Follistatin Gene Therapy for Sporadic Inclusion Body Myositis Improves Functional Outcomes.

Sporadic inclusion body myositis, a variant of inflammatory myopathy, has features distinct from polymyositis/dermatomyositis. The disease affects men more than women, most commonly after age 50. Clinical features include weakness of the quadriceps, finger flexors, ankle dorsiflexors, and dysphagia. The distribution of weakness is similar to Becker muscular dystrophy, where we previously reported improvement following intramuscular injection of an isoform of follistatin (FS344) by AAV1. For this clinical trial, rAAV1.CMV.huFS344, 6 × 1011 vg/kg, was delivered to the quadriceps muscles of both legs of six sporadic inclusion body myositis subjects. The primary outcome for this trial was distance traveled for the 6-min walk test. The protocol included an exercise regimen for each participant. Performance, annualized to a median 1-year change, improved +56.0 m/year for treated subjects compared to a decline of -25.8 m/year (p = 0.01) in untreated subjects (n = 8), matched for age, gender, and baseline measures. Four of the six treated subjects showed increases ranging from 58-153 m, whereas two were minimally improved (5-23 m). Treatment effects included decreased fibrosis and improved regeneration. These findings show promise for follistatin gene therapy for mild to moderately affected, ambulatory sporadic inclusion body myositis patients. More advanced disease with discernible muscle loss poses challenges.

Five-Year Extension Results of the Phase 1 START Trial of Onasemnogene Abeparvovec in Spinal Muscular Atrophy.

Importance: This ongoing study assesses long-term safety and durability of response in infants with spinal muscular atrophy (SMA) type 1 after dosing with onasemnogene abeparvovec gene replacement therapy. Objective: The primary objective of this ongoing study is to assess safety. The secondary objective is to determine whether developmental milestones achieved in the START phase 1 clinical trial were maintained and new milestones gained. Design, Setting, and Participants: This study is an ongoing, observational, follow-up study for continuous safety monitoring for 15 years in patients from the START phase I study (conducted May 5, 2014, through December 15, 2017) at Nationwide Children's Hospital in Columbus, Ohio. Participants were symptomatic infants with SMA type 1 and 2 copies of SMN2 previously treated with an intravenous dose of onasemnogene abeparvovec (low dose, 6.7 × 1013 vg/kg; or therapeutic dose, 1.1 × 1014 vg/kg) in START. Thirteen of 15 original START patients are included in this analysis; 2 patients' families declined follow-up participation. Data were analyzed from September 21, 2017, to June 11, 2020. Exposures: Median time since dosing of 5.2 (range, 4.6-6.2) years; 5.9 (range, 5.8-6.2) years in the low-dose cohort and 4.8 (range, 4.6-5.6) years in the therapeutic-dose cohort. Main Outcomes and Measures: The primary outcome measure was the incidence of serious adverse events (SAEs). Results: At data cutoff on June 11, 2020, 13 patients treated in START were enrolled in this study (median age, 38.9 [range, 25.4-48.0] months; 7 females; low-dose cohort, n = 3; and therapeutic-dose cohort, n = 10). Serious adverse events occurred in 8 patients (62%), none of which resulted in study discontinuation or death. The most frequently reported SAEs were acute respiratory failure (n = 4 [31%]), pneumonia (n = 4 [31%]), dehydration (n = 3 [23%]), respiratory distress (n = 2 [15%]), and bronchiolitis (n = 2 [15%]). All 10 patients in the therapeutic-dose cohort remained alive and without the need for permanent ventilation. Prior to baseline, 4 patients (40%) in the therapeutic-dose cohort required noninvasive ventilatory support, and 6 patients (60%) did not require regular ventilatory support, which did not change in long-term follow-up. All 10 patients treated with the therapeutic dose maintained previously acquired motor milestones. Two patients attained the new milestone of "standing with assistance" without the use of nusinersen. Conclusions and Relevance: The findings of this ongoing clinical follow-up of patients with SMA type 1 treated with onasemnogene abeparvovec supports the long-term favorable safety profile up to 6 years of age and provides evidence for sustained clinical durability of the therapeutic dose. Trial Registration: ClinicalTrials.gov Identifier: NCT03421977.

Impact of Age and Motor Function in a Phase 1/2A Study of Infants With SMA Type 1 Receiving Single-Dose Gene Replacement Therapy.

BACKGROUND: This study characterizes motor function responses after early dosing of AVXS-101 (onasemnogene abeparvovec) in gene replacement therapy in infants with severe spinal muscular atrophy type 1 (SMA1). METHODS: This study is a follow-up analysis of 12 infants with SMA1 who received the proposed therapeutic dose of AVXS-101 in a Phase 1 open-label study (NCT02122952). Infants were grouped according to age at dosing and baseline Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders scores: (1) early dosing/low motor, dosed age less than three months with scores <20 (n = 3), (2) late dosing, dosed at age three months or greater (n = 6), and (3) early dosing/high motor, dosed age less than three months with scores ≥20 (n = 3). RESULTS: Early dosing/low motor group demonstrated a mean gain of 35.0 points from a mean baseline of 15.7, whereas the late dosing group had a mean gain of 23.3 from a mean baseline of 26.5. The early dosing/high motor group quickly reached a mean score of 60.3, near the scale maximum (64), from a mean baseline of 44.0. Despite a lower baseline motor score, the early dosing/low motor group achieved sitting unassisted earlier than the late dosing group (mean age: 17.0 vs 22.0 months). The early dosing/high motor group reached this milestone earliest (mean age: 9.4 months). CONCLUSIONS: The rapid, significant motor improvements among infants with severe SMA1 treated with AVXS-101 at an early age highlight the importance of newborn screening and early treatment and demonstrate the therapeutic potential of AVXS-101 regardless of baseline motor function.