Phase 1 study demonstrates proof of concept for liver-targeted base modification for familial hypercholesterolemia.[1] The therapy uses base editing to deactivate the PCSK9 protein in the liver, which regulates cholesterol.[1] In three patients with heterozygous familial hypercholesterolemia (HeFH) who received the highest doses, levels of functional PCSK9 protein decreased by 47% to 84% and LDL cholesterol levels by 39% to 55% for at least 6 months.[1] Patients with HeFH have a genetic defect that prevents the liver from removing LDL cholesterol from the blood, leading to high levels and a risk of heart attack or stroke within 50 years without treatment.[1] Administration takes place by blood infusion with a base editor.[1] Conversion to a transformative therapy requires optimization of treatment efficacy, safety, patient selection, and study design.[1]