Patterns of X-linked Retinitis Pigmentosa Genetic Testing in England and Implications for Service Provision

Purpose
To establish the prevalence of retinitis pigmentosa GTPase regulator (RPGR)-associated X-linked retinitis pigmentosa (XLRP) in England.
Design
A cross-sectional prevalence study.
Participants
English National Health Service patients referred for XLRP molecular testing between 2004 and 2024.
Methods
We calculated the overall prevalence rate of RPGR-XLRP for the study period by summing the genetically confirmed cases held in a database by a single testing center, which was the sole provider of Open Reading Frame 15 (ORF15) RPGR testing in the United Kingdom, in the study period (2004 to 2024). We used this information to calculate a mortality-adjusted minimum prevalence of RPGR-XLRP per 100 000 population (2024) in England. We also investigated trends in genetic testing over time and explored equity of access by region and socio-economic status through comparisons of absolute test numbers and testing rates per 100 000 population.
Main Outcome Measures
Prevalence of RPGR-XLRP per 100 000 population, overall and stratified by region and Index of Multiple Deprivation (IMD) quintile.
Results
The estimated mortality-adjusted prevalence of RPGR-XLRP in England is 1.67 per 100 000 population (2024), corresponding to an estimated 977 living patients in 2024 from 1024 diagnoses made between 2004 and 2024. The estimated mortality-adjusted prevalence of RPGR-XLRP among males is 2.18 per 100 000 males (n = 626) and 1.17 per 100 000 females (n = 351) (2024). The mean age of test-positive patients was 44.1 years at study end date (2024). Population-standardized testing rates were broadly consistent across regions, with all regions falling within 19% of the national average, except the North West (34%), reflecting interregional referral patterns. Testing volumes (absolute numbers) per socio-economic quintile (IMD) were within 17% of the average. The number of individuals tested for ORF15 seemed to reduce after the introduction of whole genome sequencing (2019).
Conclusions
We identified an estimated 977 living patients with RPGR-associated XLRP from 2594 tested individuals, representing a large absolute number and significant population who could benefit from emerging gene therapy, with prevalence higher than other treatable inherited retinal dystrophies. We found no systematic inequities in test access by socio-economic status or region, though a decline in testing since 2020 warrants further investigation.