Early treatment of type II SMA slows rate of progression of scoliosis.

BACKGROUND: Type II spinal muscular atrophy (SMA) often leads to scoliosis in up to 90% of cases. While pharmacological treatments have shown improvements in motor function, their impact on scoliosis progression remains unclear. This study aims to evaluate potential differences in scoliosis progression between treated and untreated SMA II patients. METHODS: Treatment effect on Cobb's angle annual changes and on reaching a 50° Cobb angle was analysed in treated and untreated type II SMA patients with a minimum 1.5-year follow-up. A sliding cut-off approach identified the optimal treatment subpopulation based on age, Cobb angle and Hammersmith Functional Motor Scale Expanded at the initial visit. Mann-Whitney U-test assessed statistical significance. RESULTS: There were no significant differences in baseline characteristics between the untreated (n=46) and treated (n=39) populations. The mean Cobb angle variation did not significantly differ between the two groups (p=0.4). Optimal cut-off values for a better outcome were found to be having a Cobb angle <26° or an age <4.5 years. When using optimal cut-off, the treated group showed a lower mean Cobb variation compared with the untreated group (5.61 (SD 4.72) degrees/year vs 10.05 (SD 6.38) degrees/year; p=0.01). Cox-regression analysis indicated a protective treatment effect in reaching a 50° Cobb angle, significant in patients <4.5 years old (p=0.016). CONCLUSION: This study highlights that pharmacological treatment, if initiated early, may slow down the progression of scoliosis in type II SMA patients. Larger studies are warranted to further investigate the effectiveness of individual pharmacological treatment on scoliosis progression in this patient population.

Early neurological signs in infants identified through neonatal screening for SMA: do they predict outcome?

Neonatal screening for SMA has allowed the identification of infants who may present with early clinical signs. Our aim was to establish whether the presence and the severity of early clinical signs have an effect on the development of motor milestones. Infants identified through newborn screening were prospectively assessed using a structured neonatal neurological examination and an additional module developed for the assessment of floppy infants. As part of the follow-up, all infants were assessed using the HINE-2 to establish developmental milestones. Only infants with at least 24 months of follow-up were included. Normal early neurological examination (n = 11) was associated with independent walking before the age of 18 months while infants with early clinical signs of SMA (n = 4) did not achieve ambulation (duration follow-up 33.2 months). Paucisymptomatic patients (n = 3) achieved ambulation, one before the age of 18 months and the other 2 between 22 and 24 months.  Conclusion: Our findings suggest that early clinical signs may contribute to predict motor milestones development. What is Known: • There is increasing evidence of heterogeneity among the SMA newborns identified via NBS. • The proposed nosology describes a clinically silent disease, an intermediate category ('paucisymptomatic') and 'symptomatic SMA'. What is New: • The presence of minimal clinical signs at birth does not prevent the possibility to achieve independent walking but this may occur with some delay. • The combination of genotype at SMN locus and clinical evaluation may better predict the possibility to achieve milestones.

Longitudinal Motor Functional Outcomes and Magnetic Resonance Imaging Patterns of Muscle Involvement in Upper Limbs in Duchenne Muscular Dystrophy.

Background and Objectives: The aim of this study was to evaluate longitudinal changes using both upper limb muscle Magnetic Resonance Imaging (MRI) at shoulder, arm and forearm levels and Performance of upper limb (PUL) in ambulant and non-ambulant Duchenne Muscular Dystrophy (DMD) patients. We also wished to define whether baseline muscle MRI could help to predict functional changes after one year. Materials and Methods: Twenty-seven patients had both baseline and 12month muscle MRI and PUL assessments one year later. Results: Ten were ambulant (age range 5-16 years), and 17 non ambulant (age range 10-30 years). Increased abnormalities equal or more than 1.5 point on muscle MRI at follow up were found on all domains: at shoulder level 12/27 patients (44%), at arm level 4/27 (15%) and at forearm level 6/27 (22%). Lower follow up PUL score were found in 8/27 patients (30%) at shoulder level, in 9/27 patients (33%) at mid-level whereas no functional changes were found at distal level. There was no constant association between baseline MRI scores and follow up PUL scores at arm and forearm levels but at shoulder level patients with moderate impairment on the baseline MRI scores between 16 and 34 had the highest risk of decreased function on PUL over a year. Conclusions: Our results confirmed that the integrated use of functional scales and imaging can help to monitor functional and MRI changes over time.

