Equine Multiple Congenital Ocular Anomalies (MCOA) syndrome inPMEL17(Silver) mutant ponies: five cases

Abstract

Objective To describe the clinical phenotype and genetics of equine Multiple Congenital Ocular Anomalies (MCOA) syndrome in PMEL17 (Silver) mutant ponies. Animals studied Five presumably unrelated ponies. Procedures The ponies were examined under field conditions in their barn by slit lamp biomicroscopy, indirect ophthalmoscopy, and applanation tonometry. Blood was collected and genomic DNA extracted for MCOA genotyping using the PMEL17ex11 marker. Results One pony solely presented with temporal ciliary body cysts, suggestive of the less severe Cyst phenotype of MCOA; the animal was heterozygous at the MCOA locus. Multiple bilateral anterior segment anomalies were identified in four ponies, consistent with the more severe MCOA phenotype characterized by cornea globosa, iris hypoplasia, encircling granula iridica along the pupillary ruff, and cataracts. These animals were homozygous for the mutant MCOA allele. Four of the ponies had a silver dapple or chocolate coat color with white or flaxen manes and tails. Silver dappling was masked by the palomino coloring of a 5th pony that was homozygous at the MCOA locus. Conclusions The MCOA syndrome can be seen in ponies. The results of both clinical evaluation and genotyping resembled the previously described MCOA of both Rocky Mountain and Kentucky Mountain Saddle horses.

Ultrasonographic features of PMEL17 (Silver) mutant gene–associated multiple congenital ocular anomalies (MCOA) in Comtois and Rocky Mountain horses

“…Retinal detachment cannot always be diagnosed by routine ophthalmic examination but is easily diagnosed ultrasonographically . Retinal detachment was the least common anomaly observed in equine MCOA in our study and in previous ones . However, considering its possible impact on functional visual capacity, it is an important feature of the disease.…”

“…Originally referred to as anterior segment dysgenesis, equine Multiple Congenital Ocular Anomalies syndrome (MCOA) consists of several abnormalities predominantly localized to the anterior segment of the eye. This syndrome was originally observed in an American population of Rocky Mountain horses, was also described in pure‐bred and cross‐bred Rocky Mountain and Kentucky Mountain horses in Canada, and has been recently observed in Icelandic horses and ponies . These studies showed that MCOA is strongly related to coat color, with a high prevalence in black‐silver and bay‐silver horses.…”

“…It would be interesting to establish normal references values in breeds in which MCOA has a high prevalence. The dominant mutant allele of the Silver gene is reported to be also present in other breeds such as Icelandic horses and Shetland ponies; and it would be very interesting to compare these first descriptive and biometric results to what can be observed in these breeds.…”

Equine Multiple Congenital Ocular Anomalies and Silver Coat Colour Result from the Pleiotropic Effects of Mutant PMEL

“…While the syndrome was first described in the Rocky Mountain Horse, where it is highly prevalent, it is not limited to this breed. Additional horse breeds that have been diagnosed with MCOA syndrome include the Icelandic Horse, Shetland Pony, Exmoor Pony, American Miniature Horse, Belgian Draft and Morgan Horse, as well as the Kentucky Mountain Saddle Horse and Mountain Pleasure Horse, both of which are closely related to the Rocky Mountain Horse [1,2,3,4,5,6,7]. MCOA syndrome is inherited as an incompletely dominant trait.…”

Post mortem magnetic resonance imaging of multiple congenital ocular anomalies in a Comtois mare

“…), Shetland and Deutsches Classic ponies (Komáromy et al . ; Premont et al . ) and Miniature Horses (Plummer and Ramsey ).…”