Genetic therapies for inherited neuromuscular disorders.

Inherited neuromuscular disorders encompass a broad group of genetic conditions, and the discovery of these underlying genes has expanded greatly in the past three decades. The discovery of such genes has enabled more precise diagnosis of these disorders and the development of specific therapeutic approaches that target the genetic basis and pathophysiological pathways. Such translational research has led to the approval of two genetic therapies by the US Food and Drug Administration: eteplirsen for Duchenne muscular dystrophy and nusinersen for spinal muscular atrophy, which are both antisense oligonucleotides that modify pre-mRNA splicing. In this Review we aim to discuss new genetic therapies and ongoing clinical trials for Duchenne muscular dystrophy, spinal muscular atrophy, and other less common childhood neuromuscular disorders.

Five-Year Follow-Up and Outcomes of Noninvasive Ventilation in Subjects With Neuromuscular Diseases.

INTRODUCTION: The purpose of this study was to investigate the 5-year outcomes of noninvasive ventilation (NIV) application in different neuromuscular disease (NMD) groups. METHODS: We categorized 180 subjects who had initiated NIV between March 2001 and August 2009 into 4 groups and followed them for > 5 y. The NIV maintenance rate and average duration, applying time, and forced vital capacity (FVC) were investigated at the time NIV was initiated and 5 y after NIV initiation in each group. RESULTS: In subjects with amyotrophic lateral sclerosis (ALS), Duchenne muscular dystrophy (DMD), and spinal muscular atrophy (SMA)-congenital myopathy, the 5-year subjects who continued to use NIV over time were 22.5%, 89.4%, and 91.3%, respectively, and the average NIV maintenance durations were 21.53 ± 19.26 months, 55.22 ± 11.47 months, and 57.48 ± 8.34 months, respectively (P < .001). Median daily applying time changed from 8.0 h to 24.0 h (P < .001), from 8.0 h to 12.0 h (P < .001), and from 8.0 h to 9.0 h (P = .11) in subjects with ALS, DMD, and SMA-congenital myopathy, respectively. FVC decreased significantly after 5 y except in the group with combined SMA-congenital myopathy. CONCLUSIONS: NIV was tolerated long-term without significant increases in daily application time for most subjects with NMD. However, in individuals with ALS, development of severe bulbar symptoms can risk maintaining NIV.

Targeted sequencing of maternal plasma for haplotype-based non-invasive prenatal testing of spinal muscular atrophy.

Five pregnant women with a child affected by spinal muscular atrophy (SMA) were recruited between November 2014 and March 2015. Deletion of exons 7 and/or 8 in the SMN1 gene were identified by multiplex ligation-dependent probe amplification (MLPA), the current standard diagnostic test for SMA. Parental and fetal haplotypes of the SMN1 gene were determined in each family from haplotype-based non-invasive testing of blood samples and maternal plasma, respectively. Fetal haplotype was compared with the results of MLPA of fetal DNA obtained from amniotic fluid or chorionic villi. Parental haplotypes were constructed successfully in the five families. Assisted by the information on parental haplotype, non-invasive testing of maternal plasma identified one fetus with homozygous deletion of exons 7 and 8, two fetuses with heterozygous deletion of exons 7 and 8 and two normal fetuses. These results were consistent with the diagnosis by MLPA. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Enfermedad de Parkinson asociada a mutación del gen LRRK2, que simula atrofia multisistémica por la combinación de parkinsonismo, disautonomía precoz y gammagrafía cardíaca normal / Parkinson's disease associated to mutation of the LRRK2 gene, mimicking multisystemic atrophy due to the combination of parkinsonism, early-onset dysautonomia and normal cardiac scintigraphy

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Evaluación funcional para personas no ambulantes afectas de atrofia muscular espinal y distrofia muscular de Duchenne. Traducción y validación de la escala Egen Klassifikation 2 para la población española / Functional assessment for people unable to walk due to spinal muscular atrophy and Duchenne muscular dystrophy. Translation and validation of the Egen Klassifikation 2 scale for the Spanish population

