Perinatal-lethal Gaucher disease

Base Editing (ABE8e) via AAV9 delivery is a rationale-driven therapeutic strategy for Perinatal-lethal Gaucher disease targeting the GBA1 c.1093G>A (p.Glu365Lys) variant (Pathogenic, missense variant). The editing system (ABE8e-nSpCas9 (adenine base editor)) converts the pathogenic A back to G on the target strand, restoring the wild-type codon. Target tissue: CNS. Therapeutic goal: Correct the GBA1 c.1448T>G (p.Leu483Arg, L444P) and similar severe loss-of-function alleles (via gene correction or durable gene addition at or functionally equivalent to the native locus) to restore . Risk profile: off-target Medium (bystander bases in editing window), delivery complexity Medium, immunogenicity High (AAV pre-existing immunity).

1. Molecular basis: GBA1 NM_000157.4(GBA1):c.1093G>A (p.Glu365Lys) is classified as Pathogenic (ClinVar variation ID 4299). Molecular consequence: missense variant. Protein change: E365K, E278K, E316K, D179H, D130H, D92H. 2. Epidemiology: Perinatal-lethal Gaucher disease (PLGD) is an extremely rare, most severe end of the type 2 (acute neuronopathic) Gaucher disease spectrum. It typically presents prenatally or in the neonatal period with non-immune hydrops fetalis, collodion-baby/ichthyotic skin, arthrogryposis, respiratory failure, 3. Standard of care: Standard of care for Gaucher disease is based on enzyme replacement therapy (ERT: imiglucerase, velaglucerase alfa, taliglucerase alfa) and substrate reduction therapy (SRT: miglustat, eliglustat), with hematopoietic stem cell transplantation (HSCT) and off-label pharmacologic chaperones (e.g., ambr 4. Pipeline: Multiple ERT and SRT products have full regulatory approval for type 1 and some type 3 Gaucher disease and anchor a mature, multi-billion-dollar global market dominated by type 1 patients (WEB-01, WEB-03, WEB-06, WEB-07, PAPER-06). However, none directly address CNS pathology, and none are labeled f 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 GBA1 c.1093G>A (p.Glu365Lys) 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. 4. Delivery to CNS tissue remains a major translational bottleneck. Current vectors have limited transduction efficiency in these compartments. 4. Long-term durability, off-target genome-wide effects, and immunogenicity in the target patient population require thorough preclinical and clinical evaluation.

For GBA1 c.1342G>C (p.Asp448His), a pathogenic missense variant that produces a misfolded but catalytically competent glucocerebrosidase (GCase), pharmacological chaperone therapy (PCT) with ambroxol and substrate reduction therapy (SRT) with venglustat represent mechanistically distinct small-molecule strategies that can cross the blood-brain barrier — a critical advantage over intravenous enzyme replacement therapy (ERT, which cannot treat the neurological component). The p.Asp448His substitution (historically D409H) is associated with severe type 3 (chronic neuropathic) Gaucher disease and the rare cardiovascular subtype with aortic/mitral valve calcification.

Ambroxol is a pH-dependent pharmacological chaperone that binds to and stabilizes GCase in the endoplasmic reticulum, promoting proper folding and lysosomal trafficking. It crosses the BBB and has shown GCase activity increases in GBA1-mutant fibroblasts and Gaucher patient-derived neurons. Narita et al. (Ann Neurol 2016; PMID:27389578) conducted an open-label pilot study of high-dose oral ambroxol in neuropathic Gaucher patients, showing increased lymphocyte GCase activity and CSF GCase levels, with stabilization of neurological symptoms in some patients. Importantly, ambroxol is most effective for missense variants that produce misfolded protein (like p.Asp448His) rather than null variants that produce no protein. Venglustat (Ibiglustat, Sanofi) is a brain-penetrant glucosylceramide synthase inhibitor that reduces substrate accumulation upstream of GCase. The LEAP Phase 2 trial (NCT02843035) in GBA1-associated Parkinson disease provided proof-of-concept for CNS target engagement, though efficacy results were mixed. For Gaucher type 3, substrate reduction could complement residual GCase activity to bring glucosylceramide levels below pathogenic thresholds.

Pharmacological chaperone therapy is mutation-dependent: ambroxol stabilizes misfolded GCase that retains some structural integrity, so it works best for specific missense variants. For the perinatal-lethal form associated with p.Asp448His in homozygosity or compound heterozygosity with null alleles, the residual GCase may be too low for chaperone rescue to achieve clinically meaningful activity. Venglustat's mixed Phase 2 results in GBA-Parkinson (MOVES-PD trial did not meet primary endpoint) raise questions about SRT efficacy in established neurodegeneration. The perinatal-lethal form is typically fatal within months, leaving almost no time for oral small-molecule therapy to accumulate sufficient CNS effect. Neither ambroxol nor venglustat has been studied in controlled trials specifically for neuropathic Gaucher disease in infants. ERT (imiglucerase, velaglucerase) remains essential for managing visceral disease (hepatosplenomegaly, cytopenias) but does not address CNS pathology. The p.Asp448His variant's association with the cardiovascular subtype adds further complexity not addressed by any current therapy.

