NM_174936.4(PCSK9):c.399+1G>A

Base Editing (ABE8e) via LNP delivery is a rationale-driven therapeutic strategy for Coronary artery disease with genetically mediated dyslipidaemia (PCSK9/LDLR/LPA-driven) targeting the PCSK9 c.399+1G>A variant (Likely pathogenic, splice donor variant, intron variant). The editing system (ABE8e-nSpCas9) corrects the splice-site point mutation to restore canonical splicing, as the underlying change is a single-nucleotide transition. Target tissue: Liver. Therapeutic goal: Permanently disrupt hepatic PCSK9 at Chr1:55505647 (GRCh38) to lower lifelong LDL-cholesterol and reduce coronary artery disease events, mimicking human PCSK9 loss-of-function protection.. Risk profile: off-target Medium, delivery complexity Low, immunogenicity Low.

1. Molecular basis: PCSK9 NM_174936.4(PCSK9):c.399+1G>A is classified as Likely pathogenic (ClinVar variation ID 4277664). Molecular consequence: splice donor variant, intron variant. 2. Epidemiology: Ischaemic heart disease, predominantly coronary artery disease (CAD), is the leading cause of death worldwide and accounts for ~23.5% of DALYs among non-communicable diseases; DALYs due to ischaemic heart disease increased by ~28% from 2005 to 2015 [PAPER-01]. Elevated lipoprotein(a) affects tens of 3. Standard of care: Guideline-directed therapy for CAD combines lifestyle modification, intensive lipid lowering (high-intensity statins with add-on ezetimibe and PCSK9-directed therapies), antiplatelet and antianginal medications, and coronary revascularisation by PCI with drug-eluting stents or CABG in appropriate an 4. Pipeline: Multiple late-stage RNA-based programs target coronary risk pathways. PCSK9 mAbs are approved with completed Phase III outcomes trials (FOURIER and others) showing ~15% relative MACE reduction over ~2 years [PAPER-05, PAPER-02], and inclisiran is approved based on durable ~50% LDL-C reduction with o 5. ABE clinical validation: ABE8e (Richter et al. 2020, Nat Biotechnol) achieves ~1.7x higher editing efficiency than ABE7.10. VERVE-101 demonstrated first-in-human LNP-ABE liver editing with 55-66% PCSK9 reduction (Raal et al. 2025, NEJM). Beam Therapeutics is advancing multiple ABE programs.

1. No published data specifically correcting PCSK9 c.399+1G>A with Base Editing (ABE8e); strategy is based on general principles and must be validated preclinically. 2. PAM availability and bystander base analysis for the specific genomic context have not been performed. If no canonical NGG PAM positions the target within the editing window, PAM-flexible variants (SpRY) may be needed. 3. Long-term durability, off-target genome-wide effects, and immunogenicity in the target patient population require thorough preclinical and clinical evaluation.

In vivo adenine base editing to disrupt PCSK9 in hepatocytes represents a paradigm-shifting approach to cardiovascular disease — a single infusion to permanently lower LDL-cholesterol by mimicking the cardioprotective PCSK9 loss-of-function phenotype observed in naturally occurring human carriers. Verve Therapeutics has developed VERVE-102, an LNP-delivered adenine base editor targeting PCSK9 in liver, now in Phase 1b clinical trials (HEART-2). The c.399+1G>A splice donor variant in ClinVar illustrates the principle: loss of PCSK9 function (whether from natural variants or therapeutic editing) increases hepatocyte LDL receptor surface expression and reduces circulating LDL-C. Human genetic epidemiology provides extraordinary validation: heterozygous PCSK9 loss-of-function carriers have ~28% lower LDL-C and ~88% reduced coronary heart disease risk (Cohen et al., 2006, PMID: 16554528).

The HEART-1 Phase 1 trial of VERVE-101 (first-generation, using a different editing approach) demonstrated dose-dependent PCSK9 protein reduction (up to 84%) and LDL-C reduction (up to 55%) in patients with heterozygous familial hypercholesterolemia. VERVE-102 uses an improved GalNAc-targeted LNP formulation with an adenine base editor to install a splice-site disruption in PCSK9. Preclinical studies in non-human primates showed durable (>2 year) PCSK9 knockdown after a single IV dose. The genetic validation is uniquely strong: PCSK9 is one of the best-validated drug targets in human genetics, with decades of Mendelian randomization, clinical trial (evolocumab, alirocumab), and human genetics data supporting LDL-C lowering as causal for coronary disease reduction. Natural homozygous PCSK9 loss-of-function individuals (e.g., with Q152H) are healthy with very low LDL-C, supporting the safety of near-complete knockdown.

Off-target editing remains the primary safety concern for a therapy intended for potentially millions of patients (FH prevalence ~1 in 250). While adenine base editors have lower off-target DNA editing than Cas9 nucleases, RNA off-target deamination and rare off-target genomic edits must be comprehensively characterized. Liver inflammation (transaminase elevation) was observed in HEART-1, likely related to the LNP delivery vehicle and/or immune recognition of the editing machinery. The irreversibility of gene editing means that any unexpected long-term consequences cannot be reversed — unlike statins or PCSK9 monoclonal antibodies, which can be discontinued. For the specific c.399+1G>A variant, patients who already carry a pathogenic PCSK9 loss-of-function allele may have different risk-benefit considerations if they are already partially PCSK9-deficient. Regulatory and ethical frameworks for deploying gene editing in common diseases (beyond rare monogenic disorders) are still evolving.