XRP2, also known as Protein XRP2 and RP2, is a member of the TBCC (tubulin cofactor C) family and contains one C-CAP/cofactor C-like domain. This protein is encoded by the RP2 gene in humans. XRP2 stimulates the GTPase activity of tubulin, but does not enhance tubulin heterodimerization. XRP2 acts as guanine nucleotide dissociation inhibitor for ARL3. Defects in RP2 gene are the cause of retinitis pigmentosa type 2 (RP2), also known as X-linked retinitis pigmentosa 2 (XLRP-2). It leads to degeneration of retinal photoreceptor cells. Patients typically have night vision blindness and loss of midperipheral visual field. As their condition progresses, they lose their far peripheral visual field and eventually central vision as well.

Could be a guanine-nucleotide releasing factor. Plays a role in ciliogenesis. Probably regulates cilia formation by regulating actin stress filaments and cell contractility. Plays an important role in photoreceptor integrity. May play a critical role in spermatogenesis and in intraflagellar transport processes. May be involved in microtubule organization and regulation of transport in primary cilia.

Tyrosine-protein kinase Mer (MERTK) is a single-pass type I membrane protein which belongs to the MER/AXL/TYRO3 receptor kinase family. MERTK include two fibronectin type-III domains, two Ig-like C2-type domains, and one tyrosine kinase domain. It can’t be expressed in normal B- and T-lymphocytes, but it is usually expressed in numerous neoplastic B- and T-cell lines. MERTK could regulate many physiological processes, such as cell survival, migration, differentiation. It was demonstrated that the MERTK plays critical role in the engulfment and efficient clearance of apoptotic cells, platelet aggregation, and cytoskeleton reorganization. Not only these, it also plays an important role in inhibition of Toll-like receptors (TLRs)-mediated innate immune response by activating STAT1, which selectively induces production of suppressors of cytokine signaling SOCS1 and SOCS3. In addition, MERTK could regulate rod outer segments fragments phagocytosis in the retinal pigment epithelium (RPE)， deficiency in MERTK are the cause of retinitis pigmentosa.

PHYH belongs to the family of iron(II)-dependent oxygenases, which typically incorporate one atom of dioxygen into the substrate and one atom into the succinate carboxylate group. PHYH is expressed in liver, kidney, and T-cells, but not in spleen, brain, heart, lung and skeletal muscle. It converts phytanoyl-CoA to 2-hydroxyphytanoyl-CoA. Defects in PHYH can cause Refsum disease (RD). RD is an autosomal recessive disorder characterized clinically by a tetrad of abnormalities: retinitis pigmentosa, peripheral neuropathy, cerebellar ataxia, and elevated protein levels in the cerebrospinal fluid (CSF). Patients exhibit accumulation of the branched-chain fatty acid, phytanic acid, in blood and tissues.

Harmonin, also known as Antigen NY-CO-38 / NY-CO-37, Autoimmune enteropathy-related antigen AIE-75, Protein PDZ-73, Renal carcinoma antigen NY-REN-3, Usher syndrome type-1C protein and USH1C, is a protein that is expressed in small intestine, colon, kidney, eye and weakly in pancreas. USH1C is expressed also in vestibule of the inner ear. USH1C contains 3 PDZ (DHR) domains. USH1C may be involved in protein-protein interaction. Defects in USH1C are the cause of Usher syndrome type 1C (USH1C), also known as Usher syndrome type I Acadian variety. USH is a genetically heterogeneous condition characterized by the association of retinitis pigmentosa and sensorineural deafness. Age at onset and differences in auditory and vestibular function distinguish Usher syndrome type 1 (USH1), Usher syndrome type 2 (USH2) and Usher syndrome type 3 (USH3). Defects in USH1C are also the cause of deafness autosomal recessive type 18 (DFNB18) which is a form of sensorineural hearing loss. Sensorineural deafness results from damage to the neural receptors of the inner ear, the nerve pathways to the brain, or the area of the brain that receives sound information.