Introducción. La escala Egen Klassifikation 2 (EK2), ampliación de la escala EK, evalúa la capacidad funcional de personas con atrofia muscular espinal (AME) y distrofia muscular de Duchenne (DMD) que están en fase de silla de ruedas. Esta versión es más específica para la AME que su antecesora. Objetivo. Analizar la validez y fiabilidad de la versión española de dicha escala como instrumento de medición de la capacidad funcional en pacientes afectos de AME y DMD que están en silla de ruedas. Pacientes y métodos. Primeramente se realizó una traducción-retrotraducción al español de la versión en inglés de la EK2 y, posteriormente, se estudió la fiabilidad de la versión traducida. Para ello, se seleccionaron 39 pacientes, de edades comprendidas entre 4 y 60 años, que fueron valorados por dos observadores. Para evaluar la concordancia intraobservador se realizaron dos evaluaciones por un mismo observador, y para la interobservador, se realizó una tercera evaluación por un segundo observador. Resultados. Los valores obtenidos referidos a la puntuación total de los ítems de la escala (suma EK2) reflejan una fiabilidad intra e interobservador excelente, de 0,993 y 0,988, respectivamente. Asimismo, para cada uno de los ítems, la fiabilidad fue excelente, a excepción de un ítem, en el que fue buena. Conclusiones. La versión española de la escala EK2 es un instrumento válido y fiable para la población española como herramienta de medición de la capacidad funcional en pacientes con AME y DMD que están en silla de ruedas (AU)

Introduction. The Egen Klassifikation 2 Scale (EK2), expansion of the EK scale, assesses the functional capacity of people with spinal muscular atrophy (SMA) and Duchenne muscular dystrophy (DMD) that are in wheelchair phase. This version is more specific for SMA than its EK predecessor. Aim. To examine the validity and reliability of the Spanish version of the scale as a tool for measuring the functional capacity in patients with DMD and SMA who are in wheelchairs. Patients and methods. First, a translation-back-translation into Spanish of the English version of the EK2 was performed; later, we studied the reliability of the translated version. For this, 39 patients, aged between 4 and 60, who were evaluated by two observers, were recruited. To evaluate the intra-observer consistency, two assessments by the same observer were performed, and the inter-observer third assessment was performed by a second observer. Results. The obtained values based on the total score of the scale items (sum EK2) reflect excellent intra- and inter-observer reliability, 0.993 and 0.988 respectively. Also, for each of the items, reliability was excellent except for one item in which it was good. Conclusions. The Spanish version of the EK2 scale is a valid and reliable instrument for the Spanish population as a tool for measuring the functional capacity in patients with SMA and DMD who are in wheelchairs (AU)

Congenital lethal motor neuron disease with a novel defect in ribosome biogenesis.

OBJECTIVE: We describe a novel congenital motor neuron disease with early demise due to respiratory insufficiency with clinical overlap with spinal muscular atrophy with respiratory distress (SMARD) type 1 but lacking a mutation in the IGHMBP2 gene. METHODS: Exome sequencing was used to identify a de novo mutation in the LAS1L gene in the proband. Pathogenicity of the mutation was validated using a zebrafish model by morpholino-mediated knockdown of las1l. RESULTS: We identified a de novo mutation in the X-linked LAS1L gene in the proband (p.S477N). The mutation is in a highly conserved region of the LAS1L gene predicted to be deleterious by bioinformatic analysis. Morpholino-based knockdown of las1l, the orthologous gene in zebrafish, results in early lethality and disruption of muscle and peripheral nerve architecture. Coinjection of wild-type but not mutant human RNA results in partial rescue of the phenotype. CONCLUSION: We report a patient with a SMARD phenotype due to a mutation in LAS1L, a gene important in coordinating processing of the 45S pre-rRNA and maturation of the large 60S ribosomal subunit. Similarly, the IGHMB2 gene associated with SMARD type 1 has been suggested to have an important role in ribosomal biogenesis from its role in processing the 45S pre-rRNA. We propose that disruption of ribosomal maturation may be a common pathogenic mechanism linking SMARD phenotypes caused by both IGHMBP2 and LAS1L.

