Beam Therapeutics (NASDAQ:BEAM) reported initial clinical data from its Phase I/II trial of BEAM-301, an investigational base-editing therapy for glycogen storage disease type 1A (GSD1a), showing dose-dependent improvements in fasting tolerance and reductions in cornstarch supplementation among the first six treated patients.
The data, presented at the ESGCT Annual Congress, included three patients treated with a 20 mg dose and three patients treated with a 40 mg dose. As of an Aug. 17, 2026 cutoff, median follow-up across both cohorts was 7.6 months.
Fasting Tolerance Improved in Higher-Dose Cohort
GSD1a is a metabolic disease caused by mutations in the G6PC1 gene that impair the body’s ability to maintain glucose levels during fasting. Patients can become severely hypoglycemic within two to three hours without food or cornstarch and may require frequent doses of cornstarch throughout the day and overnight.
BEAM-301 is an mRNA-based adenine base editor and guide RNA delivered through a lipid nanoparticle, or LNP. It is designed to correct the R83C mutation in the G6PC1 gene and restore glucose-6-phosphatase activity in the liver.
At baseline, the six patients had a median fasting duration of 2.7 hours before reaching hypoglycemia, defined as glucose levels below 60 mg/dL. They also required a median of six cornstarch doses per day.
According to Chief Medical Officer Amy Simon, the median fasting duration in the 20 mg cohort increased from 2.9 hours at baseline to 4.3 hours at day 36. In the 40 mg cohort, median fasting duration increased from 2.5 hours at baseline to 15 hours, the protocol-defined maximum duration of the controlled fasting challenge.
Two of the three patients treated at 40 mg reached the 15-hour fasting limit and eliminated cornstarch supplementation entirely. The third patient in that cohort did not show increased fasting duration. Simon said the company is evaluating whether the lack of response may be related to elevated body mass index, potentially reducing liver drug exposure, or to the patient’s compound heterozygous genotype.
“Taken together, we believe these initial data demonstrate clinical proof of concept for BEAM-301,” Simon said.
Safety Findings and Next Steps
Beam said BEAM-301 showed an acceptable safety profile at both tested dose levels. The company reported no dose-limiting toxicities, treatment-related discontinuations, or Grade 4 or Grade 5 treatment-emergent adverse events.
The most frequent treatment-related adverse events were infusion-related reactions and transient elevations in transaminases, which Beam said were consistent with the known safety profile of intravenous LNPs. All transaminase elevations resolved without intervention. With the exception of one Grade 2 AST elevation, the elevations were Grade 1.
Simon said the Grade 3 infusion-related reactions may have been influenced by the use of shorter-acting steroid premedication in this patient population. Long-acting steroids are generally avoided in GSD1a because of the potential risk of metabolic decompensation. Beam has since modified its premedication regimen.
The company is enrolling patients in a 60 mg cohort to further evaluate safety and efficacy and select an optimal biological dose. Beam may also consider expanding cohorts beyond three patients and potentially opening a pediatric cohort, executives said during the question-and-answer session.
Chief Executive Officer John Evans said Beam plans to engage the FDA on a potential approval pathway after reviewing data from the 60 mg cohort. He said the company expects to seek an efficient development route given the severity and rarity of the R83C patient population. Beam estimates there are approximately 300 diagnosed U.S. patients with the mutation, though Evans said epidemiological calculations could suggest a higher figure.
Platform Strategy Extends to PKU
Beam also discussed progress in its BEAM-304 program for phenylketonuria, or PKU, an inherited metabolic disorder caused by multiple mutations in the PAH gene. The company said it has identified a third development candidate, BEAM-304C, targeting an undisclosed PKU mutation, following the prior identification of BEAM-304A and BEAM-304B.
Beam said the first three BEAM-304 candidates could potentially address up to half of U.S. PKU patients. The company plans to use a shared LNP delivery system, manufacturing approach and clinical framework across the variants while designing each editor and guide RNA for a specific disease-causing mutation.
President Giuseppe Pino Ciaramella said the FDA cleared a single investigational new drug application for BEAM-304 that enables Beam to evaluate multiple candidates under one clinical protocol. BEAM-304A is planned to enter dose escalation first, with subsequent variants potentially starting at the optimal biological dose identified for the first candidate.
Evans said the company expects the first PKU sites to open around the end of 2026 or early 2027, noting that Beam plans to conduct the study through major U.S. academic metabolic centers.
Beam also reiterated that its sickle cell disease program, risto-cel, remains on track for a potential biologics license application submission and potential first commercial launch, while its BEAM-302 program for alpha-1 antitrypsin deficiency is in pivotal development.
About Beam Therapeutics (NASDAQ:BEAM)
Beam Therapeutics Inc is a biotechnology company developing precision genetic medicines for patients with serious diseases. The company’s platform uses base editing, a form of gene editing designed to make targeted changes to individual DNA letters without creating double-strand breaks. Beam is also advancing related editing technologies and delivery systems intended to improve the precision and effectiveness of genetic treatments.
Beam’s pipeline includes investigational programs for diseases such as sickle cell disease, beta thalassemia, alpha-1 antitrypsin deficiency and glycogen storage disease type Ia.
