AAV9 gene therapy optimization for SMARD1/CMT2S: safety and long-term efficacy comparison of two vectors in a SMARD1 preclinical model

Background: Mutations in the Immunoglobulin Mu DNA Binding Protein 2 (IGHMBP2) gene cause Spinal Muscular Atrophy with Respiratory Distress type 1 (SMARD1), a rare, infantile, and fatal motor neuron disease, as well as the milder Charcot-Marie-Tooth disease type 2S (CMT2S). Gene therapy has emerged as a promising approach to correcting IGHMBP2 loss in SMARD1 models, but critical challenges remain. Methods: In this study, we compared the efficacy of two novel, optimized adeno-associated virus 9 (AAV9)-IGHMBP2 vectors, utilizing either the Chicken β-Actin (CBA) or a truncated form of the methyl-CpG-binding protein 2 (MeCP2) promoter (P546), in the SMARD1 murine model via intracerebroventricular delivery. Treated mice survival, histopathological and molecular profile were analyzed. Results: Corroborating previous findings, both constructs effectively rescued the pathological phenotype, significantly improving survival, body weight, and motor function while preserving motor neurons and neuromuscular junctions. Notably, histopathological and RNA sequencing analyses revealed, for the first time, inflammatory marker alterations in the SMARD1 spinal cord, which resolved following treatment. A comparative analysis of the two vectors demonstrated superior long-term efficacy of the P546-promoter construct. Conclusion: ICV gene therapy approach can effectively rescue SMARD1 pathological hallmarks, including astrogliosis and microgliosis. Moreover, P546-promoter construct is superior in terms of safety profile and long-term therapeutic efficacy.