The clinical phenotypes and pathogenicity of isolated cone-rod dystrophy (CORD) caused by two novel complex heterozygous variants of the CEP290 gene were analyzed using high-resolution multi-mode imaging and gene detection techniques.

A retrospective study. Two patients and two family members from a CORD family who were diagnosed by genetic testing at Henan Provincial People's Hospital in December 2021 were included in the study. All subjects underwent best-corrected visual acuity (BCVA), color fundus photography, autofluorescence, swept-source optical coherence tomography (SS-OCT), adaptive optics fundus imaging, static threshold field, full field and multiple electroretinogram (ERG) examination, as well as other systemic examinations throughout the body. The peripheral venous blood of the subjects was collected, and the whole genome DNA was extracted. DNA sequencing was performed using the Inherited Retinal Disease Kit PS400, and Sanger verification and pedigree co-segregation analysis were performed on the suspected pathogenic mutation sites. Validation was performed by Sanger sequencing, pathogenicity analysis was performed in accordance with the American College of Medical Genetics and Genomics (ACMG) guidelines. Conservation of variation among different species was analyzed by GERP++, Clustal Omega and Weblogo.

Both patients were male, and their ages were 21 and 29 years old, respectively. The right eye and left eye about BCVAs were 0.7, 0.4 and 0.3, 0.4, respectively. The full field and multiple electroretinogram ERG showed a decreased function of cones and rods, especially cones. SS-OCT showed thinning of the outer nuclear layer of macular, and attenuation of ellipsoid zone reflectivity in B-scan. Adaptive optics fundus imaging examination showed that the arrangement of cone cells in the fovea of the fovea was disordered and the density decreased, and the retinal pigment epithelial cells were seen through the atrophy of cone cells in some areas at 10°visual angle. No obvious abnormality was found in other systemic examinations of the whole body. Genetic testing showed that 2 novel compound heterozygous variants c.950T >A (p.Leu317*) (M1) and c.4144_4149del (p.Tyr1382_Glu1383del) (M2) in CEP290 were found in two patients. The first variant was predicted to be harmful in MutationTaster and CADD. GERP++ showed highly conserved among different species. The pathogenicity of the variant was suspected to be likely pathogenic according to ACMG guidelines. The pathogenicity of the second variant was uncertain significance. The parents of the proband had no similar ocular abnormalities. Verified by Sanger sequencing, it was consistent with co-separation in the family.

Patients with pure CORD caused by CEP290 gene mutation still retain better vision when the cone structure is abnormal, the density is decreased, and the function of cone and rod cells is decreased. CEP290 M1 and M2 are newly discovered nonsense mutations and newly discovered deletion mutations, which expanded the causative gene spectrum of pure CORD.

Genes; Mutation; Cone-rod dystrophy; Clinical phenotype; CEP290 gene