Recently, the US Food and Drug Administration (FDA) provided clearance to proceed with a Phase 2 clinical trial assessing HST5040 to treat children with propionic acidemia and methylmalonic acidemia, two rare inborn error of metabolism conditions that currently have limited treatment options. We talked with one of the principal investigators of the study, Marshall Summar, MD, Division Chief, Genetics and Metabolism and Director of the Rare Disease Institute at Children’s National Hospital.