FDA Clears Gene Therapy Trial for Phenylketonuria (PKU)

Beam Therapeutics has received FDA clearance to begin a clinical trial for its BEAM-304 base-editing gene therapy targeting phenylketonuria (PKU), while Merck's Capvaxive pneumococcal vaccine received expanded FDA approval for at-risk children and adolescents aged 2-17.

The FDA has cleared BEAM Therapeutics to begin a clinical trial for BEAM-304, its base-editing gene therapy candidate targeting phenylketonuria (PKU), a rare inherited metabolic disorder. The clearance marks a significant regulatory step for Beam, which announced the BEAM-304 program in early 2026 as part of its liver-targeted genetic disease pipeline. PKU is caused by mutations in the phenylalanine hydroxylase (PAH) gene, which impairs the body's ability to metabolize the amino acid phenylalanine, leading to toxic buildup that can cause severe neurological damage if untreated.

BEAM-304 uses Beam's proprietary adenine base editing technology delivered via lipid nanoparticles (LNPs) directly to liver cells, where the PAH gene is expressed. Unlike older gene therapy approaches that insert entire gene copies, base editing makes precise single-letter corrections to the DNA without creating double-strand breaks, which is intended to reduce the risk of off-target genomic disruption. PKU affects roughly 1 in 10,000 to 15,000 newborns in the United States and Europe. While dietary management and existing enzyme substitution therapies can reduce phenylalanine levels, they require lifelong adherence and do not address the underlying genetic defect. A one-time corrective gene therapy would represent a meaningful step toward a durable treatment.

Also on Wednesday, the FDA granted an expanded indication for MRK Merck's Capvaxive (pneumococcal 21-valent conjugate vaccine, PCV21), approving its use in children and adolescents aged 2-17 years who have completed a primary pediatric vaccination series and have chronic conditions that elevate pneumococcal disease risk. The approval was supported by data from Merck's Phase 3 STRIDE-13 trial. Capvaxive is now the only pneumococcal conjugate vaccine in the United States with a specific studied indication for this at-risk pediatric population, positioning it competitively against Pfizer's established Prevnar franchise. While the two FDA actions cover distinct disease areas, both reflect the agency's continued activity in rare and pediatric indications this week.