyes had an elevated risk for hearing loss, I was asked to write a small article for The Dalmatian Quarterly (from the Fall 1999 issue) entitled - Have I the right to sing the blues? The article seemed necessary because some folks had trouble believing that blue eyes were related to hearing problems. And apparently that fact is still hard to accept.
Following these earlier investigations, we collected a much
larger set of data, with the help of clinicians at the School of Veterinary
Medicine here on the Davis campus. Collette Williams was instrumental in
bringing this together, and a summary of the data, as they relate to hearing
loss is presented in tables - just click here for summary
tables. These tables present, roughly, the same evidence – that dogs with
blue eyes have a higher risk for deafness and that dogs born with a color
patch have a lower risk. The
abstract for that paper, which appeared in the journal Preventive Veterinary
Medicine (2001, Volume 48, p15-25) is available
here.
In summary, based on these two large sets of data, we see
that pigment is a critical element of hearing development.
And the Dalmatian data offer dramatic proof.
Left open is the question of how to use these observations.
It is clear that deafness is inherited and that reducing the prevalence
of blue eyes, or increasing the prevalence of dogs born with a patch, will lead
to an increase in dogs with normal hearing.
But at what cost? If
eliminating deafness in Dalmatians means dramatically altering the pigment
patterns in this breed, just what has been “won”? This decision is one that
can not be based on genetics alone, but requires breeders to address fundamental
questions about the kinds of dog they hope to create.
This data can answer questions, but the final decisions on the “best”
course of action remains, ultimately, a very human question indeed.
e-mail: trfamula@ucdavis.edu