# What is lethal white?



## Day Mares (Jul 16, 2011)

My friend has a lovely paint colt who she intends to breed with her mares when he is older.  But I'm wondering....

Apparently his sire tested as having no lethal white gene or somesuch but he (the now colt/soon stallion) has not been tested himself yet. She decided not to have him gelded on sire's pedigree.

What is it (how does it manifest in offspring) and is it something that should be known before she breeds from him? I mean is it lethal? Does it affect quality of life of horses who have this gene?

Any replies appreciated. :?


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## NdAppy (Apr 8, 2009)

Lethal white (or frame overo or OLWS) is for all intents are purposes what is it named. A horse can have one copy of the OLWS gene and be fine (heterozygous for frame). A horse only is lethal if is carriers two copies (homozygous for frame) 

You have to have horses with one copy in order to get horses that look like this - 










The problem is, when you breed two OLWS carriers together you have a 25% chance of producing a lethal (or homozygous for rame overo) foal. The foal will not survive past 72 hours and if not humanely euthinzed, it will die a horribly, horribly painful death. 

Horse can carrier the frame overo/OLWS gene and be completely solid. It is a good idea to test any horse of QH or APHA breeding to be sure of the frame overo/OLWS status before breeding.

This is a great website with lots of facts about OLWS. OLWS


I am not even going o go there with the foolish reasoning of breeding off the sire's pedigree alone... All I can say is I hope that your friend does her research and unless the colt is absolutely spectacular, that she gelds him. There are more than enough average stallions out there without adding more.


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## bubba13 (Jan 6, 2007)

Yes, it's lethal--hence the name lethal white. And even with a "clear" sire, he should still be tested, as he can still be a carrier. Either he or the mare MUST be tested and negative if you don't want to risk the heartbreak. Breed two carriers, and you've got a 25% chance of a suffering and dying foal.


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## alforddm (Oct 1, 2010)

Lethal White Overo: What you should know | Color Genetics


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## waresbear (Jun 18, 2011)

Breeders of the desireable Overo Paints live with the lethal white factor. Foal is born, lives for a day, then dies. Nothing can be done to save it. I have witnessed one lethal white. Was told by the farm owner it was the price she pays for the more desireable overos. That was a while ago, I don't know if things have changed, pretty sure the lethal white foals still die.


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## Dreamcatcher Arabians (Nov 14, 2010)

Waresbear, they don't have to be dying anymore. I have overos and I know who carries the OLWS gene and those horses never get bred to each other. It's only when both parents are carriers and both throw the gene that the foal dies, obviously neither parent is homozygous for it or they'd both be dead too. I breed the OLWS horses to either a tobiano or to a clear solid breedstock horse. If only one horse is carrying the gene, only one can pass it on and the foal will not die, at worst it will be a carrier.

I bought this young lady (an OLWS carrier) 









To be bred to this colt (a sabino who tests clear)as soon as both are old enough:









There's no way a foal of theirs will die and I have at least a 50/50 chance of color with this mating. Even if the foal ends up breedstock, it'll be a very good looking and athletic horse. There doesn't have to be a deadly downside anymore if you're careful in the matings.


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## waresbear (Jun 18, 2011)

This breeder had a stallion who carried the lethal white gene (I own him now, he's a gelding), he's sired some expensive babies (one for sold for $60,000) and she bred him to outside mares but she also bred him to her own mares. After the lethal white, I asked her why she was breeding the same mare back to him. She said all better bred overos carry the lethal white gene, her next foal from the same mare was a solid. By the way, the mare that had the lethal white was solid as well. She told me no tobianos carry that gene, only solids & overos. I don't know, just what I was told by someone who paid me to ride & show their horses, I wasn't going to argue.


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## bubba13 (Jan 6, 2007)

To clarify, though, even solids and tobianos can be LW carriers, and thus must be tested negative before being bred to another carrier. You breed two carriers together, regardless of their base color or apparent pattern, and you've got one if four odds of a lethal foal....and it's true that no vet can save them. They colic and die or you euthanize them. The gastrointestinal tracts is malformed and incomplete, as the same gene that controls the color also has a role in GI development.

