Isaralgagene civaparvovec

Fabry disease is caused by changes in the GLA gene that reduce or remove the activity of alpha-galactosidase A, an enzyme that breaks down a fatty substance called globotriaosylceramide (Gb3)^[10]. Without enough enzyme, Gb3 builds up in cells, especially in blood vessel linings, the kidneys, the heart and the nervous system, which over time can lead to kidney failure, heart disease and stroke^[10].

The approved treatments replace the enzyme from outside the body. Fabrazyme and Elfabrio are given as IV infusions every 2 weeks^[11][12]. ST-920 instead tries to have the body make the enzyme itself. ClinicalTrials.gov describes it as an AAV2/6 vector, a harmless virus shell, carrying the DNA code for human alpha-galactosidase A, given as a single IV infusion and designed to provide stable, long-term enzyme production^[7].

A 2020 mouse study by Sangamo and Mount Sinai researchers describes the approach as a GLA gene driven by a liver-specific switch, with ST-920 chosen as the optimized clinical version^[9]. PTC says ST-920 enabled long-term enzyme production and lowered Gb3 in clinical studies, and that it needs no preconditioning before the infusion^[1][2].

People with neutralizing antibodies to AAV6 were excluded from STAAR, because existing antibodies can block the virus shell^[7].

STAAR (NCT04046224) is a Phase 1/2, open-label, single-dose, dose-ranging study in adults 18 and older with Fabry disease^[7]. It started on July 23, 2019, reached primary completion on April 10, 2025 and is listed as completed, with 36 people enrolled at 18 sites^[7]. Of those sites, 9 are in the US: Irvine, Tampa, Atlanta, Chicago, Iowa City, Minneapolis, New York, Cincinnati and Fairfax, Virginia; the others are in Australia, Canada, Germany, Italy, Taiwan and the UK^[7].

After the dose-finding groups, expansion groups enrolled people with and without antibodies to the enzyme, women, and people with kidney or heart involvement^[7]. The registry's main measure was side effects up to 12 months after the infusion^[7].

The median age was 42 and the median follow-up 24 months^[4]. Sangamo said the FDA agreed that the 52-week eGFR slope can serve as an intermediate endpoint, an early measure for accelerated approval^[4]. PTC said the 104-week STAAR results are planned as confirmatory evidence for traditional approval^[2]. STAAR had no placebo or comparison group^[7].

A long-term follow-up study (NCT05039866) enrolled 32 people treated with ST-920, is active but not recruiting, and tracks long-term safety with an estimated primary completion in March 2029^[8].

ST-920 has no FDA label, so its official side effects and warnings are not set. In STAAR, Sangamo reported that most side effects were grade 1 or 2, the milder end of the scale. The most common were fever (60.6%), COVID-19 (36.4%), nasopharyngitis, a cold-like nose and throat infection (33.3%), and headache (30.3%)^[5]. Sangamo said all side effects resolved with clinical management, no one left the study for safety reasons and no one died^[5].

The results posted on ClinicalTrials.gov list 33 people in the safety count. Of these, 4 had a serious adverse event: sepsis, chest pain, enthesopathy (inflammation where a tendon attaches to bone), and in 1 person a stroke including a brain stem stroke^[7]. The posted results do not say whether these serious events were caused by ST-920^[7].

Overall, 23 of 33 people had at least 1 side effect the investigators linked to ST-920 within 12 months^[7]. Sangamo also reported that of 10 people with antibodies against the enzyme before treatment, levels fell markedly in 9 and became undetectable in 8^[5].

Sangamo Therapeutics developed ST-920 and began STAAR in July 2019^[7]. A 2020 paper by Sangamo and Mount Sinai researchers described the mouse studies behind it^[9]. Sangamo released STAAR topline results on June 24, 2025 and detailed results on September 4, 2025^[4][5]. The FDA granted ST-920 Orphan Drug, Fast Track and RMAT designations; the European Medicines Agency granted orphan designation and PRIME eligibility; and the UK MHRA admitted it to its Innovative Licensing and Access Pathway^[1].

PTC announced on August 12, 2026 that it had won ST-920 in a bankruptcy auction of Sangamo's assets^[2]. PTC said then that the nonclinical and clinical modules of the rolling application had already been submitted, with the manufacturing (CMC) package expected in the fourth quarter of 2026^[2]. PTC paid $111.0 million upfront, with up to $100.0 million more tied to US approvals^[3].

BioPharma Dive reported on August 13, 2026 that $80 million of that is due on an accelerated approval and $20 million on a full approval^[6]. PTC completed the purchase on September 21, 2026^[1]. PTC's October 29, 2026 update did not report an FDA acceptance of the application^[3].