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A cross-sectional study of nemaline myopathy supplementary figures

Citation

Amburgey, Kimberly et al. (2022), A cross-sectional study of nemaline myopathy supplementary figures, Dryad, Dataset, https://doi.org/10.5061/dryad.z08kprrb9

Abstract

Objective:  Nemaline myopathy (NM) is a rare neuromuscular condition with clinical and genetic heterogeneity. To establish disease natural history, we performed a cross-sectional study of NM, complemented by longitudinal assessment and exploration of pilot outcome measures.  

Methods: Fifty-seven individuals with NM were recruited at two family workshops, including 16 examined at both time points. Subjects were evaluated by clinical history and physical examination. Functional outcome measures included the Motor Function Measure (MFM), pulmonary function tests (PFTs), myometry, goniometry, and bulbar assessments. 

Results: The most common clinical classification was “typical congenital” (54%), whereas 42% had more severe presentations. 58% of individuals needed mechanical support, with 26% requiring wheelchair, tracheostomy, and feeding tube. The MFM scale was performed in 44/57 participants and showed reduced scores in most with little floor/ceiling effect. Of the 27 individuals completing PFTs, abnormal values were observed in 65%. Lastly, bulbar function was abnormal in all patients examined, as determined using a novel outcome measure. Genotypes included mutations in ACTA1 (18), NEB (20), and TPM2 (2). Seventeen individuals were genetically unresolved. Patients with pathogenic ACTA1 and NEB variants were largely similar in clinical phenotype. Patients without genetic resolution had more severe disease. 

Conclusion: In all, we present a comprehensive cross-sectional study of NM. Our data identify significant disabilities and support a relatively stable disease course. We identify a need for further diagnostic investigation for the genetically unresolved group. Lastly, MFM, pulmonary function tests, and the slurp test were identified as promising outcome measures for future clinical trials. 

Methods

Our cohort included male (n=27) and female (n=30) participants ages 1 to 57 years old (the age at study entry was unknown for one participant). The diagnosis of NM was based on genetic confirmation of ACTA1, NEB or TPM2 pathogenic variants (n=40) or a clinical diagnosis of nemaline myopathy based on a muscle biopsy consistent with the presence of nemaline rods (n=16) or clinical features of nemaline myopathy with a family history of nemaline rods on muscle biopsy (n=1). Of note, 33/40 of the genetically established cases also had muscle biopsy, and all biopsies contained nemaline rods.  

Participants were recruited at nemaline myopathy family conferences hosted by A Foundation Building Strength in 2009 and 2016 (White Plains, New York). A subset of participants attended both conferences during which longitudinal data was collected (n=16). The remainder of subjects participated at one time point exclusively, either 2009 (n=16) or 2016 (n=25). Subjects participating exclusively in 2009 were not re-contacted, and therefore the study team could not verify current living status.  At study entry, one deceased individual was enrolled. Ethnicity was captured for 41 participants (32 White/Caucasian, 3 Native American, 1 Middle Eastern, 4 Hispanic, 1 Asian, 1 Black/African American, and 8 Ashkenazi Jewish.  9/41 reported multiple ethnicities.  

Standard Protocol Approvals, Registrations, and Patient Consents 

Written informed consent was obtained according to the Declaration of Helsinki from all participants or a parent/legal guardian. The cross-sectional study was approved by the Institutional Review Board of Boston Children’s Hospital (IRB# M09-08-0403) (2009) and the Research Ethics Board at the Hospital for Sick Children (REB# 1000053925) (2016). All participants were de-identified and provided with unique study identifiers.    

Study Measures 

Cross-sectional data were collected on written source documentation (2009) or uploaded directly into two electronic systems, REDCap and PhenoTips (2016). At the family conferences, the following measures were assessed: medical questionnaire (including pedigree, pregnancy, birth, developmental and medical histories), physical examination, motor assessments (Gowers’ maneuver, 10 meter run test, stair climb test, Motor Function Measure 20 or 32 (MFM20, MFM32)23, and myometry), goniometry, and pulmonary function testing.  

Timed Gowers’ measured the time taken to rise from lying on the floor to standing. Reference values for the timed Gowers’ were for individuals rising from seated on the floor to standing and were calculated from an average of the mean values from ages 2-12 years old 24. Reference values for the 10 meter run test for healthy children 2 – 12 years old (range: 4.63 – 7.95 seconds) were included 24. The MFM20 was used in 2009 and the MFM32 was used in 2016, with MFM20 values extracted from the larger MFM32 dataset to facilitate comparison. The MFM reflects testing in three domains, standing and transfers (domain one), axial and proximal motor function (domain two), and distal motor function (domain three). Direct muscle strength was measured using Medical Research Council (MRC) grading. Measure of facial and trunk muscle strength is not performed with MRC grading. Myometry was preformed to quantify muscle strength at the elbow, knee and hip joints. Normalized myometry values were defined by the study physiotherapist (calculated using weight, sex, age, and handedness). Goniometry scores were measured for the elbows, knees, and ankles. Categories were defined by the study physiotherapist (Grade 0: no contracture/hyperflexibility to Grade 4: most severe contracture). Reference values for pulmonary function testing were included for forced vital capacity (FVC) 25, maximal inspiratory pressure (MIP) 26, and peak cough flow (PCF) 27. Participants were excluded from FVC% Predicted calculation if height and weight were not captured, or if they were unable to perform the assessment.  

Bulbar function was assessed via two scales: the drooling rating scale28 and the drooling impact scale29 and one quantitative test. For the drooling rating scale, drooling severity and frequency are ranked on a scale of 1 (severity: dry, frequency: never) to 5 (severity: profuse, frequency: constant). The drooling impact scale rates the extent of drooling over the past week using 10 questions on a scale of one (not at all) to ten (a lot). The slurp test was also administered which involves measuring the time to drink 4 ounces of water through a straw30.  

A severity scoring system was developed by the study team to incorporate ambulatory, respiratory, and feeding status. Scores were calculated for each participant using the following formula (6*Ambulatory (No = 1, Yes =0)) +(2*Respiratory Support (Invasive = 3, Non-Invasive day and night = 2, Non-Invasive night only = 1, No support = 0)) + (Feeding Tube (Yes = 1, No = 0)) = Severity Score.  Scores were categorized as mild (0-2) or not mild (3-13). Ambulatory status was only assessed in participants >2 years of age. Clinical classifications were based on the criteria from Ryan et al, 2001. Two participants from the 2016 cohort were excluded from clinical classification due to incomplete data.  

Data Analysis 

Missing data was excluded from analyses. Analysis mainly consisted of descriptive statistics while a subset of data was analyzed using T- tests to determine statistical significance based on two-sided p-values being <0.05. Data analysis was completed at the Hospital for Sick Children.

Usage Notes

See Methods

Funding

A Foundation Building Strength, Award: N/A

Muscular Dystrophy Association, Award: N/A

National Institute of Child Health and Human Development, Award: R01HD075802

National Institute of Child Health and Human Development, Award: U54HD090255

A Foundation Building Strength