The MER Tyrosine Kinase Protooncogene (MERTK) codes for a transmembrane receptor tyrosine kinase that plays a key role in physiological renewal of outer segments of photoreceptors. These outer segments constantly shed debris in response to light exposure, which in turn leads to the accumulation of toxic debris within the retinal pigment epithelium (RPE). Phagocytosis of photoreceptors is therefore, crucial to maintain healthy retinal function. MERTK is known to play a role in the RPE in processes such as macrophage clearance of apoptotic cells, platelet aggregation, cytoskeleton reorganization and engulfment, and as a regulator of rod outer segments fragments phagocytosis.
Mutations in the MERTK gene are known to result in a form of Retinitis Pigmentosa (RP38), characterized by retinal pigment deposits visible on fundus examination and primary loss of rod photoreceptor cells followed by secondary loss of cone photoreceptors. In addition, overexpression of MERTK has also been implicated in oncogenesis.