Sangamo's ST-920 Demonstrates Positive Slope in Kidney Function—A Major Breakthrough in Fabry Disease Gene Therapy

Sangamo Therapeutics has unveiled encouraging results from its Phase 1/2 STAAR clinical trial, showing that isaralgagene civaparvovec (ST-920), an investigational gene therapy, is achieving significant improvements in kidney function for Fabry disease patients. The positive slope observed in kidney function metrics represents a meaningful advancement in treating this rare genetic disorder, where patients typically experience progressive organ damage due to enzyme deficiency.

What the Data Shows: Positive Slope in Clinical Outcomes

The trial tracked 32 patients across different treatment backgrounds—those currently on enzyme replacement therapy (ERT), those who had paused ERT for at least six months, and those never treated with ERT. Across all participants, ST-920 demonstrated a positive annualized slope of 1.965 mL/min/1.73m² per year in estimated glomerular filtration rate (eGFR) at the 52-week mark, a metric that measures how efficiently the kidneys filter waste from the blood. For 19 patients followed for two years, the positive slope continued at 1.747 mL/min/1.73m² per year, indicating the therapy’s sustained benefit.

Beyond kidney function, the trial documented stable cardiac structure and function over one year, with consistent results across different patient subgroups. Most remarkably, patients who received ST-920 maintained elevated levels of alpha-galactosidase A (a-Gal A) activity—the enzyme missing in Fabry disease—for as long as 4.5 years in the longest-followed patient, demonstrating the durability of the gene therapy’s effects.

The Regulatory Fast Track: Accelerated Approval on the Horizon

ST-920 has received multiple FDA designations recognizing its potential: Orphan Drug status, Fast Track designation, and RMAT (Regenerative Medicine Advanced Therapy) status. More significantly, the FDA has agreed that the positive slope data from the Phase 1/2 trial—specifically the 52-week kidney function improvement—can serve as the primary basis for accelerated approval, bypassing the traditional lengthy review process.

In December 2025, Sangamo initiated a rolling submission of a Biologics License Application (BLA) to the FDA, seeking approval under this accelerated pathway. This means patients with Fabry disease could potentially access ST-920 much sooner than typical pharmaceutical development timelines would allow. Notably, ST-920 does not require the intensive preconditioning regimens that some other gene therapies demand, reducing treatment burden and safety risks.

Market Opportunity: Why This Matters

According to market research from Grandview Research, the global market for Fabry disease treatments reached $2.54 billion in 2023. With ST-920 poised as a potentially transformative therapy, the market is projected to expand to $4.93 billion by 2030, growing at a compound annual rate of 9.9%. This expansion reflects not only increased patient diagnosis and awareness but also the significant value investors and healthcare systems place on therapies that can halt or reverse disease progression.

For Fabry disease patients—predominantly children and young adults living with a progressive condition that affects kidneys, heart, nervous system, and skin—a gene therapy offering durable improvement in kidney function represents a genuine medical advance. The positive slope trajectory observed in ST-920 trials suggests that patients may experience sustained functional benefit rather than disease stabilization alone.

What’s Next

Sangamo’s clinical data team will present detailed findings in multiple platform presentations and poster sessions at the 22nd Annual WORLD Symposium in February 2026, providing the medical community with comprehensive peer-reviewed analysis of the positive slope outcomes and their implications. The rolling BLA submission process means the FDA will review data as it becomes available, potentially accelerating the approval timeline compared to traditional pathways.

With favorable safety data, durable clinical benefits, and regulatory support, ST-920 stands positioned as a potentially paradigm-shifting treatment option for Fabry disease—a rare condition where meaningful therapeutic options have historically been limited. The positive slope in kidney function metrics suggests that gene therapy may offer what many rare disease patients have long sought: the possibility of meaningful, sustained improvement rather than slowing decline.