Metachromatic leukodystrophy (MLD) is a hereditary neurodegenerative disease characterized by demyelination and motor and cognitive impairments due to deficiencies of the lysosomal enzyme arylsulfatase A (ARSA) or the saposin B activator protein (SapB). Current treatments are limited; however, gene therapy using adeno-associated virus (AAV) vectors for ARSA delivery has shown promising results. The main challenges for MLD gene therapy include optimizing the AAV dosage, selecting the most effective serotype, and determining the best route of administration for ARSA delivery into the central nervous system. This study aims to evaluate the safety and efficacy of AAV serotype 9 encoding ARSA (AAV9-ARSA) gene therapy when administered intravenously or intrathecally in minipigs, a large animal model with anatomical and physiological similarities to humans. By comparing these two administration methods, this study contributes to the understanding of how to improve the effectiveness of MLD gene therapy and offers valuable insights for future clinical applications.

Epilepsy is a brain disorder characterized by a persistent predisposition to epileptic seizures. With various etiologies of epilepsy, a significant proportion of patients develop pharmacoresistance to antiepileptic drugs, which necessitates the search for new therapeutic methods, in particular, using gene therapy. This review discusses the use of adeno-associated viral (AAV) vectors in gene therapy for epilepsy, emphasizing their advantages, such as high efficiency of neuronal tissue transduction and low immunogenicity/cytotoxicity. AAV vectors provide the possibility of personalized therapy due to the diversity of serotypes and genomic constructs, which allows for increasing the specificity and effectiveness of treatment. Promising orientations include the modulation of the expression of neuropeptides, ion channels, transcription, and neurotrophic factors, as well as the use of antisense oligonucleotides to regulate seizure activity, which can reduce the severity of epileptic disorders. This review summarizes the current advances in the use of AAV vectors for the treatment of epilepsy of various etiologies, demonstrating the significant potential of AAV vectors for the development of personalized and more effective approaches to reducing seizure activity and improving patient prognosis.

The development of gene therapies for rare hereditary disorders is hindered by small patient cohorts, incomplete characterization of natural disease history, and the impracticality of conducting long-term clinical trials. Surrogate biomarkers—quantifiable indicators predictive of clinical outcomes—represent a promising strategy to accelerate the evaluation of therapeutic efficacy. This review examines the role of surrogate endpoints in gene therapy, outlining essential validation criteria, including biological plausibility, analytical reproducibility, and clinical predictive value. Regulatory frameworks governing surrogate markers in the United States, European Union, Russia, Japan, China, and Canada are compared, with emphasis on mechanisms for expedited or conditional approval. Challenges associated with biomarker validation and extrapolation in the context of rare diseases are discussed, alongside future perspectives that integrate multi-omics technologies and artificial intelligence to enhance biomarker discovery and facilitate regulatory acceptance.

Epilepsy is a brain disease characterized by a persistent predisposition to epileptic seizures. The current issue is the development of new methods of epilepsy therapy, In particular, using gene therapy methods. Promising areas of research in this field are the modulation of the expression of a number of neuropeptides, ion channels, transcription factors, neurotrophic factors, etc., as well as the use of antisense oligonucleotides. One of the optimal vectors for the delivery of therapeutic transgenes is the adenoassociated virus (AAV), which is most often used in the gene therapy of neurological disorders due to the high transduction ability of neuronal tissues and low immunogenicity/cytotoxicity. In this study, we analyze the existing achievements in the use of AAV vectors in the treatment of epilepsy of various etiologies.

Adeno-associated viral (AAV) vectors have established themselves as a promising platform for genetic material delivery in clinical practice, evidenced by regulatory approval of multiple therapeutics. Despite proven therapeutic efficacy, safety concerns remain a critical limitation requiring systematic analysis. This review analyzes clinical data to identify mechanisms of toxicity, clinical risks, and strategies for their minimization in AAV gene therapy. The study examines dose-dependent toxicity, immune responses, and organ-specific burdens associated with systemic and local administration routes. Analysis reveals a clear correlation between systemic delivery efficacy and dose-dependent toxicity, with principal mechanisms including capsid-directed immune responses, hepatic burden, and complement system activation leading to thrombotic microangiopathy. Key determinants of the safety profile include pre-existing neutralizing antibodies, vector dose, serotype selection, and patient baseline conditions. Contemporary strategies for toxicity minimization are evolving from reactive management toward proactive risk mitigation, including prophylactic immunosuppressive regimens, vector engineering to alter tropism or reduce immunogenicity, and rigorous post-infusion monitoring. Integration of improved vector constructs, rational immunosuppressive regimens, and rigorous post-infusion surveillance has the potential to expand the therapeutic window of AAV-based gene therapy, achieving an optimal balance between efficacy and safety for a broader patient population.