Archive | Dilutions

More albino dogs

WhiteDobe
Casper, a “white” Doberman owned and photographed by Kira Vance.

In the previous post, I mentioned that one form of albinism in dogs had been formally identified in just the last few months. In October of last year, a group from Michigan State University discovered the mutation responsible for white (also called albino) Dobermans. Researchers looked at the four genes known to be involved in Oculocutaneous Albinism in human beings – OCA2, TYR, TRYP1 and SLC45A2. (“Oculocutaneous” means that both the skin and the eyes are involved.) The mutation was found on SLC45A2. Those familiar with the molecular end of horse color genetics might recognize that gene, which used to be called MATP. That is the gene where Cream was found. To someone familiar with horse color, these dogs would be the equivalent to cremellos.

There are differences, of course. In horses, Cream is quite infamously an incomplete dominant. That fact is so well known that the color is often the most effective way to explain the concept of incomplete dominance to a horseman. White in Dobermans is recessive, and so is invisible in the carriers. It might be more accurate to say this is like Pearl in horses, which is another SLC45A2 mutation. Pearl is recessive, but horses of that color typically have dark eyes.

In appearance, however, homozygous Cream and “Doberman White” are a lot alike. Both have faint residual color that is more visible where the animal would have been black. If you look at Casper, the white Doberman pictured above, you can see the faint outline of the black-and-tan pattern that a fully-pigmented individual would have. Double-diluted Cream horses are likewise not truly white, as can be seen in contrast between the white mane and tail and the pale cream of the body on the stallion below. Although not clearly visible in these photos, the dogs have pale blue eyes. Homozygous cream horse are, of course, known as blue-eyed creams (BEC) in many countries. 

cremello_3_by_sooty_bunnieSm
Cremello Saddlebred stallion, Denmarks Platinum Playboy, photographed by Estelle Low.

So is the horse above an albino? Are the horses below a carrier (palomino, to the left) and an affected (cremello, to the right)?

CremandPalo

The position of many within the horse community has been that cremellos, perlinos and smoky creams are not albinos because they do not have pink or red eyes, and because they do have some pigment. It is the position of the Doberman Club of America that because the mutation was assumed to have occurred in the same gene as Oculocutaneous Albinism in human beings, the dogs were by definition albinos. In fact, while referring to a cremello horse as in albino will probably engender a certain amount of derision in the horse community, arguing that these Dobermans are anything but albinos would get the same reaction among their breeders. So which is it? As I said in the last post, I suppose it all depends on whether you define albinism strictly or loosely.

It should be understood, too, that there are reasons behind both positions. There have been horsemen campaigning for some time to change the belief that double-diluted creams were defective. Most do say that the horses are somewhat sensitive to the sun, much like fair-skinned people are, but otherwise they contend that the horses are healthy. They would certainly not agree with the Doberman Pinscher Club of America that these horses are carrying a “deleterious mutation which affects the whole body” that is considered “a genetic defect in all creatures”, which is how that organization describes albinism. The desire not to have these horses, or other pink-skinned white horses, called “albino” is about avoiding that kind of stigma. Meanwhile, the insistence that these dogs be called albinos, and not white, is very much about placing that stigma on the dogs. Most breeders of Dobermans would like to have these dogs removed from the stud books. That is the official position of the breed club, though the structure of stud books in the dog world means that only the American Kennel Club (AKC) has that power. The AKC has a long history of inaction when it comes to denying papers based on color. Because the breed club lacks the power to ban the dogs, what is left is convincing breeders not to perpetuate the color, and buyers not to purchase the puppies. Statements made about the color have to be understood in that light.

This also ties back to the discussion about founders and their colors. However one defines albinism, and whatever one believes about the health of the white Dobermans, this statement about the source for the color is misleading.

In November 1976, a mutation occurred with the whelping of a cream colored Doberman.

The white color in Dobermans is recessive. As I mentioned in the previous post on Splashed White founders, an individual with a recessive color that appears unexpectedly is the not the founder. The initial mutation could not have first occurred in Padula’s Queen Sheba, the cream-colored female referenced in this statement, because she carried two copies of the same mutation. To be the founder, both copies of her SLC45A2 gene would have to have mutated at exactly the same time, in exactly the same way.

