Lethal White Syndrome

[JB]

Define “undesirable” LOL

People absolutely breed specifically for HYPP, which to most of us is highly, highly UNdesireable. But because those idiots think it will give them a horse with the steroid-looking musculature, which to them is desirable (and most of the rest of us think is fugly), they specifically breed for the nH horses :no:

I THINK Ghazzu was talking about HERDA, as I think that was the last thing I was talking about (but we have jumped around various mutations now I’m not sure anymore LOL). Someone mentioned a possible increase in elasticity, ie “supple horses” who are hetero HERDA - that might be a desirable trait, but how about just breeding quality horses? How about good training? More elasticity in ligaments or tendons is not always a good thing.

There is no aesthetic benefit to hetero HERDA horses. There may be a functional benefit but it can’t remotely be worth keeping that disease around

Frame/LWO obviously has the aesthetic benefit for certain color breeders, particularly the Paint breeders. Because of testing, it’s 100% possible to avoid ALL LWO foals, and there are no health issues with the hetero Frame horse.

[oldernewbie]

[QUOTE=FayeHanoverian;6858652]
The only thing positive this trait that it’s linked to is the paint frame coloring, which has been selected by humans. It’s a huge problem when people who don’t understand that we are putting animals under selective pressure that isn’t necessarily good for the animals, and instead assume that because a trait occurs it must be associated with a desirable traite. These traites aren’t usually associated with positive traites, they simply carried because breeders are inbreeding horses and not culling horses who care bad genes because often this horses have positive traites as well (this does not mean the two traites HAVE to be link, it only means they are both present in the parent). This does NOT have to be the case. It’s not an issue where the traites are tied to good traites. The mutation is tied to a developmental issue which creates incorrect development, incorrect development is what causes the pretty pattern that humans like. If both versions of the gene are incorrect one can’t compensate from the problem in the other so you see a damaging condition. One gene compensating for the lack of function in an other typically isn’t going to be a positive thing. Sickle cell is a very rare cause where this is positive since it is harder for the parasite to infect, this is NOT the normal case with carriers. In LW it’s actually unusual in the sense that carriers have what humans consider a positive traite. In most cause the traite is simple not bad in carries because one copy of the gene can compensate for the problem in the other gene NOT because there is something good about being a carrier.

It’s very very important to remember that humans are selecting for traites, these traites can be bad or good. Because they occur does not mean they are somehow associated with positive traites! More often then not they are breeding mistakes.

Here’s a good paper about LW. http://hmg.oxfordjournals.org/content/7/6/1047.full.pdf[/QUOTE]

I don’t disagree totally with what you are saying, but think it is a bit more complicated. Putting aside HYPP, which is a fairly recent mutation whose source and time is known, a lot of these other genetic problems are likely long standing. Before genetic testing was even known, or even before genes themselves were even known, humans were breeding for positive traits. But they had no way of knowing that there were any negative traits associated with those positive traits, so how could they be breeding for the negative ones? I am thinking of genetic defects in Arabs, who have been selectively bred for a very long time, most of which time was in the days when the mechanisms of genes etc were not possibly understood.

So I agree that modern day breeding may be introducing or perpetuating more negative traits, but I don’t think you can say definitively that these negative recessive genes never have any positive traits associated with them.

And I"m still somewhat baffled by throwing every horse out of the breeding pool just because they have a recessive gene, which can be tested for and bred around.

[eqsiu]

Forgot about HYPP. :no: ETA: humanity. we suck.

As for HERDA and elasticity, Ehlers-Danlos is painful and horrible in humans, but caused by several genes, some of which are dominant. Does anyone know if heterozygotes for the recessive forms have some sort of mitigated symptoms? I really doubt that hyperelasticity could ever be a good thing in horses. picturing knees snapping backwards and other gruesome things Suppleness is not the same!

[phanilah]

Re: HERDA - although heterozygotes aren’t “affected” there is a belief by “some” that the heterozygous state brings with it increased elasticity over horses who do not carry a copy of the mutation. Since it isn’t taken to an extreme, that increased elasticity (perceived or real) is thought by “some” to help with events that require a lot of mobility.

Unfortunately, a belief like this (especially if there are carriers who seem to support the theory) can be a great influence to people who are more interested in the “end point” and not the “means to get there”.

