Splash overo


NoBuckskin

Okay, maybe not love – but certainly stop worrying about it.

Like a lot of people who find horse color fascinating, I once spent no small amount of time online, spreading the Gospel of Proper Color Terminology. Surely if I just presented the facts in a convincing manner, I could save the world from people who were convinced they had palomino Arabians!

Fortunately for my own sanity, my career as a parent – begun just a few years after large numbers of horse people discovered the internet – got in the way of my missionary zeal. Toddlers do not recognize the need for uninterrupted bathroom breaks, never mind enough time to compose an extended explanation about why you really should not call your double-diluted cream an albino. Children also raised my threshold for the type of thing that required immediate action. I could live with someone on the internet being wrong; it was not like they had just painted on my bathroom walls with chocolate pudding.

Looking back, though, I see that my enforced absence from online discussions had unexpected benefits. For a researcher there is a significant downside to spending a lot of energy “correcting” wrong information. If you spend too much time telling people that some common misperception is wrong, you run the risk of having that response become automatic.  It makes it a lot harder to reassess your position, because it is a rare person that can argue a position for a long time without getting their ego involved in being proven right. From there, it is easy to overstate your case. “Your flaxen chestnut Arabian is not a palomino” becomes “there have never been palomino Arabians”, which then becomes “Arabians do not carry any dilution genes.”  The first is – or at least to date has been – true. The next statement is actually open for debate, and the last one is incorrect. (See also, here. Similarly diluted Morgans can be found here.)

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And intriguing painting of the early Twentieth Century Turkish Arabian, Übeyyan.
How accurate was this portrait? And what color was he?

The other downside to spending a lot of time correcting errors is that if you automatically dismiss something, it is really easy to overlook important information. Even when people are wrong, they may still hold a clue, a piece of the puzzle you are trying to assemble.

I sometimes get asked why I spend so much time with older documents when so much has changed in our understanding of coat color genetics. Why, for instance, spend time translating Valto Klemola’s 1931 paper on “Recessive Pied” when there are papers written just this year and last on what we now call Splashed White? Surely the new information replaces Klemola’s theory about recessive spotting in horses.

BreedingToColour


I am sure my husband also wonders why I need books about horse color published in 1912. After twenty years of losing more and more shelf space to them, he has given up asking.

But the fact is that Klemola – and many of the other earlier authors – were not entirely wrong. They were almost always working from a partial picture, but often the piece that they were seeing was not incorrect. It was simply incomplete.  Read with an understanding of the larger picture, what these older researchers have to say can still provide valuable information. The same is true for owners and breeders who may not have the same grounding in the latest scientific theories. They still have the potential to be valuable observers. It is worth being open to what they have to say, without being excessively concerned about the “correctness” of how it is said.

At the moment terminology – particularly the terms we use when talking about white patterns – are in a state of transition. We are struggling with words that do not completely fit our present understanding. I hope to tackle that in more detail in a future post. It is worth remembering, however, that the real reason for adopting a consistent set of terms is so that we may all communicate more clearly with one another. It may take a little more effort, and perhaps a few more words (and patience) than it once did, but that is ultimately the goal.

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I think I need to work on final book edits every spring, because it seems to guarantee that a paper will come out within that time period. Animal Genetics has a short communication out with three new KIT mutations and one new PAX3 in horses. There are also two papers out on KIT patterns in dogs, which is new. Before this, the piebald patterns in dogs had been mapped to MITF, which in horses is the other site for splash white. The picture above is the German Shepherd that carried the de novo mutation. (I must give a special thank you to her owner for allowing me to include it here.) I had intended to put together a longer post on this pattern, known as panda, because it touches on the subject of blue eyes in KIT mutations. She obviously has blue eyes, and her owner confirmed for me that some of her descendants have had a blue eye or blue segments in their eyes. This follows the pattern that I have seen in the historical records of some suspected Dominant White horses (also presumed to be KIT mutations). Blue eyes do seem more common in the originators, and then appear to occur sporadically – often in a less pronounced degree – in the descendants. Interestingly enough, the MITF mutations are not associated with blue eyes. In fact, this family of Shepherds was the first instance I noted where blue eyes in dogs were linked with a form of white spotting so I was particularly happy to see the mutation formally identified.

