Genotype-Phenotype Associations in an X-Linked Retinoschisis Patient Cohort: The Molecular Dynamic Insight and a Promising SD-OCT Indicator

Abstract

Purpose: This study investigated a three-dimensional indicator in spectral-domain optical coherence tomography (SD-OCT) and established phenotype-genotype correlation in X-linked retinoschisis (XLRS).

Methods: Thirty-seven patients with XLRS underwent comprehensive ophthalmic examinations, including visual acuity (VA), fundus examination, electroretinogram (ERG), and SD-OCT. SD-OCT parameters of central foveal thickness (CFT), cyst cavity volume (CCV), and photoreceptor outer segment length were assessed. CCV was defined as the sum of the areas of cyst cavities in uential B-scans, measured automatically by self-developed software (OCT-CCSEG). Structural changes of the protein associated with missense variants were quantified by molecular dynamics (MD). The correlation between genotype and phenotype was analyzed.

Results: Twenty-seven different RS1 variants were identified, including a novel variant c.336_337insT(p.L113Sfs*8). The average age of onset was 14.76 ± 15.75 years, and the mean VA was 0.84 ± 0.43 logMAR. The mean CCV was 1.69 ± 1.87 mm3, correlating significantly with CFT (R = 0.66; P < 0.01). In the genotype-phenotype analysis of missense variants, CCV significantly correlated with the structural effect on the protein of mutational changes referred to as wild type, including root-mean-square deviation (R = 0.34; P = 0.04), solvent accessible surface area (R = 0.38; P = 0.02), and surface hydrophobic area (R = 0.37; P = 0.03). The amplitude of scotopic 3.0 ERG a-waves and b-waves significantly correlated with the percentage change of the β-strand in the secondary structure (a-wave: R = -0.58, P < 0.01; b-wave: R = -0.53, P < 0.01).

Conclusions: CCV is a promising indicator to quantify the structural disorganization of XLRS retina. The OCT-CCSEG software calculated CCV automatically, potentially facilitating prognosis assessment and development of personalized treatment. Moreover, MD-involved genotype-phenotype analysis suggests an association between protein structural alterations and XLRS severity measured by CCV and ERG.

Figure 1.

Illustration of the SD-OCT scanning pattern. The scanning pattern area was 5.6 × 5.6 mm in in the XY plane, centered at the fovea, which generated a set of 25 horizontal cross-sectional B-scan images. Each OCT scan was 5.6 × 1.9 mm in the XZ plane.

Figure 2.

The CCV automated calculation system OCT–CCSEG. The input is a group of OCT scans, and the output is CCV. The system includes five modules: image boundaries detection module, image segmentation module, filter module, cavity area calculation module, and cavity volume calculation module.

Figure 3.

Representative clinical images of XLRS patients. (a) Fundus displaying a spoke-wheel–like schisis at the macula. (b) OCT showing splitting of the inner retinal layers. (c) ERG exhibiting reduced waveforms of rod and cone responses and a negative ERG waveform on scotopic 3.0 ERG.

Figure 4.

Comparison of ERG in patients and the control group. The violin and box plots illustrate scotopic 3.0 a-wave amplitude, scotopic 3.0 b-wave amplitude, and 3.0 scotopic b-wave/a-wave ratio in different groups.

Figure 5.

Age impact on VA. (a) The spline regression model of VA and age. (b–e) Kaplan–Meier survival analysis of different visual function indicators for age: survival curves for best-corrected visual acuity (BCVA) of 0.30 logMAR (b); survival curves for BCVA of 0.48 logMAR (c); survival curves for BCVA of 1.00 logMAR (d); and survival curves for BCVA of 1.30 logMAR (e).

Figure 6.

Distribution of reported variants within RS1. (a) The genomic location of the variants in the homology model of RS1 (PDB-3JD6). The RS1 domain is shown in cyan, the DS domain in lemon, and the C-terminal in pink. (b) The spectrum of the 27 RS1 variants. (c) The distribution of the variants; the frequency of variants in each exon is indicated in the bar plot. The locations of variants in the gene and the protein are marked by lines.

Figure 7.

Structure and RMSD graph of wild-type and variant forms of RS1 in MD simulation. In the 3D structure, helices are shown in red, strand in yellow, coli in cyan, disulfide bonds in orange, and variant spots in magenta. The RMSD graph shows the deviation of the backbone in the wild-type (blue) and variant (red) forms of RS1 during the MD simulation. Their difference is represented in the red box.

Figure 8.

Correlation matrix of genotype and phenotype. The value in each cell is the Pearson's correlation coefficient of two variables in the corresponding row and column. The cells with purple circles are significant results (P < 0.05).