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Discussion on Anterior Segment Dysgenesis (ASD) in horses | |
Author | Message |
Member: Lschultz |
Posted on Saturday, Jun 21, 2003 - 11:04 am: I am considering the purchase of a 9-yr.-old Rocky Mountain Pleasure gelding, and have a lot of horse experience, but no experience with genetic ocular abnormalities. The seller is reputable, and has been open about the cysts on the eyes, and that they cause no problems for the horse. Due to the remote location of their farm, the odds are that finding more than one local vet to vet the animal are minimal. Any pointers? My vets are not well-versed, as there are no RMHs around here. |
Moderator: DrO |
Posted on Sunday, Jun 22, 2003 - 10:12 am: Since the animal is a gelding, I am not sure what the issue is. The Ramey article reprinted above tells you what you need to know Linda, read it carefully.DrO |
Moderator: DrO |
Posted on Tuesday, Jan 13, 2009 - 9:13 am: Here is a study that localizes the defective genes associated with Anterior Segment Dysgenesis, which appears to now be named Equine Multiple Congenital Ocular Anomalies. As was conjectured earlier their are two forms of the disease depending on whether the horse is heterozygous or homozygous for the mutant gene. Heterozygous individuals form cysts on different parts of the eye while the homozygous individual has more serious problems with cataracts and deformities of the iris and/or cornea.DrO BMC Genet. 2008 Dec 19;9(1):88 Equine Multiple Congenital Ocular Anomalies maps to a 4.9 megabase interval on horse chromosome 6. Andersson LS, Juras R, Ramsey DT, Eason-Butler J, Ewart S, Cothran G, Lindgren G. ABSTRACT: BACKGROUND: Equine Multiple Congenital Ocular Anomalies (MCOA) synDrOme consists of a diverse set of abnormalities predominantly localized to the frontal part of the eye. The disease is in agreement with a codominant mode of inheritance in our horse material. Animals presumed to be heterozygous for the mutant allele have cysts originating from the temporal ciliary body, peripheral retina and/or iris. In contrast, animals predicted to be homozygous for the disease-causing allele possess a wide range of multiple abnormalities, including iridociliary and/or peripheral retinal cysts, iridocorneal angle abnormalities, cornea globosa, iris hypoplasia and congenital cataracts. MCOA is most common in the Rocky Mountain horse breed where it occurs at a high frequency among Silver colored horses. The Silver coat color is associated with mutations in PMEL17 that resides on ECA6q23. To map the MCOA locus we analyzed 11 genetic markers on ECA6q and herein describe a chromosome interval for the MCOA locus. RESULTS: We performed linkage analysis within 17 paternal half-sib families of the Rocky Mountain horse breed. More than half of the 131 offspring had the Cyst phenotype and about one third had MCOA. Segregation data were obtained by genotyping 10 microsatellite markers most of which are positioned on ECA6q22-23, as well as the missense mutation for the Silver phenotype in PMEL17. Significant linkage was found between the MCOA locus and eight of the genetic markers, where marker UPP5 (Theta = 0, z = 12.3), PMEL17ex11 (Theta = 0, z = 19.0) and UPP6 (Theta = 0, z = 17.5) showed complete linkage with the MCOA locus. DNA sequencing of PMEL17 in affected and healthy control individuals did not reveal any additional mutations than the two mutations associated with the Silver coat color. CONCLUSIONS: The MCOA locus can with high confidence be positioned within a 4.9 megabase (Mb) interval on ECA6q. The genotype data on UPP5, PMEL17ex11 and UPP6 strongly support the hypothesis that horses with the Cyst phenotype are heterozygous for the mutant allele and that horses with the MCOA phenotype are homozygous for the mutant allele. |