And RESPONSIBLE breeders know how to get the overo color without risking dead babies.


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## Dreamcatcher Arabians (Nov 14, 2010)

"And RESPONSIBLE breeders know how to get the overo color without risking dead babies."

That's just it, responsible breeders test their stock. I even test my Arabians who carry the Sabino gene as that's an overo trait. I've not had a purebred Arabian test positive for the OLWS gene but if I have the negative results then I don't have to worry about crossing my half arab who does carry the OLWS gene on that particular horse.


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## EthanQ (Sep 5, 2011)

what about it kills foals?


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## bubba13 (Jan 6, 2007)

^



bubba13 said:


> to clarify, though, even solids and tobianos can be lw carriers, and thus must be tested negative before being bred to another carrier. You breed two carriers together, regardless of their base color or apparent pattern, and you've got one if four odds of a lethal foal....and it's true that no vet can save them. *they colic and die or you euthanize them. The gastrointestinal tract is malformed and incomplete, as the same gene that controls the color also has a role in gi development.*


_______________


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## Day Mares (Jul 16, 2011)

*I guess that's why it's called lethal*

Thanks for the replies and info - I will go look up the sites recommended and report back to her accordingly. Her experience is with race horse studs.

*gasp* it's not only Paints and QHs that carry this gene? :shock: 

She is planning on breeding him to her paint mares next season (all 3 tested negative for OLWS) but I feel that she needs to know one way or the other. Particularly as she has TB mares too!

He is a bay overo I think. Um, so do all overos carry the gene??? No don't tell me I'll go find out!

Thanks again.


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## blue eyed pony (Jun 20, 2011)

You want to find out yourself but this is for anyone else who may be reading for their own information.

Lethal white IS the frame gene. Not all overos have it (splash and sabino are overo genes too). A horse that appears frame is not necessarily such, as sabino and splash can and do appear in the same horse, and they clash to create patterns that LOOK like frame.

I thought my filly was negative by default of colouring but after reading this thread I think I'll have her tested if I want to breed. That being said I will probably breed her to something of a breed that doesn't have the gene simply because that is where my interest lies. Always best to be safe though and I would HATE to breed a carrier that then got bred on and had a lethal white foal.


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## alforddm (Oct 1, 2010)

Overo basically means "not Tobiano" so, not all overos are LWO. Frame, Splash, and Sabino are all lumped together as an overo by the APHA. Personally I prefer to drop the Overo and designate each pattern for what it is Frame, Splash, and Sabino. Each is a separate pattern and they are NOT related to each other except by virtue of not being Tobiano.

I did want to note a few things. 1)Frame can be present alone or with any of the other patterns. For example, it is possible for a horse to carry all four patterns. So just because you have a Tobiano doesn't mean it doesn't also carry Frame. Please test before breeding to an untested or Frame (LWO) positive horse. 2)Although an all white foal is most likely homozygous for Frame, it is also possible for a foal to be born all white and NOT be homozygous. Such foals should be tested (by rush order) for LWO and monitored closely but not automatically euthanized. An all white foal that is not homozygous for LWO could carry more than one pattern or be Maximum Sabino or Dominant White. 3)Unless a fence jumping is involved Arabians do not carry Frame (ie LWO).


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## Dreamcatcher Arabians (Nov 14, 2010)

alforddm said:


> 3)Unless a fence jumping is involved Arabians do not carry Frame (ie LWO).


Because of the SCIDS, CA & LFS genes in Arabians, rather than just assume because it's a purebred it's clear, I test. That way when I have bred to an OLWS carrier, I can show a prospective buyer (who may or may not understand the whole OLWS thing) that the carrier was only bred to a 'tested clear' horse, same way I would if I had a SCIDS carrier being bred to a non-SCIDS carrier. It's a cheap test, can be run at the same time as all the other genetic testing that needs done and can bring peace of mind to a buyer. I also test the foals of a carrier horse so that I can disclose before close of sale what that horse's status will be and I send a copy of the test results with the horse. Since a lot of Arabian people know Sabino is an Overo trait but they don't understand Frame and Splash and the other pattern characteristics, I get asked if the stallion, who is not pinto or paint, carries the OLWS gene.