A 4,081 base pair deletion was identified between chr4:77,062,968-77,067,051. The deletion start site lies within the last exon of SLC45A2 and results in a loss of the last 50 amino acids of the normal protein, as well as the stop codon, and causes the addition of 191 new amino acids before a new stop codon occurs.

That is the precise change that was identified as causing the color. That exact error would need to happen twice, to the same dog, for Sheba to be the founder. That exact error would need to happen twice, to two different dogs, for her parents to be the original founders. Sheba may well have been the first ever occurrence of the color in the breed, but it did not start with her, nor with her parents. If she was purebred, and an investigation conducted by the AKC when she came to light concluded that she was, then the color came from somewhere on both sides of her extended pedigree. 

WhitePedigree

That means the mutation could be found in other lines, or outside the Doberman breed completely if it predated the formation of the breed. Sheba’s breeder claimed there was another white puppy born to this same pair prior to Sheba, but it did not survive. That would be completely expected. In fact, if this breeding were repeated it would be surprising not to have any other white puppies. Sheba was homozygous for a recessive mutation, or else she would not have been white herself. If she was homozygous, both parents were carriers. Bred together, two carriers would be expected to produce an average of 25% white puppies. After Sheba came to light, it was found that seven other unrelated dogs were registered as “white”. (Sheba’s registration attracted attention because her owner attempted to register her as “albino”, which was not an option.) Dr. Jim Edwards, then an official with the AKC, wrote to the following statement:

This investigation has uncovered an additional seven (7) Dobermans registered as “white” and not included in Shebah’s pedigree. These occur sporadically, with ages varying from two years to fifteen years. Only two of these have produced litters, and only three litters have been registered. We are continuing our investigation into these cases and will provide appropriate updates to the DPCA when our analysis is complete. I am encouraged that this number is small, remembering that color assignment is sometimes difficult for the novice breeder.

For someone interested in founders, those dogs would be of particular interest. The breed club believes that each case was one of a misidentified fawn; that is, a dog that has both the blue and the brown dilution. Fawns are an accepted, if not an especially popular, color in the Doberman breed. I am not sure of the basis for this determination, so I cannot comment on the ultimate color of those dogs. I can say that entries like that are where I look when I am searching for clues about color founders, and about the spread of color mutations in general. I would also add that when trying to track something down, confusion about color assignment works both ways; if registered whites may be in fact fawns, then registered fawns may in fact be white. I have often regretted that fact, because it would be a lot less work tracking down colors if this was not the case! But my interest in color research is purely academic, and motivated out of curiosity. Even if they were fawn – and it is quite possible they were – it would not change the fact that there were likely carriers outside of the one known line, at least at some point. Whether they still exist is an open question. Because this issue, in this breed, has been emotionally charged for some time, chances are that strict culling has been practiced in any cases of white puppies. This far down that path, it is unlikely that if the mutation was in other lines, it is anything but rare now. But the truth is that strong stigmas, while they do promote culling, also promote secrecy. When the stakes become so high, and the reaction to an unexpected white puppy less rational, even the most ethical breeder is forced to weigh the costs of total honesty. When doing my own research, I have learned to include this kind of situation in how I weigh the reliability of information.

With the discovery of the actual mutation, it should be possible to develop a test to identify the white mutation in Dobermans. Hopefully the breed club will support its development and encourage its use by all breeders. If the color is not wanted, then testing and avoiding crosses between carriers is the real answer to the problem. Widespread testing could also provide answers about where the color began, along with the facts about where it can still be found.

Continue Reading

Albino Shih Tzu

AngelFace1

This is Angel, the Shih Tzu with the mystery color mentioned in my previous post. When my friend Gretchen contacted me, she wondered if Angel might be a pale lilac dilute. That is a dog that has both the blue dilution (dd) and brown (bb). The palest shades of lilac are usually the lightest color, aside from white, that most dog owners are likely to see. Angel’s skin is not a muted brown, though, but a clear pink – quite a bit lighter than would be expected in a lilac dog.

Although lilac dogs have the palest overall tone, when it comes to skin coloring the lightest colors can often be found in recessive red dogs that are also homozygous for brown (ee and bb). In Labradors, this combination is sometimes called Dudley. As this comparison image shows, Angel’s nose color (left) is considerably lighter than the one on the Dudley Labrador (right).