What is interesting about the new equine discoveries is that they really do not fit neatly into existing naming categories. The KIT mutations have been assigned numbers in the “W” series, but at least one appears to be subtle white-booster rather than a true dominant white. I had been urged by a couple of researchers, as I got close to my publication date, to avoid the use of the term “sabino” and just use “white spotting”, and I see now why. I suspect this will become more complicated as time goes on and more mutations are identified. One thing does seem clear, and that is that several of these sites mutate often – apparently in ways both large and small!

Just as I did with the book last year, I’ll be updating the text to reflect this new information for the new full-color supplemental book. I had feared there might not be much new information, but this coupled with some of the things I have been researching in the last few months should make for a lot more content as well as more abundant (and colorful) images!

I wanted to get pictures of one of the new horses at our barn, Dutch, to use for a post on sooty patterns. Dutch was interesting because he has the very dark forehand that some sooty buckskins get. I also thought artists that read the blog might find the abrupt transition between his body color and the black front legs interesting.

I had only seen Dutch at a distance, but I had gotten the impression he had somewhat paler-than-usual eyes. Light brown eyes are not uncommon in buckskins or palominos, so that would not have been unexpected. When I got close enough to take this picture, the reflection from his eyes looked off. (All the images in this post are larger than they appear, and since the details are small, I highly recommend clicking them to see the larger version.) Instead of looking pale brown, his eyes looked like the reflective gleam was in the wrong place. That is more noticeable in this face shot.

Over the years I have learned that odd reflections in the eyes sometimes mean the horse has a blue segment, and sure enough, that was the case with Dutch. Although he has no white markings at all, both of his eyes have flecks of blue. The largest one is located close to the bottom of his right eye, and is what is giving the odd reflection.

As can be seen in that photo, he has a number of blue flecks in that eye. His iris also has irregular patches of golden brown and darker brown, giving the whole eye a marbled look. Although it was more visible in brighter light, even without the light directly hitting the eye the blue areas could be seen.

His left eye had smaller flecks of blue that were much harder to capture on film. (This is the image that would most benefit from clicking, since the flecks are so small.)

He would be an interesting horse to test for splash white. So far a couple of individuals without white markings of any kind have tested heterozygous classic splash white (SW1). Perhaps Dutch carries SW1, too. It is also possible that there is some other yet-unknown cause for the blue sections in his eyes.

Anyone who has followed the results from the new splashed white tests knows there have been some really surprising results, both in how many horses test negative, and in some of the horses that have tested positive. For those of us that had been studying “classic splash” (splashed white-1) for a while, some of these were perhaps less surprising because we knew that there were blue-eyed horses that looked somewhat like splash, but that did not produce the classic pattern (what we believed to be homozygous). But even there, there have been unexpected surprises. Probably the most dramatic was the Bald Eagle family of Australian Paints. For those that have the Gower color book, this is the splashed white family that was profiled there. I would have guessed (wrongly!) that those were homozygous classic splashes (SW1/SW1) with some type of sabino patterning.

I may have another wrong guess. I have believed that classic splash (SW1) would be found in Marwaris and Kathiawaris. There are certainly horses that have the right kind of pattern. I had hoped that the test on the blue-eyed tovero Marwari above would come up positive, but she was negative. It would have been better if we could have tested one of the horses with the classic pattern like those linked, but it is not a breed with a lot of representatives in the West, so I was tickled to have any blue-eyed horse to sample.

This test coming up negative makes me wonder if those are homozygous splashed white-1 horses, or if there is another mutation that truly makes the same pattern. The Bald Eagle horses at least have some visual differences. I had a particular interest in seeing if the classic pattern (SW1) was in the Marwaris or Kathiawaris because they are so far removed from the breeds where classic splash was first documented. When Valto Klemola found and named the splashed white pattern (what would eventually be splashed white-1) in 1931, he believed it originated in the northern European breeds. It certainly is more prevalent in those breeds than anywhere else except perhaps the American breeds. Finding it in such a genetically distant breeds like the indigenous horses of India would be really interesting, since it would suggest this particular splash mutation is very old.

