The 20-item Motor Function Measure (MFM-20) is sensitive enough to detect improvements in patients with spinal muscular atrophy (SMA) type 1 or 2 after treatment with nusinersen (Spinraza®), according to the results of a clinical trial published in Neurological Sciences.
Children between 2 and 7 years of age with SMA type 1 or SMA type 2 showed improvement over time in MFM-20 scores following treatment with nusinersen. Patients with SMA type 2 had improvements in all 3 functional domains (D1, D2, and D3) and in total score. Those with SMA type 1 showed improvements in all domains except for D1, which is focused on standing positions and transfers.
These results were in contrast to previous natural history studies of patients with SMA type 2, which show no significant change in the MFM-20, indicating that the improvements in this study were due to treatment with nusinersen.
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“Our results show the relevance of using the MFM-20 for the follow-up of young subjects treated with nusinersen,” the authors said.
Following treatment with nusinersen, all 22 patients with SMA type 1 and 13 of the 19 patients with SMA type 2 experienced an improvement in the total score of greater than 3 points during the study. The smallest changes were observed in the D1 domain for all patients with SMA type 1, experiencing a .3% improvement in scores, and patients with SMA type 2, experiencing a 1.2% increase.
MFM-20 D2 improved the most for patients with SMA type 1, with a mean change of +4.1%, while D3 improved the most for patients with SMA type 2 (+2.8%).
The sensitivity index of change in standardized response mean (SRM) was used to estimate the sensitivity of the MFM-20. The SRM showed better sensitivity to change in SMA type 1 compared to patients with SMA type 2 for all domains except D1 (D2, 0.89 vs 0.69; D3, 0.72 vs 0.53; total score, 1.22 vs 0.89).
While the MFM-20 proved to be useful for observing treatment response to nusinersen, it is only validated for patients between 2 and 7 years of age. The authors encouraged more research into the use of the full MFM-32, from which the MFM-20 was derived because it has been validated in both children and adults.
During the study, 41 participants with SMA were recruited, including 22 patients with SMA type 1 and 19 patients with SMA type 2. The patients with SMA type 1 tended to be younger at initiation of nusinersen, with a mean age of 2.08 years compared to 3.08 years for SMA type 2 (P <.01). Baseline MFM-20 scores in all domains also tended to be significantly lower in patients with SMA type 1 compared to those in SMA type 2.
Laure LG, Andreea S, Aurelie P, et al. Use of MFM-20 to monitor SMA types 1 and 2 patients treated with nusinersen. Neurol Sci. Published online September 29, 2022. doi:10.1007/s10072-022-06403-2