Cytosine base editing of LPA in transgenic mice averts large deletions.

Lipoprotein(a) (Lp(a)) is a genetically determined causal risk factor for cardiovascular disease, with approximately 20% of the population exhibiting elevated levels. While there are promising drugs in development, there are currently no approved therapies specifically designed to lower Lp(a) levels. For high-risk individuals with extreme levels of Lp(a), liver-directed genome editing could be an effective one-time solution. Genome editing approaches such as CRISPR and TALENs can reduce Lp(a) in LPA-transgenic mouse models, but they frequently induce large and potentially harmful genomic deletions. Here, we report the first application of TadA-derived cytosine base editing (CBE), delivered via helper-dependent adenovirus (HDAdV) and adeno-associated virus (AAV) vectors, to introduce premature stop codons into LPA. This strategy produced robust and durable lowering of circulating apolipoprotein(a) (apo(a)) in LPA-transgenic mice. Using SMRT-seq with single-molecule unique molecular identifiers, we quantified deletion events and found that CBE did not induce large deletions when targeting a single LPA site and produced only a small fraction (<4%) of large deletions when editing across multiple sites. In contrast, CRISPR-Cas9 cutting of LPA resulted primarily in large deletions. These findings demonstrate that CBE enables sustained reduction of circulating apolipoprotein(a) in an LPA-transgenic mouse model while largely preserving genomic integrity.