Role of child neurologists and neurodevelopmentalists in the diagnosis of cerebral palsy: A survey study.

OBJECTIVE: To contextualize the role of child neurologists and neurodevelopmentalists (CNs/NDDs) in cerebral palsy (CP) care, we review the changing landscape of CP diagnosis and survey stakeholder CNs/NDDs regarding their roles in CP care. METHODS: The optimal roles of the multiple specialties involved in CP care are currently unclear, particularly regarding CP diagnosis. We developed recommendations regarding the role of CNs/NDDs noting (1) increasing complexity of CP diagnosis given a growing number of genetic etiologies and treatable motor disorders that can be misdiagnosed as CP and (2) the views of a group of physician stakeholders (CNs/NDDs from the Child Neurology Society Cerebral Palsy Special Interest Group). RESULTS: CNs/NDDs felt that they were optimally suited to diagnose CP. Many (76%) felt that CNs/NDDs should always be involved in CP diagnosis. However, 42% said that their patients with CP were typically not diagnosed by CNs/NDDs, and 18% did not receive referrals to establish the diagnosis of CP at all. CNs/NDDs identified areas of their expertise critical for CP diagnosis including knowledge of the neurologic examination across development and early identification of features atypical for CP. This contrasts with their views on CP management, where CNs/NDDs felt that they could contribute to the medical team, but were necessary primarily when neurologic coexisting conditions were present. DISCUSSION: Given its increasing complexity, we recommend early referral for CP diagnosis to a CN/NDD or specialist with comparable expertise. This contrasts with current consensus guidelines, which either do not address or do not recommend specific specialist referral for CP diagnosis.

Modeling disease trajectory in Duchenne muscular dystrophy.

OBJECTIVE: To quantify disease progression in individuals with Duchenne muscular dystrophy (DMD) using magnetic resonance biomarkers of leg muscles. METHODS: MRI and magnetic resonance spectroscopy (MRS) biomarkers were acquired from 104 participants with DMD and 51 healthy controls using a prospective observational study design with patients with DMD followed up yearly for up to 6 years. Fat fractions (FFs) in vastus lateralis and soleus muscles were determined with 1H MRS. MRI quantitative T2 (qT2) values were measured for 3 muscles of the upper leg and 5 muscles of the lower leg. Longitudinal changes in biomarkers were modeled with a cumulative distribution function using a nonlinear mixed-effects approach. RESULTS: MRS FF and MRI qT2 increased with DMD disease duration, with the progression time constants differing markedly between individuals and across muscles. The average age at half-maximal muscle involvement (µ) occurred 4.8 years earlier in vastus lateralis than soleus, and these measures were strongly associated with loss-of-ambulation age. Corticosteroid treatment was found to delay µ by 2.5 years on average across muscles, although there were marked differences between muscles with more slowly progressing muscles showing larger delay. CONCLUSIONS: MRS FF and MRI qT2 provide sensitive noninvasive measures of DMD progression. Modeling changes in these biomarkers across multiple muscles can be used to detect and monitor the therapeutic effects of corticosteroids on disease progression and to provide prognostic information on functional outcomes. This modeling approach provides a method to transform these MRI biomarkers into well-understood metrics, allowing concise summaries of DMD disease progression at individual and population levels. CLINICALTRIALSGOV IDENTIFIER: NCT01484678.

Longitudinal timed function tests in Duchenne muscular dystrophy: ImagingDMD cohort natural history.

INTRODUCTION: Tests of ambulatory function are common clinical trial endpoints in Duchenne muscular dystrophy (DMD). Using these tests, the ImagingDMD study has generated a large data set that can describe the contemporary natural history of DMD in 5-12.9-year-olds. METHODS: Ninety-two corticosteroid-treated boys with DMD and 45 controls participated in this longitudinal study. Participants performed the 6-minute walk test (6MWT) and timed function tests (TFT: 10-m walk/run, climbing 4 stairs, supine to stand). RESULTS: Boys with DMD had impaired functional performance even at 5-6.9 years old. Boys older than 7 had significant declines in function over 1 year for 10-m walk/run and 6MWT. Eighty percent of participants could perform all functional tests at 9 years old. TFTs appear to be slightly more responsive and predictive of disease progression than the 6MWT in 7-12.9 year olds. DISCUSSION: This study provides insight into the contemporary natural history of key functional endpoints in DMD. Muscle Nerve 58: 631-638, 2018.

