What are the recommended treatments for choroideremia (choroidal retinal degeneration)?

Treatment of Choroideremia

Gene therapy with subretinal timrepigene emparvovec (AAV2-REP1 vector) is the primary therapeutic intervention for choroideremia, though recent phase 3 trials failed to meet primary visual acuity endpoints, and optimization of patient selection and surgical technique remains critical. 1

Gene Therapy: Current Evidence and Limitations

Timrepigene Emparvovec (AAV2-REP1)

• The most recent phase 3 randomized trial (2023) evaluated high-dose (1.0 × 10¹¹ vector genomes) versus low-dose (1.0 × 10¹⁰ vg) subretinal injection but failed to meet its primary endpoint of ≥15-letter ETDRS visual acuity improvement at 12 months (high-dose: 5% vs control: 0%, P=0.245). 1
• However, 14% of high-dose and 18% of low-dose patients achieved ≥10-letter improvement versus 2% of controls, suggesting potential benefit in select patients. 1
• Earlier phase 1/2 trials (2014-2018) showed more promising results, with mean visual acuity gains of 3.8-4.5 letters and improved retinal sensitivity (2.3 dB increase in dark-adapted microperimetry), particularly in patients with more preserved retinal area. 2, 3

Safety Profile

• Bilateral sequential administration is well-tolerated with predominantly mild-to-moderate treatment-emergent adverse events (TEAEs) and low serious surgical complication rates (7.6%). 4
• Retinal inflammation occurs in 45.5% of patients but is typically not associated with clinically significant vision loss at 12 months. 4
• Serious noninfective retinitis occurred in 3% of patients. 4
• Presence of baseline anti-vector neutralizing antibodies may increase risk of ocular inflammation after first-eye injection. 4

Critical Factors for Treatment Optimization

Patient Selection Criteria

• Prioritize patients with more preserved retinal area rather than late-stage disease, as this was identified as a key limitation in the phase 3 trial failure. 1
• Regions within 1° of the fundus autofluorescence (FAF) border lose retinal sensitivity most rapidly (-1.50 to -1.94 dB/year) and are projected to lose 7 dB sensitivity in approximately 3.5 years. 5
• Cone spacing z-scores increase uniformly by 0.57 per year across the residual macular area, indicating progressive photoreceptor loss. 5

Surgical Technique Considerations

• Subretinal injection following vitrectomy and retinal detachment is the standard delivery method, using up to 0.1 mL containing 1 × 10¹¹ vector genomes. 4
• Vector must be administered to the fovea; patients receiving off-foveal injections develop eccentric fixation patterns. 3
• Surgical complications including retinal detachment can reduce vision, though some patients recovered or exceeded baseline visual acuity despite this complication. 3

Timing of Bilateral Treatment

• Bilateral sequential administration can be performed with intrasurgery windows of <6-12, or >12 months without increased risk of serious adverse events. 4
• Prior timrepigene emparvovec exposure does not increase risk upon second-eye injection, and no systemic immune reaction or inoculation effect has been observed. 4

Monitoring and Endpoints

Functional Assessment

• Microperimetry for retinal sensitivity measurement is more sensitive than visual acuity for detecting treatment effects, showing 2.3 dB improvements in treated eyes versus -0.8 to -1.6 dB decline in control eyes. 3
• Dark-adapted microperimetry specifically assesses rod and cone function recovery. 3
• Visual acuity alone may underestimate treatment benefit, as patients can maintain or improve vision despite undergoing retinal detachment during surgery. 2, 3

Structural Monitoring

• Optical coherence tomography angiography to assess choriocapillaris flow deficits, which increase by 3.43% per year at 1° inside the FAF border. 5
• Adaptive optics scanning light ophthalmoscopy for cone structure assessment. 5
• Fundus autofluorescence to define the border of viable retina. 5

Common Pitfalls to Avoid

• Do not treat patients with advanced disease and minimal residual retinal area, as they are unlikely to benefit based on phase 3 trial results. 1
• Do not rely solely on visual acuity as the treatment success metric; incorporate retinal sensitivity and structural measures. 3, 5
• Screen for anti-vector neutralizing antibodies before treatment, as their presence may predict increased inflammatory complications. 4
• Ensure foveal vector delivery to avoid eccentric fixation patterns. 3