De novo and inherited deletions of the 5q13 region in spinal muscular atrophies

RNA-binding proteins as therapeutic targets in cancer

RNA-binding proteins (RBPs) have emerged as critical regulators of cancer progression, influencing virtually all hallmarks of cancer. Their ability to modulate gene expression patterns that promote or inhibit tumorigenesis has positioned RBPs as promising targets for novel anti-cancer therapies. This mini-review summarizes the current state of RBP-targeted cancer treatments, focusing on five examples, eIF4F, FTO, SF3B1, RBM39 and nucleolin. We highlight the diversity of current targeting approaches and discuss ongoing challenges including the complexity of RBP regulatory networks, potential off-target effects and the need for more specific targeting methods. By assessing the future potential of novel therapeutic avenues, we provide insights into the evolving landscape of cancer treatment and the critical role RBPs may play in next-generation therapeutics.

Concomitant telomere attrition is associated with spinal muscular atrophy in highly inbred region of North India: unraveling the thread in Kashmir region

Spinal muscular atrophy (SMA) is a rare genetic disorder that unequivocally results in the degeneration of motor neurons, leading to muscle weakness and atrophy. This condition is caused by a mutation in the survival motor neuron 1 (SMN1) gene, which inevitably results in a deficiency of the SMN protein. In present study, we investigated the potential role of telomere attrition in SMA patients. Relative telomere length in peripheral blood lymphocytes was measured by Monochrome Multiplex Quantitative Polymerase Chain Reaction (MMQPCR) in 98 subjects and we conclusively found that SMA cases exhibit telomere attrition compared to healthy controls (P = 4 × 10- 2). Moreover, significant attrition was also observed in severe form of SMA, i.e. SMA type 0 (P = 0.04) as well.Although, the exact mechanism through which telomere shortening contributes to the pathogenesis of SMA is not fully understood and is yet to be delineated. However, one possibility is that telomere shortening leads to genomic instability and DNA damage, which can contribute to motor neuron degeneration. Another possibility is that telomere shortening leads to cellular senescence, which can impair the ability of motor neurons to regenerate and repair themselves. Recent studies have suggested that telomere shortening may be a potential therapeutic target in SMA. Thus, understanding the role of SMN1 gene in disease pathogenesis & its effect on telomere length will aid in estimating the risk & prognosis of SMA in genetically less explored & highly inbred region of Kashmir, Northern India.

Diagnostic Journey of Korean Patients with Spinal Muscular Atrophy

PURPOSE

Spinal muscular atrophy (SMA) is an autosomal recessive genetic disease characterized by the loss of motor neurons in the spinal cord and brainstem, leading to muscle atrophy and weakness. To understand the diagnostic process of Korean patients with SMA, we analyzed their clinical characteristics and challenges.

MATERIALS AND METHODS

We conducted a retrospective study of 38 patients with SMA (9 type II and 29 type III) between January 2000 and September 2023. Clinical, laboratory, and genetic data were reviewed.

RESULTS

The median ages at symptom onset and diagnosis were 3.0 years [interquartile range (IQR): 1.0-7.3 years] and 25.0 years (IQR: 10.5-37.3 years), respectively. The median diagnostic delay was 19.6 years (IQR: 6.4-31.0 years). A significantly longer delay was observed in SMA type III patients (median: 21.0 years, IQR: 11.0-31.0 years) compared to SMA type II patients (median: 3.0 years, IQR: 0.9-21.0 years) (p=0.021). No significant difference was observed in the number of clinic visits before diagnosis between patients with SMA type II (median: 2.0, IQR: 1.0-4.5) and those with type III (median: 2.0, IQR: 2.0-6.0, p=0.282). The number of clinic visits before diagnosis showed no significant association with the age at symptom onset and diagnosis (p=0.998 and 0.291, respectively).

CONCLUSION

Our investigation is the first examination of the diagnostic journey of Korean patients with SMA. As treatments for SMA progress, the significance of an accurate diagnosis has increased, highlighting the importance of reviewing the diagnostic advancements made thus far.

Preconception or prenatal acceptance of SMN1 gene carrier screening and carrier rate of spinal muscular atrophy: a retrospective study in 18,818 reproductive age women in Wuhan area of China

OBJECTIVE

Spinal muscular atrophy (SMA) is an autosomal recessive disorder mainly affecting the neuromuscular system, which seriously threatens the life and health of patients. But few studies have reported the acceptance rate of SMA gene screening and SMA carrier rate in China. The present study aimed to clarify the two issues in China through a retrospective analysis of 18,818 reproductive age women in Wuhan area of China.

METHODS

The copy number (CN) of exons 7 and 8 in survival motor neuron 1 (SMN1) gene was detected by real-time quantitative PCR, and the results were verified by multiplex ligation-dependent probe amplification.

RESULTS

Carrier screening was offered to 44,953 women of childbearing age in our medical center from March, 2018, to February, 2022, of whom 18,818 were enrolled in the program. A total of 336 women were identified as carriers (1.73%; 326/18,808; without fertility history of the children with SMA). Among 18,818 reproductive age women, 286 spouses (85.12%; 286/336) were successfully recalled for screening. The results showed 17 couples at high risk of having children with SMA, of whom prenatal diagnosis was implemented in 11, and 6 fetuses were identified with SMA. All the 5 pregnant women bearing the 6 SMA fetuses chose to terminate the pregnancy by artificial abortion.

CONCLUSION

Reproductive age women and their spouses in Wuhan area showed a positive attitude toward general screening for SMA carriers. Given the high early mortality of children with SMA, screening for SMA carriers in women of reproductive age is necessary and feasible.

Screening and prenatal diagnosis of survival motor neuron gene deletion in pregnant women in Zhaoqing city, Guangdong Province

OBJECTIVE

A total of 5,200 pregnant women in Zhaoqing city, Guangdong Province, were screened to identify spinal muscular atrophy (SMA) mutation carriers to guide the prevention of SMA and prevent the birth of children with SMA.

METHODS

Exons 7 and 8 (E7 and E8) of the survival motor neuron (SMN) 1 gene were detected in women using real-time fluorescence quantitative polymerase chain reaction. SMN1 and SMN2 copy numbers in those who were initially identified as carriers were verified via targeted region capture and next-generation sequencing. When both partners were identified as carriers, prenatal diagnosis of the fetus was performed.

RESULTS

Among the screened women, 75 SMA carriers (71 cases had both E7 and E8 heterozygous deletions and 4 cases only had an E7 heterozygous deletion) were identified, with a carrier frequency of 1.44% (95% confidence interval: 1.31-1.65%). Three couples where both spouses were identified as SMA carriers, and their three fetuses were subjected to prenatal genetic analysis. Of the three, one had homozygous deletions of E7 and E8 and the other two had heterozygous deletions of E7 and E8. After a detailed prenatal consultation, the former couple decided to terminate the pregnancy.

CONCLUSION

Through screening and prenatal diagnosis of pregnant women in Zhaoqing city, Guangdong Province, the incidence of SMA can be reduced, prevention of birth defects can be improved, incidence of birth defects can be effectively minimized.