Quantitative Evaluation of Lower Extremity Joint Contractures in Spinal Muscular Atrophy: Implications for Motor Function.

PURPOSE: To quantitatively describe passive lower extremity range of motion in participants with spinal muscular atrophy (SMA) types 2 and 3, and to establish preliminary thresholds to identify individuals at risk for performing poorly on disease-specific motor function outcome measures. METHODS: Eighty participants with SMA types 2 and 3, enrolled in an international multicenter natural history study, were evaluated with lower extremity range of motion testing and the Hammersmith Functional Motor Scale-Expanded. RESULTS: A hip extension joint angle of -7.5° or less for SMA type 2 and 0° or less for SMA type 3 identified diminished motor ability with good sensitivity. For knee extension, a joint angle of -9.0° or less for SMA type 2 or 0° or less for SMA type 3 was similarly sensitive. CONCLUSIONS: Minimal hip and knee joint contractures were associated with diminished motor ability. Clinical trial designs should consider the effect of contractures on motor function.

Revised upper limb module for spinal muscular atrophy: Development of a new module.

INTRODUCTION: There is a growing need for a robust clinical measure to assess upper limb motor function in spinal muscular atrophy (SMA), as the available scales lack sensitivity at the extremes of the clinical spectrum. We report the development of the Revised Upper Limb Module (RULM), an assessment specifically designed for upper limb function in SMA patients. METHODS: An international panel with specific neuromuscular expertise performed a thorough review of scales currently available to assess upper limb function in SMA. This review facilitated a revision of the existing upper limb function scales to make a more robust clinical scale. RESULTS: Multiple revisions of the scale included statistical analysis and captured clinically relevant changes to fulfill requirements by regulators and advocacy groups. CONCLUSIONS: The resulting RULM scale shows good reliability and validity, making it a suitable tool to assess upper extremity function in the SMA population for multi-center clinical research. Muscle Nerve 55: 869-874, 2017.

Content validity and clinical meaningfulness of the HFMSE in spinal muscular atrophy.

BACKGROUND: Reports on the clinical meaningfulness of outcome measures in spinal muscular atrophy (SMA) are rare. In this two-part study, our aim was to explore patients' and caregivers' views on the clinical relevance of the Hammersmith Functional Motor Scale Expanded- (HFMSE). METHODS: First, we used focus groups including SMA patients and caregivers to explore their views on the clinical relevance of the individual activities included in the HFMSE. Then we asked caregivers to comment on the clinical relevance of possible changes of HFMSE scores over time. As functional data of individual patients were available, some of the questions were tailored according to their functional level on the HFMSE. RESULTS: Part 1: Sixty-three individuals participated in the focus groups. This included 30 caregivers, 25 patients and 8 professionals who facilitated the discussion. The caregivers provided a comparison to activities of daily living for each of the HFMSE items. Part 2: One hundred and forty-nine caregivers agreed to complete the questionnaire: in response to a general question, 72% of the caregivers would consider taking part in a clinical trial if the treatment was expected to slow down deterioration, 88% if it would stop deterioration and 97% if the treatment was expected to produce an improvement. Caregivers were informed of the first three items that their child could not achieve on the HFMSE. In response 75% indicated a willingness to take part in a clinical trial if they could achieve at least one of these abilities, 89% if they could achieve two, and 100% if they could achieve more than 2. CONCLUSIONS: Our findings support the use of the HFMSE as a key outcome measure in SMA clinical trials because the individual items and the detected changes have clear content validity and clinical meaningfulness for patients and their caregivers.

Gain and loss of upper limb abilities in Duchenne muscular dystrophy patients: A 24-month study.

Duchenne muscular dystrophy (DMD) is a neuromuscular condition characterized by muscle weakness. The Performance of upper limb (PUL) test is designed to evaluate upper limb function in DMD patients across three domains. The aim of this study is to identify frequently lost or gained PUL 2.0 abilities at distinct functional stages in DMD patients. This retrospective study analyzed prospectively collected data on 24-month PUL 2.0 changes related to ambulatory function. Ambulant patients were categorized based on initial 6MWT distance, non-ambulant patients by time since ambulation loss. Each PUL 2.0 item was classified as shift up, no change, or shift down. The study's cohort incuded 274 patients, with 626 paired evaluations at the 24-month mark. Among these, 55.1 % had activity loss, while 29.1 % had gains. Ambulant patients showed the lowest loss rates, mainly in the shoulder domain. The highest loss rate was in the shoulder domain in the transitioning subgroup and in elbow and distal domains in the non-ambulant patients. Younger ambulant patients demonstrated multiple gains, whereas in the other functional subgroups there were fewer gains, mostly tied to singular activities. Our findings highlight divergent upper limb domain progression, partly linked to functional status and baseline function.

