Beam Therapeutics reported the first human data for BEAM-301, a liver targeted lipid nanoparticle carrying base editing reagents designed to correct the R83C mutation in the G6PC1 gene, one of the most common and most severe causes of glycogen storage disease type Ia. The company called the result clinical proof of concept for genetic correction of the mutation, and the full dataset will be presented at the European Society of Gene and Cell Therapy congress in Hamburg on October 28.
Six patients had received a single intravenous infusion by the June 26, 2026 data cutoff, three at 20 mg and three at 40 mg. The efficacy signal was dose dependent. Median time to fasting hypoglycemia at baseline was 2.9 hours in the low dose cohort and 2.5 hours in the high dose cohort. By day 36 the low dose median had risen to 4.3 hours, while both evaluable patients at 40 mg reached the protocol maximum of at least 15 hours of controlled fasting, which Beam reads as restored endogenous glucose production. One high dose patient was not yet evaluable, and median follow up in that cohort was only 53 days against 313 days at the lower dose.
Starch dependence fell with it. Prescribed daily starch intake dropped from baseline by 74, 71 and 11 percent at successive follow ups in the low dose cohort, and by 71 and 92 percent in the two evaluable high dose patients. Patients with the R83C mutation normally need cornstarch every one to three hours, including overnight, to avoid hypoglycemic shock.
The safety picture is early and not clean. Every patient had at least one treatment related adverse event. Five serious adverse events resolved within two to ten days, including three Grade 3 infusion related reactions, which Beam linked in part to the shorter acting steroid premedication used in this population; the regimen has since been changed. Liver enzyme rises were transient and mostly Grade 1, and there were no dose limiting toxicities, discontinuations or deaths. With six patients, an open label design and very uneven follow up, this is a mechanism result, not an efficacy verdict. Beam hosts an investor event on October 27.