Mutations in BICD2, which encodes a golgin and important motor adaptor, cause congenital autosomal-dominant spinal muscular atrophy.

Spinal muscular atrophy (SMA) is a heterogeneous group of neuromuscular disorders caused by degeneration of lower motor neurons. Although functional loss of SMN1 is associated with autosomal-recessive childhood SMA, the genetic cause for most families affected by dominantly inherited SMA is unknown. Here, we identified pathogenic variants in bicaudal D homolog 2 (Drosophila) (BICD2) in three families afflicted with autosomal-dominant SMA. Affected individuals displayed congenital slowly progressive muscle weakness mainly of the lower limbs and congenital contractures. In a large Dutch family, linkage analysis identified a 9q22.3 locus in which exome sequencing uncovered c.320C>T (p.Ser107Leu) in BICD2. Sequencing of 23 additional families affected by dominant SMA led to the identification of pathogenic variants in one family from Canada (c.2108C>T [p.Thr703Met]) and one from the Netherlands (c.563A>C [p.Asn188Thr]). BICD2 is a golgin and motor-adaptor protein involved in Golgi dynamics and vesicular and mRNA transport. Transient transfection of HeLa cells with all three mutant BICD2 cDNAs caused massive Golgi fragmentation. This observation was even more prominent in primary fibroblasts from an individual harboring c.2108C>T (p.Thr703Met) (affecting the C-terminal coiled-coil domain) and slightly less evident in individuals with c.563A>C (p.Asn188Thr) (affecting the N-terminal coiled-coil domain). Furthermore, BICD2 levels were reduced in affected individuals and trapped within the fragmented Golgi. Previous studies have shown that Drosophila mutant BicD causes reduced larvae locomotion by impaired clathrin-mediated synaptic endocytosis in neuromuscular junctions. These data emphasize the relevance of BICD2 in synaptic-vesicle recycling and support the conclusion that BICD2 mutations cause congenital slowly progressive dominant SMA.

Mutations in BICD2 cause dominant congenital spinal muscular atrophy and hereditary spastic paraplegia.

Dominant congenital spinal muscular atrophy (DCSMA) is a disorder of developing anterior horn cells and shows lower-limb predominance and clinical overlap with hereditary spastic paraplegia (HSP), a lower-limb-predominant disorder of corticospinal motor neurons. We have identified four mutations in bicaudal D homolog 2 (Drosophila) (BICD2) in six kindreds affected by DCSMA, DCSMA with upper motor neuron features, or HSP. BICD2 encodes BICD2, a key adaptor protein that interacts with the dynein-dynactin motor complex, which facilitates trafficking of cellular cargos that are critical to motor neuron development and maintenance. We demonstrate that mutations resulting in amino acid substitutions in two binding regions of BICD2 increase its binding affinity for the cytoplasmic dynein-dynactin complex, which might result in the perturbation of BICD2-dynein-dynactin-mediated trafficking, and impair neurite outgrowth. These findings provide insight into the mechanism underlying both the static and the slowly progressive clinical features and the motor neuron pathology that characterize BICD2-associated diseases, and underscore the importance of the dynein-dynactin transport pathway in the development and survival of both lower and upper motor neurons.

TRPV4 mutations in children with congenital distal spinal muscular atrophy.

Inherited disorders characterized by motor neuron loss and muscle weakness are genetically heterogeneous. The recent identification of mutations in the gene encoding transient receptor potential vanilloid 4 (TRPV4) in distal spinal muscular atrophy (dSMA) prompted us to screen for TRPV4 mutations in a small group of children with compatible phenotype. In a girl with dSMA and vocal cord paralysis, we detected a new variant (p.P97R) localized in the cytosolic N-terminus of the TRPV4 protein, upstream of the ankyrin-repeat domain, where the great majority of disease-associated mutations reside. In another child with congenital dSMA, in this case associated with bone abnormalities, we detected a previously reported mutation (p.R232C). Functional analysis of the novel p.P97R mutation in a heterologous system demonstrated a loss-of-function mechanism. Protein localization studies in muscle, skin, and cultured skin fibroblasts from both patients showed normal protein expression. No TRPV4 mutations were detected in four children with dSMA without bone or vocal cord involvement. Adding to the clinical and molecular heterogeneity of TRPV4-associated diseases, our results suggest that molecular testing of the TRPV4 gene is warranted in cases of congenital dSMA with bone abnormalities and vocal cord paralysis.

