Research Confirms Common Feature of Type 2 SMA, Reveals Novel Insights

According to researchers, their findings warrant close surveillance of weight and BMI/age z-scores for patients with type 2 spinal muscular atrophy (SMA).

New study findings are highlighting a common feature of type 2 spinal muscular atrophy (SMA), revealing that low body mass index (BMI)/age z-score is often seen in patients with the SMA subtype. They also show that baseline scores and gender play a role in further reductions as patients age.

Findings were published in European Journal of Pediatrics.

According to the researchers, their findings warrant close surveillance of weight and BMI/age z-scores for patients with type 2 SMA and that more studies will be helpful in better understanding the possible mechanisms underlying weight issues.

The group used data from nearly 350 visits from 100 patients in Italy, finding that 28% of the measurements showed a BMI/age z-score 2 standard deviations (SDs) below. According to the researchers, there was a relatively small number of patients who had an assessment with a BMI/age z-score above 2 SDs; this was primarily observed in male patients younger than 13 years.

Across age groups, results were relatively stable for patients under the age of 5 years, after which the number of patients with BMI/age z-score 2 SDs below increased.

“The lowest BMI/age z-scores were mainly observed in patients older than 12 years in whom the BMI/age z-score values were often already [2 SDs below] at first assessment, irrespective of the age when the first assessment was performed,” wrote the researchers. “This occurred more frequently in male patients. At the other end of the spectrum, a number of boys who were [2 SDs above] between the ages of 5 and 12 shifted to ± 2SD when approaching puberty.”

Longer-term follow-up was available for 58 of the patients included in the study, offering further insights. These patients had more than 1 follow-up visited documented in the data, with a median follow-up of nearly 4 years.

These additional results revealed that baseline BMI/age z-scores and gender had significant associations with changes in scores. Among the patients included in the longer-term follow-up who after the age of 13 years had BMI/age z-score 5 SDs below, all but 1 already had baseline BMI/age z-score 2 SDs below, regardless of their age at baseline. Between genders, male patients exhibited more obvious weight changes at both extremes of the range.

SMN2 copy number, SMA function, noninvasive ventilation, nutritional status, and scoliosis surgery were not found to have a significant impact on the rate of progression.

“At variance with other studies, we had a low number of patients who underwent gastrostomy, despite the low BMI. Only 2 of the patients had a history of swallowing problems, and/or aspiration pneumonia, and they both underwent gastrostomy,” wrote the researchers. “In all the others, after introduction of supplements and dietary recommendations, the possibility of a percutaneous endoscopic gastrostomy was discussed, but as the majority of the cases with very low BMI were in their teens, they would not accept this option for a variety of reasons, including issues related to body image.”


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