Long-Term Follow-Up Cares and Check Initiative: A Program to Advance Long-Term Follow-Up in Newborns Identified with a Disease through Newborn Screening.

In the United States and around the world, newborns are screened on a population basis for conditions benefiting from pre-symptomatic diagnosis and treatment. The number of screened conditions continues to expand as novel technologies for screening, diagnosing, treating, and managing disease are discovered. While screening all newborns facilitates early diagnosis and treatment, most screened conditions are treatable but not curable. Patients identified by newborn screening often require lifelong medical management and community support to achieve the best possible outcome. To advance the long-term follow-up of infants identified through newborn screening (NBS), the Long-Term Follow-up Cares and Check Initiative (LTFU-Cares and Check) designed, implemented, and evaluated a system of longitudinal data collection and annual reporting engaging parents, clinical providers, and state NBS programs. The LTFU-Cares and Check focused on newborns identified with spinal muscular atrophy (SMA) through NBS and the longitudinal health information prioritized by parents and families. Pediatric neurologists who care for newborns with SMA entered annual data, and data tracking and visualization tools were delivered to state NBS programs with a participating clinical center. In this publication, we report on the development, use of, and preliminary results from the LTFU-Cares and Check Initiative, which was designed as a comprehensive model of LTFU. We also propose next steps for achieving the goal of a national system of LTFU for individuals with identified conditions by meaningfully engaging public health agencies, clinicians, parents, families, and communities.

Increase in Full-Length Dystrophin by Exon Skipping in Duchenne Muscular Dystrophy Patients with Single Exon Duplications: An Open-label Study.

Single exon duplications account for disease in a minority of Duchenne muscular dystrophy patients. Exon skipping in these patients has the potential to be highly therapeutic through restoration of full-length dystrophin expression. We conducted a 48-week open label study of casimersen and golodirsen in 3 subjects with an exon 45 or 53 duplication. Two subjects (aged 18 and 23 years) were non-ambulatory at baseline. Upper limb, pulmonary, and cardiac function appeared stable in the 2 subjects in whom they could be evaluated. Dystrophin expression increased from 0.94 % ±0.59% (mean±SD) of normal to 5.1% ±2.9% by western blot. Percent dystrophin positive fibers also rose from 14% ±17% at baseline to 50% ±42% . Our results provide initial evidence that the use of exon-skipping drugs may increase dystrophin levels in patients with single-exon duplications.

Parental Experiences with Newborn Screening and Gene Replacement Therapy for Spinal Muscular Atrophy.

BACKGROUND: Spinal muscular atrophy (SMA) is a genetic neurodegenerative disorder with onset predominantly in infants and children. In recent years, newborn screening and three treatments, including gene replacement therapy (Onasemnogene abeparvovec-xioi), have become available in the United States, aiding in the diagnosis and treatment of children with SMA. OBJECTIVE: To evaluate parents' experiences with newborn screening and gene replacement therapy and to explore best practices for positive newborn screen disclosure and counseling of families. METHODS: We conducted semi-structured interviews (n = 32) and online surveys (n = 79) of parents whose children were diagnosed with SMA (on newborn screening or symptomatically) and treated with gene replacement therapy. RESULTS: Gene replacement therapy was most parents' first treatment choice, although concerns regarding long term efficacy (65%) and safety (51%) were common. Information provided during the newborn screening disclosure was quite variable. Only 34% of parents reported the information provided was sufficient and expressed need for more information about treatment. Although many parents experienced denial of the diagnosis at initial disclosure, 94% were in favor of inclusion of SMA on newborn screening. Parents were almost universally anxious following diagnosis and over half remained anxious at the time of study participation with uncertainty of the future being a key concern. Many parents had difficulty processing information provided during their first clinic appointment due to its complexity and their emotional state at the time. CONCLUSIONS: Utilizing this data, we provide a recommendation for the information provided in newborn screening disclosure, propose adjustments to education and counseling during the first clinic visit, and bring awareness of parents' mental health difficulties.

Continued safety and long-term effectiveness of onasemnogene abeparvovec in Ohio.

