Fine-Mapping of Equine Multiple Congenital Ocular Anomalies on horse chromosome 6
Multiple Congenital Ocular Anomalities (MCOA) is a genetic disease that affects primarily Silver coloured horses of breeds such as the Rocky and Kentucky mountain horses. In these breeds the Silver dapple colour is very popular leading to an increase of affected horses. The major feature of the disease is ocular cysts of variable size. Large cysts also lead to a variety of secondary syndromes, for example retinal detachment. In previous studies the locus for MCOA has been mapped to an interval of 420 kb on equine chromosome six. Within this interval there are a number of genes including the PMEL17 gene that carry the mutation that is believed to cause the Silver dapple coat color. This study has focused on shortening the interval by fine-mapping using Single Nucleotide Polymorphism (SNP) markers. This was done by recovering polymorphic markers from the EcuCab 2.0 publication of equine SNPs. The genotyping was carried out using preordered primers and probes in the ABI 7900HT fast real-time PCR system. When evaluating the results two different disease haplotypes were detected, one longer and one shorter. These recombinant chromosomes helped to decrease the interval by 37 % resulting in an interval of 265 kb. This reduced the number of genes leaving sixteen to be investigated, including the PMEL17. The resulting dataset concurred to the hypothesis of a codominant inheritance pattern. A gene within the interval called SMARCC2 was chosen for sequencing due to its known importance in ocular development. The sequencing exposed a polymorphism in the intron between exon nineteen and twenty. Following studies include extended investigation of the SMARCC2 polymorphism, sequencing of other candidate genes and functional studies of the most interesting mutations.