Adults with spinal muscular atrophy: a large-scale natural history study shows gender effect on disease

The association between gait speed and falls in ambulatory adults with spinal muscular atrophy: a retrospective pilot study

Introduction

Fatigue and gait speed are established determinants of fall risk in patients with neurological disorders. However, data on adults with spinal muscular atrophy (SMA) is limited. The aim of this pilot study was to investigate falls and risk factors in adults with SMA.

Methods

A retrospective chart review of ambulatory adults with genetically confirmed 5q-SMA included: age, sex, age of symptom onset, SMN2 copy number, BMI, and 6MWT distance and speed at minutes 1, 2, and 6.

Results

Fourteen ambulatory patients were included in the analysis with an average follow-up of 36 months (range of 12-66 months). 10 patients were classified as fallers (Fall) and four as non-fallers (NFall). One faller received Risdiplam, while the remaining fallers and non-fallers received Nusinersen for the duration of the follow-up period. In the Fall cohort, the median speed at 1, 2, and 6 min were 0.92 m/s, 0.89 m/s, and 0.77 m/s, respectively, with a heterogeneous range including one faller at 1.25 m/s. In the NFall cohort, the slowest collected median recorded speeds were 1.18 m/s, 1.11 m/s, and 1.09 m/s respectively, with one non-faller at 0.56 m/s. There was no significant statistical difference between 6-min gait speeds and individuals experiencing falls. However, we found a three-fold greater decline in speed between the 6MWT first and last minute in the Fall (13.01%) compared to the NFall (5.16%). 7 of 10 patients had multiple falls (70%) with two individuals consequently losing ambulation (20%).

Discussion

These findings underscore the need for larger studies on fatigability and the importance of considering factors beyond gait speed alone.

The impact of three SMN2 gene copies on clinical characteristics and effect of disease-modifying treatment in patients with spinal muscular atrophy: a systematic literature review

Objective

To review the clinical characteristics and effect of treatment in patients with spinal muscular atrophy (SMA) and three copies of the SMN2 gene.

Methods

We conducted a literature search in October 2022 to identify English-language clinical research on SMA that included SMN2 copy number according to PRISMA guidelines.

Results

Our search identified 44 studies examining the impact of three SMN2 copies on clinical characteristics (21 on phenotype, 13 on natural history, and 15 on functional status and other signs/symptoms). In children with type I SMA or presymptomatic infants with an SMN1 deletion, three SMN2 copies was associated with later symptom onset, slower decline in motor function and longer survival compared with two SMN2 copies. In patients with SMA type II or III, three SMN2 copies is associated with earlier symptom onset, loss of ambulation, and ventilator dependence compared with four SMN2 copies. Eleven studies examined treatment effects with nusinersen (nine studies), onasemnogene abeparvovec (one study), and a range of treatments (one study) in patients with three SMN2 copies. In presymptomatic infants, early treatment delayed the onset of symptoms and maintained motor function in those with three SMN2 copies. The impact of copy number on treatment response in symptomatic patients is still unclear.

Conclusion

SMN2 copy number is strongly correlated with SMA phenotype in patients with SMN1 deletion, while no correlation was found in patients with an SMN1 mutation. Patients with three SMN2 copies show a highly variable clinical phenotype. Early initiation of treatment is highly effective in presymptomatic patients with three SMN2 copies.

Respiratory function in a large cohort of treatment-naïve adult spinal muscular atrophy patients: a cross-sectional study

Due to poor data in literature, we aimed to investigate the respiratory function in a large cohort of naïve Italian adult (≥18 years) SMA patients in a multi-centric cross-sectional study. The following respiratory parameters were considered: forced vital capacity (FVC), forced expiratory volume in one second (FEV1) and need for non-invasive ventilation (NIV). We included 145 treatment-naïve adult patients (SMA2=18, SMA3=125; SMA4=2), 58 females (40 %), with median age at evaluation of 37 years (range 18-72). Fifty-six (37 %) and 41 (31 %) patients had abnormal (<80 %) values of FVC and FEV1, respectively. Fourteen (14 %) patients needed NIV, started at median age of 21 (range 4-68). Motor function, measured by Hammersmith Functional Motor Scale Expanded and Revised Upper Limb Module as well as SMA2, loss of walking ability, surgery for scoliosis, use of NIV, and cough assisting device (CAD) were all significantly associated to lower FVC and FEV1 values, while no association with age at baseline, disease duration, gender or 6 min walking test was observed, except for a correlation between FVC and age in SMA3 walkers (p < 0.05). In conclusion, respiratory function in adult SMA patients is relatively frequently impaired, substantially stable, and significantly correlated with motor function and disease severity.

Sex Difference in Spinal Muscular Atrophy Patients - are Males More Vulnerable?

BACKGROUND

Sex is a significant risk factor in many neurodegenerative disorders. A better understanding of the molecular mechanisms behind sex differences could help develop more targeted therapies that would lead to better outcomes. Untreated spinal muscular atrophy (SMA) is the leading genetic motor disorder causing infant mortality. SMA has a broad spectrum of severity ranging from prenatal death to infant mortality to normal lifespan with some disability. Scattered evidence points to a sex-specific vulnerability in SMA. However, the role of sex as a risk factor in SMA pathology and treatment has received limited attention.

OBJECTIVE

Systematically investigate sex differences in the incidence, symptom severity, motor function of patients with different types of SMA, and in the development of SMA1 patients.

METHODS

Aggregated data of SMA patients were obtained from the TREAT-NMD Global SMA Registry and the Cure SMA membership database by data enquiries. Data were analyzed and compared with publicly available standard data and data from published literature.

RESULTS

The analysis of the aggregated results from the TREAT-NMD dataset revealed that the male/female ratio was correlated to the incidence and prevalence of SMA from different countries; and for SMA patients, more of their male family members were affected by SMA. However, there was no significant difference of sex ratio in the Cure SMA membership dataset. As quantified by the clinician severity scores, symptoms were more severe in males than females in SMA types 2 and 3b. Motor function scores measured higher in females than males in SMA types 1, 3a and 3b. The head circumference was more strongly affected in male SMA type 1 patients.

CONCLUSIONS

The data in certain registry datasets suggest that males may be more vulnerable to SMA than females. The variability observed indicates that more investigation is necessary to fully understand the role of sex differences in SMA epidemiology, and to guide development of more targeted treatments.