Appaloosa leopard-complex test

[Arne]

A new DNA test will be available soon for Appaloosa or leopard-complex coat pattern. A disorder known as congenital stationary night blindness (CSNB) a condition making it difficult or impossible to see in relatively low light has been directly linked to the leopard complex in Appaloosa horses. DNA test for the LP mutations can also provide clear information as to CSNB.

Thanks and Please contact Animal Genetics for additional information coming soon.

 

[Becky]

Thanks so much, Arne, for the information. That's great news for appaloosa breeders!

 

[cretahillsgal]

I know Diana Gilger with Mystic Rock Minis in Yukon just had her little stallion tested and he came back homozygous.

 

[Arne]

Yes, her stallion tested Homozygous positive this week. It helped explain why her stallion did not venture from the barn at night.

 

[Bonny]

Yes, her stallion tested Homozygous positive this week. It helped explain why her stallion did not venture from the barn at night.

I assume your from Animal Genetics???

Has this stallion been tested for CSNB? If not then why are you assuming he has it? Do all homozygous appaloosa have CSNB? Does the owner know your posting her results on a public forum as well as posting possible incorrect information about her stallion?

 

[Kim~Crayonboxminiatures]

CSNB is linked with homozygous LP, so if you have a horse that is homozygous for LP, they have CSNB. It's been published in the last 2 yrs or more?? by reserachers with The Appaloosa Horse Project.It's not "new" it's seems new because now with the test it is possible to confirm that an appaloosa is for sure homozygous for LP where before it was "guessing" by their parentage and pattern.

 

[Bonny]

After I posted I did read, and its over 90% (which is very high %) that homozygous appys have CSNB, and that they can have varying degrees of CSNB. Also with out having the horse tested, its not known for sure if the horse is night blind to a degree. Probable, to varying degree but not 100%.

I just find it odd that someone from a lab would confirm / deny private information on a public forum when you need a password to get your own results from them.

 

[HGFarm]

I dont understand.... how did the neighbors Morgan mare have this then? And why aren't ALL homozygous Appies showing blindness then?

 

[Bonny]

Other horses can also have CSNB. The findings in the appaloosa are related to the homozygous LP/LP.

I think I understand that almost all (90% of homozygous ) have it but its to varying degrees, so one may have more night blindness than another.

 

[HGFarm]

Here is an interesting article on this condition.... it appears that it can be sex linked and some horses are carriers and some not. CSNB has two types, complete and incomplete. Incomplete can have varying degrees from mild to a lot.

So, which type do the horses supposedly have? Is it X linked or autosomal from other genes? Have the parents been tested? Who is the carrier and how is it being passed on?

How interesting. Which lab is verifying this work on the horses? How many have been tested? Have the horses actually been tested specifically for this retinal disorder and verified by which lab? There are many other reasons for night blindness of varying degrees.

http://ghr.nlm.nih.gov/condition/x-linked-congenital-stationary-night-blindness

 

[Bonny]

This article is from the appaloosa project. It explains the finding and the information about CSNB in the appaloosa horse.

http://www.appaloosaproject.info/index.php?module=pagemaster&PAGE_user_op=view_page&PAGE_id=31

The test:

"To test for CSNB a horse must be dark-adapted or kept in a dark environment for several minutes. This will increase the sensitivity of the rod pathway. When light is flashed into the dark-adapted eye the electrical response in a horse with CSNB has a characteristic appearance that is termed a “negative ERG”. This negative ERG is different from that of a normal horse.

"At present, the only way to confirm the diagnosis is by an ERG exam. ERG stands for electroretinogram. This test is performed by a veterinary ophthalmologist – a regular veterinarian cannot do it, nor can an ocular exam alone reveal that CSNB is present. This is because the eye structure is normal when examined. In other words, all the parts are there, it is an aspect of the electrical function of the rods that is abnormal.

Also:

Inheritance of CSNB:

To be affected by CSNB, a foal must inherit two dominant copies of LP. If both parents have LP, there is a chance they’ll produce a night-blind foal. This varies depending on the genetic status of the parents. Spotted horses are heterozygous for LP, so they have a 25% chance to produce a night blind (LP/LP) foal when they are crossed on each other. For more examples and related information, see the Mendelian diagrams on the "Inheritance of CSNB" page.

 

[Arne]

I assume your from Animal Genetics???

Has this stallion been tested for CSNB? If not then why are you assuming he has it? Do all homozygous appaloosa have CSNB? Does the owner know your posting her results on a public forum as well as posting possible incorrect information about her stallion?

Sorry, Yes my name is Dr. de Kloet and I'm with FSU and Animal Genetics. I only responded to another posting about the horse earlier. I am not very familiar with the forum process. Degrees CSNB have been directly linked to LP in homozygous horses. More then 500 horses have been tested.

 

[ohmt]

Inheritance of CSNB:To be affected by CSNB, a foal must inherit two dominant copies of LP. If both parents have LP, there is a chance they’ll produce a night-blind foal. This varies depending on the genetic status of the parents. Spotted horses are heterozygous for LP, so they have a 25% chance to produce a night blind (LP/LP) foal when they are crossed on each other. For more examples and related information, see the Mendelian diagrams on the "Inheritance of CSNB" page.

If a horse can only be affected by it if inherited from BOTH sire and dam, then the gene cannot be dominant.

Here's a little something I found while reading up on this (this is an older article though):

In a study of 30 horses by Sandmeyer et al (2007) all 10 horses homozygous for LP were affected by CSNB, while none of the heterozygous or homozygous lp horses were affected (so that the LP allele is recessive for this character). In the expression study (Bellone et al, 2008) the average expression levels of TRPM1 in the retina of homozygous horses (LPLP) was only 0.05% of the level found in the other horses.

Although the exact roles of TRPM1 in patterning and night blindness aren’t yet established TRP proteins in general are thought to have a role in controlling intracellular calcium ion concentration. Decreased expression of TRPM1 in the eye and the skin may alter both cell signaling and melanocyte function (another example of a gene showing pleiotropy). The mechanisms of action are yet to be determined.

(info from http://www.horse-genetics.com/Appaloosa.html)

So it seems as though the low expression of TRPM1 proteins in homozygous LP horses is what is causing the night blindness. I wonder what more recent studies on this have been...