5q spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disease caused by absence of the SMN1 gene with three FDA approved genetic therapies which significantly improve outcomes. The AAV9 mediated gene replacement therapy, onasemnogene abeparvovec, has the greatest potential for side effects. Here we report the safety and outcomes from 46 children treated with onasemnogene abeparvovec in the state of Ohio between December 2018 and January 2023. In our cohort, onasemnogene abeparvovec treatment remained safe and no child experienced any significant adverse events, including thrombotic microangiopathy, liver failure or death. All children experienced benefit, although the benefit in those with 2 copies of SMN2 was variable. 79 % of the children treated when symptomatic had a SMN2 modifying therapy added on. With careful screening and post treatment monitoring, onasemnogene abeparvovec is safe and effective for children with SMA in the state of Ohio, but more work needs to be done to ensure optimal outcomes for all children with 2 copies of SMN2.

Exome sequencing in the pediatric neuromuscular clinic leads to more frequent diagnosis of both neuromuscular and neurodevelopmental conditions.

INTRODUCTION/AIMS: Exome sequencing (ES) has proven to be a valuable diagnostic tool for neuromuscular disorders, which often pose a diagnostic challenge. The aims of this study were to investigate the clinical outcomes associated with utilization of ES in the pediatric neuromuscular clinic and to determine if specific phenotypic features or abnormal neurodiagnostic tests were predictive of a diagnostic result. METHODS: This was a retrospective medical record review of 76 pediatric neuromuscular clinic patients who underwent ES. Based upon clinical assessment prior to ES, patients were divided into two groups: affected by neuromuscular (n = 53) or non-neuromuscular (n = 23) syndromes. RESULTS: A diagnosis was made in 28/76 (36.8%), with 29 unique disorders identified. In the neuromuscular group, a neuromuscular condition was confirmed in 78% of those receiving a genetic diagnosis. Early age of symptom onset was associated with a significantly higher diagnostic yield. The most common reason neuromuscular diagnoses were not detected on prior testing was due to causative genes not being present on disease-specific panels. Changes to medical care were made in 57% of individuals receiving a diagnosis on ES. DISCUSSION: These data further support ES as a powerful diagnostic tool in the pediatric neuromuscular clinic and highlight the advantages of ES over gene panels, including the ability to identify diagnoses regardless of etiology, identify genes newly associated with disease, and identify multiple confounding diagnoses. Rapid and accurate diagnosis by ES can not only end the patient's diagnostic odyssey, but often impacts patients' medical management and genetic counseling of families.

A genome-wide association analysis of loss of ambulation in dystrophinopathy patients suggests multiple candidate modifiers of disease severity.

The major determinant of disease severity in Duchenne muscular dystrophy (DMD) or milder Becker muscular dystrophy (BMD) is whether the dystrophin gene (DMD) mutation truncates the mRNA reading frame or allows expression of a partially functional protein. However, even in the complete absence of dystrophin, variability in disease severity is observed, and candidate gene studies have implicated several genes as modifiers. Here we present the largest genome-wide search to date for loci influencing severity in N = 419 DMD patients. Availability of subjects for such studies is quite limited, leading to modest sample sizes, which present a challenge for GWAS design. We have therefore taken special steps to minimize heterogeneity within our dataset at the DMD locus itself, taking a novel approach to mutation classification to effectively exclude the possibility of residual dystrophin expression, and utilized statistical methods that are well adapted to smaller sample sizes, including the use of a novel linear regression-like residual for time to ambulatory loss and the application of evidential statistics for the GWAS approach. Finally, we applied an unbiased in silico pipeline, utilizing functional genomic datasets to explore the potential impact of the best supported SNPs. In all, we obtained eight SNPs (out of 1,385,356 total) with posterior probability of trait-marker association (PPLD) ≥ 0.4, representing six distinct loci. Our analysis prioritized likely non-coding SNP regulatory effects on six genes (ETAA1, PARD6G, GALNTL6, MAN1A1, ADAMTS19, and NCALD), each with plausibility as a DMD modifier. These results support both recurrent and potentially new pathways for intervention in the dystrophinopathies.

A first-in-human phase I/IIa gene transfer clinical trial for Duchenne muscular dystrophy using rAAVrh74.MCK.GALGT2.

