A novel pathogenic CRB1 variant presenting as Leber Congenital Amaurosis 8 and evaluation of gene editing feasibility

Abstract

Introduction: Leber Congenital Amaurosis (LCA) is an inherited retinal disease that presents in infancy with severely decreased vision, nystagmus, and extinguished electroretinography findings. LCA8 is linked to variants in the Crumbs homolog 1 (CRB1) gene.

Case description: We report a novel CRB1 variant in a 14-year-old male presenting with nystagmus, worsening vision, and inability to fixate on toys in his infancy. Color fundus photography revealed nummular pigments in the macula and periphery. Imaging studies revealed thickened retina on standard domain optical coherence tomography and widespread atrophy of the retinal pigment epithelium on autofluorescence. Full-field electroretinography revealed extinguished scotopic and significantly reduced photopic responses. Genetic testing demonstrated a novel homozygous variant, c.3057 T > A; p.(Tyr1019Ter), in the CRB1 gene. This variant is not currently amenable to base editing, however, in silico analysis revealed several potential prime editing strategies for correction.

Conclusion: This case presentation is consistent with LCA8, suggesting pathogenicity of this novel variant and expanding our knowledge of disease-causing CRB1 variants.

Keywords: Full-field electroretinography; Gene therapy; Genotype–phenotype correlation; Leber Congenital Amaurosis; Novel CRB1 variant; Prime editing.

Fig. 1

Fundus photography of a patient with homozygous c.3057 T > A;p.(Tyr1019Ter) variants in the CRB1 gene. Color fundus photography of the right and left eyes at presentation A revealed rare nummular pigments at the macula (red arrows). Follow-up widefield fundus imaging at three B and seven C years after presentation show further pigmentary deposits at the macula and periphery (red arrows)

Fig. 2

Short-wave autofluorescence (SW-AF) and standard domain optical coherence tomography (SD-OCT) imaging studies in a patient with homozygous c.3057 T > A;p. (Tyr1019Ter) variants in the CRB1 gene. Short-wave autofluorescence (SW-AF) shows a wide central area of retinal pigment epithelium (RPE) atrophy bilaterally A. Red arrowheads indicate para-arteriolar sparing at the inferior arcades on both eyes. SD-OCT at presentation, compared to control B, revealed abnormal lamination with widespread outer nuclear layer atrophy and extensive loss of the ellipsoid zone bilaterally C. Follow-up OCT at three D and seven (E) years after presentation show further atrophy of the remaining ellipsoid zone over time

Fig. 3

Full-field electroretinogram (ffERG) recordings of a patient with homozygous c. 3057 T > A; p. Tyr1019Ter variants in the CRB1 gene. Baseline ffERG revealed a pattern of rod-cone dysfunction. Scotopic rod-specific and maximal responses were extinguished bilaterally (left and right eye responses were superimposed). Photopic 30-Hz flicker ERG had amplitudes and implicit times of 6.395 microvolts and 46 ms and 6.396 microvolts and 42 ms in the right and left eyes, respectively. Follow-up photopic ERG shows comparable 30-Hz flicker ERG amplitudes and implicit times of 7.213 microvolts and 22 ms and 5.424 microvolts and 21 ms in the right and left eyes, respectively

Fig. 4

Analysis of prime editing approaches for the correction of the c.3057 T > A;p.(Tyr1019Ter) CRB1 variant. Prime editing designs are shown utilizing the NGG prime editor with the edit at + 19 position A and the NGA prime editor with the edit at + 15 position B. 3’ extension 1 with the T4 stretch and 3’ extension 2 with the silent mutation that would disrupt the TTTT and enable delivery as plasmid DNA (B)