In a collaborative effort within the international CHARLIE consortium, researchers have developed a gene therapy strategy for the rare genetic metabolic disorder Glutaric Aciduria Type I (GA1) by inhibiting the enzyme Aminoadipate-Semialdehyde Synthase (AASS), reducing the accumulation of neurotoxic metabolites.
GA1 is caused by pathogenic variants in the GCDH gene, which encodes glutaryl-CoA dehydrogenase—an enzyme involved in the degradation of lysine, tryptophan, and hydroxylysine. Deficiency in GCDH leads to impaired oxidation and decarboxylation of glutaryl-CoA, resulting in the accumulation of specific metabolites such as glutaric acid (GA) and 3-hydroxyglutaric acid (3-OHGA). These neurotoxic intermediates predominantly accumulate in the central nervous system, due to limited cerebrovascular transport and low permeability of the blood-brain barrier. Clinically, GA1 manifests as acute encephalopathic crisis, typically occurring between 3 and 36 months of age, often triggered by catabolic stressors such as febrile illness, fasting, or surgical procedures. These episodes frequently result in irreversible bilateral striatal injury, leading to dystonia, complex movement disorders, and spasticity.
GA1 can be detected early through newborn screening and managed with lysine-restricted diets, carnitine supplementation, and emergency protocols. Despite this timely intervention approximately one-third of patients still experience striatal damage.
To address this therapeutic gap, the researchers pursued a substrate reduction therapy targeting AASS, the first enzyme in the lysine degradation pathway. They engineered artificial miRNA sequences (miR_AASS) capable of efficiently silencing Aass transcripts. Various AAV serotypes and delivery routes were evaluated with systemic neonatal administration of AAV9_miR_AASS demonstrating robust therapeutic efficacy in Gcdh−/− mice.
Expression of miR_AASS and subsequent AASS inhibition were dose-dependent in both liver and striatum of the GA1 mouse model—key tissues affected in GA1. In Gcdh−/− mice subjected to a high lysine diet (HDL), AAV-mediated AASS inhibition normalized GA and 3-OHGA levels, prevented striatal damage, and significantly improved survival. A single intravenous neonatal dose of AAV9_miR_AASS92 was sufficient to achieve long-term rescue of HLD-induced neuropathology and extend lifespan.
This study establishes proof-of-concept for targeting lysine catabolism via AASS inhibition as a therapeutic strategy for GA1. Moreover, this approach may hold promise for other disorders within the lysine degradation pathway, such as pyridoxine-dependent epilepsy (PDE).
Segur-Bailach E, Mateu-Bosch A, Bofill-De Ros X, Parés M, da Silva Buttkus P, Rathkolb B, Gailus-Durner V, Hrabě de Angelis M, Moeini P, Gonzalez-Aseguinolaza G, Tort F, Ribes A, van Karnebeek CDM, García-Villoria J, Fillat C. Therapeutic AASS inhibition by AAV-miRNA rescues glutaric aciduria type I severe phenotype in mice. Mol Ther. 2025 Jul 17:S1525-0016(25)00558-1. doi: 10.1016/j.ymthe.2025.07.022