Johansson Maria K, Jäderkvist Fegraeus Kim, Lindgren Gabriella, Ekesten Björn
Department of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, -750 07, Uppsala, SE, Sweden.
Department of Clinical Sciences, Swedish University of Agricultural Sciences, -750 07, Uppsala, SE, Sweden.
BMC Vet Res. 2017 Jun 2;13(1):153. doi: 10.1186/s12917-017-1059-7.
The syndrome Multiple Congenital Ocular Anomalies (MCOA) is a congenital eye disorder in horses. Both the MCOA syndrome and the Silver coat colour in horses are caused by the same missense mutation in the premelanosome protein (PMEL) gene. Horses homozygous for the Silver mutation (TT) are affected by multiple ocular defects causing visual impairment or blindness. Horses heterozygous for the Silver mutation (CT) have less severe clinical signs, usually cysts arising from the ciliary body iris or retina temporally. It is still unknown if the vision is impaired in horses heterozygous for the Silver mutation. A recent study reported that Comtois horses carrying the Silver mutation had significantly deeper anterior chambers of the eye compared to wild-type horses. This could potentially cause refractive errors. The purpose of the present study was to investigate if Icelandic horses with the Silver mutation have refractive errors compared to wild-type horses. One hundred and fifty-two Icelandic horses were included in the study, 71 CT horses and five TT horses. All horses were genotyped for the missense mutation in PMEL. Each CT and TT horse was matched by a wild-type (CC) horse of the same age ± 1 year. Skiascopy and a brief ophthalmic examination were performed in all horses. Association between refraction and age, eye, genotype and sex was tested by linear mixed-effect model analysis. TT horses with controls were not included in the statistical analyses as they were too few.
The interaction between age and genotype had a significant impact on the refractive state (P = 0.0001). CT horses older than 16 years were on average more myopic than wild-type horses of the same age. No difference in the refractive state could be observed between genotypes (CT and CC) in horses younger than 16 years. TT horses were myopic (-2 D or more) in one or both eyes regardless of age.
Our results indicate that an elderly Icelandic horse (older than 16 years) carrying the Silver mutation is more likely to be myopic than a wild-type horse of the same age.
多重先天性眼部异常综合征（MCOA）是马的一种先天性眼部疾病。马的MCOA综合征和银色毛色均由前黑素小体蛋白（PMEL）基因中的同一位点错义突变引起。银色突变纯合子（TT）的马会受到多种眼部缺陷的影响，导致视力受损或失明。银色突变杂合子（CT）的马临床症状较轻，通常是睫状体虹膜或视网膜颞侧出现囊肿。银色突变杂合子马的视力是否受损尚不清楚。最近一项研究报告称，携带银色突变的孔托伊斯马与野生型马相比，前房明显更深。这可能会导致屈光不正。本研究的目的是调查携带银色突变的冰岛马与野生型马相比是否存在屈光不正。152匹冰岛马被纳入研究，其中71匹CT马和5匹TT马。所有马匹都进行了PMEL错义突变的基因分型。每匹CT和TT马都与一匹年龄±1岁的野生型（CC）马匹配。对所有马匹进行了检影验光和简要的眼科检查。通过线性混合效应模型分析测试了屈光度与年龄、眼睛、基因型和性别的关联。由于TT马数量过少，未将其与对照组纳入统计分析。
年龄与基因型之间的相互作用对屈光状态有显著影响（P = 0.0001）。16岁以上的CT马平均比同龄野生型马近视程度更高。16岁以下的马，基因型（CT和CC）之间在屈光状态上未观察到差异。无论年龄大小，TT马一只或两只眼睛均为近视（-2 D或更低）。
我们的结果表明，携带银色突变的老年冰岛马（16岁以上）比同龄野生型马更易患近视。