Beth

[Ghazzu]

[QUOTE=FayeHanoverian;6858652]
The only thing positive this trait that it’s linked to is the paint frame coloring, which has been selected by humans. It’s a huge problem when people who don’t understand that we are putting animals under selective pressure that isn’t necessarily good for the animals, and instead assume that because a trait occurs it must be associated with a desirable traite. These traites aren’t usually associated with positive traites, they simply carried because breeders are inbreeding horses and not culling horses who care bad genes because often this horses have positive traites as well (this does not mean the two traites HAVE to be link, it only means they are both present in the parent). This does NOT have to be the case. It’s not an issue where the traites are tied to good traites. The mutation is tied to a developmental issue which creates incorrect development, incorrect development is what causes the pretty pattern that humans like. If both versions of the gene are incorrect one can’t compensate from the problem in the other so you see a damaging condition. One gene compensating for the lack of function in an other typically isn’t going to be a positive thing. Sickle cell is a very rare cause where this is positive since it is harder for the parasite to infect, this is NOT the normal case with carriers. In LW it’s actually unusual in the sense that carriers have what humans consider a positive traite. In most cause the traite is simple not bad in carries because one copy of the gene can compensate for the problem in the other gene NOT because there is something good about being a carrier.

It’s very very important to remember that humans are selecting for traites, these traites can be bad or good. Because they occur does not mean they are somehow associated with positive traites! More often then not they are breeding mistakes.

Here’s a good paper about LW. http://hmg.oxfordjournals.org/content/7/6/1047.full.pdf[/QUOTE]

Well, given that color is the very last criterion I’d ever consider in making a breeding decision, it was off may radar entirely.
I was thinking in terms of the people who think that all SCIDs carriers in the Arab breed should be prohibited from breeding on.

However, simply because a homozygous OLWS is a Bad Thing doesn’t mean that all frame overos ought to be prevented from reproducing, either.

[FayeHanoverian]

While it is possible that in a few cases these traites have a positive traite linked to them in most cases it is a result of inbreeding. HERDA is cased by in of Poco Bueno lines. These lines dominate cutting horse breeding thus a lot of cutting horses have them.

Arabians that have been bred for thousands of years were inbred as well, currently the most inbred horses in the world are Egypt Arabians. People have known about the power of linebreeding for years. When you breed close together you enhance recessive traites, this does NOT mean these traites are linked genetically. However, traits that would never show up normal often appear, like mutations in key developmental genes, these mutations are pretty much never going to be good. They are so important in development that one genetic copy can compensate for their loss, however, losing both is catastrophic. These are the sort of genes that determine things like where if your GI track connects up or if your skin closed up over your spine. An example of this in another species is hemophilia. It was called the royal disease because when you linebreed humans you end up with the same sort of issues.

It’s very important to differentiate between genes that are found together and genes that are linked. Linked has a very specific meaning genetically and is not likely to occur with specific genetic conditions since the genetics of performance is very complicated and certainly not controlled by only one gene.

[Ghazzu]

[QUOTE=JB;6858719]

I THINK Ghazzu was talking about HERDA[/QUOTE]

Actually, what was on my mind was the carrier state of SCIDs, which has no deleterious effects.

[Ghazzu]

[QUOTE=FayeHanoverian;6859415]
While it is possible that in a few cases these traites have a positive traite linked to them in most cases it is a result of inbreeding. HERDA is cased by in of Poco Bueno lines. These lines dominate cutting horse breeding thus a lot of cutting horses have them.

Arabians that have been bred for thousands of years were inbred as well, currently the most inbred horses in the world are Egypt Arabians. People have known about the power of linebreeding for years. When you breed close together you enhance recessive traites, this does NOT mean these traites are linked genetically. However, traits that would never show up normal often appear, like mutations in key developmental genes, these mutations are pretty much never going to be good. They are so important in development that one genetic copy can compensate for their loss, however, losing both is catastrophic. These are the sort of genes that determine things like where if your GI track connects up or if your skin closed up over your spine. An example of this in another species is hemophilia. It was called the royal disease because when you linebreed humans you end up with the same sort of issues.

It’s very important to differentiate between genes that are found together and genes that are linked. Linked has a very specific meaning genetically and is not likely to occur with specific genetic conditions since the genetics of performance is very complicated and certainly not controlled by only one gene.[/QUOTE]

Inbreeding doesn’t cause recessive genes, it merely tends to allow their expression.
Used carefully, it can be an excellent tool, much like a scalpel.
Dangerous in some hands, useful in others.

[JB]

[QUOTE=Ghazzu;6859418]
Actually, what was on my mind was the carrier state of SCIDs, which has no deleterious effects.[/QUOTE]
Gotcha. But, it doesn’t carry any benefits either, does it? There are several genes like that - benign in the hetero state but offering nothing positive either.

