The Food and Drug Administration (FDA) has granted Fast Track designation to 4D-125 for the treatment of patients with inherited retinal dystrophies due to defects in the retinitis pigmentosa GTPase regulator (RPGR) gene, including X-linked retinitis pigmentosa.

X-linked retinitis pigmentosa (XLRP) is a rare genetic disorder characterized by dysfunction and degeneration of photoreceptors in the retina leading to progressive vision loss and blindness in boys and young men. 4D-125 is a targeted gene therapy designed to deliver a functional copy of the RPGR gene to photoreceptors in the retina.

The Company is currently evaluating 4D-125 via intravitreal administration in males 18 years of age and older with XLRP caused by mutations in the RPGR gene in an open-label, multicenter phase 1/2 study ( Identifier: NCT04517149). The primary endpoints are the incidence and severity of treatment-emergent adverse events and serious adverse events. Secondary endpoints include assessments of clinical activity.

Interim results from 8 patients showed that the treatment was well tolerated with no serious adverse events or chronic inflammation observed. Moreover, anatomical retina preservation and functional improvements were reported in 2 patients who were evaluable for clinical activity.

“Patients living with XLRP currently have no approved treatments, and they suffer from progressive vision loss and blindness that reduces their quality of life and independence,” said Robert Kim, MD, Senior Vice President and Ophthalmology Therapeutic Area Head of 4DMT. “Fast Track designation is a landmark event for the program and underscores the potential of 4D-125 to address a significant unmet need for those living with XLRP.”

The FDA’s Fast Track process allows for expedited review of drugs that are expected to fill an unmet need such as providing a therapy that may be better than currently available treatments.


  1. 4D Molecular Therapeutics announces FDA Fast Track designation granted to 4D-125 for the treatment of X-linked retinitis pigmentosa. News release. January 10, 2022.
  2. 4D Molecular Therapeutics presents interim results from the ongoing 4D-125 phase 1/2 clinical trial in patients with advanced X-linked retinitis pigmentosa at the ASRS Annual Meeting. News release. October 10, 2021.