Body Composition May Be Biomarker of Motor Function in SMA Patients, Study Suggests

Higher levels of free-fat body mass and lean body mass are associated with better motor function in children with spinal muscular atrophy (SMA) types 1 and 2, a study from researchers in Italy found.

The findings highlight the importance of monitoring SMA patients’ nutrition, and suggest that these body measures could be used as potential biomarkers for disease severity in children with SMA.

The study, “Evaluation of body composition as a potential biomarker in spinal muscular atrophy,” was published in the journal Muscle & Nerve.

Despite advances in clinical management of SMA patients, there is limited data on their nutritional status or optimal nutrition management.

Recent research has shown that SMA patients’ body composition differs from that of their healthy peers. People with SMA tend to have higher body fat mass and lower fat-free mass.

Fat-free mass and lean body mass are significantly lower in SMA type 1 than in type 2.

Fat-free mass refers to all of the body components except fat, including water, bone, organs and muscle content. Lean body mass includes fat that acts as fuel to produce energy as well as other processes that are part of the body’s normal metabolism.

Dual‐energy X‐ray absorptiometry (DEXA) — a simple, fast, and non-invasive method that uses a very small dose of radiation to produce pictures of the inside of the body — is considered the gold standard for studying body composition. It was initially designed to assess bone mineral density. The potential use of body composition, as assessed by DEXA, as a biomarker of SMA severity hasn’t been determined.

The researchers set out to evaluate whether body composition was associated with motor function in 88 children ranging in age from 1 to 10 with either SMA type 1 (43 children) or type 2 (45 children).

The children, who had not previously received SMA treatment Spinraza or participated in any SMA clinical trial, were part of a large, ongoing, longitudinal, multicenter study of SMA patients’ nutritional status.

Researchers measured the children’s height, weight, and body mass index. Their nutritional status was assessed using body mass index z-scores, which measure a child’s relative weight adjusted for age and sex.

The team used the Lunar iDXA — a DEXA scan from GE Healthcare — to measure the children’s body composition, including fat-free mass (calculated by adding bone mineral content to lean body mass), body-fat percentage, fat mass, free-fat mass, and lean body mass indexes (measures of relative mass content by body surface).

Motor function was assessed using the Children’s Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP-INTEND) scale in children with SMA type 1 and using the Hammersmith Functional Motor Scale Expanded (HFMSE) in those with SMA type 2.

The assessment showed that 44% of patients were underweight; 54% of them had SMA type 1. Only one patient, who had SMA type 2, was overweight.

Body-fat mass was higher in SMA patients compared with reference values for gender- and age-matched children. Body-fat mass increased with age in patients with both types of SMA.

Body mass index, fat-free mass index, and lean mass index were moderately associated with motor function in type 1 SMA children. In children with type 2 SMA, fat-free mass index, lean mass index, and lean mass/fat mass ratio were weakly associated with motor function. Bone mass index showed no relevant predictive value of SMA type 2 patients’ motor function.

The findings suggest that fat-free body mass — especially fat-free mass index and lean mass index — is weakly to moderately linked to motor function in both SMA types 1 and 2 SMA patients.

“This is not surprising, given that the degree of muscle atrophy and residual muscle bulk, secondary to the underlying [mechanisms] of the disease, likely play a major role in determining motor function in SMA patients,” the researchers wrote.

The results “emphasize the importance of monitoring nutritional status” in SMA patients,” the researchers said.

The study also suggests that better body composition in children with SMA is associated with better motor skills, and that fat-free body mass may represent a potential biomarker for SMA disease severity.

However, the researchers noted, further studies are required to confirm these associations and to evaluate the role of DEXA scans as a secondary goal in clinical trials. They said they plan to assess body composition’s potential as a biomarker not only of disease severity but also of treatment response in SMA patients “in the near future.”