My friend’s blue-eyed mustang Jag also tested negative for all three splashed patterns and for frame. He has been pictured on the blog before, but here he is again.

It will be interesting to see how many of these horses have splash-type mutations (MITF or PAX3), or if they have unrelated mutations that also happen to give horses blue eyes.

 

As I posted briefly yesterday, the new paper on splashed white had a lot of surprising information, not the least of which was the horse pictured in yesterday’s post. A number of people wondered about his identity, and most particularly about his breed. His name is Apache du Peupe, and he is a four year-old Freiberger. The Freiberger is also called the Franches-Montagne, which sometimes leads to confusion. The horses in the picture above (courtesy of Wikimedia Commons) are quite typical examples. Freibergers are among the last of the European light draft breeds, though in more recent years many breeders have focused on a slightly lighter riding type, which is why I choose to shift them – and a few others, like the Frederiksborg – to a later volume rather than include it in the draft and coaching breeds.

Because they were originally included in the upcoming volume, I had looked into the range of colors in the breed. Apache came to my attention during that time. Freibergers were already interesting because they had a well-documented family of dominant whites. Those trace back to a white mare, Cigale, born in 1957. She was the source of what eventually became the first formally identified dominant white mutation. Hers is the mutation that got the designation W1. That is what I thought Apache was, until I realized that he was not related to Cigale. In fact, his parents did not look all that different in color from the two horses pictured above.

Here he is again, from yesterday’s post:

This is his sire, Noble Coeur. This is his dam, Muscade. Both are clear bays with socks and minimal face markings. Apache and his parents are the kind of horses that sat in my “don’t fit the theory” file when I first wrote about maximum sabinos (sabino whites) in the 1990s. The horses that did fit that theory turned out to be Sabino1, the spotting pattern that results in a white horse when homozygous. All the horses that fit the theory had parents with a high number on my ranking scale for white markings, while most of the horses in the “don’t fit” file had parents that fell short. Typically they did have some white, but it was a stretch to say they were marked like the others. Had Apache and his parents come along at that time, they would have ended up in that same file. Many of the horses there (R Khasper, White Beauty, Puchilingui) were later identified as dominant whites.

So I wondered if Apache was another new dominant white mutation. But there was another aspect to him that made me wonder, and that is why – up until yesterday when he appeared in the splashed white paper – he was in my “mystery” files. If you look closely at his picture, he looks diluted. If he were a Paint horse, or almost any other American stock or gaited breed, I would assume he was buckskin. Here are more pictures that give that impression.

Cantering (with is spin visible to show no dorsal stripe)
Conformation (quite current, shot in 2011)

That was what was so unusual about him. His parents are, as the links show, quite ordinary bays. And even allowing for the fact that he probably has a good portion of white hairs mixed in his coat, the tones give the impression that the actual hair is diluted. His owners called his unusual color “macchiato”, for the coffee drink, which suggested that he was cream-colored in person. Since his parents were not diluted, and since I had no evidence that cream (or any other dilution) was present in the Freiberger, I wondered about the accuracy of his pedigree. Pattern mutations do appear, but a pattern and a dilution all in one horse?

And now with the publication of the splashed white paper, we know that is exactly what he has: a mutation that is both a dilution and a white pattern. Researchers parent tested him using 13 markers, confirming that he really was the offspring of the parents of record. What’s more, they tested blood, hair roots and sperm to rule out mosaicism. Mosaics are animals that have two separate sets of cells with different genetic coding. Horses that are patched with black and chestnut, for example, are mosaics. Apache is, genetically speaking, all one horse with the same genetic makeup throughout his body. They also looked at the genes currently known to produce dilutions, and found nothing out of the ordinary. So he’s not a cream, a silver, champagne, pearl or dun. He is what is called a de novo mutation – something new.