In a phase 1/2, open-label dose escalation trial, we delivered rAAVrh74.MCK.GALGT2 (also B4GALNT2) bilaterally to the legs of two boys with Duchenne muscular dystrophy using intravascular limb infusion. Subject 1 (age 8.9 years at dosing) received 2.5 × 1013 vector genome (vg)/kg per leg (5 × 1013 vg/kg total) and subject 2 (age 6.9 years at dosing) received 5 × 1013 vg/kg per leg (1 × 1014 vg/kg total). No serious adverse events were observed. Muscle biopsy evaluated 3 or 4 months post treatment versus baseline showed evidence of GALGT2 gene expression and GALGT2-induced muscle cell glycosylation. Functionally, subject 1 showed a decline in 6-min walk test (6MWT) distance; an increase in time to run 100 m, and a decline in North Star Ambulatory Assessment (NSAA) score until ambulation was lost at 24 months. Subject 2, treated at a younger age and at a higher dose, demonstrated an improvement over 24 months in NSAA score (from 20 to 23 points), an increase in 6MWT distance (from 405 to 478 m), and only a minimal increase in 100 m time (45.6-48.4 s). These data suggest preliminary safety at a dose of 1 × 1014 vg/kg and functional stabilization in one patient.

Intron mutations and early transcription termination in Duchenne and Becker muscular dystrophy.

DMD pathogenic variants for Duchenne and Becker muscular dystrophy are detectable with high sensitivity by standard clinical exome analyses of genomic DNA. However, up to 7% of DMD mutations are deep intronic and analysis of muscle-derived RNA is an important diagnostic step for patients who have negative genomic testing but abnormal dystrophin expression in muscle. In this study, muscle biopsies were evaluated from 19 patients with clinical features of a dystrophinopathy, but negative clinical DMD mutation analysis. Reverse transcription-polymerase chain reaction or high-throughput RNA sequencing methods identified 19 mutations with one of three pathogenic pseudoexon types: deep intronic point mutations, deletions or insertions, and translocations. In association with point mutations creating intronic splice acceptor sites, we observed the first examples of DMD pseudo 3'-terminal exon mutations causing high efficiency transcription termination within introns. This connection between splicing and premature transcription termination is reminiscent of U1 snRNP-mediating telescripting in sustaining RNA polymerase II elongation across large genes, such as DMD. We propose a novel classification of three distinct types of mutations identifiable by muscle RNA analysis, each of which differ in potential treatment approaches. Recognition and appropriate characterization may lead to therapies directed toward full-length dystrophin expression for some patients.

Phenotypic Spectrum of Dystrophinopathy Due to Duchenne Muscular Dystrophy Exon 2 Duplications.

BACKGROUND AND OBJECTIVES: To describe the phenotypic spectrum of dystrophinopathy in a large cohort of individuals with DMD exon 2 duplications (Dup2), who may be particularly amenable to therapies directed at restoring expression of either full-length dystrophin or nearly full-length dystrophin through utilization of the DMD exon 5 internal ribosome entry site (IRES). METHODS: In this retrospective observational study, we analyzed data from large genotype-phenotype databases (the United Dystrophinopathy Project [UDP] and the Italian DMD network) and classified participants into Duchenne muscular dystrophy (DMD), intermediate muscular dystrophy (IMD), or Becker muscular dystrophy (BMD) phenotypes. Log-rank tests for time-to-event variables were used to compare age at loss of ambulation (LOA) in participants with Dup2 vs controls without Dup2 in the UDP database and for comparisons between steroid-treated vs steroid-naive participants with Dup2. RESULTS: Among 66 participants with Dup2 (UDP = 40, Italy = 26), 61% were classified as DMD, 9% as IMD, and 30% as BMD. Median age at last observation was 15.4 years (interquartile range 8.79-26.0) and 75% had been on corticosteroids for at least 6 months. Age at LOA differed significantly between participants with Dup2 DMD and historical controls without Dup2 DMD (p < 0.001). Valid spirometry was limited but suggested a delay in the typical age-related decline in forced vital capacity and 24 of 55 participants with adequate cardiac data had cardiomyopathy. DISCUSSION: Some patients with Dup2 display a milder disease course than controls without Dup2 DMD, and prolonged ambulation with corticosteroids suggests the potential of IRES activation as a molecular mechanism. As Dup2-targeted therapies reach clinical applications, this information is critical to aid in the interpretation of the efficacy of new treatments.