Two-Year Longitudinal Changes in Lower Limb Strength and Its Relation to Loss in Function in a Large Cohort of Patients With Duchenne Muscular Dystrophy.

OBJECTIVE: The main objective of this study was to examine the effect of disease on strength in two functionally important lower limb muscles for a period of 2 yrs in children with Duchene muscular dystrophy. DESIGN: Seventy-seven Duchene muscular dystrophy children participated in this study. Plantar flexors, knee extensors, strength, and performance on timed tests (6-min walk, 4-stairs, 10-m walk, supine-up) were assessed yearly for 2 yrs. Multivariate normal regression was used to assess changes in strength over time in the Duchene muscular dystrophy group. Spearman correlations were computed to examine relationship between strength and function. RESULTS: Normalized plantar flexor and knee extensor strength showed a significant decrease (P < 0.05) over 2 yrs, with larger declines in knee extensor. At baseline, knee extensor strongly correlated with performance on timed tests. However, plantar flexor strength was found to be a stronger predictor of loss in ambulatory function. Modest correlations (r = 0.19-0.34) were found between the decline in strength and functional performance over 2 yrs. CONCLUSIONS: This study describes the loss of lower limb strength in a large cohort of Duchene muscular dystrophy children for 2 yrs. The findings support that lower limb strength alone cannot account for the decline in performance on functional tests, and the role of other contributing factors, such as compensatory strategies, should be considered.

Skeletal muscle magnetic resonance biomarkers correlate with function and sentinel events in Duchenne muscular dystrophy.

OBJECTIVE: To provide evidence for quantitative magnetic resonance (qMR) biomarkers in Duchenne muscular dystrophy by investigating the relationship between qMR measures of lower extremity muscle pathology and functional endpoints in a large ambulatory cohort using a multicenter study design. METHODS: MR spectroscopy and quantitative imaging were implemented to measure intramuscular fat fraction and the transverse magnetization relaxation time constant (T2) in lower extremity muscles of 136 participants with Duchenne muscular dystrophy. Measures were collected at 554 visits over 48 months at one of three imaging sites. Fat fraction was measured in the soleus and vastus lateralis using MR spectroscopy, while T2 was assessed using MRI in eight lower extremity muscles. Ambulatory function was measured using the 10m walk/run, climb four stairs, supine to stand, and six minute walk tests. RESULTS: Significant correlations were found between all qMR and functional measures. Vastus lateralis qMR measures correlated most strongly to functional endpoints (|ρ| = 0.68-0.78), although measures in other rapidly progressing muscles including the biceps femoris (|ρ| = 0.63-0.73) and peroneals (|ρ| = 0.59-0.72) also showed strong correlations. Quantitative MR biomarkers were excellent indicators of loss of functional ability and correlated with qualitative measures of function. A VL FF of 0.40 was an approximate lower threshold of muscle pathology associated with loss of ambulation. DISCUSSION: Lower extremity qMR biomarkers have a robust relationship to clinically meaningful measures of ambulatory function in Duchenne muscular dystrophy. These results provide strong supporting evidence for qMR biomarkers and set the stage for their potential use as surrogate outcomes in clinical trials.

Safety and Efficacy of Repeat Open-Label AbobotulinumtoxinA Treatment in Pediatric Cerebral Palsy.

This was a prospective, repeat-treatment, open-label study (NCT01251380) of abobotulinumtoxinA for the management of lower limb spasticity in children who had completed a double-blind study. Children (2-17 years) received injections into the gastrocnemius-soleus complex, and other distal and proximal muscles as required (maximum total dose per injection cycle: 30 U/kg or 1000U). A total of 216 of the 241 double-blind patients entered the extension study and 207 received ≥1 open label injection into the gastrocnemius-soleus; 17-24% of patients also had injections into the hamstrings. The most frequent adverse events were related to common childhood infections and the most frequent treatment-related adverse event was injection site pain (n = 10). There was no evidence of a cumulative effect on adverse events. Sustained significant clinical improvements in muscle tone (Modified Ashworth Scale), spasticity (Tardieu Scale), overall clinical benefit (Physicians Global Assessment), and goal attainment (Goal Attainment Scale) were also observed across treatment cycles.

AbobotulinumtoxinA (Dysport®) Improves Function According to Goal Attainment in Children With Dynamic Equinus Due to Cerebral Palsy.