[mbm]

[QUOTE=JB;6859499]
Gotcha. But, it doesn’t carry any benefits either, does it? There are several genes like that - benign in the hetero state but offering nothing positive either.[/QUOTE]

but - how do you know that? perhaps for those breeding, there are positive reasons to breed the carriers… using Connemara’s as an example: many carriers of HWSS are fantastic ponies and should not be lost… in fact some of the most well known sport Cons are carriers… and to not breed them would be a crime.

[JB]

I get it in the case of breeds that are “endangered” or just not that numerous. But the QH and the TB and the Arab? There just isn’t any good reason to breed carriers of many of these diseases.

[Ghazzu]

[QUOTE=JB;6859531]
I get it in the case of breeds that are “endangered” or just not that numerous. But the QH and the TB and the Arab? There just isn’t any good reason to breed carriers of many of these diseases.[/QUOTE]

The Arab gene pool ain’t as large as you might think.
And if you can avoid breeding carrier to carrier, why dump the other genetic variability that would be preserved?

[eqsiu]

@FayeHanoverian;6859415

An example of this in another species is hemophilia. It was called the royal disease because when you linebreed humans you end up with the same sort of issues.

NO. Hemophilia in European Royalty spread because Queen Victoria was a carrier (and thought to have been a spontaneous mutation rather than an inherited trait) and had two carrier daughters and a hemophiliac son. They in turn produced four affected/carrier individuals who then produced 8 affected/carrier individuals. No inbreeding involved in the passage of that trait. Yes, royal married royal (which is why Queen Elizabeth II and Prince Phillip are second and thrid cousins) which led to inbreeding. But the hemophilia was separate. You should have used the Habsburgs and mandibular prognathism as your example.

[FayeHanoverian]

[QUOTE=eqsiu;6859558]
NO. Hemophilia in European Royalty spread because Queen Victoria was a carrier (and thought to have been a spontaneous mutation rather than an inherited trait) and had two carrier daughters and a hemophiliac son. They in turn produced four affected/carrier individuals who then produced 8 affected/carrier individuals. No inbreeding involved in the passage of that trait. Yes, royal married royal (which is why Queen Elizabeth II and Prince Phillip are second and thrid cousins) which led to inbreeding. But the hemophilia was separate. You should have used the Habsburgs and mandibular prognathism as your example.[/QUOTE]

My thought since most of these traits are linked to a particular individual who carried a mutation, it’s very similar to hemophilia. Impressive for HVPP and Poco Bueno for HERDA. These traits are then enhanced in a particular population because the genetics of particular individuals make up a large percent of the genetics in the population. Small population plus close crossed lead to more recessive traits being expressed. I really worry when people start saying things like, these traits must be beneficial without any solid evidence.

I understand the desire to preserve genetics, however, it’s so immoral to produce animals who will suffer horribly. I don’t think I could ever be part of a registry that turned a blind eye to the welfare of the animals that are produced by their members.

Linebreeding has to be coupled with culling and careful breeding, I find it really discouraging that this doesn’t seem to be happening. I think that a careful infusion of outside genetics into small breeding populations, like the Connemaras, might help breeders preserve the genetics they want without breeding animals who suffer horribly genetic conditions. For those who know more about this issue what do you think?

[phanilah]

Is it possible to post a .pdf file in this forum?

Beth

[DawnJL]

[QUOTE=JB;6859531]
I get it in the case of breeds that are “endangered” or just not that numerous. But the QH and the TB and the Arab? There just isn’t any good reason to breed carriers of many of these diseases.[/QUOTE]

First it is important to be clear that “carriers” of recessive deleterious alleles do not carry a disease the way many viral diseases can be “carried”. “Carriers” of a recessive allele are heterozygous for an allele that is ONLY harmful in the homozygous state. With testing for specific deleterious recessive alleles, breeders can choose to NEVER produce a foal that expresses the harmful/lethal condition.

Since I believe that producing healthy offspring should be a primary goal of all breeding, I support eliminating animals from breeding populations that are either heterozygous or homozygous for any dominant deleterious alleles (like HYPP and PSSM).

I also think that it is prudent to avoid introducing deleterious recessive genes into populations where they do not currently exist. (For example in requiring Arabians to test clear for SCID, CA, and LFS as a condition for eligibility for approval in WB breeding books.) However, in breeding populations where one or more deleterious recessives exist, are distributed in the population, and tests are available – responsible breeding choices will be complicated by the existence of these alleles in some otherwise exemplary breeding animals.