Validity and Reliability of the Neuromuscular Gross Motor Outcome.

BACKGROUND: Approved treatments in spinal muscular atrophy (SMA) have resulted in unprecedented gains for many individuals. Use of available outcomes, typically developed for a specific type of SMA, do not cover the range of progression, often resulting in a battery of functional testing being completed at visits. Our objective was to validate the Neuromuscular Gross Motor Outcome (GRO) as a tool to quantify function in SMA across the span of abilities. METHODS: Patients with genetically confirmed SMA completed functional testing at each visit including the Neuromuscular GRO and other appropriate gross motor outcomes. RESULTS: We enrolled 91 patients with SMA types 1 to 3 between 8 days and 32.1 years. The GRO utilizes a 0- to 2-point scale with scores in our cohort ranging from 1 to 95 points with no floor or ceiling effect. GRO scores were significantly different across functional categories (P < 0.001) and treatment status (P = 0.01) and correlated to other functional assessments (P ≤ 0.001). All patients were measured using the GRO, whereas traditional outcomes were only appropriate on 36% to 59% of our cohort. CONCLUSION: The Neuromuscular GRO quantifies function across the span of age and abilities included in our cohort, allowing for continuous longitudinal monitoring on one scale to reduce the burden of testing in our heterogeneous clinic population.

Absence of Significant Off-Target Splicing Variation with a U7snRNA Vector Targeting DMD Exon 2 Duplications.

Exon skipping therapies for Duchenne muscular dystrophy that restore an open reading frame can be induced by the use of noncoding U7 small nuclear RNA (U7snRNA) modified by an antisense exon-targeting sequence delivered by an adeno-associated virus (AAV) vector. We have developed an AAV vector (AAV9.U7-ACCA) containing four U7snRNAs targeting the splice donor and acceptor sites of dystrophin exon 2, resulting in highly efficient exclusion of DMD exon 2. We assessed the specificity of splice variation induced by AAV9.U7-ACCA delivery in the Dmd exon 2 duplication (Dup2) mouse model through an unbiased RNA-seq approach. Treatment-related effects on pre-mRNA splicing were quantified using local splicing variation (LSV) analysis. Filtering the transcriptome for differences in treatment-related splicing resulted in only 16 candidate off-target LSVs. Only a single candidate off-target LSV was found in both skeletal and cardiac muscle tissue and occurred at a known variable cassette exon. In contrast, four LSVs represented significant on-target correction of Dmd exon 2 splicing and transcriptome analysis showed correction of known dystrophin-deficient gene dysregulation. We conclude that the absence of off-target splicing induced by treatment with the U7-ACCA vector supports the continued clinical development of this approach.

Time is muscle: A recommendation for early treatment for preterm infants with spinal muscular atrophy.

Implementation of newborn screening for spinal muscular atrophy (SMA) in 33 US states and increased genetic carrier screening have led to an increase in early, presymptomatic diagnosis of SMA. Early treatment is critically important and is recommended for presymptomatic infants with two to four copies of survival motor neuron 2. Currently, no specific treatment recommendations exist for preterm infants with SMA. The US Food and Drug Administration does not recommend using onasemnogene abeparvovec-xioi in preterm infants. Some insurance companies interpret "preterm" to be less than 40 weeks gestational age (GA) instead of the commonly accepted 37 weeks GA, which can be a barrier to treatment access. Given the risk of rapid decline in some infants, we recommend treatment of preterm infants when they reach 37 weeks GA, based on the definitions of term GA from the World Health Organization and Centers for Disease Control and Prevention, assuming all other treatment criteria are met.

Spinal Muscular Atrophy.

Spinal muscular atrophy is one of the most common neuromuscular disorders of childhood and has high morbidity and mortality. Three different disease-modifying treatments were introduced in the last 4 years: nusinersen, onasemnogene abeparvovec, and risdiplam. These agents have demonstrated safety and efficacy, but their long-term benefits require further study. Newborn screening programs are enabling earlier diagnosis and treatment and better outcomes, but respiratory care and other supportive measures retain a key role in the management of spinal muscular atrophy. Ongoing efforts seek to optimize gene therapy vectors, explore new therapeutic targets beyond motor neurons, and evaluate the role of combination therapy.

