Evaluation of the Retbindin Gene as a Candidate for Retinal Diseases

Abstract

Abstract: : Purpose: Retbindin is a novel gene that is predominantly expressed in the retina. It has homology to known riboflavin and folate binding genes and may be involved in binding and transport of a similar ligand in the retina. Its expression data makes it a strong functional candidate for retinal disease. We performed mutation screening in panels of Lebers Congenital Amaurosis (LCA), autosomal recessive Retinitis Pigmentosa (arRP), autosomal dominant RP (adRP) and Cone-Rod patients to determine whether this gene is implicated in the molecular pathology of these disease phenotypes. Novel exons and alternative spliced transcripts are described. Methods: Full-length Retbindin IMAGE cDNA clones were sequenced. Novel exons and alternative transcribed products were identified based on cDNA and genomic sequence comparison. Retbindin expression was examined by PCR amplification of a gene specific STS in multiple tissue cDNAs (Clonetech). Mutation screening of the coding region (6 exons) was performed by PCR and direct sequencing on panels of 41 LCA, 325 adRP, 111 arRP, 45 simplex and 44 Cone Dystrophy patients. Results: Alternative transcription is exclusively limited to the 5’ region of the transcript. Two novel exons were found and both demonstrated internal exon splicing. These novel transcripts extended the open reading frame by an additional 57 amino acids. Retbindin expression was predominant in retina and brain cDNAs, lower in the testes and thymus, and absent from a variety of other tissues. Two silent changes, Pro41Pro and Thr45Thr, were found in an adRP and an LCA patient respectively. Two missense polymorphisms (Gly106Ser, Gly265Ala) were found in a large number of patients with different forms of retinal disease and in control DNAs. A Val170Met change was found in only one adRP proband but it did not cosegregate with disease in the respective family. Conclusion: No pathological sequence changes in the coding region and splice site boundaries of Retbindin were found in our cohort of patients with retinal disease. However, Retbindin may still be involved as intronic and promoter changes and gross rearrangements are difficult to assess and it is possible this gene may cause a form of retinal disease not included in our patient set. Nevertheless, even without a retinopathy association, its high retinal expression makes the pursuit for understanding its function essential.

Keywords: candidate gene analysis • degenerations/dystrophies • gene/expression