Assessing the Role of Aquaporin 4 in Skeletal Muscle Function

Water transport across the biological membranes is mediated by aquaporins (AQPs). AQP4 and AQP1 are the predominantly expressed AQPs in the skeletal muscle. Since the discovery of AQP4, several studies have highlighted reduced AQP4 levels in Duchenne muscular dystrophy (DMD) patients and mouse models, and other neuromuscular disorders (NMDs) such as sarcoglycanopathies and dysferlinopathies. AQP4 loss is attributed to the destabilizing dystrophin-associated protein complex (DAPC) in DMD leading to compromised water permeability in the skeletal muscle fibers. However, AQP4 knockout (KO) mice appear phenotypically normal. AQP4 ablation does not impair physical activity in mice but limits them from achieving the performance demonstrated by wild-type mice. AQP1 levels were found to be upregulated in DMD models and are thought to compensate for AQP4 loss. Several groups investigated the expression of other AQPs in the skeletal muscle; however, these findings remain controversial. In this review, we summarize the role of AQP4 with respect to skeletal muscle function and findings in NMDs as well as the implications from a clinical perspective.

Current treatments of spinal muscular atrophy in adults

Spinal muscular atrophy (SMA) is a rare autosomal recessive neuromuscular disorder related to motor neuron degeneration. SMA patients present generally severe muscular weakness and atrophy, which can reduce life expectancy and lead to severe functional disability. In recent years, the management of this condition has been revolutionized by the development of innovative therapies that target alternative splicing of pre-messenger SMN2 RNA by antisense oligonucleotides or small molecules and by the approval of the first vector-based SMN1 gene therapy. The high significance of the trials in children led to fast-tracking of these therapies to all SMA patients despite the absence of data in adults. Real-life data are progressively providing a better understanding of the expected benefits and tolerability. They also highlight the difficulties of evaluating these patients and the need to take into account the patients' reported expectations and outcome. A review of the main data in adult patients is presented. The mechanisms of action of these innovative therapies are discussed as well as the limits of evaluations of these therapies in adults with longstanding severe amyotrophy.

Childhood spinal muscular atrophy

Spinal muscular atrophy (SMA) is caused by biallelic mutations in the SMN1 (survival motor neuron 1) gene on chromosome 5q13.2, which leads to a progressive degeneration of alpha motor neurons in the spinal cord and in motor nerve nuclei in the caudal brainstem. It is characterized by progressive proximally accentuated muscle weakness with loss of already acquired motor skills, areflexia and, depending on the phenotype, varying degrees of weakness of the respiratory and bulbar muscles. Over the past decade, disease-modifying therapies have become available based on splicing modulation of the SMN2 with SMN1 gene replacement, which if initiated significantly modifies the natural course of the disease. Newborn screening for SMA has been implemented in an increasing number of centers; however, available evidence for these new treatments is often limited to a small spectrum of patients concerning age and disease stage.

Phosphorothioate modification improves exon-skipping of antisense oligonucleotides based on sulfonyl phosphoramidates in mdx mouse myotubes

2'-O-Methyl (2'-OMe) antisense oligonucleotides (AOs) possessing a various number of 4-(trimethylammonio)butylsulfonyl or tosyl phosphoramidates (N+ and Ts-modifications, respectively) instead of a native phosphodiester linkage were designed to skip exon-23 in dystrophin pre-mRNA transcript in mdx mice myotubes. AOs bearing several zwitterionic N+ modifications in the sequence had remarkably increased thermal stability towards complementary mRNA in comparison with 2'-OMe-RNAs having negatively charged Ts and phosphorothioate (PS) linkages. However, only Ts-modified AOs exhibited a similar level of exon skipping in comparison with fully modified PS-containing 2'-OMe-RNA, whereas the exon skipping induced by N+ modified AOs was much lower with no exon-skipping detected for AOs having seven N+ modifications. The level of exon-skipping was improved once Ts and especially N+ moieties were used in combination with PS-modification, most likely through improved cellular and nuclear uptake of AOs. These results provide new insights on expanding the design of novel chemically modified AOs based on phosphate modifications.

Autosomal Recessive Cerebellar Atrophy and Spastic Ataxia in Patients With Pathogenic Biallelic Variants in GEMIN5

The hereditary ataxias are a heterogenous group of disorders with an increasing number of causative genes being described. Due to the clinical and genetic heterogeneity seen in these conditions, the majority of such individuals endure a diagnostic odyssey or remain undiagnosed. Defining the molecular etiology can bring insights into the responsible molecular pathways and eventually the identification of therapeutic targets. Here, we describe the identification of biallelic variants in the GEMIN5 gene among seven unrelated families with nine affected individuals presenting with spastic ataxia and cerebellar atrophy. GEMIN5, an RNA-binding protein, has been shown to regulate transcription and translation machinery. GEMIN5 is a component of small nuclear ribonucleoprotein (snRNP) complexes and helps in the assembly of the spliceosome complexes. We found that biallelic GEMIN5 variants cause structural abnormalities in the encoded protein and reduce expression of snRNP complex proteins in patient cells compared with unaffected controls. Finally, knocking out endogenous Gemin5 in mice caused early embryonic lethality, suggesting that Gemin5 expression is crucial for normal development. Our work further expands on the phenotypic spectrum associated with GEMIN5-related disease and implicates the role of GEMIN5 among patients with spastic ataxia, cerebellar atrophy, and motor predominant developmental delay.

Restoring SMN Expression: An Overview of the Therapeutic Developments for the Treatment of Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disorder and one of the most common genetic causes of infant death. It is characterized by progressive weakness of the muscles, loss of ambulation, and death from respiratory complications. SMA is caused by the homozygous deletion or mutations in the survival of the motor neuron 1 (SMN1) gene. Humans, however, have a nearly identical copy of SMN1 known as the SMN2 gene. The severity of the disease correlates inversely with the number of SMN2 copies present. SMN2 cannot completely compensate for the loss of SMN1 in SMA patients because it can produce only a fraction of functional SMN protein. SMN protein is ubiquitously expressed in the body and has a variety of roles ranging from assembling the spliceosomal machinery, autophagy, RNA metabolism, signal transduction, cellular homeostasis, DNA repair, and recombination. Motor neurons in the anterior horn of the spinal cord are extremely susceptible to the loss of SMN protein, with the reason still being unclear. Due to the ability of the SMN2 gene to produce small amounts of functional SMN, two FDA-approved treatment strategies, including an antisense oligonucleotide (AON) nusinersen and small-molecule risdiplam, target SMN2 to produce more functional SMN. On the other hand, Onasemnogene abeparvovec (brand name Zolgensma) is an FDA-approved adeno-associated vector 9-mediated gene replacement therapy that can deliver a copy of the human SMN1. In this review, we summarize the SMA etiology, the role of SMN, and discuss the challenges of the therapies that are approved for SMA treatment.

Drug Discovery of Spinal Muscular Atrophy (SMA) from the Computational Perspective: A Comprehensive Review

Spinal muscular atrophy (SMA), one of the leading inherited causes of child mortality, is a rare neuromuscular disease arising from loss-of-function mutations of the survival motor neuron 1 (SMN1) gene, which encodes the SMN protein. When lacking the SMN protein in neurons, patients suffer from muscle weakness and atrophy, and in the severe cases, respiratory failure and death. Several therapeutic approaches show promise with human testing and three medications have been approved by the U.S. Food and Drug Administration (FDA) to date. Despite the shown promise of these approved therapies, there are some crucial limitations, one of the most important being the cost. The FDA-approved drugs are high-priced and are shortlisted among the most expensive treatments in the world. The price is still far beyond affordable and may serve as a burden for patients. The blooming of the biomedical data and advancement of computational approaches have opened new possibilities for SMA therapeutic development. This article highlights the present status of computationally aided approaches, including in silico drug repurposing, network driven drug discovery as well as artificial intelligence (AI)-assisted drug discovery, and discusses the future prospects.