Carrier screening for spinal muscular atrophy (SMA) in 107,611 pregnant women during the period 2005-2009: a prospective population-based cohort study.

BACKGROUND: Spinal muscular atrophy (SMA) is the most common neuromuscular autosomal recessive disorder. The American College of Medical Genetics has recently recommended routine carrier screening for SMA because of the high carrier frequency (1 in 25-50) as well as the severity of that genetic disease. Large studies are needed to determine the feasibility, benefits, and costs of such a program. METHODS AND FINDINGS: This is a prospective population-based cohort study of 107,611 pregnant women from 25 counties in Taiwan conducted during the period January 2005 to June 2009. A three-stage screening program was used: (1) pregnant women were tested for SMA heterozygosity; (2) if the mother was determined to be heterozygous for SMA (carrier status), the paternal partner was then tested; (3) if both partners were SMA carriers, prenatal diagnostic testing was performed. During the study period, a total of 2,262 SMA carriers with one copy of the SMN1 gene were identified among the 107,611 pregnant women that were screened. The carrier rate was approximately 1 in 48 (2.10%). The negative predictive value of DHPLC coupled with MLPA was 99.87%. The combined method could detect approximately 94% of carriers because most of the cases resulted from a common single deletion event. In addition, 2,038 spouses were determined to be SMA carriers. Among those individuals, 47 couples were determined to be at high risk for having offspring with SMA. Prenatal diagnostic testing was performed in 43 pregnant women (91.49%) and SMA was diagnosed in 12 (27.91%) fetuses. The prevalence of SMA in our population was 1 in 8,968. CONCLUSION: The main benefit of SMA carrier screening is to reduce the burden associated with giving birth to an affected child. In this study, we determined the carrier frequency and genetic risk and provided carrier couples with genetic services, knowledge, and genetic counseling.

Nuchal translucency measurement in fetuses with spinal muscular atrophy.

OBJECTIVE: Spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disorder with a high carrier frequency in the general population. The severity of this disorder indicates the importance of early prenatal detection. In medical literature, there are a few published case reports of enlarged nuchal translucency (NT) measurement in association with a diagnosis of SMA in the fetus. Our goal is to determine whether SMA in infants is associated with a history of an increased NT measurement during pregnancy. METHODS: Using contact information obtained through SMA family support groups, women who had recently given birth to infants affected with SMA were identified and queried about NT ultrasound results during the pregnancy. NT values were confirmed via ultrasound report to determine whether SMA was associated with a history of an enlarged NT measurement. RESULTS: Twelve SMA affected infants with confirmed NT results during the pregnancy were identified. All fetuses had normal NT values ranging from 0.7 to 2.4 mm. CONCLUSION: In this series, SMA did not appear to be associated with an enlarged NT.

Alterations in the ankyrin domain of TRPV4 cause congenital distal SMA, scapuloperoneal SMA and HMSN2C.

Spinal muscular atrophies (SMA, also known as hereditary motor neuropathies) and hereditary motor and sensory neuropathies (HMSN) are clinically and genetically heterogeneous disorders of the peripheral nervous system. Here we report that mutations in the TRPV4 gene cause congenital distal SMA, scapuloperoneal SMA, HMSN 2C. We identified three missense substitutions (R269H, R315W and R316C) affecting the intracellular N-terminal ankyrin domain of the TRPV4 ion channel in five families. Expression of mutant TRPV4 constructs in cells from the HeLa line revealed diminished surface localization of mutant proteins. In addition, TRPV4-regulated Ca(2+) influx was substantially reduced even after stimulation with 4alphaPDD, a TRPV4 channel-specific agonist, and with hypo-osmotic solution. In summary, we describe a new hereditary channelopathy caused by mutations in TRPV4 and present evidence that the resulting substitutions in the N-terminal ankyrin domain affect channel maturation, leading to reduced surface expression of functional TRPV4 channels.

