Low body mass index (BMI)/age z-scores are frequent features in type 2 spinal muscular atrophy (SMA), according to a new study published in the European Journal of Pediatrics. Moreover, BMI decreases as age increases.

The results showed that patients with low BMI/age z-scores at baseline were at higher risk of developing more reductions. This finding highlights the need to carefully monitor weight and BMI/age z-scores in patients with type 2 SMA.

“Further studies, including assessments of chewing and swallowing and of lean/fat body mass, will help to better understand the possible mechanisms underlying weight issues,” the researchers said.

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To establish potential differences in BMI in relation to ventilation, motor function, and SMN2 gene copy number, a team of researchers led by Eugenio Mercuri, MD, PhD, analyzed a large cohort of 102 patients with type 2 SMA aged 0 to 20 years. The researchers collected data from the patients for a total of 344 visits.

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During these visits, the weight of the patients ranged from 3.9 kg to 83 kg. Their BMIs ranged from 8.4 to 31.6 with 28% of patients being underweight and 9% of them being overweight.

The BMI/age z-scores were relatively stable below 5 years of age with an increasing number of patients being underweight after 5 years of age. The BMI/age z-scores of patients were wider in the range after 13 years of age.

There was also a difference in the BMI/age z-scores among the different age subgroups, ie below 5 years of age, between 5 and 12 years of age, and at 13 years of age and above. Baseline BMI/age z-scores and gender were significantly contributing to the changes but other variables were not.

A reduction in BMI/age z-score over time depends on BMI/age z-score at baseline and on gender, the researchers said. Therefore, the underscores need to regularly assess anthropometric factors in patients with type 2 SMA.


Ferrantini G, Coratti G, Onesimo R, et al. Body mass index in type 2 spinal muscular atrophy: a longitudinal study. Eur J Pediatr. Published online January 19, 2022. doi:10.1007/s00431-021-04325-3