What is lethal white? - Page 4 - The Horse Forum
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post #31 of 35 Old 09-22-2011, 09:24 AM
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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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post #32 of 35 Old 09-22-2011, 10:09 AM
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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.

Last edited by alforddm; 09-22-2011 at 10:15 AM.
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post #33 of 35 Old 09-22-2011, 01:41 PM
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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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post #34 of 35 Old 09-22-2011, 02:10 PM
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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.

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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post #35 of 35 Old 09-22-2011, 07:43 PM
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Thanks for the correction guys. Good to know how it actually works.
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