Sarepta Therapeutics (SRPT) surged 35% after reporting the first clinical data from its siRNA platform, licensed from Arrowhead Pharmaceuticals. SRP-1001 achieved 90-93% knockdown of disease-driving genes in FSHD, with no dose-limiting toxicities. Jefferies projects $1B+ peak sales for each of the two programs.

Maze Therapeutics (MAZE) dropped over 30% on Wednesday despite the positive APOL1 kidney data we reported yesterday. Analysts flagged the small sample size (n=15) and questioned whether efficacy extends robustly beyond the severe FSGS subgroup. This is an important market correction to yesterday's scientific read.

Rocket Pharma's Kresladi PDUFA for LAD-I gene therapy lands tomorrow.

Rocket Pharma (Tomorrow, March 28): Kresladi PDUFA for LAD-I gene therapy. This is the company's second FDA attempt after a 2024 rejection on manufacturing issues. Approval would include a Priority Review Voucher worth $100M+, which is critical to extending Rocket's cash runway.

ACC.26 (March 28-30): American College of Cardiology in New Orleans starts tomorrow. Watch for cardiovascular outcomes data and GLP-1 cardio-metabolic crossover presentations.

Sarepta Registrational Path: Management is expected to meet with the FDA in late Q2 2026 to discuss an accelerated approval pathway for SRP-1001 based on the biomarker data. Registrational trials could start by year-end 2026.

Orforglipron (April 10): Lilly's oral GLP-1 target action date is two weeks away.

What Happened: Sarepta Therapeutics (SRPT) reported the first clinical results from its next-generation siRNA platform, and the data landed with massive force. The stock surged approximately 35% in a single session, marking the company's largest one-day gain in nearly a decade.

The Data: Sarepta presented Phase 1/2 results from two programs built on a proprietary targeted delivery system licensed from Arrowhead Pharmaceuticals (ARWR) in a landmark deal worth $825M upfront ($500M cash + $325M equity premium) with up to $10B in total milestones, which closed in February 2025:

The Safety: No dose-limiting toxicities were observed in either program. Importantly, no kidney or magnesium issues that plagued earlier siRNA candidates were reported.

Executive Impact: This is a massive pivot story. Sarepta spent years trying to build a gene therapy franchise beyond Duchenne muscular dystrophy, with highly mixed results. The Arrowhead deal gave Sarepta access to the TRiM delivery platform, enabling siRNA to penetrate muscle tissue far more efficiently than older technologies. Jefferies called the results "competitive" and "strong," projecting over $1 billion in peak sales for each program. Sarepta is officially no longer a one-disease company.

What Happened: In yesterday's email, we covered Maze Therapeutics' (MAZE) positive Phase 2 HORIZON data for MZE829 in APOL1-mediated kidney disease. The stock was initially up 9% in pre-market, but by the close, MAZE had dropped over 30%.

What Changed: The clinical data itself didn't change; the market's assessment of the data's scalability did. Truist noted that with efficacy appearing most robust in a small, severe FSGS subset, there are questions around the breadth of therapeutic impact across broader AMKD. Mizuho acknowledged the drug "looks better" than Vertex's inaxaplin in cross-trial comparisons (62% vs 43% uACR reduction), but noted Wall Street is "getting hung up" with the numbers in the broad population.

The Core Issue: Only 15 patients were enrolled. The FSGS subgroup had just 5 patients. While the data is genuinely encouraging from a scientific standpoint, the sample size makes it impossible for institutional investors to size a position with confidence.

Our Take: The data is still the first clinical proof-of-concept in a genetically defined kidney disease population, and the FSGS signal beats the closest competitor. But the market reaction is a brutal reminder that proof-of-concept in 15 patients is a long way from a registrational program.

The Setup: Rocket Pharmaceuticals (RCKT) faces a March 28 PDUFA for Kresladi, a lentiviral gene therapy for leukocyte adhesion deficiency type I (LAD-I). The FDA rejected Kresladi in 2024, with concerns centered entirely on manufacturing and characterization rather than clinical efficacy.

The Binary: An approval grants Rocket a Priority Review Voucher (recently valued at $100M+) and the first approved treatment for a devastating pediatric immune disorder. A second CRL would significantly damage investor confidence in the platform's manufacturing viability. This is as binary as it gets in gene therapy.