Molecular Probes

Early-onset SCN2A developmental and epileptic encephalopathy is caused by SCN2A gain-of-function variants. Here we describe the clinical experience with intrathecally administered elsunersen, a gapmer antisense oligonucleotide targeting SCN2A, in a female preterm infant with early-onset SCN2A developmental and epileptic encephalopathy, in an expanded access program. Before elsunersen treatement, the patient was in status epilepticus for 7 weeks with a seizure frequency of 20-25 per hour. Voltage-clamp experiments confirmed impaired channel inactivation and increased persistent current consistent with a gain-of-function mechanism. Elsunersen treatment demonstrated a favorable safety profile with no severe or serious adverse events reported after 19 intrathecal administrations over 20 months. After administration in combination with sodium channel blockers, status epilepticus was interrupted intermittently and ultimately ceased after continued dosing. A >60% reduction in seizure frequency corresponding to five to seven seizures per hour was observed, which has been sustained during follow-up until the age of 22 months. These data provide preliminary insights on the safety and efficacy of elsunersen in a preterm infant. Additional investigation on the benefits of elsunersen in clinical trials is warranted.

Of the around 7,000 known rare diseases worldwide, disease-modifying treatments are available for fewer than 5%, leaving millions of individuals without specialized therapeutic strategies. In recent years, antisense oligonucleotides (ASOs) have shown promise as individualized genetic interventions for rare genetic diseases. However, there is currently no consensus on which disease-causing DNA variants are suitable candidates for this type of genetic therapy. The patient identification working group of the N=1 Collaborative (N1C), alongside an international group of volunteer assessors, has developed and piloted consensus guidelines for assessing the eligibility of pathogenic DNA variants for ASO treatments. We herein present the N1C VARIANT (variant assessments toward eligibility for antisense oligonucleotide treatment) guidelines, including the guiding scientific principles and our approach to consensus building. Pathogenic, disease-causing variants can be assessed for the three currently best-established ASO treatment approaches: splice correction, exon skipping, and downregulation of RNA transcripts. A genetic variant is classified as "eligible," "likely eligible," "unlikely eligible," or "not eligible" in relation to the different approaches or as "unable to assess." We also review key considerations related to assessing the upregulation of transcripts from the wild-type allele, an emerging ASO therapeutic strategy. We provide additional tools and training materials to enable clinicians and researchers to use these guidelines for their eligibility assessments. With this initial edition of our N1C VARIANT guidelines, we provide the rare genetic disease community with guidance on how to identify suitable candidates for variant-specific ASO-based therapies and the possibility of integrating such assessments into routine clinical practice.

RNA-based therapies, particularly small interfering RNA (siRNA) and antisense oligonucleotides (ASOs), represent a promising modality class with the potential to target previously "undruggable" proteins, and with potential for precision medicine approach. The successful development of these therapeutics relies on a comprehensive understanding of several key factors, including bioconjugation, bioanalytical techniques, biotransformation, tissue distribution, computational modeling and simulation, and clinical pharmacology. Bioconjugation strategies are essential for enhancing metabolic stability, facilitating cellular uptake, and targeting specific tissues, thereby improving efficacy and minimizing dosing. Tailored bioanalytical methods are crucial for assessing pharmacokinetics (PK) and pharmacodynamics, with particular emphasis on tissue PK in cases where plasma PK does not reflect therapeutic activity. Biotransformation and tissue distribution studies are essential, although a less comprehensive package may be adequate for well-established chemistry. Given the unique properties of oligonucleotides, computational modeling plays a critical role in predicting drug behavior in target tissues, supporting dose optimization. Clinical pharmacology for oligonucleotides is less complex than for small molecules, as they are less likely to interact with common drug metabolizing enzymes or transporter proteins. This white paper, developed by the Innovation and Quality (IQ) Consortium Nucleic Acids Working Group, consolidates industry insights and recommendations to inform best practices and regulatory guidelines, ensuring the safe and efficient development of siRNA and ASO therapies.

Inherited muscular dystrophies are a heterogeneous group of diseases, caused by different types of genetic mutations. RNA therapies, and particularly antisense oligonucleotides, offer a palette of therapeutic strategies to either reduce the production of harmful proteins or to restore or increase protein expression. Consequently, they offer therapeutic promise for multiple forms of muscular dystrophies. This review outlines the different RNA therapy types considered for the treatment of Duchenne muscular dystrophy, facioscapulohumeral muscular dystrophy and myotonic dystrophy, emphasizing the strategies used to deliver these therapies to skeletal muscle with a focus on approaches that have reached the clinical trial stage.