Beam Therapeutics (BEAM) investor relations material

BEAM-301 study design

• Open-label Phase I/II single-dose IV study in GSD1a patients with R83C; six treated (three each at 20 mg and 40 mg); median follow-up 7.6 months (range 1.9–16.6) at the Aug. 17, 2026 cutoff.

• The 60 mg cohort is enrolling 3–6 patients to assess safety, fasting tolerance and changes in starch supplementation.

BEAM-301 clinical findings

• Median time to fasting hypoglycemia rose from 2.9 to 4.3 hours at Day 36 in the 20 mg cohort, and from 2.5 to 15.0 hours in the 40 mg cohort.

• At 40 mg, 2 of 3 patients reached the 15-hour maximum controlled fast, with glucose generally remaining in the euglycemic range.

• Two of 3 patients at 40 mg stopped starch supplementation at their latest assessments; CGM showed more time euglycemic and less hyperglycemic despite reduced starch, with no overall increase in hypoglycemia time.

• The 40 mg nonresponder had BMI above 50; lower liver exposure from fixed dosing and compound heterozygosity were proposed as possible factors.

• Findings were described as clinical proof of concept for single-dose correction intended to restore endogenous glucose production.

Safety and dose evaluation

• Safety was described as acceptable and consistent with IV LNP risks; no dose-limiting toxicities, treatment-related discontinuations or Grade 4/5 treatment-emergent adverse events were reported.

• Four of six patients had serious treatment-related adverse events, including three Grade 3 infusion reactions; diarrhea and rhabdomyolysis also resolved.

• Infusion-related reactions and transient transaminase elevations were most frequent; liver enzyme elevations resolved without treatment, with all but one Grade 2 AST elevation classified as Grade 1.

• Steroid premedication and infusion regimens were modified after Grade 3 infusion reactions; investigators supported escalation to 60 mg.