The new thing that he has is a mutation at the same location as splashed white, which is the MITF gene. The color Apache’s breeders named Macchiato is a form of splashed white. Technically that makes four identified splashed white patterns, although researchers declined to name his SW4, perhaps in deference to what his breeders were already calling the color. So far the other MITF mutation for which we have numerous examples to study, SW1, does not seem to have the diluting component. The third, SW3, is said to be rare and none beyond the two horses pictured in the paper have come to light so far. Neither of those two horses appear diluted, but two is not a lot of data, especially when one is too white to really evaluate base color on anyway.

But what is interesting is that Apache’s mutation has a human equivalent. The human Tietz Syndrome is caused by a similar mutation. The Office of Rare Diseases Research describes Tietz Syndrome this way:

Tietz syndrome is a genetic condition characterized by profound hearing loss from birth, fair skin, and light-colored hair. This condition is caused by mutations in the MITF gene.

A second human MITF mutation causes Waardenburg Syndrome. Again from the Office of Rare Diseases Research:

Waardenburg syndrome is a group of genetic conditions that can cause hearing loss and changes in coloring (pigmentation) of the hair, skin, and eyes.

So a similar mutation in human beings causes pale hair, piebald patches (in the Waardenburg Syndrome) and pale eyes. It also causes deafness, which was also true for Apache, who tested to be deaf.

That raises the question of whether or not other as-yet-unidentified splashed white patterns might not have a dilution component like that seen in Apache. Certainly several of the horses from the Bald Eagle line have a very similar base color to Apache du Peupe. I had assumed that, being stock horses, the were getting their diluted color from the other parent. It would certainly be worth looking at the members of that family to confirm that those with diluted base colors actually had a diluted parent. That isn’t something that ever would have occurred to me to look for, because “dilution” and “white pattern” were completely separate categories of colors up until yesterday. As I said, it is an exciting time to study horse color, because there really is something new to learn all the time!

So that’s three of the four mutations. Someone probably noticed that one got skipped. That is SW2, and if Macchiato complicates how we categorize mutations, that one complicates how we are naming them. I’ll open that can of worms in the next post!

The long-awaited splashed white paper has now been published in PLoS Genetics. The full article can be read here.

As a number of people predicted, the MITF gene is involved, but there are also some surprises. One of them is that the authors looked into the odd case of the Freiberger stallion, Apache. Above is his picture from the paper, and the link from his name will take you to a site with more pictures. His owners called his odd color and pattern “macchiato.” He’s been in my “mystery” files since I first stumbled across him a year or so ago, so I was tickled to see that he was included in the paper.

It will take me a day or so, but I will try to put up a plain English summary of the paper. It is an exciting time for those of us interested in animal coloration!

More information keeps coming in from the new Splashed White tests being offered by UC Davis. Horses that have tested positive for the second version of the splash mutation (SW2) have been identified. Only a few have been made public,  but links to those have been added to the Splashed White Project page. So far the positive results have been consistent with the rumor that the SW2 mutation is present in the Gunner line of Paint Horses.

For many, the biggest surprises with the new tests have been how many horses have tested negative. I had suspected that might happen, because I knew that blue eyes were not a reliable indicator that a horse could or would produce the classic pattern. Finding horses without the classic pattern testing negative was something I expected. What I didn’t expect at all was to find horses that tested negative with the classic pattern. And now that is exactly what has happened.

Those that have read Jeanette Gower’s book Horse Color Explained may remember the Australian splash line of Bald Eagle. Several horses from this family are pictured in the book, and more can be seen at the Dunsplashin Stud website. They have classic splash patterns, but so far they have all tested negative for all three genes. What is even more interesting is that, speaking to breeders, it is clear that this particular family show this pattern with just one copy of their gene. Unlike the SW1 mutation, which presents as a classic pattern when it is homozygous, the Bald Eagle horses have the classic pattern – and produce it – with only one gene. One breeder stated that it was thought that the color was homozygous lethal, which is what is thought to be true of SW2 and SW3.

With each new pattern test, it becomes more clear that there are a lot more pattern mutations that previously understood. Because the Bald Eagle line is a sizable family, it seems likely that their mutation – which may be unique to them – will be identified in time. But the discovery that they look so much like the SW1 horses, yet have some other mutation, is another sign that we probably have a lot more patterns than was previously thought, and a lot of them probably look a lot alike.

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