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SMA Growth Patterns Differ From General Pediatric Percentiles


Recent research identified spinal muscular atrophy (SMA)–specific growth percentiles, aiming to improve clinical management of the nutritional aspects of the disease.

In children with spinal muscular atrophy (SMA), nutritional aspects are a key part of multidisciplinary disease management, especially in regard to the swallowing and gastrointestinal problems related to SMA. A recent study published in the Orphanet Journal of Rare Diseases aims to provide a better understanding of growth patterns in treatment-naive SMA to improve the clinical and nutritional management of these patients.

Due to the nature of SMA, the study authors note that utilizing nutritional reference data developed for healthy children increases the risk of insufficient nutritional support in SMA patients. Even so, there is often a lack of standardized and coordinated nutritional assessment for SMA patients specifically.

The research focused on the most severe forms of SMA, types 1 and 2. Children affected with type 1 SMA (SMA1) are unable to sit without assistance, and those with SMA type 2 (SMA2) can sit, but are unable to walk without assistance. The availability of disease-modifying treatments and evolving standards of care have improved the management of SMA and patients’ quality of life, making nutritional status assessment an aspect of increasing importance.

The multicenter study of 215 patients with SMA aimed to analyze the growth pattern of those with SMA compared with general growth standards. A total of 133 SMA1 (mean age, 0.6 years; range, 0.4-1.6 years) and 82 SMA2 (mean age, 4.1 years; range, 2.1-6.7 years) patients were recruited. Roughly half of the participants were female.

The overall cohort included patients recruited between April 2015 and May 2018 at 5 clinical SMA referral centers in Italy who met the following criteria:

  • Genetic confirmation of 5q-autosomal recessive SMA (either due to homozygous deletions or to compound heterozygous mutations in the SMN1 gene)
  • Clinically confirmed diagnosis of SMA1 or SMA2
  • Age 0 to 11.99 years
  • clinical management according to the best supportive care based on the Consensus Statement for SoC in SMA
  • absence of acute medical conditions in the 15 days before the assessment
  • not involved in any experimental pharmacological trials at the time of the assessment

Data were collected on each patient’s body weight (BW; in kg) and supine length (SL; in cm) using a published standardized procedure to calculate each patient’s body mass index (BMI) z-score (BMI = BW [kg]/SL2 [m2]). Clinical variables, including type of breathing (spontaneous compared with mechanical ventilation) and type of feeding (oral compared with nasogastric tube or gastrostomy), were collected 1 day before nutritional assessment.

SMA-specific growth percentiles were developed using the LMS method, which calculates percentile values by age. Then, researchers compared the patterns with World Health Organization growth chart data by superimposing the newly generated growth percentiles over the age range 0 to 5 years for the SMA1 patients and 0 to 10 years for the SMA2 patients. Those with z-scores less than –1 were considered under the normal range, between –1 and 1 were considered normal, between 1 and 2 were considered overweight, and higher than 2 were considered obese.

Weight and BMI were significantly lower in children with SMA1 than in healthy children of both sexes and age classes. The mean z-score for weight was –1.334, and for BMI, –2.339. SL was variable, with girls in the SMA1 cohort longer than their healthy peers up until 1 year of age (z-score = 1.02) but then generally following the typical growth pattern thereafter. In boys with SMA1, SL was similar to the general patterns in all age classes.

SMA2 patients had lower weights overall (mean z-score = –1.084) in both sexes up until 6 years of age before starting to follow the general growth pattern. The exception were 6% of boys, who were heavier than the general population with a z-score of 1.654. SL was similar in both boys and girls up to 3 years of age, but shorter in girls thereafter. BMI was generally lower in both sexes up to 6 years of age (mean z-score = –1.262) but was similar to the general pediatric population after 6 years. Boys were an exception and were heavier at older ages, with a mean z-score of 1.54.

In the overall cohort, children with SMA using mechanical ventilation had significantly lower weight and BMI z-scores than patients spontaneously breathing. Tube-fed SMA1 patients had lower BW and BMI compared with orally fed patients.

The data move toward better understanding the natural progression of SMA and can help improve the clinical and nutritional management of patients. The effects of SMA treatment on growth can also be assessed against growth patterns specific to SMA patients.


Amicis R, Baranello G, Foppiani A, et al. Growth patterns in children with spinal muscular atrophy. Orphanet J Rare Dis. 2021;16(1):375. doi:10.1186/s13023-021-02015-9

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