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More albino dogs

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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. 

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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)?

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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. 

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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.

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Searching for another founder

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An elderly Finnhorse, descendent of the stallion Eversti

In the previous post about founders, I talked about the search for the origins of the silver dilution. I wanted to present another case study that highlights some of the challenges in tracing color lines, this time with classic splash white (SW1). We tend to talk about this form of splash white as being incompletely dominant, with the heterozygous horses tending to show very little white and the homozygous horses having the more distinctive “classic” form of the pattern. When the pattern was first described in 1931, however, it was called Recessive Pied. This was in contrast with Dominant Pied, which we now call tobiano. Later the author, Valto Klemola, proposed changing Dominant and Recessive Pied to “Piebald” and “Splashed White” respectively.

By visiting the Splashed White Project page, and clicking on the button to display heterozygous SW1 horses, it is easy to see why Klemola would have considered the pattern recessive; the horses in that group do not look like pintos. In fact, there is a growing understanding that in breeds with minimal white markings, horses can carry the SW1 mutation without showing unusual – or sometimes any – white or blue eyes. With that reality in mind, classic splash behaves enough like a recessive that it illustrates how the search for a founder is different when the color is not visible in the carriers.

Klemola noted how the pattern sometimes surprised breeders.

In the native breeds of Northern Europe what at first glance looks like a piebald foal may be produced from quite normally-colored parents. This surprising phenomenon has given rise to many fantastic explanations among the breeders…

That observation comes from the second paper, published in the Journal of Heredity in 1933. The earlier paper, published in Zeitschrift für Züchtung, included pictures of Danish and Swedish horses with the classic splash pattern. But the main focus was on the Finnhorse stallion Eversti, who was known for producing both blue eyes and occasional pinto patterns. Although he was only mentioned in passing in the 1933 paper, the earlier one provided extensive details about both his ancestors and his descendants, all of which point to the likelihood that he was heterozygous for SW1. Eversti was a black horse with white markings, but his paternal great-granddam was a blue-eyed pinto (“glasäugig und bunt”). When dealing with historical records, SW1 horses are rarely identified as pintos unless they are homozygous. Had the color been unique to Finnhorses, she could not have been the founder. One truth about recessive colors is that the founder would not actually be the new color. Remember each specific mutation is a one-time event. To display a recessive trait, an animal must be homozygous – it must have two of the same mutation. So even if his pinto great-grandmother had been the first known splashed white, she could have been ruled out as the actual founder. The real founder appears somewhere on both sides of her pedigree, and he or she was probably quite unremarkable. The original mutation could spread pretty far before two descendants were crossed, and the result was a very obvious pinto.

Klemola knew that splashed white was not unique to the Finnhorse, so that unnamed pinto mare was never considered as the founder. As he noted, the same pattern occurred in other Northern European breeds, so the original mutation happened before those breeding groups separated. In more recent times, the same type of pattern was observed in breeds as diverse as the Pasos of Puerto Rico and the Marwaris of India. When a pattern is found across a broad range of breeds and regions, that usually means that the mutation is old. Like other old mutations – silver, tobiano, leopard complex – it is unlikely that much will ever been known about the horse that carried that first SW1 mutation.

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Oregon Ice On Fire, a descendant of the Morgan mare Royal-Glo, is heterozygous for SW1

The most that may be possible is to identify some of the sources for the pattern within some of the modern breeds. Now that a test is available for the pattern, carriers can be identified even when they have not produced the more obvious classic pattern. With enough testing information, lines that carry SW1 can be identified. This process has already started in the Morgan breed, where Royal-Glo and Lady In Lace, and ultimately their ancestor Rhythm Lovely Lady, have been named as likely sources. It may be possible from there to connect those horses to some of the early American lines that predated the stud books, since some of those were noted for producing blue eyes. This is perhaps as far back as it may be possible to go with the history of the pattern in America. 