The potential role of miRNA therapies in spinal muscle atrophy

Spinal muscular atrophy (SMA) is a neurodegenerative disease caused by low levels of full-length survival motor neuron (SMN) protein due to the loss of the survival motor neuron 1 (SMN1) gene and inefficient splicing of the survival motor neuron 2 (SMN2) gene, which mostly affects alpha motor neurons of the lower spinal cord. Despite the U.S. Food and Drug Administration (FDA) approved SMN-dependent therapies including Nusinersen, Zolgensma® and Evrysdi™, SMA is still a devastating disease as these existing expensive drugs may not be sufficient and thus, remains a need for additional therapies. The involvement of microRNAs (miRNAs) in SMA is expanding because miRNAs are important mediators of gene expression as each miRNA could target a number of genes. Hence, miRNA-based therapy could be utilized in treating this genetic disorder. However, the delivery of miRNAs into the target cells remains an obstacle in SMA, as there is no effective delivery system to date. This review highlights the potential strategies for intracellular miRNA delivery into target cells and current challenges in miRNA delivery. Furthermore, we provide the future prospects of miRNA-based therapeutic strategies in SMA.

Spinal Muscular Atrophy: In the Challenge Lies a Solution

The path from gene discovery to therapy in spinal muscular atrophy (SMA) has been a highly challenging endeavor, but also led to one of the most successful stories in neurogenetics. In SMA, a neuromuscular disorder with an often fatal outcome until recently, with those affected never able to sit, stand, or walk, children now achieve these motoric abilities and almost age-based development when treated presymptomatically. This review summarizes the challenges along this 30-year journey. It is also meant to inspire early-career scientists not to give up when things become difficult but to try to uncover the biological underpinnings and transform the challenge into the next big discovery. Without doubt, the improvements seen with the three therapeutic strategies in SMA are impressive; many open questions remain and are discussed in this review.

Spinal Muscular Atrophy: The Use of Functional Motor Scales in the Era of Disease-Modifying Treatment

Spinal muscular atrophy (SMA) is a genetic condition characterized by progressive motoneuron loss. Infants affected by SMA type 1 do not gain developmental milestones and acutely decline, requiring ventilatory support. Several scales are used to assess motor disability and its progression in SMA. Recently, 3 disease-modifying therapies have been approved for SMA patients: nusinersen, an intrathecal antisense oligonucleotide enhancing SMN protein production by the SMN2 gene, risdiplam, also influencing the SMN2 gene to stimulate SMN production but administered orally, and onasemnogene abeparvovec-xioi, an SMN1 gene replacement therapy. Thus, the functional scales should now be applicable for patients improving their motor function over time to assess treatment efficacy. In this paper, we compare different functional scales used in SMA patients. Their usefulness in different SMA types, age groups, and feasibility in daily clinical practice is described below. Some changes in motor function assessments in SMA are also suggested.

The Small-Molecule Flunarizine in Spinal Muscular Atrophy Patient Fibroblasts Impacts on the Gemin Components of the SMN Complex and TDP43, an RNA-Binding Protein Relevant to Motor Neuron Diseases

The motor neurodegenerative disease spinal muscular atrophy (SMA) is caused by alterations of the survival motor neuron 1 (SMN1) gene involved in RNA metabolism. Although the disease mechanisms are not completely elucidated, SMN protein deficiency leads to abnormal small nuclear ribonucleoproteins (snRNPs) assembly responsible for widespread splicing defects. SMN protein localizes in nuclear bodies that are lost in SMA and adult onset amyotrophic lateral sclerosis (ALS) patient cells harboring TDP-43 or FUS/TLS mutations. We previously reported that flunarizine recruits SMN into nuclear bodies and improves the phenotype of an SMA mouse model. However, the precise mode of action remains elusive. Here, a marked reduction of the integral components of the SMN complex is observed in severe SMA patient fibroblast cells. We show that flunarizine increases the protein levels of a subset of components of the SMN-Gemins complex, Gemins2-4, and markedly reduces the RNA and protein levels of the pro-oxydant thioredoxin-interacting protein (TXNIP) encoded by an mRNA target of Gemin5. We further show that SMN deficiency causes a dissociation of the localization of the SMN complex components from the same nuclear bodies. The accumulation of TDP-43 in SMN-positive nuclear bodies is also perturbed in SMA cells. Notably, TDP-43 is found to co-localize with SMN in nuclear bodies of flunarizine-treated SMA cells. Our findings indicate that flunarizine reverses cellular changes caused by SMN deficiency in SMA cells and further support the view of a common pathway in RNA metabolism underlying infantile and adult motor neuron diseases.

Diagnostic journey in Spinal Muscular Atrophy: Is it still an odyssey?

Background

The advent of new therapies has increased the need to achieve early diagnosis in Spinal Muscular Atrophy (SMA). The aim of the present study was to define the age of diagnosis in the three main types of SMA with pediatric-onset and the timing between the recognition of clinical signs and confirmed genetic diagnosis.

Methods

All patients with a confirmed diagnosis of type I, II, III SMA followed in 5 Italian centers were included in this study, assessing age at symptoms onset, presenting sign or symptom, age at diagnosis, interval between clinical onset and diagnosis and type of medical investigations conducted in order to obtain the diagnosis.

Results

The cohort included 480 patients, 191 affected by SMA type I, 210 by type II and 79 by type III. The mean age at diagnosis was 4.70 months (SD ±2.82) in type I, 15.6 months (SD±5.88) in type II, and 4.34 years (SD±4.01) in type III.

The mean time between symptom onset and diagnosis was 1.94 months (SD±1.84) in type I, 5.28 months (SD±4.68) in type II and 16.8 months (SD±18.72) in type III.

Conclusions

Our results suggest that despite improved care recommendations there is still a marked diagnostic delay, especially in type III. At the time new therapies are becoming available more attention should be devoted to reducing such delay as there is consistent evidence of the benefit of early treatment.

Carrier Screening and Prenatal Diagnosis for Spinal Muscular Atrophy in 13,069 Chinese Pregnant Women

Spinal muscular atrophy (SMA) is a relatively common, life-shortening, autosomal recessive neuromuscular disease. The carrier frequency of SMA ranges from approximately 0.98% to 2.02%, depending on ethnicity. The American College of Medical Genetics has therefore recommended population screening for SMA carrier status, regardless of race or ethnicity. We performed the largest-scale carrier screening for SMA carriers in mainland China. Carrier screening was offered to 36,470 pregnant women between July 2017 and June 2019, of whom 13,069 women accepted the screening program [35.83%; 95% credibility interval (CI), 35.34%-36.33%]. Copy numbers of exons 7 and 8 in the SMN1 gene were detected by real-time quantitative PCR, and the results were confirmed by multiplex ligation-dependent probe amplification. A total of 231 women were identified as carriers (1.77%; 95% CI, 1.56%-2.01%), indicating a carrier prevalence of approximately 1:56 in the population. After detailed genetic counseling, 207 paternal partners were recalled and tested. Both partners were carriers in 10 couples, of whom prenatal diagnosis was implemented in seven, and one fetus was diagnosed with SMA. Carrier screening could provide couples with informed reproductive choices. Our workflow and experience of carrier screening may facilitate the popularization of SMA carrier screening in mainland China.

