Researchers found that type 1 spinal muscular atrophy (SMA) is associated with lower weight, while types 2 and 3 with shorter height, as published in Muscle & Nerve.

The observational retrospective study led by Darras included 91 patients with SMA who had previously undergone genetic testing to confirm the diagnosis and were currently complying with only supportive care. Of all participants, 28 had type 1 SMA, and 63 were types 2 and 3.

Patients with type 1 had overall lower weight vs types 2 and 3 with a median of -7.5%. Types 2 and 3 were generally shorter than type 1, showcasing a mean of -3.0%, with no significant differences among the latter, probably due to great variability between patients, the researchers said.

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To achieve these results, 3 different centers of the Neuromuscular Clinical Research Network in the US recorded the weight, height, body mass index according to age, weight-for-length, and absolute and relative deviations following the growth charts from the World Health Organization and Centers for Disease Control and Prevention, and later compared the data from individuals with type 1 vs type 2 and 3.

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Other findings of the study correlate with previous reports on SMA; for example, the overall median weight was well below the 50th percentile in all types, even in patients who received feeding support. Regardless, patients with type 1 showcased a much higher need for feeding support, with 61% receiving such treatment, vs 11% in types 2 and 3 combined. Furthermore, only 3.6% of type 1 individuals were overweight, while none were obese.

“More research is needed to understand which factors influence growth longitudinally, and how to accurately capture growth in patients with SMA,” the authors concluded.

“Further research should investigate the best time to provide feeding support to avoid underweight, especially in patients with Type 1, and how to avoid the risk of overfeeding, especially in patients with Types 2/3 SMA.”


Darras B, Guye S, Hoffart J, et al. Distribution of weight, stature and growth status in children and adolescents with spinal muscular atrophy: an observational retrospective study in the United States. Muscle & Nerve. Published online April 6, 2022. doi:10.1002/mus.27556