In the case of the Finnhorse, Eversti proved to be an influential stallion. His great-great-grandson, Murto, is one of the four male lines in the breed. Both Murto and his son, Eri-Aaroni, were chestnuts with flashy white markings. Intiaani, the first Finnhorse that tested positive for one copy of SW1, carried 21 lines to Murto through the female side of her pedigree alone. Eleven of those were though Eri-Aaroni. And yet that influence is probably the best argument against the color coming from Murto. It is difficult to find a modern Finnhorse without multiple lines to Murto – and by extension, to Eversti. If Murto carried SW1, breeders should have started to see classic splash offspring among his linebred descendants. Yet until the results came back from Intiaani’s test, it was widely assumed that the pattern could no longer be found in Finnhorses. That would suggest that the source for the mutation came through one of the less common lines to Eversti, or even one of the other lines that go back to Eversti’s sire Jalo (grandson of the blue-eyed pinto mare). The flashy white on Murto and Eri-Aaroni may well be unrelated to SW1.

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Eri-Aaroni, a son of Murto and one of the most influential stallions in the Finnhorse breed

There are quite a few horses that have either tested positive for a single copy of SW1, or that have produced the classic pattern, that look like Eri-Aaroni (pictured above). A fair number of the known splash white producers in the Welsh Mountain Pony have similar markings. There are also quite a few breeds where these types of markings are common, like the Arabian, yet SW1 is not believed to be present. That complicates the search for sources in breeds where a variety of white-producing mutations are found – which is actually the case in most breeds. Even the presence of blue eyes in a line may not indicate the presence of SW1 in breeds where it is known to be, because some blue-eyed horses have been testing negative for the (currently) known forms of splash white.

With luck those other blue-eyed horses will prove to have a newer mutation. That is the case with the other four formally identified forms of splashed white. The founder of the most common of those, SW2, is a known individual. While she was not named outright in the original paper, the information given matched that of the 1987 Quarter Horse mare, Katie Gun, dam of the famed reining horse, Gunner. The suspected founders of the other three were all born in the last two decades, which would suggest that mutations of this type are more common than originally thought.

And this is probably a good place to jump over to the subject of my friend’s albino dog, since that involves recessive genes, separate mutations producing similar colors, and the search for founders. I’ll start that topic in the next day or two.

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More on founders

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Fascination, a son of Trot by Trot’s grandson Chestnut

In the previous post I talked about how novel colors are the result of a mutation that occurs in a single, founding animal. I wanted to use a couple of different colors to illustrate this idea, and talk about what that means for anyone researching color in a given breed. In this post, I’ll talk about the search for the founder of the silver dilution. 

The silver dilution first came to the attention of researchers through the work of the early geneticist W. E. Castle. Castle had authored a number of articles that appeared in the American Shetland Pony Journal, and in 1953 he published the paper “Silver Dapple, A Unique Color Variety Among Shetland Ponies” in the Journal of Heredity. In that article, Castle concludes that silver originated with the American Shetland mare, Trot 31.

The first pony known to have shown this color (doubtless a mutation) was the mare Trot 31, born in 1886, the color being described as “fawn”.

It was reasonable for Dr. Castle to draw the conclusion that Trot was the founder for the mutation, because he had been told that her color had never been seen before, and that only her descendants possessed it. Since a study of her offspring and their production records already proved that the color was dominant, then the logical explanation for its sudden appearance was that she was the source for the mutation. This conclusion was flawed, in part because the interaction between the base colors (black, bay and chestnut) was not well understood. Castle and others had concluded that chestnut was the equivalent to Brown, a recessive version of black in mice and dogs. But there was another problem: the breeder was not entirely truthful about his ponies. In the same article, Dr. Castle quotes Mr. Bunn, the owner of Trot.

[Trot] was the only pony of this color in America and was also a beautiful color… However, every one of the ponies you now see of this color was the produce or descended from Chestnut. His granddam Trot was the only mare ever known to have that color of all the Shetlands ever bred or known.