Lack of Toxicity in Nonhuman Primates Receiving Clinically Relevant Doses of an AAV9.U7snRNA Vector Designed to Induce DMD Exon 2 Skipping.

Therapeutic exon skipping as a treatment for Duchenne muscular dystrophy (DMD) has largely concentrated on the delivery of antisense oligomers to treat out-of-frame exon deletions. Here we report on the preclinical development of an adeno-associated virus (AAV)-encapsidated viral vector containing four copies of the noncoding U7 small nuclear RNA (U7snRNA), each targeted to either the splice donor or the splice acceptor sites of DMD exon 2. We have previously shown that delivery of this vector (scAAV9.U7.ACCA) to the Dup2 mouse model results in expression of full-length dystrophin from wild-type DMD mRNA, as well as an internal ribosome entry site (IRES)-driven isoform translated only in the absence of exon 2 (deletion exon 2 [Del2] mRNA). Here we present the data from a rigorous dose escalation toxicity study in nonhuman primates, encompassing two doses (3 × 1013 and 8 × 1013 vg/kg) and two time points (3 and 6 months postinjection). No evidence for significant toxicity was seen by biochemical, histopathologic, or clinical measures, providing evidence for safety that led to initiation of a first-in-human clinical trial.

Overview of gene therapy in spinal muscular atrophy and Duchenne muscular dystrophy.

Both 5q-linked spinal muscular atrophy (SMA) and Duchenne muscular dystrophy (DMD) are fatal monogenic neuromuscular disorders caused by loss-of-function mutations. SMA is an autosomal recessive disorder affecting motor neurons that is typically caused by homozygous whole-gene deletions of SMN1. DMD is an X-linked recessive muscle disease most often due to exon deletions, but also duplications and smaller sized variants within the DMD gene. Gene replacement therapy offers the opportunity to correct the underlying genetic defect by the introduction of a functional gene. We review the transformative work from clinical trials to United States Food and Drug Administration approval of onasemnogene abeparvovec-xioi in SMA and its application in clinical practice and the early results of microdystrophin delivery in DMD. We also review the introduction of antisense oligonucleotides to alter pre-messenger RNA splicing to promote exon inclusion (as in nusinersen in SMA) or exclusion (as in eteplirsen in DMD) into neuromuscular therapeutics. There are multiple promising novel genetically mediated therapies on the horizon, which in aggregate point towards a hopeful future for individuals with SMA and DMD.

Natural History of Steroid-Treated Young Boys With Duchenne Muscular Dystrophy Using the NSAA, 100m, and Timed Functional Tests.

INTRODUCTION: Clinical trials targeting younger cohorts of boys with Duchenne muscular dystrophy are necessary as earlier intervention may maximize treatment effect. Boys with Duchenne muscular dystrophy often have gross motor delays very early in life, and although they gain skills, they are on a lower trajectory than typical peers. Quantifying the natural rate of motor maturation in Duchenne muscular dystrophy from an early age permits identification of deviations from the expected trajectory related to treatment effects. METHODS: The purpose of our study was to define the natural history in boys aged from ≥3 to <8 years using the North Star Ambulatory Assessment (NSAA), 100-meter timed test (100m), 10-meter walk/run (10m), time to rise (Rise), and 4-stair climb (4SC). Assessments were completed as standard of care during regularly scheduled clinic visits. RESULTS: One hundred sixty-two boys with DMD aged 3.1 to 7.9 years on glucocorticoids were evaluated using one or more of the following tests as appropriate for age: NSAA (N = 158; 3.1-7.9 years), 100m (N = 131; 3.4-7.9 years), 10m (N = 162; 3.1-7.9 years), Rise (N = 160; 3.1-7.9 years), and 4SC (N = 153; 3.1-7.9 years). Longitudinal data are presented by age in a subcohort (N = 64). CONCLUSIONS: Our study documents the baseline function of boys with DMD who are being treated with corticosteroids. These data will be useful to compare ongoing and future therapeutic intervention(s) for DMD.

Gene Therapy for Spinal Muscular Atrophy: Safety and Early Outcomes.

