Enzyme replacement and substrate reduction therapy for GBA1 p.Leu483Pro: established treatments and the unmet need for neuronopathic Gaucher

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.