Complete sequencing of the SMN2 gene in SMA patients detects SMN gene deletion junctions and variants in SMN2 that modify the SMA phenotype

Spinal muscular atrophy (SMA) is a progressive motor neuron disease caused by loss or mutation of the survival motor neuron 1 (SMN1) gene and retention of SMN2. We performed targeted capture and sequencing of the SMN2, CFTR, and PLS3 genes in 217 SMA patients. We identified a 6.3 kilobase deletion that occurred in both SMN1 and SMN2 (SMN1/2) and removed exons 7 and 8. The deletion junction was flanked by a 21 bp repeat that occurred 15 times in the SMN1/2 gene. We screened for its presence in 466 individuals with the known SMN1 and SMN2 copy numbers. In individuals with 1 SMN1 and 0 SMN2 copies, the deletion occurred in 63% of cases. We modeled the deletion junction frequency and determined that the deletion occurred in both SMN1 and SMN2. We have identified the first deletion junction where the deletion removes exons 7 and 8 of SMN1/2. As it occurred in SMN1, it is a pathogenic mutation. We called variants in the PLS3 and SMN2 genes, and tested for association with mild or severe exception patients. The variants A-44G, A-549G, and C-1897T in intron 6 of SMN2 were significantly associated with mild exception patients, but no PLS3 variants correlated with severity. The variants occurred in 14 out of 58 of our mild exception patients, indicating that mild exception patients with an intact SMN2 gene and without modifying variants occur. This sample set can be used in the association analysis of candidate genes outside of SMN2 that modify the SMA phenotype.

Therapeutic Antisense Oligonucleotides Are Coming of Age

The first published description of therapeutic applications of antisense oligonucleotide (ASO) technology occurred in the late 1970s and was followed by the founding of commercial companies focused on developing antisense therapeutics in the late 1980s. Since the late 1980s, there has been steady progress in improving the technology platform, taking advantage of advances in oligonucleotide chemistry and formulations as well as increased understanding of the distribution and safety of ASOs. There are several approved ASO drugs and a broad pipeline in development. In addition, advances in understanding human disease, including the genetic basis for most monogenic diseases and the availability of the full human genome sequence, have created numerous therapeutic applications for the technology. I summarize the state of the technology and highlight how advances in the technology position ASOs to be an important contributor to future medicines.

Dysregulation of microRNA metabolism in motor neuron diseases: Novel biomarkers and potential therapeutics

In the last 15 years, several classes of small regulatory RNAs have been identified, uncovering the widespread impact of non-coding elements in the human genome on cell homeostasis and human diseases. MicroRNAs (miRNAs) are a family of small, non-coding RNAs, which exert silencing of mRNA targets in a sequence-dependent fashion. Many miRNAs are specifically expressed in the central nervous system, where they display roles in differentiation, neuronal survival, neuronal plasticity and learning. On the other hand, deregulated miRNA/mRNA expression networks are deeply involved in neurodegeneration. Recent findings suggest a role for miRNAs in the pathogenesis of motor neuron diseases. In particular, cell-specific changes in miRNA profile are involved in the motor neuron disease phenotype and might be implicated in their selective vulnerability. Exploitation of noncoding RNAs, in particular miRNAs, for therapeutic strategies is being assessed for implementing current therapies. In this regard, the neuroprotective potential of certain miRNAs could represent a promising potential tool to improve therapies for motor-neuron diseases. This review focuses on emerging roles of miRNAs in motor neuron diseases and on their impact on neuron life-span and integrity.

Specific Gene Capture Combined with Restriction-Fragment Release for Directly Fluorescent Genotyping of Single-Nucleotide Polymorphisms in Diagnosing Spinal Muscular Atrophy

In this study, a fast and simple fluorescent genotyping strategy, streptavidin magnetic beads combined with biotin-coupled PCR and restriction-fragment release, was developed for determination of nucleotide variants. This method was further applied for analyzing SMN1 gene in diagnosis of spinal muscular atrophy (SMA). After biotin-coupled PCR, the streptavidin magnetic beads would capture the biotin-labeled SMN genetic fragments, and then the restriction enzyme of HPY188I could only digest and release the fluorescent end of SMN1 genetic fragment into the supernatant. Therefore, the SMN1 gene could be easily fluorescently quantified, and SMN2 would not, for diagnosis of SMA. The copy number of the SMN1 gene could be regressed using the relative fluorescent unit versus the known copy number, and the coefficient of correlation is equal to 0.9617 ( r = 0.9617). In this research, a total of 16 blind DNA samples were analyzed, including 6 wild types, 5 carriers, and 5 SMA patients. Importantly, this fast, simple, and highly efficient method is universal for detection of all nucleotides variants by replacing the specific restriction enzyme. This technique has the potency to be served as a tool for fast and accurate diagnosis of genotypes in clinical medicine.

Discovery of a Small Molecule Probe That Post-Translationally Stabilizes the Survival Motor Neuron Protein for the Treatment of Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is the leading genetic cause of infant death. We previously developed a high-throughput assay that employs an SMN2-luciferase reporter allowing identification of compounds that act transcriptionally, enhance exon recognition, or stabilize the SMN protein. We describe optimization and characterization of an analog suitable for in vivo testing. Initially, we identified analog 4m that had good in vitro properties but low plasma and brain exposure in a mouse PK experiment due to short plasma stability; this was overcome by reversing the amide bond and changing the heterocycle. Thiazole 27 showed excellent in vitro properties and a promising mouse PK profile, making it suitable for in vivo testing. This series post-translationally stabilizes the SMN protein, unrelated to global proteasome or autophagy inhibition, revealing a novel therapeutic mechanism that should complement other modalities for treatment of SMA.

Molecular inversion probes equipped with discontinuous rolling cycle amplification for targeting nucleotide variants: Determining SMN1 and SMN2 genes in diagnosis of spinal muscular atrophy

The novel techniques of molecular inversion probes (MIPs) combined with discontinuous rolling cycle amplification (DRCA) was developed for determination of the multi-nucleotide variants at single base. The different-length MIPs, a padlock-probe based technology, are designed to simultaneously recognize the identical nucleotide variants. After ligation and DRCA, the different-length genetic products representing the certain genotypes could be simply determined by the short-end capillary electrophoresis (CE) method. By using MIPs-DRCA method, the various gene dosages of SMN1 and SMN2 genes in homologous or heterologous subjects were successfully quantified for diagnosis of spinal muscular atrophy (SMA). The length of the MIP for SMN1 gene was 106 bp, and for SMN2 gene was 86 bp. After method optimization, the MIP products of SMN1 and SMN2 were well separated with the resolution of 1.13 ± 0.17 (n = 3) within 10 min. There were total of 56 DNA blind samples analyzed by this strategy, including 38 wild types, 12 carriers and 6 SMA patients, and the data of gene dosages was corresponding to those analyzed by conformation sensitive CE and denatured high performance liquid chromatography (DHPLC) methods. This MIPs-DRCA method which could be applied to simultaneously genotype multi nucleotide variants at single base, such as K-ras gene, was very feasible for determination of genetic diseases in clinical.

Compensatory axon sprouting for very slow axonal die-back in a transgenic model of spinal muscular atrophy type III

KEY POINTS

Smn+/- transgenic mouse is a model of the mildest form of spinal muscular atrophy. Although there is a loss of spinal motoneurons in 11-month-old animals, muscular force is maintained. This maintained muscular force is mediated by reinnervation of the denervated fibres by surviving motoneurons. The spinal motoneurons in these animals do not show an increased susceptibility to death after nerve injury and they retain their regenerative capacity. We conclude that the hypothesized immaturity of the neuromuscular system in this model cannot explain the loss of motoneurons by systematic die-back.

