Gene Therapy for Children Age 6 Months to 5 Years with Spinal Muscular Atrophy Type 2 Effective in Clinical Trial

Children age 6 months to 5 years with spinal muscular atrophy (SMA), treated with onasemnogene (AVXS-101; Zolgensma, Bannockburn, IL) are showing improvements in motor function. In the STRONG (NCT03381729) phase 1/2 clinical study, 1 of 3 different doses of onasemnogene is being intrathecally administered to children who are unable to sit or walk at enrollment in the study.

Interim data analysis at mean time of 9.3 months posttreatment for the 31 children treated to date showed children age 2 to 5 years achieved a mean increase of 5.9 points on the Hammersmith Functional Motor Scale-Expanded (HFMSE) scale—almost double what is considered a clinically meaningful change. 

Since treatment, 18 motor milestones have been achieved among the 16 patients who received 6.0 x 10¹³ vg or 1.2 x 10¹⁴ vg onasemnogene, including 2 patients who gained the ability to stand independently, 1 of whom went on to walk alone. Since treatment, 4 motor milestones have been achieved among 12 patients in who received 1.2x1014 vg onasemnogene, including 1 patient who gained the ability to walk with assistance. Data from the third dose (2.4 x 10¹⁴ vg) were not announced.

“These results—although early—are extremely encouraging for families who hope to see their children with SMA type 2 experience meaningful improvement in motor function and important milestones, like standing and walking, following a one-time intrathecal administration of Zolgensma,” said Douglas M. Sproule, MD, vice president, SMA therapeutic head, AveXis. “These data, along with long-term follow-up data from the STR1VE and SPR1NT studies, support a continually advancing body of evidence on the clinical impact gene therapy treatment may have for those fighting this devastating and rare genetic disease, regardless of type or severity.” 

In the STRONG study, for children 6 months to 2 years of age the primary efficacy endpoint is the ability to stand without support for at least 3 seconds. In those more than age 2 to 5 years, the primary efficacy endpoint is change in score from baseline.For both groups, the secondary efficacy endpoint is the ability to walk independently for at least 5 steps