Congenital form of spinal muscular atrophy predominantly affecting the lower limbs: a clinical and muscle MRI study.

We describe clinical and muscle magnetic resonance imaging (MRI) findings in 11 cases (three familial and eight sporadic) with the form of spinal muscular atrophy characterised by predominant involvement of the lower limbs with weakness of the proximal and distal muscles and marked atrophy of the distal leg and foot muscles. All patients presented at birth with talipes, which were in extension in seven of the 11. Arm muscle and function were preserved and lower limbs appeared to be disproportionately shorter compared to trunk and upper limbs. Functional abilities were markedly affected and only one of the 11 is able to walk independently for long distances, while six require support of crutches and two use callipers for walking. One child lost ambulation following a fall. The course of the disease is relatively stable and the progression of disability appeared to be related mostly to increased contractures rather than to loss of muscle strength. Respiratory and cardiac function were well preserved. A neurogenic disorder was suggested by electromyography and/or muscle biopsy in all patients, while motor nerve conduction was consistently normal. Muscle MRI of the thighs revealed diffuse atrophic appearance with relative hypertrophy of the adductor longus and of the semitendinosus. Genetic studies excluded the involvement of the survival motor neuron gene but none of these families was sufficiently informative to study linkage to the locus on chromosome 12q23-q24 previously found to be involved in patients with similar phenotype. In our experience this form of spinal muscular atrophy affecting predominantly the lower limbs is a relatively common form and should be considered in the differential diagnosis of infants with talipes and weakness in the lower limbs. The identical clinical and imaging features of the sporadic and familial cases suggest that these cases are likely to be affected by the same condition.

Localisation of the gene for a dominant congenital spinal muscular atrophy predominantly affecting the lower limbs to chromosome 12q23-q24.

Spinal muscular atrophies are a heterogeneous group of disorders. They differ in time of onset, clinical presentation, progression, severity and mode of inheritance. In 1985 a Dutch family was described with a dominant, non-progressive spinal muscular atrophy presenting at birth with arthrogryposis (MIM 600175). Linkage analysis was performed in this family. After having excluded the loci for Werdnig-Hoffmann's disease and for dominant distal spinal muscular atrophy with upper limb predominance, we were able to localise the gene to a 10 cM interval between the markers D12S78 and D12S1646 on chromosome 12q23-q24. Recently, dominant scapuloperoneal spinal muscular atrophy has been localised to an overlapping interval. However, the clinical appearances of scapuloperoneal spinal muscular atrophy and the present disorder make allelism unlikely. In 1994, a second Dutch family with a disorder similar to the present one was described. We excluded linkage to markers of the 12q23-q24 region in this family and thereby proved genetic heterogeneity of this type of dominant, congenital and nonprogressive spinal muscular atrophy.

Congenital autosomal dominant distal spinal muscular atrophy.

We present a father and son with congenital foot deformity. The father at age 41 years used crutches and the son at 7 years walked unaided. Both had atrophy and weakness of lower leg muscles and mild proximal and hand intrinsic weakness. Knee and ankle myotactic reflexes were absent and sensation was intact. Creatine kinase level was normal, nerve conduction studies wer normal and electromyography showed chronic neurogenic change. In both, nerve biopsies were normal and muscle biopsies showed type 1 predominance. The boy's serum hexosaminidase, spinal MRI and SMN gene were normal. This may be the first well documented example of congenital autosomal dominant distal spinal muscular atrophy affecting legs and arms.

Dominant congenital benign spinal muscular atrophy.

The affected members of the family described in this article exhibit congenital nonprogressive atrophy and weakness of lower limb muscles in association with contractures. Clinical and laboratory findings support a dominant lower motor neuron disorder. DNA analysis excluded linkage of the disease with SMA markers on the long arm of chromosome 5. The condition must be differentiated from congenital and infantile SMA, from "arthrogryposis multiplex congenita, distal type," and from non hereditary types of congenital arthrogryposis.