Multiple congenital ocular anomalies in Icelandic horses.
Authors: Andersson Lisa S, Axelsson Jeanette, Dubielzig Richard R, Lindgren Gabriella, Ekesten Björn
Journal: BMC veterinary research
Summary
# Editorial Summary: Multiple Congenital Ocular Anomalies in Icelandic Horses Multiple congenital ocular anomalies (MCOA) syndrome, a hereditary eye condition previously identified solely in Silver-coloured Rocky Mountain horses and linked to a mutation in the PMEL17 gene (exon 11) responsible for silver coat colour, has been discovered in Icelandic horses, suggesting the condition is not breed-specific but rather represents a more widespread genetic problem. Andersson and colleagues screened Icelandic horses for ocular abnormalities and genetic markers associated with MCOA, revealing that homozygous carriers present with the full MCOA phenotype featuring multiple defects, whilst heterozygous carriers predominantly manifest isolated iris, ciliary body or retinal cysts. This finding fundamentally challenges the assumption that MCOA represents a recent, Rocky Mountain Horse-specific mutation, and indicates that clinicians and breeders must now consider screening beyond traditionally affected breeds. For breeding programmes and clinical practice, the presence of this condition in genetically distant populations underscores the importance of ophthalmological examination in horses carrying the silver coat colour allele, regardless of breed background, and highlights the value of genetic testing to identify both homozygous and heterozygous carriers before breeding decisions are made.
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Practical Takeaways
- •Breeders of Silver-colored horses in multiple breeds (not just Rocky Mountain horses) should screen for ocular anomalies, as this is a hereditary condition with broader breed distribution than originally described
- •Understanding the genotype-phenotype relationship allows differentiation between severely affected homozygous horses and heterozygous carriers that may have milder presentations
- •Genetic testing and selective breeding strategies should be implemented across affected breeds to reduce prevalence of this congenital defect
Key Findings
- •MCOA syndrome previously thought restricted to Rocky Mountain horses was identified in Icelandic horses, indicating broader genetic distribution than previously believed
- •Disease-causing mutation is located within the PMEL17 gene region on chromosome associated with Silver coat color
- •Homozygous horses display multiple ocular defects (MCOA-phenotype) while heterozygous horses predominantly present with iris, ciliary body, or retinal cysts (Cyst-phenotype)