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## Corporal (Jul 29, 2010)

It's very simple--lethal white occurs when you breed a foal from a low gene pool. When it happens in the wild, the animals die and then they cannot pass on these harmful genes. It's such a shame bc it's ALL about color. I guess I just don't want to participate in producing pretty horses that die bc of bred-in genetic abnormalities. So has the purebred dog world gone, and so goes the purebred horse world.
My mare,"Warren's Cindy" (KMHSA) is a breeding stock paint, all chestnut (or...er...some color of chocolate), with one brown eye and one blue eye and has been bred 4x. She has produced 2 solid foals and 2 spotted foals, and one of the spotted foals had 2 blue eyes, as well.
I also think that you can find some very nice horses whose breeders reject them bc they come out solid...like Cindy's breeder did. _(I bought her from her 2nd owner, who found value in her.)_


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## alforddm (Oct 1, 2010)

> It's very simple--lethal white occurs when you breed a foal from a low gene pool. When it happens in the wild, the animals die and then they cannot pass on these harmful genes.


The frame pattern (aka Lethal White Overo) does occur in wild (feral) horses that live and thrive. Horses with a single copy of the mutation are not affected except to the extent that they usually show a pretty white pattern. It also has nothing to do with the size of the gene pool as it occurs in many different breeds with a wide variety of genetic diversity. Affected foals can easily be avoided by testing your breeding stock and not breeding to frame to frame. As Dreamcatcher Arabians pointed out it is an inexpensive test.


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## Corporal (Jul 29, 2010)

alforddm, I appreciate that. I'm not looking to offend ANYONE. I do, however notice an increase in health problems in horses that are the result of breeding to a type or a color--it's a current trend. I'm not referring to an upright shoulder, or a straight leg or a weak back, but I think "lethal" white says it all. I just don't want anybody to breed a horse (or dog) that isn't healthy bc of the genetic mix that they intentionally choose. I guess you could say that I "campaign" against this.
I have talked to a lot of horse people, many who sternly maintain that it will be okay to breed this or that, understanding that there are documented health problems, bc they've found one specimin that didn't have it. _I'll tell you, one time was enough for me._ Here is a picture of my QH gelding, "Dandy Silver Moon." 








1987
He was a gorgeous cremmelo, great attitude and willing. He went blind at age 7. I, for one, will not EVER buy another cremmelo. I understand it's referred to as an "Isabella Palomino," and you can make out his blaze, in contrast to a dappled, ivory coat. I was stunned when my Vet discovered his sight problem, but he told me the defect was genetic. Even IF it only happens periodically, I do not think breeding this improves these horses. Again, I am sorry to offend anyone but *I get very attached to my horses*, and I cannot afford to keep one crippled by a genetic defect as a pasture-pet. OP, Please consider outcrossing your mare for the color you want.


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## Poseidon (Oct 1, 2010)

The way you're referring to Lethal white makes it sound as serious as HYPP. A horse with one copy of Frame has no issues. It's usually just a rather loudly colored horse. A horse with two copies _will_ die, but one copy is completely harmless. HYPP will have symptoms and affect an N/H horse. A horse with one copy of HYPP shouldn't be bred at all, even to an N/N horse because there is a chance that foal will be N/H and be affected. 

If you breed a OLW Positive horse to a OLW negative horse, your foal won't die of lethal white. I'm not saying it's not a serious problem, but a simple, inexpensive test will save you from breeding a dead foal.


