Detailed comparison of phenotype between male patients carrying variants in exons 1-14 and ORF15 of RPGR

AAV-RPGR Gene Therapy Rescues Opsin Mislocalisation in a Human Retinal Organoid Model of RPGR-Associated X-Linked Retinitis Pigmentosa

Variants within the Retinitis Pigmentosa GTPase regulator (RPGR) gene are the predominant cause of X-Linked Retinitis Pigmentosa (XLRP), a common and severe form of inherited retinal disease. XLRP is characterised by the progressive degeneration and loss of photoreceptors, leading to visual loss and, ultimately, bilateral blindness. Unfortunately, there are no effective approved treatments for RPGR-associated XLRP. We sought to investigate the efficacy of RPGRORF15 gene supplementation using a clinically relevant construct in human RPGR-deficient retinal organoids (ROs). Isogenic RPGR knockout (KO)-induced pluripotent stem cells (IPSCs) were generated using established CRISPR/Cas9 gene editing methods targeting RPGR. RPGR-KO and isogenic wild-type IPSCs were differentiated into ROs and utilised to test the adeno associated virus (AAV) RPGR (AAV-RPGR) clinical vector construct. The transduction of RPGR-KO ROs using AAV-RPGR successfully restored RPGR mRNA and protein expression and localisation to the photoreceptor connecting cilium in rod and cone photoreceptors. Vector-derived RPGR demonstrated equivalent levels of glutamylation to WT ROs. In addition, treatment with AAV-RPGR restored rhodopsin localisation within RPGR-KO ROs, reducing mislocalisation to the photoreceptor outer nuclear layer. These data provide mechanistic insights into RPGRORF15 gene supplementation functional potency in human photoreceptor cells and support the previously reported Phase I/II trial positive results using this vector construct in patients with RPGR-associated XLRP, which is currently being tested in a Phase III clinical trial.

Novel hemizygous single-nucleotide duplication in RPGR in a patient with retinal dystrophy and sensorineural hearing loss

BACKGROUND

The RPGR gene has been associated with X-linked cone-rod dystrophy. This report describes a variant in RPGR detected with exome sequencing (ES). Genes like RPGR have not always been included in panel-based testing and thus genome-wide tests such as ES may be required for accurate diagnosis.

METHODS

The Texome Project is studying the impact of ES in medically underserved patients who are in need of genomic testing to guide diagnosis and medical management. The hypothesis is that ES could uncover diagnoses not made by standard medical care.

RESULTS

A 58-year-old male presented with retinitis pigmentosa, sensorineural hearing loss, and a family history of retinal diseases. A previous targeted gene panel for retinal disorders had not identified a molecular cause. ES through the Texome Project identified a novel, hemizygous variant in RPGR (NM_000328.3: c.1302dup, p.L435Sfs*18) that explained the ocular phenotype.

CONCLUSIONS

Continued genetics evaluation can help to end diagnostic odysseys of patients. Careful consideration of genes represented when utilizing gene panels is crucial to ensure an accurate diagnosis. Medically underserved populations are less likely to receive comprehensive genetic testing in their diagnostic workup. Our report is an example of the medical impact of genomic medicine implementation.

Characterization of Retinal Function Using Microperimetry-Derived Metrics in Both Adults and Children With RPGR-Associated Retinopathy

PURPOSE

To investigate microperimetry testing of retinitis pigmentosa GTPase regulator gene (RPGR)-associated retinopathy in a cohort of children and adults.

DESIGN

Prospective observational case series.

METHODS

The coefficient of repeatability and intraclass correlation coefficient (ICC) of mean sensitivity (MS) were calculated for mesopic microperimetry. Best-corrected visual acuity (BCVA), contrast sensitivity (CS), MS, total volume (V_TOT), and central 3-degree field volume (V₃) from volumetric and topographic analyses were acquired.

RESULTS

The study recruited 76 individuals with RPGR (53 adults, 23 children). The mean follow-up period was 2.8 years. The ICC values for MS, V_TOT, and V₃ were 0.982 dB (95% CI, 0.969-0.989 dB), 0.970 dB-steradian (sr) (95% CI, -0.02658 to 0.03691 dB-sr), and 0.986 dB-sr (95% CI, 0.978-0.991), respectively. The r values for interocular MS, V_TOT, and V₃ were 0.97 (P < .01), 0.97 (P < .01), and 0.98 (P < .01), respectively, indicating strong interocular correlation. The interocular correlation of progression for MS, V_TOT, and V₃ was 0.81 (P < .01), 0.64 (P < .01), and 0.81 (P < .01), respectively. There was no statistically significant difference in the interocular progression rates for MS or V_TOT. V₃ did show a statistically significant difference. Most patients lost retinal sensitivity rapidly during their second and third decades of life.

CONCLUSIONS

The high degree of reproducibility of results and the good interocular correlation lends this method to accurately monitoring disease progression, as well as supporting validation of the use of MP in assessing the outcomes of gene therapy clinical treatment trials.