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Multiple Congenital Ocular Anomalies (MCOA) / Silver Coat
| Acronym: | MCOA |
| Gene: | PMEL |
| Mutation: | g.73665304C>T |
| Inheritance: | Autosomal co-dominant |
| Sample type: | WBE (Whole Blood EDTA), HA (Hairs - with roots) |
Genetics and characteristics
Multiple congenital ocular anomalies (MCOA) is an inherited eye disease that affects several horse breeds. Horses with MCOA have eye anomalies, mainly peripheral cysts or, in severe cases, fluid-filled cysts of the iris, ciliary body and retina, miotic pupils, and cataract. The disease is often associated with the silver dilution mutation or silver coat colour. MCOA is caused by a genetic mutation in the premelanosome protein (PMEL) gene responsible for the production of eumelanin in the melanosome and normal pigmentation. The missense mutation in the PMEL gene causes a premature stop codon and truncated protein, leading to premature greying of the coat due to loss of melanocytes and all the mentioned associated symptoms.
MCOA is inherited as an autosomal co-dominant disease, and displays a dose effect, meaning that horses with two copies of the mutation will have more severe symptoms than horses carrying only one copy. MCOA affects several breeds of horses, such as Icelandic, Kentucky Mountain Saddle, Missouri Foxtrotter, and Rocky Mountain. The disease is incurable, but early detection by genetic testing can help identify affected horses in the population and prevent further breeding by the mating pairs selection.
Results Reported As
Test Result |
Interpretation of test result |
Healthywith normal coat color |
Horse is healthy and does not have the gene with MCOA associated mutation. |
Affected - less severewith Silver coat |
Horse is affected and has one copy of the gene with MCOA associated mutation. Horse is likely to develop less severe signs of the disease and will have silver coat color. |
Affected - more severewith Silver coat |
Horse is affected and has two copies of the gene with MCOA associated mutation. Horse is likely to develop more severe signs of the disease and will have silver coat color. |
References:
Andersson, L. S., Wilbe, M., Viluma, A., Cothran, G., Ekesten, B., Ewart, S., & Lindgren, G. (2013). Equine Multiple Congenital Ocular Anomalies and Silver Coat Colour Result from the Pleiotropic Effects of Mutant PMEL. PLoS ONE, 8(9), e75639. doi:10.1371/journal.pone.0075639