A Safety and Efficacy of Intrathecally Administered ION283 in Patients With Lafora Disease

Inclusion Criteria: General Inclusion Criteria * Must give written informed consent (and assent if indicated by patient's age and in accordance with local requirements) and be willing/able to comply with all study requirements. * Aged 10-18 (inclusive) years old at the time of informed consent. * Non-pregnant and non-lactating females * All male participants and women of childbearing potential must refrain from sperm/egg donation from the time of signing the informed consent/assent form until at least 12 weeks (approximately 5 half-lives of ION283) after the dose of Study Drug. * For participants engaged in sexual relations of childbearing potential, highly effective contraception must be used from the time of signing the informed consent/assent form until at least 12 weeks (approximately 5 half-lives of ION283) after receiving Study Drug. Target Inclusion Criteria * Genetically confirmed diagnosis of Lafora disease before or at enrollment (documented pathogenic mutations in known causative genes (EPM2A/laforin, EPM2B/NHLRC1/malin) * Must have LDPS score ≥ 9 and LDPS motor subscore of ≥ 2 (independent ambulation- walking 10 steps independently) Exclusion Criteria * Clinically significant abnormalities in medical history (e.g., previous stroke within 6 months of Screening, major surgery within 3 months of Screening) or physical examination * Platelet count \< 80,000/mm3 or any other clinically significant laboratory abnormalities that would render a patient unsuitable for inclusion. * History of bleeding diathesis or coagulopathy * Active infection requiring systemic antiviral or antimicrobial therapy that will not be completed prior to Study Day 1 * Unwillingness to comply with study procedures, including follow-up, as specified by this protocol, or unwillingness to cooperate fully with the Investigator * Contraindication or unwillingness to undergo lumbar puncture * Known history of, or positive test for human immunodeficiency virus (HIV), hepatitis C or chronic hepatitis B * Moderate-to-severe hepatic impairment or renal impairment. * Malignancy within 5 years, except for basal or squamous cell carcinoma of the skin, carcinoma in situ of the cervix that has been successfully treated or benign pediatric tumors. Patients with a history of other malignancies that have been treated with curative intent and which have no recurrence within 5 years may also be eligible if approved by the Sponsor's Medical Monitor * Uncontrolled hypertension defined as: for patients \< 13 years old, BP ≥ 95th percentile + 12 mmHg, or ≥ 140/90 mmHg, whichever is lower for patients ≥ 13 years old, BP ≥ 140/90 mmHg * Previous treatment with an oligonucleotide (including small interfering ribonucleic acid \[siRNA\]) within 4 months of Screening if single dose received, or within 12 months of Screening if multiple doses received; or history of hypersensitivity to ION283 or its excipients; or history of hypersensitivity to any ASO. This exclusion criterion does not apply to COVID-19 mRNA vaccinations * History of alcohol or drug abuse within 12 months of Screening, or current drug or alcohol abuse * Has enrolled in any clinical trial or used any investigational agent or device, or has participated in any investigational procedure, within the 30 days, or within 5 half-lives of investigational agent, whichever is longer, before screening or does so concurrently with this study * Use of antiplatelet or anticoagulant therapy within the 14 days prior to Screening (with the exception of aspirin ≤ mg/day) or anticipated use during the study, including but not limited to clopidogrel, dipyridamole, warfarin, dabigatran, rivaroxaban, and apixaban