Ophthalmological and genetic findings associated with CRB1 dysfunction in autosomal recessive retinitis pigmentosa

Abstract

Abstract Introduction Retinitis pigmentosa (RP) is an inherited disease of the retina. It is characterized by progressive degeneration of the retinal photoreceptor cells. This pathology is due to mutations in CRB1 gene that is encoded by the crumbs homolog 1 (CRB1) protein. The aim of this study is to identify the mutations in Algerian patients with Retinitis Pigmentosa and to assess their structural, and functional implications as well as their correlation with clinico-pathology features. Patients and methods This study was performed in collaboration with the ophthalmological department of Farhat Hached Hospital, Sousse, Tunisia. Whole-exome sequencing was performed on an Algerian female patient (IV.3) presenting RP. Polymerase chain reaction (PCR) followed by Direct Sanger sequencing were performed in all family’s members (III3, III4, IV.3, IV4 and IV5,) to validate the mode of inheritance and confirm the disease segregation. Bioinformatics tools, including PolyPhen, were used to predict the pathogenicity through a scoring system, while SWISS-MODEL, PyMOL, InterProt and AlphaFold Server were performed for CRB1 structural modeling and to assess the impact of the mutations on its three-dimensional structure stability and flexibility. Results Based on the ophthalmological investigation, including fundus examination, Fluorescein Angiography (FA), and Optical Coherence Tomography (OCT), the two affected sisters (IV.3 and IV.4) exhibited a mottled fundus appearance with widespread areas of Retinal Pigment Epithelium (RPE) atrophy. FA demonstrated multiple hyperfluorescent areas consistent with window defects due to RPE loss, interspersed with relatively hypofluorescent regions corresponding to advanced chorioretinal atrophy. A relatively preserved central hyperfluorescent island was observed. OCT revealed marked degeneration of the outer retinal layers, with thinning of the photoreceptor layer, particularly in the peripheral retina. These findings initially suggested a choroideremia-like phenotype. Whole-exome sequencing identified a homozygous pathogenic variant in CRB1 gene (p.Glu710Val) in two affected sisters (IV.3 and IV4) by the autosomal recessive Retinitis Pigmentosa form, while no pathogenic variants were detected in CHM gene. The structural analysis revealed that the residue 710 is located in a domain Laminin G-like (LG) of the crumbs homolog 1 (CRB1) protein rather than in a calcium-binding EGF-like domain. The p.Glu710Val substitution abolishes a stabilizing hydrogen bond with Gln853, thereby disrupting the local interaction network within the Laminin G–like domain. The loss of this polar interaction may reduce local structural stability and alter the microenvironment of this domain. Conclusion This is the first ophthalmological and molecular report of autosomal recessive Retinitis Pigmentosa in Algerian patients. Although ophthalmological investigation initially suggested a choroideremia-like phenotype, whole-exome sequencing identified a pathogenic CRB1variant, while only benign variants were detected in CHM gene. This case highlights the phenotypic overlap between inherited retinal dystrophies and underscores the importance of combining comprehensive ophthalmic assessment with molecular genetic testing for accurate diagnosis.