This secondary analysis of a large (n = 241), randomized, double-blind study evaluated the efficacy of 2 doses of abobotulinumtoxinA + standard of care (SOC) versus placebo + SOC in enabling children with dynamic equinus due to cerebral palsy to achieve their functional goals using Goal Attainment Scaling. Most parents/caregivers selected goals targeting aspects of gait improvement as most relevant. Mean (95% confidence interval) Goal Attainment Scaling T scores at week 4 were higher for both abobotulinumtoxinA groups versus placebo (treatment difference vs placebo: 10 U/kg/leg: 5.32 [2.31, 8.32], P = .0006, and 15 U/kg/leg 4.65 [1.59, 7.71], P = .0031). Superiority of both abobotulinumtoxinA doses versus placebo was maintained at week 12. Best goal attainment T scores were higher in the abobotulinumtoxinA groups versus placebo for the common goals of improved walking pattern, decreased falling, decreased tripping, and improved endurance. These findings demonstrate that single injections of abobotulinumtoxinA (10 and 15 U/kg/leg) significantly improved the ability of pediatric cerebral palsy patients to achieve their functional goals.

Multicenter prospective longitudinal study of magnetic resonance biomarkers in a large duchenne muscular dystrophy cohort.

OBJECTIVE: The aim of this study was to describe Duchenne muscular dystrophy (DMD) disease progression in the lower extremity muscles over 12 months using quantitative magnetic resonance (MR) biomarkers, collected across three sites in a large cohort. METHODS: A total of 109 ambulatory boys with DMD (8.7 ± 2.0 years; range, 5.0-12.9) completed baseline and 1-year follow-up quantitative MR imaging (transverse relaxation time constant; MRI-T2 ), MR spectroscopy (fat fraction and (1) H2 O T2 ), and 6-minute walk test (6MWT) measurements. A subset of boys completed additional measurements after 3 or 6 months. RESULTS: MRI-T2 and fat fraction increased significantly over 12 months in all age groups, including in 5- to 6.9-year-old boys. Significant increases in vastus lateralis (VL) fat fraction were observed in 3 and 6 months. Even in boys whose 6MWT performance improved or remained stable over 1 year, significant increases in MRI-T2 and fat fraction were found. Of all the muscles examined, the VL and biceps femoris long head were the most responsive to disease progression in boys with DMD. INTERPRETATION: MR biomarkers are responsive to disease progression in 5- to 12.9-year-old boys with DMD and able to detect subclinical disease progression in DMD, even within short (3-6 months) time periods. The measured sensitivity of MR biomarkers in this multicenter study may be critically important to future clinical trials, allowing for smaller sample sizes and/or shorter study windows in this fatal rare disease.

AbobotulinumtoxinA for Equinus Foot Deformity in Cerebral Palsy: A Randomized Controlled Trial.

BACKGROUND: Although botulinum toxin is a well-established treatment of focal spasticity in cerebral palsy, most trials have been small, and few have simultaneously assessed measures of muscle tone and clinical benefit. METHODS: Global, randomized, controlled study to assess the efficacy and safety of abobotulinumtoxinA versus placebo in cerebral palsy children with dynamic equinus foot deformity. Patients were randomized (1:1:1) to abobotulinumtoxinA 10 U/kg/leg, 15 U/kg/leg, or placebo injections into the gastrocnemius-soleus complex (1 or both legs injected). In the primary hierarchical analysis, demonstration of benefit for each dose required superiority to placebo on the primary (change in Modified Ashworth Scale from baseline to week 4) and first key secondary (Physician's Global Assessment at week 4) end points. RESULTS: Two hundred and forty-one patients were randomized, and 226 completed the study; the intention to treat population included 235 patients (98%). At week 4, Modified Ashworth Scale scores significantly improved with abobotulinumtoxinA; mean (95% confidence interval) treatment differences versus placebo were -0.49 (-0.75 to -0.23; P = .0002) for 15 U/kg/leg and -0.38 (-0.64 to -0.13; P = .003) for 10 U/kg/leg. The Physician's Global Assessment treatment differences versus placebo of 0.77 (0.45 to 1.10) for 15 U/kg/leg and 0.82 (0.50 to 1.14) for 10 U/kg/leg were also significant (both Ps < .0001). The most common treatment-related adverse event was muscular weakness (10 U/Kg/leg = 2; placebo = 1). CONCLUSIONS: AbobotulinumtoxinA improves muscle tone in children with dynamic equinus resulting in an improved overall clinical impression and is well tolerated.

