Evaluation of body composition as a potential biomarker in spinal muscular atrophy

Nutrition outcomes of disease modifying therapies in spinal muscular atrophy: A systematic review

The nutritional implications of spinal muscular atrophy (SMA) are profound. Disease modifying therapies (DMT) have improved clinical outcomes. This review describes the impact of DMT on nutrition outcomes. A systematic search strategy was applied across seven databases until May 2023. Eligible studies measured nutrition outcomes in individuals with SMA on DMT (nusinersen, risdiplam or onasemnogene abeparvovec [OA]) compared to untreated comparators. Nutrition outcomes included anthropometry, feeding route, swallowing dysfunction, dietary intake, dietetic intervention, nutritional biochemistry, metabolism, gastrointestinal issues and energy expenditure. Articles retrieved were screened in duplicate, data were extracted and appraised systematically. Sixty three articles from 54 studies were included; 41% (n = 22) investigated nusinersen in pediatric participants with SMA type 1. Anthropometry (n = 18), feeding route (n = 39), and swallowing dysfunction (n = 18) were the most commonly reported outcomes. In combined pediatric and adult cohorts, BMI z-score remained stable post nusinersen therapy. The proportion of children with SMA requiring enteral nutrition was stable post nusinersen therapy. Ability to thrive at age 1.5 years was higher in children treated in early infancy with OA compared to historical controls. Significant heterogeneity existed across study population characteristics and outcome measures. Nusinersen may prevent deterioration in some nutrition outcomes; and OA in early infancy may be associated with improved nutrition outcomes. Timing of DMT initiation is an important consideration for future nutrition research. Studies investigating nutrition as a primary outcome of DMT, using consistent outcome measures are required for nutritional management strategies for this cohort to be appropriately tailored.

Neuromuscular disorders in the omics era

Neuromuscular disorders encompass a spectrum of conditions characterized by primary lesions within the peripheral nervous system, which include the anterior horn cell, peripheral nerve, neuromuscular junction, and muscle. In pediatrics, most of these disorders are linked to genetic causes. Despite the considerable progress, the diagnosis of these disorders remains a challenging due to wide clinical presentation, disease heterogeneity and rarity. It is noteworthy that certain neuromuscular disorders, once deemed untreatable, can now be effectively managed through novel therapies. Biomarkers emerge as indispensable tools, serving as objective measures that not only refine diagnostic accuracy but also provide guidance for therapeutic decision-making and the ongoing monitoring of long-term outcomes. Herein a comprehensive review of biomarkers in neuromuscular disorders is provided. We highlight the role of omics-based technologies that further characterize neuromuscular pathophysiology as well as identify potential therapeutic targets to guide treatment strategies.

Biomarkers in 5q-associated spinal muscular atrophy-a narrative review

5q-associated spinal muscular atrophy (SMA) is a rare genetic disease caused by mutations in the SMN1 gene, resulting in a loss of functional SMN protein and consecutive degeneration of motor neurons in the ventral horn. The disease is clinically characterized by proximal paralysis and secondary skeletal muscle atrophy. New disease-modifying drugs driving SMN gene expression have been developed in the past decade and have revolutionized SMA treatment. The rise of treatment options led to a concomitant need of biomarkers for therapeutic guidance and an improved disease monitoring. Intensive efforts have been undertaken to develop suitable markers, and numerous candidate biomarkers for diagnostic, prognostic, and predictive values have been identified. The most promising markers include appliance-based measures such as electrophysiological and imaging-based indices as well as molecular markers including SMN-related proteins and markers of neurodegeneration and skeletal muscle integrity. However, none of the proposed biomarkers have been validated for the clinical routine yet. In this narrative review, we discuss the most promising candidate biomarkers for SMA and expand the discussion by addressing the largely unfolded potential of muscle integrity markers, especially in the context of upcoming muscle-targeting therapies. While the discussed candidate biomarkers hold potential as either diagnostic (e.g., SMN-related biomarkers), prognostic (e.g., markers of neurodegeneration, imaging-based markers), predictive (e.g., electrophysiological markers) or response markers (e.g., muscle integrity markers), no single measure seems to be suitable to cover all biomarker categories. Hence, a combination of different biomarkers and clinical assessments appears to be the most expedient solution at the time.

