Yunji Kim

Literature Review of Collie Eye Anomaly

Started Oct. 17, 2023

Abstract or project description

The topic of Yunji's project is Collie Eye Anomaly, a recessive genetic disorder common in collie-type dogs. The project is to write a literature review consolidating currently known information on the genetic disorder. Individual topics to focus on within the literature review will include the clinical presentation of collie eye anomaly (CEA), the genetic basis for the disorder, (genotype), the connection between genotype and phenotype, potential treatment/therapies, and the impact/importance of the disorder. If applicable, gaps in the current research and understanding of the disorder will be acknowledged and addressed by highlighting recommended research areas for the broader research community going forward. Extra attention may be spent learning and reviewing more advanced genetic and anatomical concepts than traditionally taught at a high school level.

UPDATED: Collie eye anomaly (CEA) is a recessive genetic disorder which affects a wide variety of breeds; the most common being collies. The causation of CEA is the deletion of 7799 bp which is located in the intronic part of the NHEJ1 (non-homologous end-joining factor 1) gene on chromosome 37; however, the mechanism of action of how the genotype is correlated to the phenotypic expression of the disease is still unknown in canines. PCR is the current detection method to help diagnose CEA and has seen many improvements over the years. Newer studies have shown that select high CEA frequency breeds express the disease’s phenotype without the NHEJ1 mutation documented in earlier studies. This suggests the existence of multiple different genotypes responsible for CEA that have yet to be discovered. Observing analogous NHEJ1 gene mutations within humans that also cause similar documented ocular defects can contribute to a better understanding of the mechanism of action of the canines’ deletion of the NHEJ1 gene segment in relation to CEA. Human medicine studies have identified that the intronic segment of NHEJ1 gene that is deleted in genetic ocular defects is also an enhancer for another gene necessary for normal eye development, the Indian Hedgehog gene (ihh). The author of this paper theorizes that this mechanism of action is conserved between species and can therefore explain how the deletion of the NHEJ1 gene segment can cause CEA. It is also further theorized that dogs with CEA phenotypic expression lacking the NHEJ1 mutation could possess mutations to other enhancers to the ihh gene or direct mutations within the ihh gene itself. Further canine research to confirm or reject these hypotheses is needed. This research could lead to future preventive genetic testing or even gene therapies for CEA.