COAT COLOR PLEIOTROPISMS

IN ENGLISH SHEPHERDS

© 2005 by Vivian Flynt

What is a “pleiotropism” (pronounced ply-AWT-ruh-pizzum) you ask? It is a genetic term used to describe the phenomenon that occurs when the expression of one trait – in this case hair coat color – somehow connects to the expression of other distinct, seemingly unrelated physical abnormalities.

Most English Shepherd fanciers are aware that Aussie, Collie, and Sheltie breeders avoid breeding a merle-colored dog to another merle because of the serious genetic defects associated with “double merles”. While some of the offspring of such unions may be fine, most double merles will suffer one or more of a wide range of congenital problems – including deafness, blindness, sterility, and serious heart conditions. In fact, the damage is so heinous that most double-merle fetuses don’t even survive pregnancy. Double merles are a classic example of a coat color pleiotropism.

Not a problem, I can hear you saying, English Shepherds don’t come in merle. And you’re right – our breed certainly dodged that bullet by being non-merle. But that doesn’t mean English Shepherd coat color inheritance is totally unaffected by pleiotropisms. Our breed does have a couple of pigmentation pleiotropic bugaboos we must contend with: Piebald’s and Lethal Silvers.

PIEBALDS

The piebald gene is most often associated with the white or near-white breeds, such as Samoyeds, Great Pyrenees, and Dalmatians. But it also occurs in Bulldogs, Boston Terriers, and any number of breeds, including English Shepherds, whose coats have white pattern inheritance.

Color wise, English Shepherds are a mantled breed. Think of their color as a blanket draped overtop the dog. Their white markings occur in the Irish pattern and are mainly on the dog’s underside and extremities. In some English Shepherds white markings can also occur as spots, signifying the presence of the spotting gene.

The Irish pattern is incompletely dominant, meaning it’s expressed at varying degrees. Typically, it’s expressed first on the chest, belly, and toes, and then spreads out from there. A black & tan English Shepherd with a spot of white on its chest does carry some of the Irish pattern genes, just not to the same extent as some other sheppy’s.

Interestingly, patterns such as Irish pattern always alight themselves at the same location on the dog’s body, instead of simply appearing as random spots. This is because when the dog is an embryo a certain area of skin cells on the tummy side of the embryo are genetically programmed for the white color and it is simply a big blob there. As the pup develops its legs, head, etc., these cells migrate with their respective parts and become the Irish pattern.

Try this test: Take your English Shepherd and lay him on his back. Push his paws up to his chest and bring his nose downward a bit. You can then see how all the white lines up, and if his hind legs were in a fetal position, this would too.

On a continuum from the least amount of white to the most white, English Shepherds can be:

                  Non-white factored (NWF),

                  White factored (WF),

ê                  Excessive white factored (EWF),

ò                  Piebald (PD), or

                  Extreme piebald (EPD).

Simply put, the further you progress down the continuum towards more white, the more expression the piebald gene will have. In all probability piebald inheritance in English Shepherds is recessive.

•NON-WHITE FACTORED With non-white factored (NWF) English Shepherds color predominates. They have minimal white markings. A black & tan or a solid colored are probably the most extreme examples of a NWF English Shepherd. Most common examples of NWF English Shepherds are any color mantle with at least one or more of the typical white Irish pattern markings: white legs and/or feet, a dab of white on the chin or chest, and a white-tipped tail.

•WHITE FACTOREDWhite factored (WF) English Shepherds carry more Irish pattern white. They will have white stifles, and/or belly white that connects to the white on their hind legs.

•EXCESSIVE WHITE FACTOREDExcessive-white factored (EWF) English Shepherds carry even more Irish pattern white. They will have the same distinguishing markings as a WF, along with white above the hock or behind the withers. Sometimes the dog has streaks of white extending upwards from its belly white (also known as “overos”).If the dog also has small patch(es) of white in the mantle (usually atop the hip or on the back) and/or a face that is half white with white extending over the eye (commonly known as “split-faced”), it signifies the presence of the spotting gene.

