*8.3. MERTK*

Mutations in *MERTK* (MER proto-concogene, tyrosine kinase) account for about 1% of arRP. *Mertk* was found to be overexpressed (six-fold) in Swedish Vallhund dogs with a retinal dystrophy [169]. After whole genome sequencing of an a ffected dog, an intact LINE-1 insertion was identified in intron one of *Mertk*. A LINE-1 retrotransposon is a long interspersed repetitive element that is found in all mammalian genomes [170]. It is unclear how this insertion results in overexpression of the *Mertk* transcript and subsequent development of retinal disease. More in-depth investigation of this mechanism will aid a better understanding of how retrotransposon insertions can modify gene

regulation/expression, ultimately leading to disease, in addition to understanding the specific role of overexpression of the *MERTK* transcript in the context of retinal disease [171].
