ABCA4 Versus PRPH2-Associated Retinopathy: Clinical and Electrophysiological Findings

The purpose of this study was to characterize the clinical features, electrophysiology, and variant spectrum in ABCA4- and PRPH2-retinopathies and to identify novel electrodiagnostic biomarkers to differentiate between these two genotypes.

We conducted an international multicenter case-control study of patients with a clinical and genetic diagnosis of ABCA4- or PRPH2-retinopathy. Age at symptom onset, best-corrected visual acuity (BCVA), electroretinography (ERG) components, and fundus autofluorescence (FAF) imaging were compared. Subgroup exploratory analysis was performed on those patients with a phenotype similar to central areolar choroidal dystrophy ("CACD-like"), those with flecks distributed throughout the posterior pole ("fleck-like") and a healthy control group. Receiver operating characteristic (ROC) analysis was performed to determine the optimal cutoff for ERG parameters to distinguish PRPH2- from ABCA4-retinopathy.

This study included 155 patients with ABCA4-retinopathy, 133 patients with PRPH2-retinopathy, and 52 healthy controls. Significant electrophysiological biomarkers included the light-adapted (LA)30 hertz (Hz) flicker and LA3.0 single flash b-wave peak time (P < 0.001) for the "CACD-like" group with an area under the ROC curve (AUROC) of 0.78 and 0.76 and cutoff thresholds of 27.8 ms or 31.7 ms providing 77% and 85% sensitivity, respectively. Conversely, in the "fleck-like" group, the dark-adapted (DA)0.01 b-wave amplitude and DA3 a-wave amplitude (P < 0.001) had the highest AUROC, namely 0.88 and 0.88, respectively, with cutoff thresholds of 85 µV and 109 µV providing 93% and 88% sensitivity, respectively.

Unique ERG profiles can distinguish PRPH2- from ABCA4-retinopathy. The LA30 Hz peak time and DA0.01 b-wave amplitude may have clinical utility in predicting and interpreting the genotype in patients with overlapping retinal phenotypes.