Patient reported outcome measure for upper limb in Duchenne muscular dystrophy: correlation with PUL2.0.

The increasing pressure to include non ambulant Duchenne muscular dystrophy (DMD) boys in clinical trials has highlighted the need for outcome measures that could address the impact of upper limb function on activities of daily living. The aim of the present study was to establish the correlation between the recently developed Patient Reported Outcome Measure for the upper limb (PROM UL) and the observer rated functional scale Performance of Upper Limb (PUL 2.0) in a large cohort of DMD boys and young adults. As part of a larger natural history study, non ambulant DMD patients were assessed using PUL2.0 and PROM UL. One hundred and twenty-five concurrent PUL 2.0 and PROM UL evaluations from 60 non ambulant DMD boys were taken into consideration. The total PROM UL scores showed a strong correlation with both PUL 2.0 total scores and with PUL 2.0 entry item score. The strong correlation between the two tools confirms the clinical meaningfulness of the PUL2.0 and that the PROM UL can help to detect the gradient of progression of upper limb involvement.

Longitudinal Analysis of PUL 2.0 Domains in Ambulant and Non-Ambulant Duchenne Muscular Dystrophy Patients: How do they Change in Relation to Functional Ability?

BACKGROUND: The performance of upper limb 2.0 (PUL) is widely used to assess upper limb function in DMD patients. The aim of the study was to assess 24 month PUL changes in a large cohort of DMD patients and to establish whether domains changes occur more frequently in specific functional subgroups. METHODS: The PUL was performed in 311 patients who had at least one pair of assessments at 24 months, for a total of 808 paired assessments. Ambulant patients were subdivided according to the ability to walk: >350, 250-350, ≤250 meters. Non ambulant patients were subdivided according to the time since they lost ambulation: <1, 1-2, 2-5 or >5 years. RESULTS: At 12 months, the mean PUL 2.0 change on all the paired assessments was -1.30 (-1.51--1.05) for the total score, -0.5 (-0.66--0.39) for the shoulder domain, -0.6 (-0.74--0.5) for the elbow domain and -0.1 (-0.20--0.06) for the distal domain.At 24 months, the mean PUL 2.0 change on all the paired assessments was -2.9 (-3.29--2.60) for the total score, -1.30 (-1.47--1.09) for the shoulder domain, -1.30 (-1.45--1.11) for the elbow domain and -0.4 (-1.48--1.29) for the distal domain.Changes at 12 and 24 months were statistically significant between subgroups with different functional abilities for the total score and each domain (p < 0.001). CONCLUSION: There were different patterns of changes among the functional subgroups in the individual domains. The time of transition, including the year before and after loss of ambulation, show the peak of negative changes in PUL total scores that reflect not only loss of shoulder but also of elbow activities. These results suggest that patterns of changes should be considered at the time of designing clinical trials.

Point-of-care lung and diaphragm ultrasound in a patient with spinal muscular atrophy with respiratory distress type 1.

Spinal muscular atrophy with respiratory distress type 1 (SMARD1, OMIM #604,320), is a rare autosomal recessive disease resulting from degeneration of motor neurons in the anterior horns, which leads irreversible diaphragmatic palsy and progressive distal symmetrical muscular weakness. Respiratory distress is the main symptom and is severe, rapidly progressive, and frequently requiring invasive ventilation. Despite diaphragm being one of the target organ of the disease, no specific study has been done using ultrasound.We report diaphragm and lung ultrasound findings of a 13-month-old girl affected by SMARD1 (homozygosis c.1540G > A mutation in IGHMPB2 gene) with respiratory failure requiring permanent mechanical ventilation since birth and we discuss the role of diaphragmatic and lung ultrasound in this category of patients and its clinical implications.

Oral and Swallowing Abilities Tool (OrSAT) in nusinersen treated patients.

