In Vivo Base Editing of Rescues Type 3 Long QT Syndrome in Mice.

Background: Pathogenic variants in can result in long QT syndrome type 3, a life-threatening genetic disease. Adenine base editors can convert targeted A T base pairs to G C base pairs, offering a promising tool to correct pathogenic variants.

Methods: We generated a long QT syndrome type 3 mouse model by introducing the T1307M pathogenic variant into the gene. The adenine base editor was split into 2 smaller parts and delivered into the heart by adeno-associated virus serotype 9 (AAV9-ABEmax) to correct the T1307M pathogenic variant.

Results: Both homozygous and heterozygous T1307M mice showed significant QT prolongation. Carbachol administration induced Torsades de Pointes or ventricular tachycardia for homozygous T1307M mice (20%) but not for heterozygous or wild-type mice. A single intraperitoneal injection of AAV9-ABEmax at postnatal day 14 resulted in up to 99.20% transcripts corrected in T1307M mice. mRNA correction rate >60% eliminated QT prolongation; mRNA correction rate <60% alleviated QT prolongation. Partial correction resulted in cardiomyocytes heterogeneity, which did not induce severe arrhythmias. We did not detect off-target DNA or RNA editing events in ABEmax-treated mouse hearts.

Conclusions: These findings show that in vivo AAV9-ABEmax editing can correct the variant allele, effectively ameliorating arrhythmia phenotypes. Our results offer a proof of concept for the treatment of hereditary arrhythmias.