Castle then adds that those who study genetics “call such abrupt origins mutations”. But Trot was not as unique as the previous quote might suggest. Her breeder had a full brother, Baron Keithsburg, who was also silver. When a horse has a sibling with the same color, that is proof that the color did not originate with them, and attention has to turn to one of the two parents. In the case of Trot and Baron Keithsburg, their sire Jeff was said to be of the same color. But perhaps Mr. Bunn did not lie outright, because Jeff was not actually a Shetland Pony. By multiple accounts, including Mr. Bunn himself, Jeff was an imported Welsh Pony.  (Jeff is discussed briefly in the chapter on Hackneys in Volume I of Equine Tapestry, and more of his story will come up in Volume II, which covers the pony breeds.)

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Chestnut, grandson of the silver “founder” Trot

The article about Trot did prompt at least one reader to write to Dr. Castle to say the color was not unique to Trot or even to Shetlands. She pointed to a half-tone photograph of Skerryvore, a Highland Pony stallion pictured in Lady Wentworth’s Thoroughbred Racing Stock. Images of Skerryvore are fairly easy to find, since he was often held up as a model of “improved” pony type. Those familiar with the dappling on silver dilutes will probably recognize right away, even in a half-tone, that Skerryvore was an ordinary dapple grey. (The image in his entry for allbreedpedigree.com is even more telling of his true color.)

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Skerryvore, Champion of the prestigious Highland and Agricultural Society Show in 1909 and 1911

Perhaps Dr. Castle had further information about other Highland Ponies, because the color was present, if not with Skerryvore, among the ponies of his time. Rhum Laddie, the stallion found in the pedigrees of most modern silver dilute Highlands, would have been a contemporary of Skerryvore. Or perhaps other Shetland breeders had alerted him to the discrepancies in the story he was given about Trot. Either way, Castle published an addendum shortly after the original article, stating that the color probably had older origins. It seems few read this, because the idea that this was a color unique to Shetlands – and to American Shetlands in particular – persisted for decades. In fact, when the first Welsh Pony tested positive for silver, there were vocal accusations that his American breeders must have slipped in American Shetland blood.

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Rhum Mary V, modern silver dapple Highland Pony

That kind of situation, where a color becomes so closely associated with a specific breed, tended to muddy the waters before there were genetic tests. Testing has allowed researchers to determine if a color in one breed is in fact the same color in another. When the same color is found in separate breeds, then barring dishonest pedigree records, that is proof that the mutation dates back to a time before the two groups separated. This fact is used as a way to guess the age of some mutations. If the same mutation is spread widely across a group of breeds with no documented connection, like yesterday’s example with grey, then it is pretty safe to assume the mutation is quite old. This can also be used to guess at the possible origins of a mutation, if it predates recorded pedigrees. When a mutation clusters with a group of related breeds, then it tends to suggest that it arose in the animals that were used to develop those breeds. The pearl dilution, for instance, is suspected to have Spanish origins because so many of the breeds were it is found have Spanish blood. These are still guesses, since it is quite possible for a mutation to occur in one population, spread to a second area as an outcross, while the color in the original area dies out. Still, this type of hypothesis can be useful when trying to guess how likely a horse may carry a given mutation – and how worthwhile it may be to send out hairs for a test.

Using the oldest breed with a positive test for silver, the Icelandic, it can be proven that this particular mutation dates back to at least 982 AD, which was when Iceland banned importation of new horses. There is another avenue to investigate questions about original mutations, however, which has been discussed in previous posts on this blog. It is possible to test ancient remains for mutations. In a study that did just that, the silver mutation was found in Siberian remains dating back to the Iron Age. That date might get pushed back further, if earlier remains with the mutation come to light, but we will likely never know much about the founding horse or pony. The long span of time since he or she lived does explain why the color has spread to so many diverse breeds. Because it often produces a very deep color (something generally preferred in the modern stud book era), and two traits that have wide appeal (dappling and flaxen manes and tails), in many cases it has been spared the kind of selective pressure that has reduced the prevalence of the some of the other dilute colors. In the next post, I’ll talk about splash white, what we can guess about its origins, and how it managed to survive in so many populations.

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