ABSTRACT

Spinal muscular atrophy (SMA) is a common autosomal recessive disorder in humans and is the leading genetic cause of infantile death. Patients lack the SMN1 gene with the severity of the disease depending on the number of copies of the highly homologous SMN2 gene. Although motoneuron death in the Smn+/- transgenic mouse model of the mildest form of SMA, SMA type III, has been reported, we have used retrograde tracing of sciatic and femoral motoneurons in the hindlimb with recording of muscle and motor unit isometric forces to count the number of motoneurons with intact neuromuscular connections. Thereby, we investigated whether incomplete maturation of the neuromuscular system induced by survival motoneuron protein (SMN) defects is responsible for die-back of axons relative to survival of motoneurons. First, a reduction of ∼30% of backlabelled motoneurons began relatively late, at 11 months of age, with a significant loss of 19% at 7 months. Motor axon die-back was affirmed by motor unit number estimation. Loss of functional motor units was fully compensated by axonal sprouting to retain normal contractile force in four hindlimb muscles (three fast-twitch and one slow-twitch) innervated by branches of the sciatic nerve. Second, our evaluation of whether axotomy of motoneurons in the adult Smn+/- transgenic mouse increases their susceptibility to cell death demonstrated that all the motoneurons survived and they sustained their capacity to regenerate their nerve fibres. It is concluded the systematic die-back of motoneurons that innervate both fast- and slow-twitch muscle fibres is not related to immaturity of the neuromuscular system in SMA.

Validation of a high resolution NGS method for detecting spinal muscular atrophy carriers among phase 3 participants in the 1000 Genomes Project

Background

Spinal muscular atrophy (SMA) is the most common pan-ethnic cause of early childhood death due to mutations in a single gene, SMN1. Most chromosome 5 homologs have a functional gene and dysfunctional copy, SMN2, with a single synonymous base substitution that results in faulty RNA splicing. However, the copy number of SMN1 and SMN2 is highly variable, and one in 60 adults worldwide are SMA carriers. Although population-wide screening is recommended, current SMA carrier tests have not been incorporated into targeted gene panels.

Methods

Here we describe a novel computational protocol for determining SMA carrier status based solely on individual exome data. Our method utilizes a Bayesian hierarchical model to quantify an individual’s carrier probability given only his or her SMN1 and SMN2 reads at six loci of interest.

Results

We find complete concordance with results obtained with the current qPCR-based testing standard in known SMA carriers and affecteds. We applied our protocol to the phase 3 cohort of the 1,000 Genomes Project and found carrier frequencies in multiple populations consistent with the present literature.

Conclusion

Our process is a convenient, robust alternative to qPCR, which can easily be integrated into the analysis of large multi-gene NGS carrier screens.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-015-0246-2) contains supplementary material, which is available to authorized users.

A simple and precise diagnostic method for spinal muscular atrophy using a quantitative SNP analysis system

A simple and precise diagnostic method for spinal muscular atrophy (SMA) using high-resolution CE-based single-strand conformation polymorphism (CE-SSCP) was developed in this study. SMA is a common genetic disorder caused by an abnormality in the relative copy numbers of SMN1 and its centromeric copy SMN2, which differ only in two nucleotides, namely at exons 7 and 8. Therefore, the precise discrimination of the differences in sequence as well as their relative quantities is crucial for the diagnosis of SMA. Multiplex ligation-dependent probe amplification and sequence-sensitive DNA separation using hydroxyethyl cellulose and hydroxypropyl cellulose blended polymer matrix are currently the available methods used in the diagnosis of SMA. However, these methods are limited by their extended hybridization step and low resolution. In this study, the simultaneous discrimination of SMN exons 7 and 8 was successfully demonstrated using high-resolution CE-SSCP. Unlike the previously reported alternative method, single base differing amplicons were baseline-separated because of its extraordinary resolution, thus providing accurate and precise quantification of each paralog.

Self-locomotion and spatial language and spatial cognition: insights from typical and atypical development

Various studies have shown that occurrence of locomotion in infancy is correlated with the development of spatial cognitive competencies. Recent evidence suggests that locomotor experience might also be important for the development of spatial language. Together these findings suggest that locomotor experience might play a crucial role in the development of linguistic-cognitive spatial skills. However, some studies indicate that, despite their total deprivation of locomotor experience, young children with spinal muscular atrophy (SMA) have the capacity to acquire and use rich spatial representations including good spatial language. Nonetheless, we have to be cautious about what the striking performances displayed by SMA children can reveal on the link between motor and spatial development, as the dynamics of brain development in atypically developing children are different from typically developing children.

Universal fluorescent tri-probe ligation equipped with capillary electrophoresis for targeting SMN1 and SMN2 genes in diagnosis of spinal muscular atrophy

This is the first ligase chain reaction used for diagnosis of spinal muscular atrophy (SMA). Universal fluorescent tri-probe ligation (UFTPL), a novel strategy used for distinguishing the multi-nucleotide alternations at single base, is developed to quantitatively analyze the SMN1/SMN2 genes in diagnosis of SMA. Ligase chain reaction was performed by adding three probes including universal fluorescent probe, connecting probe and recognizing probe to differentiate single nucleotide polymorphisms in UFTPL. Our approach was based on the two UFTPL products of survival motor neuron 1 (SMN1) and SMN2 genes (the difference of 9 mer) and analyzed by capillary electrophoresis (CE). We successfully determined various gene dosages of SMN1 and SMN2 genes in homologous or heterologous subjects. By using the UFTPL-CE method, the SMN1 and SMN2 genes were fully resolved with the resolution of 2.16±0.37 (n=3). The r values of SMN1 and SMN2 regression curves over a range of 1-4 copies were above 0.9944. Of the 48 DNA samples, the data of gene dosages were corresponding to that analyzed by conformation sensitive CE and denatured high-performance liquid chromatography (DHPLC). This technique was found to be a good methodology for quantification or determination of the relative genes having multi-nucleotide variants at single base.

New developments in exon skipping and splice modulation therapies for neuromuscular diseases

INTRODUCTION

Antisense oligonucleotide (AON) therapy is a form of treatment for genetic or infectious diseases using small, synthetic DNA-like molecules called AONs. Recent advances in the development of AONs that show improved stability and increased sequence specificity have led to clinical trials for several neuromuscular diseases. Impressive preclinical and clinical data are published regarding the usage of AONs in exon-skipping and splice modulation strategies to increase dystrophin production in Duchenne muscular dystrophy (DMD) and survival of motor neuron (SMN) production in spinal muscular atrophy (SMA).

AREAS COVERED

In this review, we focus on the current progress and challenges of exon-skipping and splice modulation therapies. In addition, we discuss the recent failure of the Phase III clinical trials of exon 51 skipping (drisapersen) for DMD.

EXPERT OPINION

The main approach of AON therapy in DMD and SMA is to rescue ('knock up' or increase) target proteins through exon skipping or exon inclusion; conversely, most conventional antisense drugs are designed to knock down (inhibit) the target. Encouraging preclinical data using this 'knock up' approach are also reported to rescue dysferlinopathies, including limb-girdle muscular dystrophy type 2B, Miyoshi myopathy, distal myopathy with anterior tibial onset and Fukuyama congenital muscular dystrophy.

Perceptions of equine-assisted activities and therapies by parents and children with spinal muscular atrophy

PURPOSE

To identify the physical and psychosocial effects of equine-assisted activities and therapies (EAATs) on children with spinal muscular atrophy (SMA) from the perspective of the children and their parents.

METHODS

The families of all eligible children with SMA, who reported participation in EAAT, from a Western metropolitan academic center were contacted and invited to participate. This study implemented qualitative, semistructured interviews of children with SMA and their parents.

RESULTS

Three themes emerged from the qualitative content analysis: physical/psychosocial benefits; relationship development with the horses, instructors, and children; and barriers to continued EAAT engagement.

CONCLUSIONS

The data suggest that the overall EAAT experience was a source of enjoyment, self-confidence, and normalcy for the children with SMA. The results of this study provide preliminary support for the use of EAAT among children with SMA.

