RecruitingDevice studyStudy of an Intrathecal Port and Catheter System for Subjects With Spinal Muscular AtrophyThe primary objective of the clinical investigation is to demonstrate successful clinical use of the ThecaFlex DRx™ System in delivering nusinersen in subjects with spinal muscular atrophy (SMA). All enrolled subjects will undergo implantation of the investigational device (ThecaFlex DRx™ System) and will be followed for 12 months after receiving the implant. The 12-month data will be used to assess the primary endpoint support a Pre-Market Approval (PMA) application.