Magnetic resonance imaging and spectroscopy assessment of lower extremity skeletal muscles in boys with Duchenne muscular dystrophy: a multicenter cross sectional study.

INTRODUCTION: Duchenne muscular dystrophy (DMD) is an X-linked recessive disorder that results in functional deficits. However, these functional declines are often not able to be quantified in clinical trials for DMD until after age 7. In this study, we hypothesized that (1)H2O T2 derived using (1)H-MRS and MRI-T2 will be sensitive to muscle involvement at a young age (5-7 years) consistent with increased inflammation and muscle damage in a large cohort of DMD subjects compared to controls. METHODS: MR data were acquired from 123 boys with DMD (ages 5-14 years; mean 8.6 SD 2.2 years) and 31 healthy controls (age 9.7 SD 2.3 years) using 3-Tesla MRI instruments at three institutions (University of Florida, Oregon Health & Science University, and Children's Hospital of Philadelphia). T2-weighted multi-slice spin echo (SE) axial images and single voxel 1H-MRS were acquired from the lower leg and thigh to measure lipid fraction and (1)H2O T2. RESULTS: MRI-T2, (1)H2O T2, and lipid fraction were greater (p<0.05) in DMD compared to controls. In the youngest age group, DMD values were different (p<0.05) than controls for the soleus MRI-T2, (1)H2O T2 and lipid fraction and vastus lateralis MRI-T2 and (1)H2O T2. In the boys with DMD, MRI-T2 and lipid fraction were greater (p<0.05) in the oldest age group (11-14 years) than the youngest age group (5-6.9 years), while 1H2O T2 was lower in the oldest age group compared to the young age group. DISCUSSION: Overall, MR measures of T2 and lipid fraction revealed differences between DMD and Controls. Furthermore, MRI-T2 was greater in the older age group compared to the young age group, which was associated with higher lipid fractions. Overall, MR measures of T2 and lipid fraction show excellent sensitivity to DMD disease pathologies and potential therapeutic interventions in DMD, even in the younger boys.

Examination of effects of corticosteroids on skeletal muscles of boys with DMD using MRI and MRS.

OBJECTIVE: To evaluate the effects of corticosteroids on the lower extremity muscles in boys with Duchenne muscular dystrophy (DMD) using MRI and magnetic resonance spectroscopy (MRS). METHODS: Transverse relaxation time (T2) and fat fraction were measured by MRI/MRS in lower extremity muscles of 15 boys with DMD (age 5.0-6.9 years) taking corticosteroids and 15 corticosteroid-naive boys. Subsequently, fat fraction was measured in a subset of these boys at 1 year. Finally, MRI/MRS data were collected from 16 corticosteroid-naive boys with DMD (age 5-8.9 years) at baseline, 3 months, and 6 months. Five boys were treated with corticosteroids after baseline and the remaining 11 served as corticosteroid-naive controls. RESULTS: Cross-sectional comparisons demonstrated lower muscle T2 and less intramuscular (IM) fat deposition in boys with DMD on corticosteroids, suggesting reduced inflammation/damage and fat infiltration with treatment. Boys on corticosteroids demonstrated less increase in IM fat infiltration at 1 year. Finally, T2 by MRI/MRS detected effects of corticosteroids on leg muscles as early as 3 months after drug initiation. CONCLUSIONS: These results demonstrate the ability of MRI/MRS to detect therapeutic effects of corticosteroids in reducing inflammatory processes in skeletal muscles of boys with DMD. Our work highlights the potential of MRI/MRS as a biomarker in evaluating therapeutic interventions in DMD.

Ataluren treatment of patients with nonsense mutation dystrophinopathy.

INTRODUCTION: Dystrophinopathy is a rare, severe muscle disorder, and nonsense mutations are found in 13% of cases. Ataluren was developed to enable ribosomal readthrough of premature stop codons in nonsense mutation (nm) genetic disorders. METHODS: Randomized, double-blind, placebo-controlled study; males ≥ 5 years with nm-dystrophinopathy received study drug orally 3 times daily, ataluren 10, 10, 20 mg/kg (N=57); ataluren 20, 20, 40 mg/kg (N=60); or placebo (N=57) for 48 weeks. The primary endpoint was change in 6-Minute Walk Distance (6MWD) at Week 48. RESULTS: Ataluren was generally well tolerated. The primary endpoint favored ataluren 10, 10, 20 mg/kg versus placebo; the week 48 6MWD Δ=31.3 meters, post hoc P=0.056. Secondary endpoints (timed function tests) showed meaningful differences between ataluren 10, 10, 20 mg/kg, and placebo. CONCLUSIONS: As the first investigational new drug targeting the underlying cause of nm-dystrophinopathy, ataluren offers promise as a treatment for this orphan genetic disorder with high unmet medical need.