•PIEBALDPiebald (PD) English Shepherds are dogs who carry 50% or more white. The Irish pattern is still apparent, it’s just that there is a lot more of it. In English Shepherds piebald can be expressed throught all-white heads (like those commonly associated with Old English Sheepdogs), split-faces with white extending over the eye and/or the ear, or white that crosses the back.

•EXTREME PIEBALDExtreme piebald (EPD) English Shepherds are primarily white with a few colored spots on their body, generally near the tail and/or the ears. The Irish pattern is gone, replaced by a predominantly white coat color with spots. In Collies and Shelties extreme piebalds are white-bodied dogs with color only on the head and are known as “color-headed whites”. I’ve yet to see a color-headed white English Shepherd.

Granted, English Shepherds with “full show white” are flashy and piebald English Shepherds can elicit oohs and aahs. Unfortunately, the piebald gene can cause degeneration in the formation of the blood vessels that supply areas of the ear vital to hearing. Combine the piebald gene with blue eyes and the percentage increases considerably that the dog will be deaf. Now you know why the various breed standards have historically cautioned breeders that more than one-third white is a no-no, as are blue eyes.

When an English Shepherd has a lot of white in its coat, especially on the head, some pigment may be missing from its eyes too, and that would make the eyes totally or partially blue. Studies of at-risk breeds have found that both blue eye(s) with lots of white on the face or any eye color with even a little white on the ears are strongly correlated to congenital deafness. Granted, blue eyes can also occur independently. I suspect we’ve got more than one way genetically to get blue eyes. What I am referring to here is blue eye(s) resulting from a lack of pigmentation.

According to Jerold S. Bell, DVM, researchers have found that a lack of pigment (melanin) cells reaching the inner ear in the developing embryo leads to collapse and death of the nerve cells required for hearing. While the quantity of pigment cells in the developing embryo is genetically controlled, the migration of the pigment cells to the developing inner ear occurs by chance. If there are fewer pigment cells, the chances of some not reaching one or both ears and causing deafness are greater. This combination of genetics and chance explains why the inheritance of congenital deafness remains unpredictable.

So while the homozygous piebald gene is absolutely necessary for the hearing disorder to be present, there are other genes that must also be present for deafness to occur – a phenomenon referred to as “polygenicity”. Hearing loss in affected puppies begins between three and four weeks of age, with complete deafness occurring by week five. The mode of inheritance of canine deafness has not been found to follow a simple recessive, dominant, or sex-linked pattern. Male and female dogs are affected equally.

To complicate things even more, some animals exhibit unilateral deafness (deaf in one ear) while others are totally deaf (bilaterally deaf, or deaf in both ears). English Shepherds who are unilaterally deaf are usually able to compensate just enough that their owners don’t even suspect they are hearing impaired. When you include all breeds, there are two to three unilaterally deaf dogs for every bilaterally deaf dog. Unfortunately, there is no significant statistical difference between unilaterally and bilaterally deaf dogs in the production of deaf progeny. So unless English Shepherd breeders select against both unilaterally and bilaterally deaf dogs, congenital deafness will persist.

According to breeders of breeds with a high risk of congenital deafness, it is easy to identify a bilaterally deaf puppy. The only way to positively identify unilaterally deaf puppies, though, is through electro-diagnostic testing. A Brainstem Auditory Evoked Response (BAER) test can be performed anytime after five weeks of age.

Thankfully, most English Shepherd breeders consider predominantly white dogs to be culls and only place them in non-breeding homes. Therefore, bilateral deafness remains very, very rare in our breed. While it’s perfectly fine to be enamored with your piebalds, using such dogs as breeding stock can have serious, long-term consequences. So before you jump into breeding white English Shepherds, please realize your actions could hasten the day when all English Shepherd breeders routinely have to BAER test all their puppies to determine which are able to hear.