INTRODUCTION: The aim of the study was to longitudinally assess swallowing abilities in nusinersen-treated patients with type 1 spinal muscular atrophy. METHODS: Twenty infants with type 1 SMA (11 female and 9 male) treated with nusinersen between 3 weeks and 15 months of age, were assessed using the Oral and Swallowing Abilities Tool (OrSAT). The duration of the follow-up after treatment ranged between 12 months and 62 months. RESULTS: Twelve of the 20 infants had normal swallowing and there was no need for tube feeding at the time treatment started. Ten of the 12 had consistently normal swallowing with no need for tube feeding on follow-up. The other two required tube feeding but they regained the ability to eat some food by mouth.The remaining 8 infants already had tube feeding inserted at the time treatment started: 4 of them also had tracheostomy and they showed no changes on the OrSAT Scale. The other 4 who had tube feeding but no tracheostomy had partial functional improvement. CONCLUSION: Our results suggest that the degree of functional impairment at the time treatment is started can help to predict the progression of swallowing abilities. The use of a structured assessment also helped to detect partial improvements.

Long term follow-up of scoliosis progression in type II SMA patients.

The aim of this study is to retrospectively assess onset and progression of scoliosis in type II SMA patients not treated with the approved disease modifying treatments. Scoliosis was evaluated by measuring the scoliosis angle on X-ray obtained in the anteroposterior view in sitting position (Cobb's angle method). Eighty-four patients had at least one assessment of scoliosis angle (287 assessments). There was a positive correlation between age and scoliosis angles (p<0.001) with a progressive increase of scoliosis with age. When subdividing the population by HFMSE score (<10; 11-22;> 22), there was a progressive increase in scoliosis angles with decreasing HFMSE scores. The difference between HFMSE categories was significant (p<0.001). Fifty-four patients had at least two assessments at 6-month distance and were retained for the longitudinal analysis. Using a mixed model, age, functional status and scoliosis angle at baseline were predictive on scoliosis progression. The mean annual rate of increase of scoliosis angle was 5.63 (95%CI: 4.74-6.52). Our results confirm the progression of scoliosis in untreated type II SMA providing details of the progression in relation to different variables. With different therapeutical options being available in many countries, our findings will provide reference data for establishing possible differences in the trajectories of progression with treated type II individuals.

Early Gross Motor Milestones in Duchenne Muscular Dystrophy.

BACKGROUND: Over the last few years there has been increasing attention to detect early signs of impairment in young Duchenne muscular dystrophy boys but less has been reported on whether the delay may also affect the very early aspects of motor development, such as gross motor milestones. OBJECTIVE: The aim of this study was to retrospectively assess the age when early motor milestones were achieved in Duchenne muscular dystrophy. METHODS: The study is a retrospective analysis of data collected as part of a larger natural history project. Information on past medical history, collected at the time the boys were seen for the first time, were recorded and re available on clinical notes and on electronic CRF. RESULTS: Data were collected in 134 DMD boys. Sitting was achieved at 7.04 months. The % of DMD boys not achieving sitting by 9.4 months was 10%, ranging from 2% in the boys with mutations before exon 44 to 33% in those beyond exon 63. Walking was achieved at a mean age of 16.35 months. The % of DMD boys not achieving independent walking by 18 months was 17%, ranging from 9% in the boys with mutations between 44 and 51 to 42% in those beyond exon 63. CONCLUSIONS: Our results showed that the risk of a delay in sitting and walking was increasingly high in patients with mutations predictive of the involvement of different brain dystrophin isoforms.

Oral and Swallowing Abilities Tool (OrSAT) for Type 1 SMA Patients: Development of a New Module.

We describe the development of a new tool specifically designed to record oral abilities, swallowing and, more generally, feeding in young type 1 SMA patients, to be used during the first 24 months of life.The tool is composed by a checklist and a separate section summarizing the functional abilities into levels of feeding/swallowing impairment. The checklist includes 12 questions assessing aspects thought to be clinically meaningful for a type 1 SMA population and developmentally appropriate for infants during the first months of life. Each item is graded with a score of 0 or 1, depending on the child's ability to perform the activity. As some items are age-dependent, the number of items to be used, and therefore the maximum score, changes with increasing age. The levels of feeding/swallowing impairment include four levels that can be identified using easily identifiable clinical criteria.In an attempt to validate the tool in an untreated population we applied it to 24 type 1 SMA patients (age range: 2.3-24.1 months, mean: 10.8) in whom the same information collected by the new tool had been previously recorded using a less-structured format.When patients were classified in three groups according to the Dubowitz decimal classification, there was a significant difference both at baseline and at follow-up (p < 0.001). The items assessing fatigue during the nursing sessions were the most frequently impaired even in infants who did not have any other obvious clinical sign of swallowing difficulties.