Angel2

The pink skin was consistent on the pads of her paws as well. This extreme absence of skin pigmentation is particularly striking to anyone accustomed to looking at dogs. As I mentioned in the previous post, dogs do not have pink skin under their white markings in the same what that a horse will. Unlike horses, white markings that cover the nose do not give a dog a pink nose. Dogs seem very inclined to retain at least some pigment in their skin, which is what makes a truly pink-skinned dog stand out.

AngelPaw
Pink Angel toes!

Historically, dogs like Angel have been called albinos. That is true even though most have blue, green or even hazel eyes. They also have traces of color in their fur, making it possible to discern hints of things like black-and-tan patterns, black masks or white markings. To someone immersed in the world of horse color, that would sound like a mistake. It is an article of faith in the horse color community that albinos must be white with pink or red eyes. Yet albino is the term used not only by owners and breeders, but in scientific literature. Researchers have told me that albino is a term that can be used strictly or more loosely. That is one reason why it is so very difficult to get a definitive answer to the question, “Can a true albino have blue eyes instead of pink?” It really does depend on who you ask!

Angel3
Angel has hazel-colored eyes, but would still be called an albino dog

I had first become aware of dogs like Angel when I stumbled across a paper on albino Pekingese when doing research on the Hanoverian Creams. I was also aware of a handful of of other more modern cases, mostly among the smaller Asian breeds. What I did not realize until I began looking was that while still quite rare, this type of coloring is more widely distributed among the different breeds (and even among what are probably pariah dogs) than I had originally assumed.

The timing of this could not have been better, too, because at least one type of albinism (or extreme dilution, if you prefer) in dogs was identified in just the last few months. The particulars of that mutation will be especially interesting to horse color researchers, but it merits a separate post. In the meantime, I have set up a new Pinterest board with a wide range of images of albino dogs. I tried to pick ones that showed the range of color in the eyes and the fur. As with the other Pinterest boards, I have tried to be sure to link the pins back to their original site to preserve the photographic credits. In the case of some of these pins, following those links will take you to further information and more photos.

And just a final note. Angel is in the care of the Crossroads Shih Tzu Rescue in Tallahassee, Florida, and is looking for her forever home. You can find more information on her Petfinder page.

Continue Reading

Dilutions in dogs

BrownNBlue

A friend of mine who works in rescue recently sent a picture of a Shih Tzu, asking my opinion on her unusual color. Because I am very fond of dogs, posts about them appear here from time to time. They are a very interesting species for those who study color because, like horses, the genetic mechanisms involved have been the subject of a great deal of research in the last few years. In this particular case, the subject happens to touch on a number of relevant topics, including the possibility (thanks to genetic testing) of differentiating between visually similar colors, and the challenge presented when it comes to categorizing and naming colors.

But before I post about Angel, the unusual Shih Tzu, I thought it might be a good idea to explain – for those more familiar with horses – the more common diluted colors in dogs. I suspect that Angel is an albino dog, which is to say that she probably does not have some combination of the factors discussed here. I’ll talk more about just what albino does mean in the context of dogs in subsequent posts. For now, this is a post about what Angel is not.

Some quick dog-to-horse translations

I should probably start by saying that dogs, like all other mammals, have two basic types of pigment: eumelanin (black) and pheomelanin (red). There are some differences both in how color works in dogs, and also in the classifications and semantics. For instance, what horsemen call red pigment is often called yellow in dogs. That is understandable, since pheomelanic dogs are more often a tan or golden color, while the deep chestnut brown common in red horses is relatively rare. However, because red is familiar to readers of this blog, that is the general term I will be using for pheomelanin.

The other problematic term is Brown, which here refers to the color found in chocolate Labradors. Brown in horses is something quite different. To make matters even more confusing, in some dog breeds this color is called red. It is also sometimes called liver, but like brown that means something very different in horses. Brown is also not usually classified as a dilution, but is most often referred to as an alternate form of black pigment. For simplicity, I have used the term “dilution” in a more general sense, meaning anything that makes the fur, skin and eyes lighter. Just be aware that Brown is often spoken of as being separate from the other colors described here, and that using “dilution” as an overall category is somewhat unique to the horse color community. 

Blue

The Doberman Pinscher on the left in the image above is a Blue dilute. While the color is most commonly called blue, the formal term for the mutation is Dilution. It alters black pigment in both the skin and the hair to a slate-gray. Dilution also alters red pigment to a more muted tone, though the effect is more subtle than with the black.