Serum leptin levels in children and adolescents with spinal muscular atrophy types 2 and 3✰

AIM

It has been reported that in patients with spinal muscular atrophy (SMA), lower levels of motor function are associated with hyperleptinemia. Additionally, hyperleptinemia has been found to be more frequent in underweight SMA patients. Therefore, we aimed to analyze serum leptin levels in patients with SMA.

METHOD

This was a cross-sectional study of pediatric patients (2-19 years old) with SMA types 2 and 3. The investigations included anthropometric measurements, assessment of pubertal status, motor function evaluation using the Hammersmith Functional Motor Scale - Expanded (HFMSE), and serum leptin levels.

RESULTS

In total, 37 patients (22 with type 2 and 15 with type 3 SMA) were included in the study. The male-to-female ratio was 1:1.3 and 62.2% of patients were prepubertal. No statistically significant correlation was found between the HFMSE score and leptin levels, r_s(35) = 0.24, p = 0.15. There was, however, a strong positive relationship between the body mass index (BMI) z-score and leptin levels, r_s(35) = 0.87, p < 0.001.

CONCLUSION

Serum leptin levels do not seem to be a useful marker of disease severity in children and adolescents with types 2 and 3 SMA. As in the general pediatric population, leptin levels are strongly correlated with BMI, which is a surrogate measure of body fat.

Growth patterns in children with spinal muscular atrophy

Background

Spinal muscular atrophy (SMA) is a neuromuscular disorder characterized by muscle atrophy and weakness. SMA type 1 (SMA1) is the most severe form: affected infants are unable to sit unaided; SMA type 2 (SMA2) children can sit, but are not able to walk independently. The Standards of Care has improved quality of life and the increasing availability of disease-modifying treatments is progressively changing the natural history; so, the clinical assessment of nutritional status has become even more crucial. Aims of this multicenter study were to present the growth pattern of treatment-naïve SMA1 and SMA2, and to compare it with the general growth standards.

Results

Body Weight (BW, kg) and Supine Length (SL, cm) were collected using a published standardized procedure. SMA-specific growth percentiles curves were developed and compared to the WHO reference data. We recruited 133 SMA1 and 82 SMA2 (48.8% females). Mean ages were 0.6 (0.4–1.6) and 4.1 (2.1–6.7) years, respectively. We present here a set of disease-specific percentiles curves of BW, SL, and BMI-for-age for girls and boys with SMA1 and SMA2. These curves show that BW is significantly lower in SMA than healthy peers, while SL is more variable. BMI is also typically lower in both sexes and at all ages.

Conclusions

These data on treatment-naïve patients point toward a better understanding of growth in SMA and could be useful to improve the clinical management and to assess the efficacy of the available and forthcoming therapies not only on motor function, but also on growth.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-021-02015-9.

Nutritional, Gastrointestinal and Endo-Metabolic Challenges in the Management of Children with Spinal Muscular Atrophy Type 1

The management of patients with spinal muscular atrophy type 1 (SMA1) is constantly evolving. In just a few decades, the medical approach has switched from an exclusively palliative therapy to a targeted therapy, transforming the natural history of the disease, improving survival time and quality of life and creating new challenges and goals. Many nutritional problems, gastrointestinal disorders and metabolic and endocrine alterations are commonly identified in patients affected by SMA1 during childhood and adolescence. For this reason, a proper pediatric multidisciplinary approach is then required in the clinical care of these patients, with a specific focus on the prevention of most common complications. The purpose of this narrative review is to provide the clinician with a practical and usable tool about SMA1 patients care, through a comprehensive insight into the nutritional, gastroenterological, metabolic and endocrine management of SMA1. Considering the possible horizons opened thanks to new therapeutic frontiers, a nutritional and endo-metabolic surveillance is a crucial element to be considered for a proper clinical care of these patients.

Evaluation of Metabolic Effects of Nusinersen in Patients with Spinal Muscular Atrophy

Nusinersen is the first disease-modifying therapy for spinal muscular atrophy (SMA), but there are few data on potential long-term endocrinological and metabolic systemic effects of this novel treatment as well as metabolic alterations in SMA itself. In this retrospective and multicentric study, we analyzed anthropometric, endocrinological, and motor function data of 81 pediatric and adult patients with SMA1 to 3 undergoing treatment with nusinersen. In 39 patients (51%), we observed a slight increase in body mass index (BMI) centiles under treatment with nusinersen, especially in patients with SMA2 and in pediatric patients between 3.1 and 12 years. A correlation to the SMN2 copy number or motor function was not found. Additionally, length centiles decreased significantly under treatment. The results of longitudinal endocrinological assessments were interpreted as not clinically significant in most patients; in three patients, the signs of an altered glucose metabolism were present. Our study indicates a putative effect of treatment with nusinersen on BMI, which might be due to a conjoint effect of weight gain and reduction of height velocity, without evidence of correlation to increased muscle function. Further studies need to address specific effects of targeted therapies such as nusinersen or onasemnogene abeparvovec on body composition including fat and muscle mass.