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## jannette (Aug 24, 2011)

EthanQ there digestive system doesnt develop....colon lacks nerves to send flush colon and it becomes impacted...like cholic symptoms...very painfull death.... we just baught a mare in july that apperantly was bred back to a frame she is b/w frame...i new nothing when we baught her. now all we can do is x our fingers...not cool. breeder didnt say a word. i found out here on the forum


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## bubba13 (Jan 6, 2007)

Corporal said:


> alforddm, I appreciate that. I'm not looking to offend ANYONE. I do, however notice an increase in health problems in horses that are the result of breeding to a type or a color--it's a current trend. I'm not referring to an upright shoulder, or a straight leg or a weak back, but I think "lethal" white says it all. I just don't want anybody to breed a horse (or dog) that isn't healthy bc of the genetic mix that they intentionally choose. I guess you could say that I "campaign" against this.
> I have talked to a lot of horse people, many who sternly maintain that it will be okay to breed this or that, understanding that there are documented health problems, bc they've found one specimin that didn't have it. _I'll tell you, one time was enough for me._ Here is a picture of my QH gelding, "Dandy Silver Moon."
> 
> 
> ...


In the picture, which I realize could be misleading, that appears to be a pale palomino, not a cremello. But neither color is associated with eye or blindness issues. Correlation does not equal causation, and to refuse another horse of that color (no matter which) is, no pun intended, extremely short-sighted.

It's not a sign of inbreeding or man-manipulated genetics, either. Appaloosas actually _are_ very much prone to a myriad of serious eye issues, yet their pattern has existed in the wild for millenia.


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## Dreamcatcher Arabians (Nov 14, 2010)

jannette said:


> bred back to a frame she is b/w frame...i new nothing when we baught her. now all we can do is x our fingers...not cool. breeder didnt say a word. i found out here on the forum


 
Breeder's who do these things and do not disclose are the scum of the earth. Notice they sold the mare on so that if the foal is OLWS and dies THEY don't have to deal with the heartache! That just burns me right up. It's wrong on so many levels I can't even start to enumerate them. I'm sorry someone did this to you, without making sure you had all the info you needed to make an informed decision.


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## jannette (Aug 24, 2011)

thanx dreamcatcher, i was raging mad when i found out:evil:....she informed us she has been in business for years and never had problem blablabla...she offerd to buy mare back but she's great girl and i wont do that to her regardless, not her fault. she has good home now....and i make sure anyone i know, knows what her practice is. my horses are more then livestock theyre my babies so im just hoping for the best


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## CessBee (Dec 6, 2008)

Ok, I am making the assumption here that LW must be found very near the gene loci of the colouring that is associated with. That would explain why it is possible for there to be solid coloured horses which carry the mutation.

I like genetics haha and am just spit balling ideas here.

It is not as bad as HYPP because of the fact that if the horse is homozygous for the gene it is dead, unlike with HYPP which if I am not mistaken can have hidden symptoms which do not show up. And is easily managed if the right precautions and study is done before the breeding takes place.


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## Day Mares (Jul 16, 2011)

Okay. Now I have to go look up HYPP, unless anyone wants to enlighten me?


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## blue eyed pony (Jun 20, 2011)

I don't know a huge amount about it but it is a genetic problem with the muscles that can cause seizures. It's been traced back to the stallion Impressive. It's believed to be incomplete dominant which means that if a horse has one copy of the gene it is still affected, but if it has two copies it is MUCH more seriously affected.

Responsible breeders and QH/paint associations around the world are trying to stamp it out without losing the bloodline as it consistently seems to breed a highly desirable type.

I actually don't know what HYPP stands for though :\ probably some really technical scientific thing that makes no sense to most people anyway.


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## Poseidon (Oct 1, 2010)

Hyperkalemic Periodic Paralysis
Horse HYPP

I can't remember because it's almost 3am, but I think the AQHA requires a horse to be tested before registered if it has Impressive lines. If the world were truly a perfect place, people would only be breeding N/N horses and the disease would be bred out. However, they don't. There was a catalogue of QHs in the office at my barn. The cover had 6 foals on it, two were N/H. _On the cover._ It seems that they try to justify breeding N/H horses because some don't obviously show symptoms of being affected.