Current advances in drug development in spinal muscular atrophy

PURPOSE OF REVIEW

Spinal muscular atrophy (SMA) is a pediatric neuromuscular condition characterized by progressive proximal muscle weakness. It is one of the most common genetic causes of infant mortality across different races and is caused by mutation of the survival of motor neuron 1 (SMN1) gene on chromosome 5q13.

RECENT FINDINGS

To date, there have been many therapeutics developments for SMA targeting various potential pathways such as increasing SMN gene expression, enhancing SMN2 exon 7 inclusion, neuroprotection, cell replacement, and gene therapy.

SUMMARY

Although SMA remains an incurable disease to date, recent advances in the field of basic and translational research have enhanced our understanding of the pathogenesis of the disease and opened new possibilities for therapeutic intervention. This article reviews and highlights past and current translational research on SMA therapeutics.

Calcium binding is essential for plastin 3 function in Smn-deficient motoneurons

The actin-binding and bundling protein, plastin 3 (PLS3), was identified as a protective modifier of spinal muscular atrophy (SMA) in some patient populations and as a disease modifier in animal models of SMA. How it functions in this process, however, is not known. Because PLS3 is an actin-binding/bundling protein, we hypothesized it would likely act via modification of the actin cytoskeleton in axons and neuromuscular junctions to protect motoneurons in SMA. To test this, we examined the ability of other known actin cytoskeleton organizing proteins to modify motor axon outgrowth phenotypes in an smn morphant zebrafish model of SMA. While PLS3 can fully compensate for low levels of smn, cofilin 1, profilin 2 and α-actinin 1 did not affect smn morphant motor axon outgrowth. To determine how PLS3 functions in SMA, we generated deletion constructs of conserved PLS3 structural domains. The EF hands were essential for PLS3 rescue of smn morphant phenotypes, and mutation of the Ca(2+)-binding residues within the EF hands resulted in a complete loss of PLS3 rescue. These results indicate that Ca(2+) regulation is essential for the function of PLS3 in motor axons. Remarkably, PLS3 mutants lacking both actin-binding domains were still able to rescue motor axons in smn morphants, although not as well as full-length PLS3. Therefore, PLS3 function in this process may have an actin-independent component.

Enhanced expression of the central survival of motor neuron (SMN) protein during the pathogenesis of osteoarthritis

The identification of new components implicated in the pathogenesis of osteoarthritis (OA) might improve our understanding of the disease process. Here, we investigated the levels of the survival of motor neuron (SMN) expression in OA cartilage considering the fundamental role of the SMN protein in cell survival and its involvement in other stress-associated pathologies. We report that SMN expression is up-regulated in human OA compared with normal cartilage, showing a strong correlation with the disease severity, a result confirmed in vivo in an experimental model of the disease. We further show that the prominent inflammatory cytokines (IL-1β, TNF-α) are critical inducers of SMN expression. This is in marked contrast with the reported impaired levels of SMN in spinal muscular atrophy, a single inherited neuromuscular disorder characterized by mutations in the smn gene whereas OA is a complex disease with multiple aetiologies. While the precise functions of SMN during OA remain to be elucidated, the conclusions of this study shed light on a novel pathophysiological pathway involved in the progression of OA, potentially offering new targets for therapy.

Validating therapeutic targets through human genetics

More than 90% of the compounds that enter clinical trials fail to demonstrate sufficient safety and efficacy to gain regulatory approval. Most of this failure is due to the limited predictive value of preclinical models of disease, and our continued ignorance regarding the consequences of perturbing specific targets over long periods of time in humans. 'Experiments of nature' - naturally occurring mutations in humans that affect the activity of a particular protein target or targets - can be used to estimate the probable efficacy and toxicity of a drug targeting such proteins, as well as to establish causal rather than reactive relationships between targets and outcomes. Here, we describe the concept of dose-response curves derived from experiments of nature, with an emphasis on human genetics as a valuable tool to prioritize molecular targets in drug development. We discuss empirical examples of drug-gene pairs that support the role of human genetics in testing therapeutic hypotheses at the stage of target validation, provide objective criteria to prioritize genetic findings for future drug discovery efforts and highlight the limitations of a target validation approach that is anchored in human genetics.

Spinal muscular atrophy due to a "de novo" 1.3 Mb deletion: implication for genetic counseling

We report a 3-year-old female with type I spinal muscular atrophy (SMA) born to a young and non-consanguineous couple. The child presented at two months of life with intense muscle weakness affecting predominantly proximal portions of the limbs, especially the legs, muscle hypotonia, fasciculation of the tongue, and severe respiratory muscle involvement. She remained in an intensive care unit with an assisted ventilation system from the fourth month of life. She died at 3 years of age from pulmonary infection. Molecular analysis confirmed the diagnosis of SMA but revealed that only the father was an asymptomatic carrier. Because SMN1 is mapped in a complex region containing repetitive elements due to an inverted duplication of approximately 500 kb, we carry out an SNP array and detected a 1.3 Mb deletion including the SMN1 and SMN2 genes that explain the disease.

Therapeutic strategies for the treatment of spinal muscular atrophy

Spinal muscular atrophy (SMA) is an inherited neurodegenerative disease that results in progressive dysfunction of motor neurons of the anterior horn of the spinal cord. SMA is caused by the loss of full-length protein expression from the survival of motor neuron 1 (SMN1) gene. The disease has a unique genetic profile as it is autosomal recessive for the loss of SMN1, but a nearly identical homolog, SMN2, acts as a disease modifier whose expression is inversely correlated to clinical severity. Targeted therapeutic approaches primarily focus on increasing the levels of full-length SMN protein, through either gene replacement or regulation of SMN2 expression. There is currently no US FDA approved treatment for SMA. This is an exciting time as multiple efforts from academic and industrial laboratories are reaching the preclinical and clinical testing stages.

Prospective cohort study of spinal muscular atrophy types 2 and 3

OBJECTIVE

To characterize the natural history of spinal muscular atrophy type 2 and type 3 (SMA 2/3) beyond 1 year and to report data on clinical and biological outcomes for use in trial planning.

METHODS

We conducted a prospective observational cohort study of 79 children and young adults with SMA 2/3 who participated in evaluations for up to 48 months. Clinically, we evaluated motor and pulmonary function, quality of life, and muscle strength. We also measured SMN2 copy number, hematologic and biochemical profiles, muscle mass by dual x-ray absorptiometry (DXA), and the compound motor action potential (CMAP) in a hand muscle. Data were analyzed for associations between clinical and biological/laboratory characteristics cross-sectionally, and for change over time in outcomes using all available data.

RESULTS

In cross-sectional analyses, certain biological measures (specifically, CMAP, DXA fat-free mass index, and SMN2 copy number) and muscle strength measures were associated with motor function. Motor and pulmonary function declined over time, particularly at time points beyond 12 months of follow-up.

CONCLUSION

The intermediate and mild phenotypes of SMA show slow functional declines when observation periods exceed 1 year. Whole body muscle mass, hand muscle compound motor action potentials, and muscle strength are associated with clinical measures of motor function. The data from this study will be useful for clinical trial planning and suggest that CMAP and DXA warrant further evaluation as potential biomarkers.

Raising obstetricians' awareness of spinal muscular atrophy: towards early detection and reproductive planning

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder that is caused by degeneration of α motor neurons in the spinal cord anterior horns. This degeneration can lead to progressive atrophy of proximal muscles, weakness, respiratory failure and death in severe cases. SMA is the most common neuromuscular disease of childhood and one of the main causes of infant death, with no cure in sight. This review highlights the impact of the disease in families, summarizes genetics and ultrasound advances, discusses how obstetricians can work towards its early detection and explores the options for reproductive planning.

