SMA Growth Patterns Differ From General Pediatric Percentiles

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

Due to the nature of SMA, the study authors note that using nutritional reference data developed for healthy children increases the risk of inadequate nutritional support in SMA patients. Yet there is often a lack of standardized and coordinated nutritional assessment for specific SMA patients.

The study focused on the most severe forms of SMA, types 1 and 2. Children with type 1 SMA (SMA1) cannot sit unaided, and children with type 2 SMA (SMA2) can sit, but cannot 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 was designed to analyze the growth pattern of people with SMA compared to 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) were recruited . About half of the participants were women.

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

Genetic confirmation of 5q autosomal recessive SMA (either by homozygous deletions or by compound heterozygous mutations in the SMN1 gene) Clinically confirmed diagnosis of SMA1 or SMA2 Age 0 to 11.99 years Clinical management according to best supportive care based on the consensus statement for SoC in SMAabsence of acute medical conditions in the 15 days prior to assessment at time of assessment not involved in experimental pharmacology studies

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

SMA-specific growth percentiles were developed using the LMS method, which calculates percentile values ​​by age. Next, researchers compared the patterns with data from the World Health Organization growth chart by superimposing the newly generated growth percentiles across the age range of 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 below the normal range, between -1 and 1 were considered normal, between 1 and 2 were considered overweight, and above 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 being taller than their healthy peers up to age 1 year (z-score = 1.02), but generally following the typical growth pattern thereafter. In boys with SMA1, SL was similar to the general patterns in all age classes.

SMA2 patients generally had a lower weight (mean z-score = –1,084) in both sexes up to the age of 6 years before starting to follow the general growth pattern. The exception was 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 after that. BMI was generally lower in both sexes up to 6 years of age (mean z-score = –1.262), but was comparable to the general pediatric population after 6 years. Boys were an exception and were heavier in old age, 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 spontaneous breathing patients. Tube-fed SMA1 patients had lower BW and BMI compared to orally fed patients.

The data lead to a better understanding of the natural progression of SMA and may help improve clinical and nutritional management of patients. The effects of SMA treatment on growth can also be assessed by 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

Comments are closed.