This blue Italian Greyhound is another example. Notice that his eyes are not particularly pale. While many Dilute dogs have gray or amber eyes, there does seem to be a range of possible eye colors. The coat can vary quite a bit, too, so that some Dilute Blues are quite dark. On genetically red dogs in particular, it can be easy to miss some of the darker shades of Dilution because the only sign may be a dark blue (rather than black) nose.

BlueIggy

Dilution is a recessive gene, which is why blue dogs can occur unexpectedly in litters. It is believed that there is more than one version of the mutation for blue, though at the moment only one form can be detected by testing. There is no known equivalent mutation in horses. There is a mutation to the same gene (MLPH) in cats which dilutes black to blue and red to cream. That mutation is responsible for the distinctive blue coloring in the KoratChartreux and Russian Blue breeds.  

Brown

The brown Miniature Pinscher in the picture at the top of the post has had her black fur and skin is replaced with chocolate brown. Like most brown dogs, her eyes are amber. Brown does not alter red pigment, which is why the tan points are still a clear red-gold. In colors that involve a mix of red and black fur, this mutation will turn the black areas brown while the red areas remain unchanged.

BrownRidge
Black-masked sable Rhodesian Ridgeback, with chocolate replacing the black on the mask and the sable shading 

Like the blue dilution, brown dogs are found in a range of shades from dark to light. In my own experience, it seems that brown dogs with some degree of red pigment (sables, brindles, tan-pointed) are often paler in shade than brown dogs that are genetically black, like this German Shorthaired Pointer.

DarkBrown

Dogs have black-pigmented skin, which is why genetically red dogs like Golden Retrievers and Irish Setters have black noses. When a red-pigmented dog inherits the brown color, the fur color does not change but the skin is brown.

ChocoYellow
Labrador showing the effect of brown on a genetically red (ee) dog

Like Dilution, in dogs Brown is recessive. There are three known versions of the mutation, all of which can be identified by testing. There does not appear to be a visual difference between each one, or combinations of the three. Although mutations to the same gene (TYRP1) are found in many mammals, including mice, cats, and cows, there is no similar mutation in horses. You can find references to Brown in older papers on horses, though, because for some time it was theorized that chestnut was the result of Brown. The paper mentioned in the previous post about Silver in Shetlands assumes the presence of Brown in horses, which makes for confusing reading if you are not aware of this discarded theory! (An alteration to the same gene in people is responsible for the blonde hair seen in some Solomon Islanders.)

Isabella or Lilac

This is not a separate mutation, but rather a combination of the two previous colors. Dogs that are both Brown (bb) and Dilute (dd) are a pale shade of taupe gray with pale gray skin and green-gray eyes. The best-known breed with this kind of color is the Weimaraner, but it can occur in any breed where both brown and blue are found.

LilacNBlue
The Pit Bull to the left is lilac (brown and blue), while the one to the right is just blue

Cream and White

Both Blue and Brown have been identified at the molecular level. There are also dogs that appear to be pale cream or even white, though they have ordinary black pigmented skin and dark eyes. These American Eskimos are a good example of the whiter form of the this kind of coloring. In some breeds, like the Afghan Hound, the color of the coat could more accurately be called cream. Even some Golden Retrievers and yellow Labradors could more accurately be called cream than yellow. (We used to say of our own very pale dog that he was a vanilla, rather than a yellow, Labrador.)

Eskies

To date all the white and cream dogs have proven to be genetically red (ee). Because they have black noses, eye and lip rims, and dark eyes, the assumption is that they have some factor that dilutes red (but not black) pigment. Sponenberg proposed calling the factor Intensity (I), so that is sometimes how it is notated. The mechanism behind the color is not yet known, however. An added complication with dogs is that white patterning that covers the face – even extensive areas of the face – does not alter the color of the nose. (Notice the extensive white on the face of the blue Pit Bull, yet his nose retained color.) Theoretically, a dog with an extreme piebald pattern might not look much different from a dog with extremely diluted red pigment, so it is possible that some all-white dogs are not actually dilutes at all.

That is a quick overview of the more common things that make for pale dogs. The next post will have pictures of Angel, and a little historical background on albino dogs.

Continue Reading