Mutations in the RNA exosome component gene EXOSC3 cause pontocerebellar hypoplasia and spinal motor neuron degeneration

RNA exosomes are multi-subunit complexes conserved throughout evolution¹ and emerging as the major cellular machinery for processing, surveillance, and turnover of a diverse spectrum of coding and non-coding RNA substrates essential for viability². By exome sequencing, we discovered recessive mutations in exosome component 3 (EXOSC3) in four siblings with infantile spinal motor neuron disease, cerebellar atrophy, progressive microcephaly, and profound global developmental delay, consistent with pontocerebellar hypoplasia type 1 [PCH1; OMIM 607596]^3–6. We identified mutations in EXOSC3 in an additional 8 of 12 families with PCH1. Morpholino knockdown of exosc3 in zebrafish embryos caused embryonic maldevelopment with small brain and poor motility, reminiscent of human clinical features and largely rescued by coinjected wildtype but not mutant exosc3 mRNA. These findings represent the first example of an RNA exosome gene responsible for a human disease and further implicate dysregulation of RNA processing in cerebellar and spinal motor neuron maldevelopment and degeneration.

Drug treatment for spinal muscular atrophy types II and III

BACKGROUND

Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells, which leads to progressive muscle weakness. Children with SMA type II do not develop the ability to walk without support and have a shortened life expectancy, whereas children with SMA type III develop the ability to walk and have a normal life expectancy. There are no known efficacious drug treatments that influence the disease course of SMA. This is an update of a review first published in 2009.

OBJECTIVES

To evaluate whether drug treatment is able to slow or arrest the disease progression of SMA types II and III and to assess if such therapy can be given safely. Drug treatment for SMA type I is the topic of a separate updated Cochrane review.

SEARCH METHODS

We searched the Cochrane Neuromuscular Disease Group Specialized Register (8 March 2011), Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 1), MEDLINE (January 1991 to February 2011), EMBASE (January 1991 to February 2011) and ISI Web of Knowledge (January 1991 to March 8 2011). We also searched clinicaltrials.gov to identify as yet unpublished trials (8 March 2011).

SELECTION CRITERIA

We sought all randomised or quasi-randomised trials that examined the efficacy of drug treatment for SMA types II and III. Participants had to fulfil the clinical criteria and have a deletion or mutation of the survival motor neuron 1 (SMN1) gene (5q11.2-13.2) that was confirmed by genetic analysis.The primary outcome measure was to be change in disability score within one year after the onset of treatment. Secondary outcome measures within one year after the onset of treatment were to be change in muscle strength, ability to stand or walk, change in quality of life, time from the start of treatment until death or full time ventilation and adverse events attributable to treatment during the trial period.

DATA COLLECTION AND ANALYSIS

Two authors independently reviewed and extracted data from all potentially relevant trials. Pooled relative risks and pooled standardised mean differences were to be calculated to assess treatment efficacy. Risk of bias was systematically analysed.

MAIN RESULTS

Six randomised placebo-controlled trials on treatment for SMA types II and III were found and included in the review: the four in the original review and two trials added in this update. The treatments were creatine (55 participants), phenylbutyrate (107 participants), gabapentin (84 participants), thyrotropin releasing hormone (9 participants), hydroxyurea (57 participants), and combination therapy with valproate and acetyl-L-carnitine (61 participants). None of these studies were completely free of bias. All studies had adequate blinding, sequence generation and reports of primary outcomes.None of the included trials showed any statistically significant effects on the outcome measures in participants with SMA types II and III. One participant died due to suffocation in the hydroxyurea trial and one participant died in the creatine trial. No participants in any of the other four trials died or reached the state of full time ventilation. Serious side effects were infrequent.

AUTHORS' CONCLUSIONS

There is no proven efficacious drug treatment for SMA types II and III.

Drug treatment for spinal muscular atrophy type I

BACKGROUND

Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells of the spinal cord, which leads to progressive muscle weakness. Children with SMA type I will never be able to sit without support and usually die by the age of two years. There are no known efficacious drug treatments that influence the course of the disease. This is an update of a review first published in 2009.

OBJECTIVES

To evaluate whether drug treatment is able to slow or arrest the disease progression of SMA type I, and to assess if such therapy can be given safely. Drug treatment for SMA types II and III is the topic of a separate updated Cochrane review.

SEARCH METHODS

We searched the Cochrane Neuromuscular Disease Group Specialized Register (8 March 2011), CENTRAL (The Cochrane Library 2011, Issue 1), MEDLINE (January 1991 to February 2011), EMBASE (January 1991 to February 2011) and ISI Web of Knowledge (January 1991 to 8 March 2011). We searched the Clinical Trials Registry of the U.S. National Institute of Health (www.ClinicalTrials.gov) (8 March 2011) to identify additional trials that had not yet been published.

SELECTION CRITERIA

We sought all randomised or quasi-randomised trials that examined the efficacy of drug treatment for SMA type I. Participants had to fulfil the clinical criteria and have a deletion or mutation of the SMN1 gene (5q11.2-13.2) confirmed by genetic analysis.The primary outcome measure was time from birth until death or full time ventilation. Secondary outcome measures were development of rolling, sitting or standing within one year after the onset of treatment, and adverse events attributable to treatment during the trial period.

DATA COLLECTION AND ANALYSIS

Two authors (RW and AV) independently reviewed and extracted data from all potentially relevant trials. For included studies, pooled relative risks and standardised mean differences were to be calculated to assess treatment efficacy.

MAIN RESULTS

One small randomised controlled study comparing riluzole treatment to placebo for 10 SMA type 1 children was identified and included in the original review. No further trials were identified for the update in 2011. Regarding the primary outcome measure, three of seven children treated with riluzole were still alive at the ages of 30, 48 and 64 months, whereas all three children in the placebo group died; but the difference was not statistically significant. Regarding the secondary outcome measures, none of the children in the riluzole or placebo group developed the ability to roll, sit or stand, and no adverse effects were observed. For several reasons the overall quality of the study was low, mainly because the study was too small to detect an effect and because of baseline differences. Follow-up of the 10 included children was complete.

AUTHORS' CONCLUSIONS

No drug treatment for SMA type I has been proven to have significant efficacy.

Homozygous SMN2 deletion is a protective factor in the Swedish ALS population

Abnormal survival motor neuron 1 (SMN1)-copy number has been associated with an increased risk of amyotrophic lateral sclerosis (ALS) in French and Dutch population studies. The aim of this study was to determine whether SMN gene copy number increases the risk of ALS or modulates its phenotype in a cohort of Swedish sporadic ALS (SALS) patients. In all, 502 Swedes with SALS and 502 Swedish controls matched for gender and age were enrolled. SMN1 and SMN2 gene copy numbers were studied by a semi-quantitative PCR method. A genotype-phenotype comparison was performed in order to determine whether SMN genes modulate the phenotype of ALS. The results were also compared with our previously reported French cohort of ALS patients. There was no difference between Swedish patients and controls in the frequency of SMN1 and SMN2 copy numbers. The frequency of SMN1 gene copies differed significantly between the French and Swedish ALS populations. The duration of the disease was significantly longer in the Swedish cohort with homozygous deletions of SMN2 when compared with the French cohort. Abnormal SMN1 gene copy number cannot be considered as a universal genetic susceptibility factor for SALS and this result underlines the importance of reproducing association gene studies in groups from different origins. We also suggest that SMN2 gene copy number might have different effects on ALS progression in disparate human populations.

Drug treatment for spinal muscular atrophy type I

BACKGROUND

Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells of the spinal cord, which leads to progressive muscle weakness. Children with SMA type I will never be able to sit without support and usually die by the age of two years. There are no known efficacious drug treatments that influence the course of the disease. This is an update of a review first published in 2009.

