New study explores links between BMI and motor function in children with SMA
Findings show trends in movement scores, not all statistically significant
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Better nutritional status, including higher BMI, was linked to trends in motor function in children with SMA.
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Higher BMI was associated with better gross motor function, though results were mixed.
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Fine motor skills appeared to worsen with higher BMI in children with SMA who could sit independently.
Children with spinal muscular atrophy (SMA) showed trends suggesting that nutritional status may be linked to motor function, according to a study in Poland that tracked 38 children over one year.
Researchers found that increases in BMI — a measure of body fat based on weight and height — were associated with higher motor function scores across groups, including among children unable to sit independently and those able to walk, although most of these associations were not statistically significant at the group level.
BMI linked to motor function trends in children with SMA
In contrast, fine motor skills appeared to worsen as BMI increased in children who could sit independently.
The study, “A detailed analysis of the effects of body parameters on motor function and fine motor skills measured at one-year intervals in patients with spinal muscular atrophy,” was published in BMC Pediatrics.
SMA is chiefly caused by mutations in the SMN1 gene that result in a deficiency of the SMN protein, which is essential for muscle health. The loss of this protein leads to dysfunction and death of motor neurons — the nerve cells that coordinate movement — causing SMA symptoms.
Previous studies suggest that body composition and nutritional status may affect motor function and daily abilities in children with SMA. In particular, children with a low BMI z-score — a measure of whether a child is at a healthy weight for their height, age and sex — may be at higher risk of greater motor impairment.
In this study, researchers in Poland analyzed how BMI and body weight were associated with motor function and fine motor skills in 38 children with SMA, ages 2 to 16. The group included 20 children with SMA type 2, 10 with SMA type 3, and eight with SMA type 1.
Study tracks motor function and nutritional status over one year
The children were treated with either Evrysdi (risdiplam) or Spinraza (nusinersen) after these therapies became available in Poland. Three groups were analyzed: nine children were unable to sit on their own (non-sitters), 23 could maintain a stable sitting position for five seconds (sitters, with SMA types 2 or 3), and six could walk independently for at least 10 meters (walkers, all with SMA type 3).
Non-sitters and sitters started treatment at an average age of about 6 years, while walkers began treatment between ages 3 and 11.
Motor function and nutritional status were assessed twice over one year. Motor function was measured using the Children’s Hospital of Philadelphia Infant Test (CHOP-INTEND) for non-sitters, while the Hammersmith Functional Motor Scale–Expanded (HFMSE) and the Revised Upper Limb Module scale (RULM), which assesses fine motor skills in the arm and hand, were used for children who could sit or walk.
The HFMSE assesses 33 motor tasks, including lying and rolling, sitting, crawling and kneeling, standing, and walking.
Most non-sitters were underweight, and none were obese based on BMI z-scores. Motor function improved in six children in this group, with one showing clinically significant improvement, while two experienced worsening motor skills.
The sitters group showed the greatest variation in HFMSE scores, with 10 children experiencing worsening motor function and eight showing improvement, mainly in tasks such as four-kneeling and transitioning from high kneeling to one-legged kneeling. Both height and weight increased significantly, but BMI did not change. In this group, the number of both underweight and overweight children increased during the study.
Motor outcomes varied across SMA groups based on mobility
In the walkers group, results showed improvements in some HFMSE tasks, such as transitioning from straight kneeling to one-legged kneeling, stair climbing, and forward jumping. Most children in this group had a healthy weight. Their BMI did not change during the one-year follow-up period.
Overall, there was a trend that as BMI increased, gross motor function improved in all groups, although these trends were not statistically significant. Conversely, in the sitters group, fine motor skills appeared to worsen as BMI increased.
Overall, this study demonstrated that “the assessment of individual components of motor function and fine motor skills reveals the actual changes that occur over time in patients with SMA,” the team concluded.
“Our study involved a small group of children with SMA who were under the care of a single clinical center,” the investigators noted as a study limitation.
