RPGR-Related Retinopathy: Clinical Features, Molecular Genetics, and Gene Replacement Therapy

Retinitis pigmentosa GTPase regulator (RPGR) gene variants are the predominant cause of X-linked retinitis pigmentosa (XLRP) and a common cause of cone-rod dystrophy (CORD). XLRP presents as early as the first decade of life, with impaired night vision and constriction of peripheral visual field and rapid progression, eventually leading to blindness. In this review, we present RPGR gene structure and function, molecular genetics, animal models, RPGR-associated phenotypes and highlight emerging potential treatments such as gene-replacement therapy

Prognostication in Stargardt disease using Fundus Autofluorescence: Improving Patient Care

PURPOSE: To explore fundus autofluorescence (FAF) imaging as an alternative to electroretinogram (ERG), as a non-invasive, quick, and readily interpretable method to predict disease progression in Stargardt disease (STGD). DESIGN: Retrospective case series of patients who attended Moorfields Eye Hospital (London, UK). SUBJECTS: Patients with STGD who met the following criteria were included: (i) biallelic disease-causing variants in ABCA4, (ii) ERG testing performed inhouse with an unequivocal ERG group classification, and (iii) ultra-widefield (UWF) FAF imaging performed up to 2 years before or after the ERG. METHODS: Patients were divided into three ERG groups based on retinal function and three FAF groups according to the extent of the hypoautofluorescence and their retinal background appearance. FAF imaging of 30 and 55° were also subsequently reviewed. MAIN OUTCOME MEASURES: ERG/FAF concordance and its association with baseline visual acuity and genetics. RESULTS: 234 patients were included in the cohort. 170 patients (73%) had the same ERG and FAF group, 33 (14%) had a milder FAF than ERG group, and 31 (13%) had a more severe FAF than ERG group. Children under the age of 10 (n=23) had the lowest ERG/FAF concordance, 57% (9 out of the 10 with discordant ERG/FAF had milder FAF than ERG), and adults with adult onset had the highest (80%). Missense genotypes were more commonly seen in the mildest phenotypes. In 97% and 98% of the cases, respectively, 30° and 55° FAF imaging matched with the group defined by UWF FAF. CONCLUSIONS: We demonstrate that FAF imaging is an effective modality to determine the extent of retinal involvement and thereby inform prognostication, by comparing FAF to the current gold standard of ERG testing to determine retinal involvement and thereby prognosis. In 80% of patients in our large molecularly proven cohort we were able to predict if the disease was confined to the macula or also affected the peripheral retina. Children assessed at a young age, with at least one null variant, early disease onset, and/or poor initial VA may have wider retinal involvement than predicted by FAF alone and/or progress to a more severe FAF phenotype over time

Structure of the myosin motor domain and acto-myosin cycle.

<p>A. Cartoon representation of the motor domain structure (PDB ID: 4PA0 [<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1005826#pcbi.1005826.ref008" target="_blank">8</a>]), with the subdomains highlighted in different colours and OM shown as purple spheres. The motor domain is connected to the rest of myosin through the lever arm and the regulatory domain (not shown). B. Simplified representation of the acto-myosin cycle, where myosin switches between actin-bound (bottom) and -unbound (top) states and between up and down conformations of the lever arm.</p

Pathways connecting the OM-binding site and the G-helix in the contact change network.

<p>The shortest paths connecting V698 (magenta) and G helix residues (red) in the network of OM-Apo contact changes are represented as yellow edges. The paths are calculated from a consensus contact change matrix calculated over all the simulations. Only contacts with a change in frequency larger than 0.1 were considered. The edge thickness is proportional to the difference between OM and Apo contact frequency. For each pair of endpoints, the top 5 shortest paths are represented. The nodes in the paths are represented as spheres coloured according to the subdomain they belong to and with a radius proportional to the number of paths going through them. The top 10 residues for number of paths are also labelled.</p

Bending of the relay helix during the MD simulations.

<p>The relay helix bending was measured by calculating the angle formed by residues I478, F489 and E500 (C^α atoms only). The central plot shows the probability distribution of the angle values observed during Apo (green hues) and OM-bound (blue hues) simulations. Arrows indicate the approximate value of the angle measured for representative experimental structures of the pre-power stroke state (PDB IDs shown). Apo trajectories showed a higher propensity for bent conformations (lower angles) than OM-bound simulations. The insets show representative Apo bent (green, left) and OM-bound straight (cyan, right) structures. Experimental structures of the relay helix in the near-rigor (NR, white, PDB ID: 1SR6) and pre-power stroke (PPS, magenta, PDB ID: 1QVI) state from scallop myosin are also represented as reference.</p

Collective motions in Apo and OM-bound simulations.

<p>A. Porcupine representation of PC1 (top panels) and PC2 (bottom) in ApoA1 (left panels) and OMA1 (right) simulations. The orange spikes show the direction and relative amplitude of motion of each residue along the PC. The approximate direction of the CLD hinge axis is also shown for Apo simulations (orange arrows). The two insets show the anti-correlated (Apo) and correlated (OM-bound) motions of the CLD (blue) and SH3 (green) subdomains. B. DynDom dynamic domain decomposition for ApoA1 PC1 (top) and the recovery stroke (bottom). The analysis was performed on the structures with minimum and maximum PC1 value from the MD simulation and on the experimental structures representing the pre-power stroke (PDB ID: 1QVI) and near-rigor (PDB ID: 1SR6) states for the recovery stroke. The fixed (white) and moving (yellow) domains identified by DynDom are shown, together with the hinge axis (orange) and the hinge regions (magenta).</p

Network of inter-residue contacts in the OM-binding site.

<p>Red edges connect pairs of residues that are found in contact for at least 70% of the simulation. All the residues within 8 Å from OM were included in the analysis. Contacts are reported for replica 1 only (see <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1005826#pcbi.1005826.s014" target="_blank">S4 Fig</a> for all the replicas). For each chain, pairs that were consistently found in contact in both OM-bound simulations and in none of the Apo ones are labelled.</p

OM-protein interactions.

<p>A. X-ray structure of the OM-binding site in cardiac myosin (PDB ID: 4PA0, chain A). Residues within contact distance from OM are shown as sticks and coloured according to the subdomain they belong to. B. Frequency of OM-residue contacts during OM-bound MD simulations. Each bar represents the fraction of the simulated time for which the corresponding residue was found in contact with OM (minimum distance between any non-hydrogen atom < 4 Å). Residues are labelled for frequencies larger than 0.5.</p

Comparison of dynamic cross-correlation networks.

<p>Difference DCCM matrices (ΔDCCM) calculated between pairs of OM-bound and Apo simulations are mapped onto the initial structures of each OM-bound simulation. Edges connect residue pairs that have a positive (red) and a negative (green) ΔDCCM value, using a threshold of 0.16. Residues in the OM-binding site are represented as yellow spheres, while the CLD domain is coloured in blue.</p

Mapping of C^α RMSF profiles onto the cMotorD structure.

<p>RMSF values from Apo and OM-bound simulations are colour mapped onto the cMotorD structure from blue (0 Å) to red (3.4 Å). The average structure is used for each simulation. The thickness of the tube representation is proportional to the RMSF value. High flexibility regions and the OM binding site are also labelled.</p