OBJECTIVES

To evaluate whether drug treatment is able to slow or arrest the disease progression of SMA type I, and to assess if such therapy can be given safely. Drug treatment for SMA types II and III is the topic of a separate updated Cochrane review.

SEARCH METHODS

We searched the Cochrane Neuromuscular Disease Group Specialized Register (8 March 2011), CENTRAL (The Cochrane Library 2011, Issue 1), MEDLINE (January 1991 to February 2011), EMBASE (January 1991 to February 2011) and ISI Web of Knowledge (January 1991 to 8 March 2011). We searched the Clinical Trials Registry of the U.S. National Institute of Health (www.ClinicalTrials.gov) (8 March 2011) to identify additional trials that had not yet been published.

SELECTION CRITERIA

We sought all randomised or quasi-randomised trials that examined the efficacy of drug treatment for SMA type I. Participants had to fulfil the clinical criteria and have a deletion or mutation of the SMN1 gene (5q11.2-13.2) confirmed by genetic analysis.The primary outcome measure was time from birth until death or full time ventilation. Secondary outcome measures were development of rolling, sitting or standing within one year after the onset of treatment, and adverse events attributable to treatment during the trial period.

DATA COLLECTION AND ANALYSIS

Two authors (RW and AV) independently reviewed and extracted data from all potentially relevant trials. For included studies, pooled relative risks and standardised mean differences were to be calculated to assess treatment efficacy.

MAIN RESULTS

One small randomised controlled study comparing riluzole treatment to placebo for 10 SMA type 1 children was identified and included in the original review. No further trials were identified for the update in 2011. Regarding the primary outcome measure, three of seven children treated with riluzole were still alive at the ages of 30, 48 and 64 months, whereas all three children in the placebo group died; but the difference was not statistically significant. Regarding the secondary outcome measures, none of the children in the riluzole or placebo group developed the ability to roll, sit or stand, and no adverse effects were observed. For several reasons the overall quality of the study was low, mainly because the study was too small to detect an effect and because of baseline differences. Follow-up of the 10 included children was complete.

AUTHORS' CONCLUSIONS

No drug treatment for SMA type I has been proven to have significant efficacy.

Drug treatment for spinal muscular atrophy types II and III

BACKGROUND

Spinal muscular atrophy (SMA) is caused by degeneration of anterior horn cells, which leads to progressive muscle weakness. Children with SMA type II do not develop the ability to walk without support and have a shortened life expectancy, whereas children with SMA type III develop the ability to walk and have a normal life expectancy. There are no known efficacious drug treatments that influence the disease course of SMA. This is an update of a review first published in 2009.

OBJECTIVES

To evaluate whether drug treatment is able to slow or arrest the disease progression of SMA types II and III and to assess if such therapy can be given safely. Drug treatment for SMA type I is the topic of a separate updated Cochrane review.

SEARCH METHODS

We searched the Cochrane Neuromuscular Disease Group Specialized Register (8 March 2011), Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 1), MEDLINE (January 1991 to February 2011), EMBASE (January 1991 to February 2011) and ISI Web of Knowledge (January 1991 to March 8 2011). We also searched clinicaltrials.gov to identify as yet unpublished trials (8 March 2011).

SELECTION CRITERIA

We sought all randomised or quasi-randomised trials that examined the efficacy of drug treatment for SMA types II and III. Participants had to fulfil the clinical criteria and have a deletion or mutation of the survival motor neuron 1 (SMN1) gene (5q11.2-13.2) that was confirmed by genetic analysis.The primary outcome measure was to be change in disability score within one year after the onset of treatment. Secondary outcome measures within one year after the onset of treatment were to be change in muscle strength, ability to stand or walk, change in quality of life, time from the start of treatment until death or full time ventilation and adverse events attributable to treatment during the trial period.

DATA COLLECTION AND ANALYSIS

Two authors independently reviewed and extracted data from all potentially relevant trials. Pooled relative risks and pooled standardised mean differences were to be calculated to assess treatment efficacy. Risk of bias was systematically analysed.

MAIN RESULTS

Six randomised placebo-controlled trials on treatment for SMA types II and III were found and included in the review: the four in the original review and two trials added in this update. The treatments were creatine (55 participants), phenylbutyrate (107 participants), gabapentin (84 participants), thyrotropin releasing hormone (9 participants), hydroxyurea (57 participants), and combination therapy with valproate and acetyl-L-carnitine (61 participants). None of these studies were completely free of bias. All studies had adequate blinding, sequence generation and reports of primary outcomes.None of the included trials showed any statistically significant effects on the outcome measures in participants with SMA types II and III. One participant died due to suffocation in the hydroxyurea trial and one participant died in the creatine trial. No participants in any of the other four trials died or reached the state of full time ventilation. Serious side effects were infrequent.

AUTHORS' CONCLUSIONS

There is no proven efficacious drug treatment for SMA types II and III.

Therapeutic developments in spinal muscular atrophy

Spinal muscular atrophy (SMA), a potentially devastating disease marked by progressive weakness and muscle atrophy resulting from the dysfunction and loss of motor neurons of the spinal cord, has emerged in recent years as an attractive target for therapeutic intervention. Caused by a homozygous mutation to the Survival of Motor Neurons 1 (SMN1) gene on chromosome 5q, the severity of the clinical phenotype in SMA is modulated by the function of a related protein, Survival of Motor Neurons 2 (SMN2). SMN2 predominantly produces an unstable SMN transcript lacking exon 7; only about 10% of the transcription product produces a full-length, functional SMN protein. Several therapeutic strategies have targeted this gene with the goal of producing increased full-length SMN transcript, thereby modifying the underlying mechanism. Drugs that have increased SMN2 function, in vitro, are now explored for potential therapeutic benefit in this disease. Alternative approaches, including neuroprotective, muscle anabolic, gene and cell replacement strategies, also hold promise. The recent advances in preclinical research and the development of a wider range of animal models for SMA continue to provide cautious optimism that effective treatments for SMA will eventually emerge.

[Spinal muscular atrophy: frequent cause of congenital hypotonia in Morocco]

INTRODUCTION

Congenital hypotonia is a non specific symptom frequently seen in newborns and infants, and whose etiological diagnosis is often difficult due to the lack of specialized and affordable explorations. Childhood-onset proximal spinal muscular atrophy (SMA) is an autosomal recessive disorder caused by degeneration of the anterior horn cells of the spinal cord, leading to progressive paralysis with muscular atrophy. In more than 95% of the cases, it results from deletion of exon 7 of the SMN gene localized on 5q13, easily identified by molecular biology.

OBJECTIVE

To determine the prevalence of the deletion of exon 7 of the SMN gene in congenital hypotonia with an unknown cause in Morocco.

PATIENTS AND METHODS

We investigated the deletion of exon 7 of the SMN gene in 87 newborns and infants with congenital hypotonia. The cause of congenital hypotonia could not be determined in 60 of them, while 27 had electrophysiological evidence for an involvement of the anterior horn cells.

RESULTS

The homozygous deletion of the SMN gene was detected in 23 of the newborns with unknown cause for hypotonia (38%) and in 21 of the infants whose electromyogram suggested infantile spinal amyotrophy (78%).

CONCLUSION

This study underlines the advantages of a systematic search for the deletion of exon 7 of the SMN gene in every infant suffering from congenital hypotonia due to an unknown cause, particularly when the child's vital prognosis is at stake. This genetic test, easily implemented, should be systematically proposed after an attentive clinical evaluation in countries where the etiological diagnosis of congenital hypotonia is not systematic.