Respiratory function and therapeutic expectations in DMD: families experience and perspective.

OBJECTIVE: The aim of this study was to use a structured questionnaire in a large cohort of Duchenne Muscular Dystrophy (DMD) patients to assess caregivers and patients views on respiratory function and to establish if their responses were related to the patients' age or level of functional impairment. METHODS: Questionnaires were administered to caregivers in 205 DMD patients of age between 3 and 36 years (115 ambulant, 90 non-ambulant), and to 64 DMD patients (3 ambulant, 61 non-ambulant) older than 18 years, subdivided into groups according to age, FVC, ambulatory and ventilatory status. RESULTS: Some differences were found in relation to FVC % values (p = 0.014), ambulatory (p = 0.043) and ventilatory status (p = 0.014). Nearly half of the caregivers expected deterioration over the next years, with the perspective of deterioration more often reported by caregivers of non-ambulant (p = 0.018) and ventilated patients (p = 0.004). Caregivers appeared to be aware of the relevance of respiratory function on quality of life (84%) showing willingness to enter possible clinical trials if these were aiming to stabilize the progression of respiratory function with a very high number of positive responses across the spectrum of age, FVC, ambulatory and ventilatory status. The boys older than 18 years showed similar results. CONCLUSIONS: Our study showed that the concern for respiratory function increases with age and with the reduction of FVC or the need for ventilation, but the need for intervention was acknowledged across the whole spectrum of age and functional status.

Ultrasound assessment of diaphragmatic function in type 1 spinal muscular atrophy.

OBJECTIVE: To investigate ultrasound features of diaphragm motion and function in type 1 spinal muscular atrophy (SMA-1) patients. DESIGN: Prospective study. PATIENTS: The study cohort included SMA-1 children younger than 18-year-old. Control subjects included type 2 and type 3 SMA and other neuromuscular disorders younger than 18-year-old. METHODOLOGY: Diaphragm ultrasound evaluating diaphragmatic excursion, speed of diaphragmatic contraction, duration of the respiratory cycle, inspiratory/expiratory relationship, end-inspiratory and -expiratory thickness, thickening fraction, and pattern of contractility. The interrater reliability for each variable was established by calculation of Cohen's k coefficient. RESULTS: Twenty-three SMA-1 patients and 12 controls were evaluated. Diaphragm ultrasound values were within normal ranges in all study cohort patients and no difference was found with controls. There was a gradient of diaphragm function with SMA 1.9 subgroup having the best and SMA 1.1 having the worst parameters, particularly in end-inspiratory thickness and diaphragmatic excursion (P = .031 and P = .041, respectively). Seventy-four percent of SMA-1 patients had a dysmotility pattern of diaphragm contraction, mostly represented in SMA 1.9 subgroup (P = .001). This pattern was observed in 92.8% of children on noninvasive ventilation (NIV) for less than 16 hours/d of and in 20% patients with invasive ventilation or NIV for more than 16 hours/d (P = .027). The dysmotility pattern was never observed in the control group. The levels of interobserver agreement were high for "diaphragm irregularities," "inspiratory/expiratory relationship," and "diaphragm thickness," and good for the other variables. CONCLUSIONS: Ultrasound can be used to evaluate diaphragm function and contractility in SMA-1 children, providing additional information to the clinical examination and functional respiratory tests, describing a characteristic contractility pattern in these patients. Longitudinal studies are needed to understand the impact of diaphragm dysmotility and other parameters on long-term outcome in SMA-1 patients.

Long-term progression in type II spinal muscular atrophy: A retrospective observational study.

OBJECTIVE: To report the long-term progression in a cohort of patients with type II spinal muscular atrophy (SMA) assessed with the Hammersmith Functional Motor Scale-Expanded. METHODS: Seventy-three patients (age 2.6-25 years) were included in the study. Twenty-eight of the 73 were first assessed before the age of 5 years and had been followed up for ≈5 years or longer. We observed an overall progression that was not linear. A piecewise regression analysis showed an improvement of scores in the younger patients with a point of slope change at ≈5 years of age, a decline between 5 and 13 years of age, and stability/slower decline after that. RESULTS: Patients with the lowest scores at baseline had the earliest onset of scoliosis and a higher need for noninvasive ventilation compared to those with higher scores. Our results confirm that on the long-term follow-up all patients with type II SMA show a clear and progressive decline. CONCLUSION: The severity of functional impairment at baseline can help to predict the magnitude of changes over time and the overall progression, including onset of scoliosis and need for noninvasive ventilation.

