Reply To: those pesky unwanted mutations

[Jennifer]

The study (linked in the article) says that 100% of the albino Dobies examined displayed photophobia (light sensitivity); they had no other vision problems. I don’t know whether dogs with piebald-linked blue eyes, e.g. some white Boxers and some Dalmatians, commonly show light sensitivity, or for that matter whether dogs with blue eyes due to other causes commonly do either (merles, Huskies etc.). I haven’t noticed my dog squinting her one blue eye in sunlight, but it might be I just haven’t been paying attention, or it might be that she has protective factors that albinos don’t (e.g. her eyelids are black, and her eye doesn’t seem to be quite as icy-pale as an albino’s, which might have to do with different extent of pigment loss in the iris).

The link between being a high-white piebald and going deaf early in puppyhood isn’t fully understood, but it has something to do with the fact that pigment cells participate in ion exchange in the vascular networks around them, including helping stabilize potassium in the vascular networks supplying the cochlea. And certain forms of piebald mutations (there are several, with high-white piebalds tending to carry multiple mutations at once in the gene involved) can delay or block the migration to and/or establishment of pigment cells within the inner ear during fetal development. If no pigment cells are present in the inner ear by early puppyhood, when the cochlea is completing development, then ion exchange doesn’t happen properly, and the cochlea winds up effectively wasting away due to neuron death, rather than maturing to allow normal hearing by the time the ear canals open (around 3 weeks after birth). There are no really large-scale studies on this AFAIK, but by most estimates to date, the rates of deafness in high-white piebalds average around 10-20%, varying by breed. Albino dogs, by contrast, do have a normal distribution of pigment cells–they’re just not able to make pigment with them–so they’re spared this increased risk of deafness.

White GSDs aren’t piebald, though; they’re carrying a recessive mutation on a different gene (the same one that causes most GSDs to have black face masks) which in effect turns off their ability to produce black pigment in their fur (but not in their skin and eyes). For reasons that aren’t yet fully clear, dogs with this mutation also tend to have much paler red pigment than other dogs of their breed or type, so that they often appear white, cream, or yellow (other examples of this include American Eskimos, Maltese, yellow Labs, etc.). This particular mutation is not known to have any health effects. It’s possible that early GSD breeders mistook the white of white GSDs for piebald white, which dog breeders in general had long recognized was linked to an increased risk of deafness in puppyhood. Other claims I’ve heard are that white was considered unfavorable in a guard breed (too visible at night), or that it was simply an article of Nazi pseudoscience that white-furred animals are “weaker” in some ill-defined way (the effective “ban” on white GSDs happened only after breeding came under control of the Nazi regime). At any rate, the “ban” never wound up getting lifted after WWII. The UK Kennel Club did recently announce plans to recognize the White Swiss Shepherd, specifically, as a separate breed, so it’s likely the AKC will eventually follow suit–though if so that won’t help white GSDs who don’t descend from FCI-registered White Swiss Shepherd lines, which I’m pretty sure most US white GSDs don’t. The thing is, due to their many decades of isolation, US white GSDs will almost inevitably have fallen so far behind the mainstream GSD population in terms of the rigors of selection undergone, that they probably really are de facto an “inferior” population at this point, at least from the POV of a good working-line or show-line breeder.