As for “why” using some carriers of deleterious recessive alleles for breeding may be a better choice than immediately eliminating all such carriers:

Reason #1 relates to how massive selection against a single gene will shift the frequency of ALL genes in the population --including the real risk of other “bad” genes that may be lurking at a low frequency being increased in frequency. Here’s a cautionary tale of what happened when Basenji breeders made what seemed the most responsible choice and eliminated all carriers of a recessive genetic disorder when a test was developed: “Bad Genes”

Reason #2 is that they hypothetical scenario of “just use the horses of similar caliber that are not carriers” is sometimes belied by the cases where the most exemplary individual of a desired lineage or phenotype is a carrier. If there is no comparable substitute, then using the carrier with clear mates may well be the most responsible choice for long term breeding goals. The goal when using carriers of deleterious recessives is to breed forward the desirable traits from those otherwise exemplary carrier individuals to obtain offspring that have the desirable traits and are clear for the deleterious recessive. Since clear is a more desirable status than carrier (particularly for stallions), over time the frequency of carriers for the deleterious recessives will go down.

Reason #3 (regarding LWS in particular) The coloration that results from the expression of the LWS allele in the heterozygous state is “desirable” for some color breeders and “neutral” for non-color breeders. The homozygous state is lethal and thus undesirable ethically and economically for all. In the case of this allele, the carrier state involves expression of a trait (frame overo coloration) that is desirable within certain breeding groups so (unlike with LFS, CA, SCID, HERDA and any other deleterious recessives that do not convey an advantage) diminishing the frequency of this allele may not be desirable while NOT producing homozygous foals IS still an optimal goal. Education regarding the test and how to use it to avoid LWS affected foals is clearly needed. Enforcement of testing where possible may be useful, but dissemination of information on the LWS test and the consequences of NOT testing is essential to raising awareness and changing the paradigm. The desirable coloration can be bred for while also avoiding LWS affected foals, but responsible choices require knowledge and implementation of the test as a management tool!

Since this is the sport horse breeding forum, note that if breeders who selectively breed using a carrier of one of these testable recessive deleterious genes are breeding for performance horses, carrier offspring are perfectly healthy and can me marketed as performance horses which supports the goal of diminishing the frequency of carriers in the breeding pool over time while minimizing the risks associated with a massive purge of carriers of recessive deleterious traits from the breeding population.

Having genetic screening tests is a fantastic tool for avoiding producing afflicted offspring as a primary goal while preserving genetic diversity of GOOD traits.

The landscape definitely changes when breeders have the ability to screen breeding stock for deleterious recessive genes. I suspect that Friesian breeders would love to have tests for hydrocephalus and dwarfism.

As a breeder of Arabians I can say that having tests for the SCID, CA, and LFS mutations provides HUGE peace of mind because it gives me the power to TOTALLY AVOID ever producing a foal that is afflicted with any of these horrible conditions and allows me to choose whether or not to breed any carrier to clear matches. In an ideal world, I could make all my dream matches without using any carriers, but I am grateful that the test allows me to consider the use of a carrier with a clear mate if that match is otherwise a path to forwarding long term breeding goals. I wish all heritable traits were so simple to manage!!! Knowledge is power; these tests empower breeders to make responsible, informed breeding choices and should be utilized for the good of the breed(s).

[Dazednconfused]

[QUOTE=JB;6859499]
Gotcha. But, it doesn’t carry any benefits either, does it? There are several genes like that - benign in the hetero state but offering nothing positive either.[/QUOTE]

Well, I have no science to back this up, which usually isn’t my style. But some of the Arab breeds most beautiful individuals have been carriers of SCID (and CA for that matter), particularly with SCID, they often seek to be particularly exceptional individuals. This is only a big picture observation on my part (I’m thinking Tornado, Nariadni, Versace, and the Real McCoy off the top of my head). This is not to say that all SCID carriers are exceptional, but the frequency appears to be heightened at least IMHO.

[rmh_rider]

Ok, since we are talking about the lethal white, I see a stallion advertised, and he is a descendent of Impressive.

I see he is advertised with the phrase:

HYPP - N/N, OLWs - Pos.

I know what the HYPP means, but my question is what is the “OLWs - Pos.” mean??

He is a palomino overo. Has the typical Impressive halter body btw. He is advertised on a stallion auction roster, so I would believe all wording would be correct with regards to spelling, etc.

[skydy]

He carries the lethal white gene.

[Laurierace]

[QUOTE=skydy;6864251]
He carries the lethal white gene.[/QUOTE]

Which if I understand correctly, isn’t a “bad” thing, right? It just is what it is and one needs to be certain he is never bred to a mare who also carries the gene, right? Unlike HYPP.