A homozygous missense mutation in the IRBP gene (RBP3) associated with autosomal recessive retinitis pigmentosa.
Interphotoreceptor retinoid-binding protein (IRBP) has been considered essential for normal rod and cone function, as it mediates the transport of retinoids between the photoreceptors and the retinal pigment epithelium. This study was performed to determine whether mutations in the IRBP gene (RBP3) are associated with photoreceptor degeneration. A consanguineous family was ascertained in which four children had autosomal recessive retinitis pigmentosa (RP). Homozygosity mapping performed with SNP microarrays revealed only one homozygous region shared by all four affected siblings. Sequencing of RBP3, contained in this region, was performed in this family and others with recessive RP. Screening was also performed on patients with various other forms of retinal degeneration or malfunction. Sequence analysis of RBP3 revealed a homozygous missense mutation (p.Asp1080Asn) in the four affected siblings. The mutation affects a residue that is completely conserved in all four homologous modules of the IRBP protein of vertebrate species and in C-terminal-processing proteases, photosynthesis enzymes found in bacteria, algae, and plants. Based on the previously reported crystal structure of Xenopus IRBP, the authors predict that the Asp1080-mediated conserved salt bridge that appears to participate in scaffolding of the retinol-binding domain is abolished by the mutation. No RBP3 mutations were detected in 395 unrelated patients with recessive or isolate RP or in 680 patients with other forms of hereditary retinal degeneration. Mutations in RBP3 are an infrequent cause of autosomal recessive RP. The mutation Asp1080Asn may alter the conformation of the IRBP protein by disrupting a conserved salt bridge.
PubMed ID: 19074801
PMC ID: PMC2823395
Article link: Invest Ophthalmol Vis Sci.
Grant support: EY00169 NEI NIH HHS , EY009412 NEI NIH HHS , EY08683 NEI NIH HHS , P30-EY014104 NEI NIH HHS , P30 EY014104-06A2 NEI NIH HHS , R01 EY000169-36 NEI NIH HHS , R01 EY008683-15 NEI NIH HHS , R01 EY009412-14 NEI NIH HHS , R01 EY009412-17 NEI NIH HHS , P30 EY014104 NEI NIH HHS , R01 EY009412 NEI NIH HHS , TGM06D01 Telethon
Genes referenced: grb10 rbp3