The biopharmaceutical company Scholar Rock plans to initiate a phase 3 clinical trial by the end of 2021 to evaluate apitegromab in patients with type 2 and type 3 spinal muscular atrophy (SMA) who cannot walk, according to a press release by the company.

The chief medical officer of Scholar Rock, Yung Chyung, MD, said the company is working toward “establishing apitegromab as the potential first muscle-directed therapy to treat SMA.”

The plan to initiate the phase 3 trial is based on results from the phase 2 TOPAZ study, which were presented as 2 posters at the World Muscle Society (WMS) Virtual Congress on September 23, 2021.

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According to the posters, 63% of patients with SMA type 2 who received nusinersen before 5 years of age for at least 2 years and 20 mg/kg of apitegromab experienced at least 6 point gains in their Hammersmith Functional Motor Scale Expanded (HFMSE) scores. The mean improvement from baseline in HFMSE on top of background therapy was +7.1 points.

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Moreover, 64% of patients with SMA type 2 or 3, aged 5 to 21 years, who could not walk and were treated with 20 mg/kg of apitegromab, obtained 1 or more point increases in HFMSE from baseline. Almost a third of these patients (29%) obtained 3 or more point increases. Improvements in the Revised Upper Limb Module (RULM) were also recorded. 

Overall, 39% of patients obtained 1 or more point increases from baseline on the revised Hammersmith scale (RHS) and 22% obtained 3 or more point increases.

The second poster showcased insights into the target engagement and exposure levels of apitegromab in preclinical studies, phase 1 trials in healthy volunteers, and the TOPAZ trial.

“These additional analyses from the TOPAZ phase 2 trial further reinforce our enthusiasm for the potential of apitegromab to improve motor function for patients with SMA, and provide exploratory insights in both the ambulatory and nonambulatory populations,” Dr. Chyung stated.

Apitegromab is an experimental monoclonal antibody that specifically binds to proforms of myostatin, inhibiting the activation of myostatin.


Scholar Rock presents additional data analyses from the apitegromab TOPAZ phase 2 trial at the World Muscle Society 2021 Virtual Congress. News release. Scholar Rock; September 23, 2021.

Crawford T, Darras B, Day J. Apitegromab in SMA: an analysis of multiple endpoints and PD relationships to efficacy in the TOPAZ trial. Abstract presented at: World Muscle Society (WMS) Virtual Congress; September 23, 2021; Virtual.