Mutations in γ adducin are associated with inherited cerebral palsy.

OBJECTIVE: Cerebral palsy is estimated to affect nearly 1 in 500 children, and although prenatal and perinatal contributors have been well characterized, at least 20% of cases are believed to be inherited. Previous studies have identified mutations in the actin-capping protein KANK1 and the adaptor protein-4 complex in forms of inherited cerebral palsy, suggesting a role for components of the dynamic cytoskeleton in the genesis of the disease. METHODS: We studied a multiplex consanguineous Jordanian family by homozygosity mapping and exome sequencing, then used patient-derived fibroblasts to examine functional consequences of the mutation we identified in vitro. We subsequently studied the effects of adducin loss of function in Drosophila. RESULTS: We identified a homozygous c.1100G>A (p.G367D) mutation in ADD3, encoding gamma adducin in all affected members of the index family. Follow-up experiments in patient fibroblasts found that the p.G367D mutation, which occurs within the putative oligomerization critical region, impairs the ability of gamma adducin to associate with the alpha subunit. This mutation impairs the normal actin-capping function of adducin, leading to both abnormal proliferation and migration in cultured patient fibroblasts. Loss of function studies of the Drosophila adducin ortholog hts confirmed a critical role for adducin in locomotion. INTERPRETATION: Although likely a rare cause of cerebral palsy, our findings indicate a critical role for adducins in regulating the activity of the actin cytoskeleton, suggesting that impaired adducin function may lead to neuromotor impairment and further implicating abnormalities of the dynamic cytoskeleton as a pathogenic mechanism contributing to cerebral palsy.

Skeletal muscles of ambulant children with Duchenne muscular dystrophy: validation of multicenter study of evaluation with MR imaging and MR spectroscopy.

PURPOSE: To validate a multicenter protocol that examines lower extremity skeletal muscles of children with Duchenne muscular dystrophy (DMD) by using magnetic resonance (MR) imaging and MR spectroscopy in terms of reproducibility of these measurements within and across centers. MATERIALS AND METHODS: This HIPAA-compliant study was approved by the institutional review boards of all participating centers, and informed consent was obtained from each participant or a guardian. Standardized procedures with MR operator training and quality assurance assessments were implemented, and data were acquired at three centers by using different 3-T MR imaging instruments. Measures of maximal cross-sectional area (CSAmax), transverse relaxation time constant (T2), and lipid fraction were compared among centers in two-compartment coaxial phantoms and in two unaffected adult subjects who visited each center. Also, repeat MR measures were acquired twice on separate days in 30 boys with DMD (10 per center) and 10 unaffected boys. Coefficients of variation (CVs) were computed to examine the repeated-measure variabilities within and across centers. RESULTS: CSAmax, T2 from MR imaging and MR spectroscopy, and lipid fraction were consistent across centers in the phantom (CV, <3%) and in the adult subjects who traveled to each site (CV, 2%-7%). High day-to-day reproducibility in MR measures was observed in boys with DMD (CSAmax, CV = 3.7% [25th percentile, 1.3%; 75th percentile, 5.1%]; contractile area, CV = 4.2% [25th percentile, 0.8%; 75th percentile, 4.9%]; MR imaging T2, CV = 3.1% [25th percentile, 1.2%; 75th percentile, 4.7%]; MR spectroscopy T2, CV = 3.9% [25th percentile, 1.5%; 75th percentile, 5.1%]; and lipid fraction, CV = 4.7% [25th percentile, 1.0%; 75th percentile, 5.3%]). CONCLUSION: The MR protocol implemented in this multicenter study achieved highly reproducible measures of lower extremity muscles across centers and from day to day in ambulatory boys with DMD.

Use of skeletal muscle MRI in diagnosis and monitoring disease progression in Duchenne muscular dystrophy.