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## alforddm (Oct 1, 2010)

> Ok, I am making the assumption here that LW must be found very near the gene loci of the colouring that is associated with. That would explain why it is possible for there to be solid coloured horses which carry the mutation.


No, frame is located on _EDNRB _which is also responsible for Waardenburg Syndrome in humans which is known for white patches of skin as well as other more significant problems. 

Every other white pattern can also be found in minimal form. This thread as some pictures of some VERY minimal tested Tobianos. 
Check out this tobi tail! | Equine Color Genetics


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## bubba13 (Jan 6, 2007)

The frame gene IS the lethal gene. They are one and the same. And frame is not the only white pattern that is lethal in the homozygous form. All the variants of dominant white are, as well.


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## alforddm (Oct 1, 2010)

bubba13 said:


> The frame gene IS the lethal gene. They are one and the same. And frame is not the only white pattern that is lethal in the homozygous form. All the variants of dominant white are, as well.


This is indeed correct. The difference, for those who may not know, is that DW is embryonic lethal very early in the pregnancy with the mare generally being able to be re-bred the same season. It doesn't result in a live foal that dies soon after birth.


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## bubba13 (Jan 6, 2007)

In some cases, doesn't it, depending on the variant? It's been awhile since I read the paper, and I don't have time to look it up now--could be wrong, but I thought there were occasional cases that mimicked lethal (frame) white almost exactly.


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## alforddm (Oct 1, 2010)

There was a case of a foal that was born with a new DW mutation that died a few weeks after birth. He however was heterozygous for the mutation. The researchers thought that the death may have been related to the mutation but weren't able to say for sure. 

De novo mutation of KIT discovered as a result of a non-hereditary white coat colour pattern - Holl - 2010 - Animal Genetics - Wiley Online Library

Here is the link to the paper. As far as I know there are no incidents of homozygous DW foals being born. Although, what may happen when you breed two different types of DW together hasn't been ascertained. For example, no one knows what may happen with a W2 x W4 breeding. The researchers couldn't say for sure and there hasn't been enough cross DW mutation breeding to know for sure.

I just wanted to add that if you find a born live homozygous DW I would be thrilled to get more information.


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## bubba13 (Jan 6, 2007)

OK, I may have been mistaken, or at least the answer is unknown. Of interest: PLoS Genetics: Allelic Heterogeneity at the Equine KIT Locus in Dominant White (W) Horses

Some tidbits:

A complete loss of function of KIT causes prenatal *or perinatal* lethality due to anemia.

Many _KIT_ regulatory mutations exist that produce severe pigmentation phenotypes in the heterozygous state. However, some of the murine structural mutations, such as the _KitW-42J_ mutation, also lead to an almost complete depigmentation in the heterozygous state. In the mouse, mutations causing a pronounced dominant depigmentation phenotype typically also lead to mild anemia and reduced male fertility even in the heterozygous state.

In horses, dominant white was reported to cause embryonic lethality in the homozygous state [4]. However, this report on the embryonic lethality was derived from the analysis of offspring phenotype ratios in a single herd segregating one or more unknown mutations. As there is now evidence for allelic heterogeneity, it remains to be proven whether all equine dominant white mutations cause embryonic lethality in the homozygous state. While this is certainly likely for the two nonsense mutations found in Franches-Montagnes Horses and Arabians, it should not necessarily be assumed for the two reported missense mutations or for any of the other as-yet unknown _W_ mutations.


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## alforddm (Oct 1, 2010)

Here is a very good article on DW That talks about the more recently discovered mutations and also discusses the possibility of viable homozygous offspring. 
http://duncentralstation.com/PDF/KITGeneMutations-Castle.pdf

There is also this paper which is referenced in the above article. I haven't been able to read it as I don't have access. =(
Seven novel KIT mutations in horses with white coat colour phenotypes - Haase - 2009 - Animal Genetics - Wiley Online Library


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## CessBee (Dec 6, 2008)

Thanks for the correction guys. Good to know how it actually works.


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