Metabolic Dysfunction in Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive genetic disorder leading to paralysis, muscle atrophy, and death. Significant advances in antisense oligonucleotide treatment and gene therapy have made it possible for SMA patients to benefit from improvements in many aspects of the once devastating natural history of the disease. How the depletion of survival motor neuron (SMN) protein, the product of the gene implicated in the disease, leads to the consequent pathogenic changes remains unresolved. Over the past few years, evidence toward a potential contribution of gastrointestinal, metabolic, and endocrine defects to disease phenotype has surfaced. These findings ranged from disrupted body composition, gastrointestinal tract, fatty acid, glucose, amino acid, and hormonal regulation. Together, these changes could have a meaningful clinical impact on disease traits. However, it is currently unclear whether these findings are secondary to widespread denervation or unique to the SMA phenotype. This review provides an in-depth account of metabolism-related research available to date, with a discussion of unique features compared to other motor neuron and related disorders.

Diminished muscle oxygen uptake and fatigue in spinal muscular atrophy

OBJECTIVE

To estimate muscle oxygen uptake and quantify fatigue during exercise in ambulatory individuals with spinal muscular atrophy (SMA) and healthy controls.

METHODS

Peak aerobic capacity (VO_2peak ) and workload (W_peak ) were measured by cardiopulmonary exercise test (CPET) in 19 ambulatory SMA patients and 16 healthy controls. Submaximal exercise (SME) at 40% W_peak was performed for 10 minutes. Change in vastus lateralis deoxygenated hemoglobin, measured by near-infrared spectroscopy, determined muscle oxygen uptake (ΔHHb) at rest and during CPET and SME. Dual energy X-ray absorptiometry assessed fat-free mass (FFM%). Fatigue was determined by percent change in workload or distance in the first compared to the last minute of SME (Fatigue_SME ) and six-minute walk test (Fatigue_6MWT ), respectively.

RESULTS

ΔHHb-PEAK, ΔHHb-SME, VO_2peak , W_peak , FFM%, and 6MWT distance were lower (P < 0.001), and Fatigue_6MWT and Fatigue_SME were higher (P < 0.001) in SMA compared to controls. ΔHHb-PEAK correlated with FFM% (r = 0.50) and VO_2peak (r = 0.41) only in controls. Only in SMA, Fatigue_6MWT was inversely correlated with W_peak (r = -0.69), and Fatigue_SME was inversely correlated with FFM% (r = -0.55) and VO_2peak (r = -0.69).

INTERPRETATION

This study provides further support for muscle mitochondrial dysfunction in SMA patients. During exercise, we observed diminished muscle oxygen uptake but no correlation with aerobic capacity or body composition. We also observed increased fatigue which correlated with decreased aerobic capacity, workload, and body composition. Understanding the mechanisms underlying diminished muscle oxygen uptake and increased fatigue during exercise in SMA may identify additional therapeutic targets that rescue symptomatic patients and mitigate their residual disease burden.

Spinal muscular atrophy: Broad disease spectrum and sex-specific phenotypes

Spinal muscular atrophy (SMA) is one of the major genetic disorders associated with infant mortality. More than 90% of cases of SMA result from deletions of or mutations in the Survival Motor Neuron 1 (SMN1) gene. SMN2, a nearly identical copy of SMN1, does not compensate for the loss of SMN1 due to predominant skipping of exon 7. The spectrum of SMA is broad, ranging from prenatal death to infant mortality to survival into adulthood. All tissues, including brain, spinal cord, bone, skeletal muscle, heart, lung, liver, pancreas, gastrointestinal tract, kidney, spleen, ovary and testis, are directly and/or indirectly affected in SMA. Accumulating evidence on impaired mitochondrial biogenesis and defects in X chromosome-linked modifying factors, coupled with the sexual dimorphic nature of many tissues, point to sex-specific vulnerabilities in SMA. Here we review the role of sex in the pathogenesis of SMA.