Studies have shown promise in using various approaches of magnetic resonance imaging (MRI) and magnetic resonance spectroscopy to evaluate skeletal muscle involvement in Duchenne muscular dystrophy. However, these studies have mainly been performed using a cross-sectional design, and the correlation of these MRI changes with disease progression and disease severity has not been fully elucidated. Overall, skeletal muscle MRI is a powerful and sensitive technique in the evaluation of muscle disease, and its use as a biomarker for disease progression or therapeutic response in clinical trials deserves further study.

A comparison of the changes in the energy cost of walking between children with cerebral palsy and able-bodied peers over one year.

For ambulatory children with cerebral palsy, the assessment of walking energy efficiency is utilized to determine functional changes following surgical, pharmacologic, or orthotic interventions. While the assessment of energy efficiency is considered a useful outcome tool, minimal information exists about the changes in energy efficiency over one year in children with cerebral palsy at different gross motor function classification system (GMFCS) levels and whether the patterns of change are similar to their able-bodied peers. The purpose of this study was to determine whether energy efficiency variables change similarly over one year in children with cerebral palsy by GMFCS level and whether they differ from their age-matched peers. Forty-five able-bodied children and 34 children with cerebral palsy, GMFCS levels I-III participated in the study. Energy efficiency variables were measured at baseline and at 12 months using a Cosmed K4b2. All subjects walked at their self-selected velocity for testing around a 33 m track. Baseline velocity and net non-dimensional cost (NNcost) differed by GMFCS level and between the able-bodied peers and all GMFCS levels. Children in GMFCS level III had the highest cost and the slowest velocity. When controlling for age and baseline values, significant differences in the magnitude of change were seen in velocity between children in GMFCS level III and children in GMFCS level I and II and their able-bodied peers. In comparison to their able-bodied peers, all GMFCS levels had an increase in NNcost over one year when controlling for age and baseline NNcost, with the difference in magnitude increasing by GMFCS level. Consistent with the literature, children with cerebral palsy had an increase in NNcost over one year in comparison to their able-bodied peers, which increased with GMFCS level. This finding demonstrates that when evaluating the change in walking energy efficiency with maturation and therapeutic intervention, comparisons should be made by GMFCS level.

Definition and classification of hyperkinetic movements in childhood.

Hyperkinetic movements are unwanted or excess movements that are frequently seen in children with neurologic disorders. They are an important clinical finding with significant implications for diagnosis and treatment. However, the lack of agreement on standard terminology and definitions interferes with clinical treatment and research. We describe definitions of dystonia, chorea, athetosis, myoclonus, tremor, tics, and stereotypies that arose from a consensus meeting in June 2008 of specialists from different clinical and basic science fields. Dystonia is a movement disorder in which involuntary sustained or intermittent muscle contractions cause twisting and repetitive movements, abnormal postures, or both. Chorea is an ongoing random-appearing sequence of one or more discrete involuntary movements or movement fragments. Athetosis is a slow, continuous, involuntary writhing movement that prevents maintenance of a stable posture. Myoclonus is a sequence of repeated, often nonrhythmic, brief shock-like jerks due to sudden involuntary contraction or relaxation of one or more muscles. Tremor is a rhythmic back-and-forth or oscillating involuntary movement about a joint axis. Tics are repeated, individually recognizable, intermittent movements or movement fragments that are almost always briefly suppressible and are usually associated with awareness of an urge to perform the movement. Stereotypies are repetitive, simple movements that can be voluntarily suppressed. We provide recommended techniques for clinical examination and suggestions for differentiating between the different types of hyperkinetic movements, noting that there may be overlap between conditions. These definitions and the diagnostic recommendations are intended to be reliable and useful for clinical practice, communication between clinicians and researchers, and for the design of quantitative tests that will guide and assess the outcome of future clinical trials.

An analysis of disease severity based on SMN2 copy number in adults with spinal muscular atrophy.

To evaluate the effect of SMN2 copy number on disease severity in spinal muscular atrophy (SMA), we stratified 45 adult SMA patients based on SMN2 copy number (3 vs. 4 copies). Patients with 3 copies had an earlier age of onset and lower spinal muscular atrophy functional rating scale (SMAFRS) scores and were more likely to be non-ambulatory. There was, however, no difference between the groups in quantitative muscle strength or pulmonary function testing. Functional scale may be a more discriminating outcome measure for SMA clinical trials.