For GBA1 c.1448T>C (p.Leu483Pro, historically L444P), the most common variant associated with neuronopathic Gaucher disease (types 2 and 3), enzyme replacement therapy (ERT) with imiglucerase, velaglucerase alfa, or taliglucerase alfa effectively treats visceral manifestations (hepatosplenomegaly, cytopenias, bone disease) but does not cross the blood-brain barrier and therefore fails to address the devastating neurological progression that defines the perinatal lethal and type 2/3 phenotypes. Substrate reduction therapy (SRT) with eliglustat (oral, Cerdelga) inhibits glucosylceramide synthase to reduce substrate accumulation and is approved for GD1 but similarly lacks CNS penetration. Homozygous p.Leu483Pro is strongly associated with neuronopathic disease, and this variant produces a severely misfolded glucocerebrosidase with <5% residual activity.

ERT has transformed the natural history of type 1 Gaucher disease since its introduction in 1991 (PMID: 1680484, Barton et al.). Imiglucerase normalizes hematologic parameters and reduces organomegaly in >90% of treated patients. For p.Leu483Pro homozygotes with type 3 GD, ERT controls systemic disease but neurological decline continues. Eliglustat Phase 3 trials (ENGAGE, ENCORE, EDGE) demonstrated non-inferiority to imiglucerase for maintaining disease control in GD1 with the convenience of oral dosing. The p.Leu483Pro substitution disrupts hydrophobic packing in the TIM barrel catalytic domain of GCase, causing ER retention and proteasomal degradation rather than lysosomal trafficking. Pharmacological chaperones (ambroxol, isofagomine) that stabilize mutant GCase folding and enhance lysosomal delivery are under investigation — ambroxol has shown CSF penetration and is being evaluated in small trials for neuronopathic GD (PMID: 26920685). Notably, GBA1 variants are also the strongest genetic risk factor for Parkinson disease, with therapeutic implications extending beyond Gaucher itself.

The fundamental unmet need for p.Leu483Pro homozygotes is CNS-penetrant therapy. ERT proteins (~67 kDa glycoproteins) do not cross the BBB. Intrathecal ERT delivery has been explored but requires invasive repeated lumbar punctures and has not demonstrated clear neurological benefit in clinical studies. SRT with current agents (eliglustat, miglustat) also lacks sufficient CNS penetration for neuronopathic disease; miglustat does cross the BBB but showed inconsistent neurological benefit in GD3 trials. Pharmacological chaperones like ambroxol are BBB-penetrant and mechanistically attractive for p.Leu483Pro (which produces a foldable but unstable protein), but clinical evidence remains limited to open-label studies. Gene therapy (AAV-GBA1) targeting CNS and liver is in preclinical development but faces challenges including achieving adequate CNS biodistribution and managing the immunogenicity of GCase in patients with minimal endogenous enzyme. The perinatal lethal phenotype associated with homozygous p.Leu483Pro presents before diagnosis is typically made, leaving an extremely narrow intervention window.

For the severe neuropathic forms of Gaucher disease (types 2 and 3, including perinatal-lethal), AAV-mediated GBA1 gene therapy targeting the CNS is the most promising emerging approach, as current enzyme replacement therapy (ERT, imiglucerase/velaglucerase) does not cross the blood-brain barrier. The p.Arg502Cys variant is associated with severe disease and produces a misfolded glucocerebrosidase with severely reduced catalytic activity. AAV gene therapy delivering functional GBA1 to neurons and macrophage-lineage cells could address both the visceral and neurological components of the disease.

Gaucher disease results from biallelic GBA1 mutations causing deficiency of glucocerebrosidase (GCase), leading to accumulation of glucosylceramide and glucosylsphingosine in lysosomes of macrophages and neurons. The p.Arg502Cys substitution (historically R463C in older nomenclature) disrupts a conserved residue in domain III of GCase involved in protein stability, resulting in ER retention and degradation via ERAD. Prevail Therapeutics (acquired by Eli Lilly) developed PR001 (LY3884961), an AAV9 vector delivering GBA1 via intracisternal injection, initially for GBA1-associated Parkinson disease and neuronopathic Gaucher disease. A Phase 1/2 trial (NCT04411654) was initiated. Preclinical studies in Gba1 knock-in and conditional knockout mice showed that AAV-GBA1 delivery to the CNS reduced glucosylsphingosine accumulation, improved neuroinflammation markers, and extended survival in severe models. For visceral disease, ERT remains the standard, but the perinatal-lethal form is refractory to ERT due to fulminant neurodegeneration.

Perinatal-lethal Gaucher disease (type 2) is typically fatal within the first 2 years of life, creating an extremely narrow treatment window. Prenatal or neonatal gene therapy delivery would be needed, which poses extreme technical and ethical challenges. The p.Arg502Cys variant in homozygosity or in compound heterozygosity with other severe alleles (e.g., L444P) produces the most severe phenotypes where neurodegeneration may be too advanced at birth for postnatal intervention. AAV-mediated gene therapy must transduce both neurons and microglia/macrophages — the primary storage cells — and AAV9 transduces neurons more efficiently than myeloid cells, potentially leaving the macrophage compartment undertreated. Anti-AAV9 maternal antibodies could neutralize the vector in neonatal patients. The PR001 trial focused primarily on GBA-Parkinson disease, and specific efficacy data for perinatal Gaucher are not available.