Newly calculated growth curves reveal that children with spinal muscular atrophy (SMA) with type 1 (SMA1) and type 2 (SMA2) generally weigh less than healthy peers.

The results published in the Orphanet Journal of Rare Diseases demonstrated that the supine length of children with SMA was more variable over gender, age, and SMA type. The combination of weight and supine length contributed to SMA body mass index (BMI) values, which were shown to be significantly lower than healthy peers.

“This study provides, for the first time, growth curves derived from a large, well-characterized sample of treatment-naïve SMA1 and SMA2 children,” according to the authors.

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In both SMA1 and SMA2 patients, girls appeared to have more linear weight and length curves compared to boys. Male patients showed decreases in the rate of change at around 3 years of age for SMA1, and about 6 years of age for SMA2.

When compared to World Health Organization (WHO) growth percentiles, both sexes of SMA1 children had lower weights than healthy peers at all age classes (P ≤.001). Girls with SMA1 were longer than their peers until age 1 (P ≤.001) when they began to follow the general pediatric population (P =.869). Boys with SMA1 followed the general population lengths (P =.192).

In SMA2 patients, both sexes were lower in weight than their peers (P ≤.001) until age 6, when they began to follow the general pediatric population (P =.132). Supine length was similar to WHO percentiles for SMA2 boys and girls until age 3 when girls started to be shorter than their healthy peers.

Overall, the study recruited 133 SMA1 patients and 82 SMA2 patients with mean ages of 0.6 (interquartile range (IQR), 0.4–1.6) and 4.1 (IQR, 2.1–6.7) years, respectively. Patient weights were collected to 0.1 kg by having children be held by a guardian standing on a scale. Supine lengths were measured with the children lying on a table with legs as straight as possible. For children with scoliosis or contractures, 3 segmental measurements were taken and added together.


De Amicis R, Baranello G, Foppiani A, et al. Growth patterns in children with spinal muscular atrophy. Orphanet J Rare Dis. 2021;16(1). doi:10.1186/s13023-021-02015-9