LETHAL SILVERS

Geneticists consider the lethal silver pleiotropism to be relatively uncommon. In fact, most people outside of Collies and Shetland Sheepdogs have probably never heard of lethal silver. In the aforementioned breeds, however, breeders are all too familiar with it.

The “silver” in lethal silver refers to the dull gray color of a circulated silver dollar. Also known as “gray collie syndrome”, lethal silver is so named because of the unique hair color associated with the pleiotropism. The hereditary condition that results in a uniform gray-, beige-, or charcoal-colored birth coat also causes other, more serious, physical abnormalities. Lethal silvers may exhibit a multitude of problems including poor eyesight or blindness, undeveloped gonads, the inability to absorb nutrients in the small intestines, skeletal deformities, and a degeneration of the cartilage in the growth plates of their bones.

Usually the physical abnormalities are so severe that affected puppies die shortly after being born. Of those who do survive birth (and who in turn are not rejected by their dams), the problems are so apparent that their lives are often humanely ended by the breeder. This pleiotropism exists in English Shepherds, though I believe it is extremely rare. The incidents I have heard of involve the black & white and black & tan color patterns – recessive color patterns that must be bred closely to avoid being lost.

In Collies and Shelties lethal silvers who manage to survive puppyhood usually die from cyclic hematopoesis. The lethal silver gene is considered incomplete in our breed because affected English Shepherds do not develop the episolic lack of white blood cells associated with this rare blood disorder. Thus, lethal silver is not yet lethal in English Shepherds. In all likelihood the polygenic traits necessary for the condition to progress to cyclic hematopoesis have not fully developed in our breed.

Perhaps the very low incidence of close familial breedings in English Shepherds can explain why the lethal silver gene remains incomplete. Presently, the lethal silver pleiotropism is only associated with English Shepherd lines that have been inbred for a prolonged period. Thankfully, English Shepherd breeders’ historic disdain for close breeding has helped limit the severity of the lethal silver gene.

With present day English Shepherd breeders placing less emphasis on “keeping the colors pure,” I hoped to see lethal silvers decline drastically. But could our breed face new pressures as the popularity of dilute coat colors increases? Because the dilution gene is recessive to the gene that allows full expression of dark pigment, breeders who want to produce blues, chocolates, and crèmes might be tempted to breed closely. But there are other ways to keep the dilution factor from being diminished.

Breeding dilute to dilute is not a problem as long as breeders don’t rely on inbreeding to keep the dilution factor. It’s not breeding dilute coat colors, anymore than it’s breeding black & white- and black & tan-patterned dogs, that’s causing lethal silvers in English Shepherd litters. The pleiotropism only occurs in consistently inbred families. Breeders of dilutes, just like black & white and black & tan color pattern breeders, must remember that prolonged inbreeding in general is not a good idea.

It’s better to breed wisely, and not rely on frequent inbreeding’s to get you where you want to go. Careful selection of breeding stock, coupled with the avoidance of close breedings on families known to have produced lethal silvers, should keep this English Shepherd pleiotropism from following the route it did in Collies and Shelties and coming fatal.

IN CONCLUSION

The old saying “knowledge is power” is very appropriate here. It is imperative that all English Shepherd breeders be informed of the negative ramifications involved when breeding certain individuals. Prospective English Shepherd owners need to understand the genetic abnormalities that exist within our breed, and not unwittingly provide a market for the sale of unique-looking, albeit possibly defective, dogs. While the outward appearance of some of these individuals may be pleasing to the eye, we must be alert for the long-term damage these dogs can do to the English Shepherd breed.

The color and marking descriptions in the English Shepherd standards provide us with a roadmap for steering clear of two dangerous coat color pleiotropisms. Every English Shepherd fancier bears an ethical responsibility to the breed to see it continues healthy, vigorous, and sound. Let’s all do what we can to minimize the incidence and severity of pleiotropisms in this great