BACKGROUND AND OBJECTIVES: Historically, autosomal recessive 5q-linked spinal muscular atrophy (SMA) has been the leading inherited cause of infant death. SMA is caused by the absence of the SMN1 gene, and SMN1 gene replacement therapy, onasemnogene abeparvovec-xioi, was Food and Drug Administration approved in May 2019. Approval included all children with SMA age <2 years without end-stage weakness. However, gene transfer with onasemnogene abeparvovec-xioi has been only studied in children age ≤8 months. METHODS: In this article, we report key safety and early outcome data from the first 21 children (age 1-23 months) treated in the state of Ohio. RESULTS: In children ≤6 months, gene transfer was well tolerated. In this young group, serum transaminase (aspartate aminotransferase and alanine aminotransferase) elevations were modest and not associated with γ glutamyl transpeptidase elevations. Initial prednisolone administration matched that given in the clinical trials. In older children, elevations in aspartate aminotransferase, alanine aminotransferase and γ glutamyl transpeptidase were more common and required a higher dose of prednisolone, but all were without clinical symptoms. Nineteen of 21 (90%) children experienced an asymptomatic drop in platelets in the first week after treatment that recovered without intervention. Of the 19 children with repeated outcome assessments, 11% (n = 2) experienced stabilization and 89% (n = 17) experienced improvement in motor function. CONCLUSIONS: In this population, with thorough screening and careful post-gene transfer management, replacement therapy with onasemnogene abeparvovec-xioi is safe and shows promise for early efficacy.

Spinal Muscular Atrophy in the Treatment Era.

Spinal muscular atrophy is an autosomal-recessive degenerative neuromuscular disease that has historically been categorized into 5 types based on the individual's best functional ability. Two rather remarkable treatments have recently been approved for commercial use, and both have markedly changed the natural history of this disease. Here the authors report several cases of individuals, ranging from infants to adults, to highlight diagnostic considerations, along with initial and long-term treatment considerations in these individuals who now have the potential for stabilization to significant improvement in functional outcomes.

Clinical Phenotypes of DMD Exon 51 Skip Equivalent Deletions: A Systematic Review.

BACKGROUND: Eteplirsen, the first FDA-approved RNA-modifying therapy for DMD, is applicable to ∼13% of patients with DMD. Because multiple exonic deletions are amenable to exon 51 skipping, the isoforms resulting from the various exon 51-skipped transcripts may vary in stability, function, and phenotype. OBJECTIVE/METHODS: We conducted a detailed review of dystrophinopathy published literature and unpublished databases to compile phenotypic features of patients with exon 51 "skip-equivalent" deletions. RESULTS: Theoretically, 48 different in-frame transcripts may result from exon 51 skipping. We found sufficient clinical information on 135 patients carrying mutations that would result in production of 11 (23%) of these transcripts, suggesting the remainder have not been identified in vivo. The majority had mild phenotypes: BMD (n = 81) or isolated dilated cardiomyopathy (n = 3). Particularly interesting are the asymptomatic (n = 10) or isolated hyperCKemia (n = 20) patients with deletions of exons 45- 51, 48- 51, 49- 51 and 50- 51. Finally, 16 (12%) had more severe phenotypes described as intermediate (n = 2) or DMD (n = 14), and 6 reports had no definitive phenotype. CONCLUSIONS: This review shows that the majority of exon 51 "skip-equivalent" deletions result in milder (BMD) phenotypes and supports that exon 51 skipping therapy could provide clinical benefit, although we acknowledge that other factors, such as age at treatment initiation or ongoing standard of care, may influence the degree of benefit.

The Genotypic and Phenotypic Spectrum of BICD2 Variants in Spinal Muscular Atrophy.

The bicaudal D cargo adaptor 2 (BICD2) gene encodes a conserved cargo adaptor protein required for dynein-mediated transport. Inherited and de novo variants in BICD2 cause SMALED2 (spinal muscular atrophy lower extremity dominant 2), and a subset have recently been reported to cause severe, often lethal disease. However, a true genotype-phenotype correlation for BICD2 has not been performed, and cases described to date are scattered among at least 14 publications. In this review, we identify the characteristics of disease-causing variants in BICD2 that distinguish them from benign variation and perform genotype-phenotype correlations for 99 BICD2 variant carriers from 35 families. ANN NEUROL 2020;87:487-496.