Inclusion Criteria:

• Patient must be ≥ 2.5 years of age.
• Patient and/or authorized representative must be willing and able to give informed consent/assent and any authorizations required by local law for participation in the study.
• Patient and their caregiver must be willing and able (in the Investigator’s opinion) to comply with all protocol requirements.
• Patient must have completed dosing with STK-001 and the End of Study Visit in Study STK-001-DS-101, with an acceptable safety profile per Investigator judgment.
• Patient must have satisfactory compliance with study visits and procedures in Study STK-001-DS-101 per Investigator and Sponsor judgment.
• Patient must meet age-appropriate institutional standard practices for intrathecal (IT) drug administration procedures.
• Patient and/or family (or caretaker) must be sufficiently fluent in English or Spanish to be able to complete questionnaires relevant to this study.
• Patient must have completed Study STK-001-DS-101 within 4 weeks of the start of their participation in Study STK-001-DS-501, unless approved by the Sponsor.

Exclusion Criteria:

• Patient has met any withdrawal criteria from Study STK-001-DS-101.
• Patient is currently being treated as maintenance therapy with an antiepileptic drug acting primarily as a sodium channel blocker including phenytoin, carbamazepine, oxcarbazepine, lamotrigine, lacosamide, or rufinamide.
• Patient has clinically significant unstable medical conditions other than epilepsy.
• Patient has had clinically relevant symptoms or a clinically significant illness (in the judgment of the Investigator) at Screening or prior to dosing on Day 1, other than epilepsy.
• Patient has a spinal deformity or other condition that may alter the free flow of CSF or has an implanted CSF drainage shunt.
• Patient has clinically significant (in the judgment of the Investigator) abnormal laboratory values at baseline or prior to dosing on Day 1.
• Patient has aspartate aminotransferase (AST) or alanine aminotransferase (ALT) > 3-fold upper limit of normal (ULN), serum creatinine > ULN or platelet count < lower limit of normal at baseline and upon repeat testing.
• Patient has clinically significant abnormalities (in the judgment of the Investigator) in the 12-lead ECG measured at Screening/Baseline (This includes 12-lead ECG from STK-001-DS-101 [Visit 6 or Visit 9], if STK-001-DS-101 Visit 6 or Visit 9 and STK-001-DS-501 Visit 1 are the Same Day).
• Patient has a psychiatric or behavioral disorder which, in the opinion of the Investigator, may interfere with the patient’s participation in the study.
• Patient is currently taking, or within 4 weeks prior to Screening/Baseline has taken any anticoagulant (including but not limited to heparins, warfarin and other vitamin K antagonists, dabigatran, rivaroxaban and apixaban), or within 7 days prior to Screening/Baseline, has taken any antiplatelet (including but not limited to aspirin, non-steroidal anti-inflammatory drugs, clopidogrel, ticlopidine. and dipyridamole).
• Patient is a female of childbearing potential, or patient is a fertile male with female partner(s) of childbearing potential, unless willing to ensure that they or their partners use effective contraception throughout the duration of the study and for at least 6 months after their last dose of STK-001.
• . Patient is a female who is lactating or planning pregnancy during the duration of the study and for at least 6 months after their last dose of STK-001.
• Patient has any other significant disease or disorder which, in the opinion of the Investigator, may either put the patient at risk because of participation in the study, may influence the results of the study, or may affect the patient’s ability to participate in the study.
• Patient has been treated (or is being treated) with an investigational product (other than STK-001) since participating in Study STK-001-DS-101.
• Patient is participating in an observational study, unless approved by the Sponsor.

Note: Other protocol defined Inclusion/Exclusion criteria may apply.

Eligibility last updated 4/25/23. Questions regarding updates should be directed to the study team contact.