SMA treatment linked to improved upper limb function in new study

Treatment with Evrysdi (risdiplam) was associated with stable overall motor function and improved upper limb function in a small Chinese study of 15 people with spinal muscular atrophy (SMA).

Upper limb function scores increased in the type 2 group and the combined types 3–4 group, although neither change was statistically significant. Participants with types 3–4 SMA also showed a nonsignificant trend toward better walking ability. Participants started treatment at a median age of 29 years, highlighting the potential value of maintaining motor function in older patients who have lived with SMA for many years.

“These findings, particularly the stabilization or improvement across key motor domains, align with the therapeutic goals in this older patient population, where halting disease progression is a primary clinical objective,” the researchers wrote.

The study, “Effectiveness and safety of risdiplam in Chinese adolescents and adults with spinal muscular atrophy: a prospective real-world study,” was published in BMC Neurology.

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SMA is mainly caused by mutations in the SMN1 gene that reduce production of SMN, a protein essential for the survival of motor neurons, the nerve cells that control muscle movement. The loss of these cells leads to progressive muscle weakness and wasting.

Evrysdi helps the SMN2 gene produce more functional SMN protein. Normally, this gene produces only a small amount of working SMN protein compared with the SMN1 gene. People with more SMN2 gene copies generally have milder SMA.

Although studies from several countries have supported Evrysdi’s safety and effectiveness, real-world evidence from Chinese adolescents and adults with SMA remains limited. Evrysdi is sold in the U.S. by Genentech.

To learn more, researchers followed 15 patients with SMA, eight males and seven females. Symptoms began at a median age of 1 year, but the median age at diagnosis was 15. Participants started Evrysdi at a median age of 29 and were followed for a median of 1.4 years.

Nine participants had type 3 SMA (60%), five had type 2 SMA, and one had type 4 SMA. At the start of treatment, five could not sit independently, eight could sit but not walk, and two could walk. Twelve participants (80%) had deletions affecting both copies of the SMN1 gene. Of the 14 with available genetic data, 11 (78.6%) had three copies of exon 7 of the SMN2 gene.

Researchers assessed motor function using two measures: the Hammersmith Functional Motor Scale Expanded (HFMSE), which tracks overall motor abilities, and the Revised Upper Limb Module (RULM), which measures how well patients can use their arms, hands, and fingers. They also measured lung function using forced vital capacity (FVC), walking ability using the six-minute walk test (6MWT), and overall functioning using the Revised Amyotrophic Lateral Sclerosis Functional Rating Scale (ALSFRS-R).

Overall motor function, lung function, and daily functioning remained stable during follow-up. However, upper limb function improved significantly, with median RULM scores rising from 18 to 21 points.

The two participants who were able to walk when the study began walked farther on the six-minute walk test at follow-up. The other 13 participants remained unable to walk.

Upper limb gains seen across SMA types, but not statistically significant

When researchers analyzed results separately by SMA type, upper limb function improved in the type 2 group and the combined types 3–4 group, although neither change was statistically significant. Participants with types 3–4 SMA also showed a trend toward better walking ability, but that change was not statistically significant.

According to the researchers, “the positive trend in RULM scores—particularly among patients with type [3 or 4] SMA, a population typically less responsive to treatment—indicates clinical benefit.”

According to the researchers, all 15 participants showed improvement or stability in their overall condition on the Clinical Global Impression improvement scale, with 40% showing what the researchers described as significant subjective improvement.

Having more copies of exon 7 of the SMN2 gene was associated with greater improvement in upper limb function. No significant association was found between diagnostic delay and changes in the measured outcomes.

Evrysdi was generally well tolerated, with no adverse events reported during follow-up.

The researchers noted several study limitations, including the small number of participants, relatively short follow-up, and lack of an untreated comparison group. “Future studies with larger cohorts and longer follow-up will be essential to fully establish [Evrysdi]’s long-term efficacy and safety in SMA patients,” the researchers wrote.