In Vitro Modeling as a Tool for Testing Therapeutics for Spinal Muscular Atrophy and IGHMBP2-Related Disorders

Area of Science:

• Neuroscience
• Genetics
• Molecular Biology

Background:

• Spinal Muscular Atrophy (SMA) is a leading genetic cause of infant mortality, primarily due to SMN1 gene mutations.
• Mutations in IGHMBP2 cause a spectrum of disorders including Spinal Muscular Atrophy with Muscular Distress type 1 (SMARD1) and Charcot-Marie-Tooth 2S (CMT2S), lacking clear genotype-phenotype correlations.
• Developing robust in vitro models is crucial for understanding disease mechanisms and testing therapeutic interventions for these rare genetic neuromuscular disorders.

Purpose of the Study:

• To optimize a patient-derived in vitro model system for studying Spinal Muscular Atrophy (SMA) and IGHMBP2-related disorders (SMARD1/CMT2S).
• To investigate the pathogenesis of SMA and SMARD1/CMT2S using induced neurons (iNs) derived from patient cell lines.
• To evaluate the efficacy of AAV gene therapy in correcting cellular phenotypes in SMA and SMARD1/CMT2S patient-derived iNs.

Main Methods:

• Generated and characterized induced neurons (iNs) from cell lines of patients with SMA and SMARD1/CMT2S.
• Treated the generated iNs with AAV9-mediated gene therapies: AAV9.SMN for SMA and AAV9.IGHMBP2 for IGHMBP2 disorders.
• Assessed neuronal morphology, specifically neurite length and neuronal conversion, to evaluate treatment response.

Main Results:

• Patient-derived iNs from both SMA and SMARD1/CMT2S groups exhibited characteristic short neurite length and neuronal conversion defects.
• SMA iNs showed a partial rescue of morphological phenotypes following in vitro treatment with AAV9.SMN.
• SMARD1/CMT2S iNs demonstrated improved neurite length after IGHMBP2 restoration via gene therapy, with variable responses across different patient lines.
• The protocol facilitated the classification of an uncertain IGHMBP2 variant in a suspected SMARD1/CMT2S patient.

Conclusions:

• The optimized in vitro model system provides a valuable platform for studying SMA and SMARD1/CMT2S pathogenesis and gene function.
• AAV gene therapy demonstrates potential for rescuing cellular phenotypes in both SMA and SMARD1/CMT2S, offering hope for treatment development.
• This research advances the understanding of genotype-phenotype variability in IGHMBP2 disorders and aids in the development of targeted therapies.