Clinical phenotypes and trajectories of disease progression in type 1 spinal muscular atrophy.

The advent of clinical trials has highlighted the need for natural history studies reporting disease progression in type 1 spinal muscular atrophy. The aim of this study was to assess functional changes using the Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND) scale in a cohort of type 1 infants. Nutritional and respiratory longitudinal data were also recorded. Patients were classified according to the severity of the phenotype and age of onset. SMN2 copies were also assessed. Twenty patients were included, eight with early onset most severe phenotype, eight with the more typical type 1 phenotype and 4, who achieved some head control, with a milder phenotype. Both baseline values and trajectories of progression were different in the three subgroups (p = 0.0001). Infants with the most severe phenotype had the lowest scores (below 20) on their first assessment and had the most rapid decline. Those with the typical phenotype had scores generally between 20 and 40 and also had a fast decline. The infants with the milder phenotype had the highest scores, generally above 35, and a much slower deterioration. Infants with three SMN2 copies had an overall milder phenotype and milder progression while two SMN2 copies were found in all three subgroups.

Functional levels and MRI patterns of muscle involvement in upper limbs in Duchenne muscular dystrophy.

The aim of the study was to evaluate the spectrum of upper limb functional activities and imaging finding in a cohort of patients affected by Duchenne muscular dystrophy. Thirty-one patients of age between 5 and 29 years were included in the study (17 ambulant and 14 non-ambulant). They were all assessed using the Performance of Upper Limb (PUL) test and muscle MRI of shoulder, arm and forearm in order to establish if the functional scores obtained at shoulder, mid and distal level related to specific patterns of involvement in each upper limb segment on muscle MRI. At shoulder level, latissimus dorsi, serratus anterior, infraspinatus and subscapularis were always involved, even in patients with full functional scores at shoulder level. Diffuse and severe involvement of all muscles was found in the patients with a PUL shoulder functional score of ≤ 5. At arm level biceps brachii, brachialis and triceps were generally concordantly involved or spared. Some degree of involvement could already be detected in patients with reduced scores on the PUL mid domain. They were generally severely involved in patients with functional scores less than 6 at mid-level. At distal level supinator and pronator muscles were often involved, followed by brachioradialis and, less frequently, by the muscles of the flexor compartment. The extensor muscles were generally completely spared. A diffuse and severe involvement was found only in patients who had very low scores (8 or below) on the PUL distal domain. The integrated use of functional scales and imaging allowed to establish patterns of involvement at each level, and the functional scores that were more frequently associated with diffuse and severe involvement.

Ambulatory function in spinal muscular atrophy: Age-related patterns of progression.

Individuals with spinal muscular atrophy (SMA) type 3 are able to walk but they have weakness, gait impairments and fatigue. Our primary study objective was to examine longitudinal changes in the six-minute walk test (6MWT) and to evaluate whether age and SMA type 3 subtype are associated with decline in ambulatory function. Data from three prospective natural history studies were used. Seventy-three participants who performed the 6MWT more than once, at least 6 months apart, were included; follow-up ranged from 0.5-9 years. Only data from patients who completed the 6MWT were included. The mean age of the participants was 13.5 years (range 2.6-49.1), with 52 having disease onset before age 3 years (type 3A). At baseline, type 3A participants walked a shorter distance on average (257.1 m) than type 3B participants (390.2 m) (difference = 133.1 m, 95% confidence interval [CI] 71.8-194.3, p < 0.001). Distance walked was weakly associated with age (r = 0.25, p = 0.04). Linear mixed effects models were used to estimate the mean annual rate of change. The overall mean rate of change was -7.8 m/year (95% CI -13.6 --2.0, p = 0.009) and this did not differ by subtype (type 3A: -8.5 m/year, type 3B: -6.6 m/year, p = 0.78), but it did differ by age group (< 6: 9.8 m/year; 6-10: -7.9 m/year; 11-19: -20.8 m/year; ≥ 20: -9.7 m/year; p = 0.005). Our results showed an overall decline on the 6MWT over time, but different trajectories were observed depending on age. Young ambulant SMA patients gain function but in adolescence, patients lose function. Future clinical trials in ambulant SMA patients should consider in their design the different trajectories of ambulatory function over time, based on age.