Spinal muscular atrophy: classification, diagnosis, management, pathogenesis, and future research directions

Role of circulating biomarkers in spinal muscular atrophy: insights from a new treatment era

Spinal muscular atrophy (SMA) is a lower motor neuron disease due to biallelic mutations in the SMN1 gene on chromosome 5. It is characterized by progressive muscle weakness of limbs, bulbar and respiratory muscles. The disease is usually classified in four different phenotypes (1-4) according to age at symptoms onset and maximal motor milestones achieved. Recently, three disease modifying treatments have received approval from the Food and Drug Administration (FDA) and the European Medicines Agency (EMA), while several other innovative drugs are under study. New therapies have been game changing, improving survival and life quality for SMA patients. However, they have also intensified the need for accurate biomarkers to monitor disease progression and treatment efficacy. While clinical and neurophysiological biomarkers are well established and helpful in describing disease progression, there is a great need to develop more robust and sensitive circulating biomarkers, such as proteins, nucleic acids, and other small molecules. Used alone or in combination with clinical biomarkers, they will play a critical role in enhancing patients' stratification for clinical trials and access to approved treatments, as well as in tracking response to therapy, paving the way to the development of individualized therapeutic approaches. In this comprehensive review, we describe the foremost circulating biomarkers of current significance, analyzing existing literature on non-treated and treated patients with a special focus on neurofilaments and circulating miRNA, aiming to identify and examine their role in the follow-up of patients treated with innovative treatments, including gene therapy.

The Relationship between Body Composition, Fatty Acid Metabolism and Diet in Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive condition that results in pathological deficiency of the survival motor neuron (SMN) protein. SMA most frequently presents itself within the first few months of life and is characterized by progressive muscle weakness. As a neuromuscular condition, it prominently affects spinal cord motor neurons and the skeletal muscle they innervate. However, over the past few decades, the SMA phenotype has expanded to include pathologies outside of the neuromuscular system. The current therapeutic SMA landscape is at a turning point, whereby a holistic multi-systemic approach to the understanding of disease pathophysiology is at the forefront of fundamental research and translational endeavours. In particular, there has recently been a renewed interest in body composition and metabolism in SMA patients, specifically that of fatty acids. Indeed, there is increasing evidence of aberrant fat distribution and fatty acid metabolism dysfunction in SMA patients and animal models. This review will explore fatty acid metabolic defects in SMA and discuss how dietary interventions could potentially be used to modulate and reduce the adverse health impacts of these perturbations in SMA patients.

Antisense Drugs Make Sense for Neurological Diseases

The genetic basis for most inherited neurodegenerative diseases has been identified, yet there are limited disease-modifying therapies for these patients. A new class of drugs-antisense oligonucleotides (ASOs)-show promise as a therapeutic platform for treating neurological diseases. ASOs are designed to bind to the RNAs either by promoting degradation of the targeted RNA or by elevating expression by RNA splicing. Intrathecal injection into the cerebral spinal fluid results in broad distribution of antisense drugs and long-term effects. Approval of nusinersen in 2016 demonstrated that effective treatments for neurodegenerative diseases can be identified and that treatments not only slow disease progression but also improve some symptoms. Antisense drugs are currently in development for amyotrophic lateral sclerosis, Huntington's disease, Alzheimer's disease, Parkinson's disease, and Angelman syndrome, and several drugs are in late-stage research for additional neurological diseases. This review highlights the advances in antisense technology as potential treatments for neurological diseases.

A Prospective, Crossover Survey Study of Child- and Proxy-Reported Quality of Life According to Spinal Muscular Atrophy Type and Medical Interventions

BACKGROUND

Spinal muscular atrophy is an autosomal-recessive, progressive neuromuscular disease associated with extensive morbidity. Children with spinal muscular atrophy have potentially increased life spans due to improved nutrition, respiratory support, and novel pharmaceuticals.

OBJECTIVES

To report on the quality of life and family experience for children with spinal muscular atrophy with attentiveness to patient- and proxy-concordance and to stratify quality of life reports by spinal muscular atrophy type and medical interventions.

METHODS

A prospective, crossover survey study inclusive of 58 children (26 spinal muscular atrophy type I, 23 type II, 9 type III) and their family caregivers at a free-standing Midwestern children's hospital. Twenty-eight families completed the 25-item PedsQL 3.0 Neuromuscular Module. Forty-four participants completed the 36-item PedsQL Family Impact Module and 47 completed the Caregiver Priorities and Child Health Index of Life with Disabilities (CPCHILD) questionnaire.

RESULTS

The PedsQL Family Impact Module demonstrated significant differences between spinal muscular atrophy types I and II in functioning domains including physical, emotional, social, and family relations (P < .03). Child self-report and proxy report surveys demonstrated significant differences between spinal muscular atrophy types in the communication domains (P < .003). Children self-reported their quality of life higher than proxy report of child quality of life. Gastrostomy tube (P = .001) and ventilation support (P = .029) impacted proxy-reported quality of life perspectives, whereas nusinersen use did not. Spinal surgery was associated with improved parental quality of life and family impact (P < .03).

CONCLUSIONS

The measurement and monitoring of quality of life for children with spinal muscular atrophy and their families represents an implementable priority for care teams.

Overexpression of SMN2 Gene in Motoneuron-Like Cells Differentiated from Adipose-Derived Mesenchymal Stem Cells by Ponasterone A

Cell therapy and stem cell transplantation strategies have provided potential therapeutic approaches for the treatment of neurological disorders. Adipose-derived mesenchymal stem cells (ADMSCs) are abundant adult stem cells with low immunogenicity, which can be used for allogeneic cell replacement therapies. Differentiation of ADMSCs into acetylcholine-secreting motoneurons (MNs) is a promising treatment for MN diseases, such as spinal muscular atrophy (SMA), which is associated with the level of SMN1 gene expression. The SMN2 gene plays an important role in MN disorders, as it can somewhat compensate for the lack of SMN1 expression in SMA patients. Although the differentiation potential of ADMSCs into MNs has been previously established, overexpression of SMN2 gene in a shorter period with a longer survival has yet to be elucidated. Ponasterone A (PNA), an ecdysteroid hormone activating the PI3K/Akt pathway, was studied as a new steroid to promote SMN2 overexpression in MNs differentiated from ADMSCs. After induction with retinoic acid, sonic hedgehog, forskolin, and PNA, MN phenotypes were differentiated from ADMSCs, and immunochemical staining, specific for β-tubulin, neuron-specific enolase, and choline acetyltransferase, was performed. Also, the results of real-time PCR assay indicated nestin, Pax6, Nkx2.2, Hb9, Olig2, and SMN2 expression in the differentiated cells. After 2 weeks of treatment, cultures supplemented with PNA showed a longer survival and a 1.2-fold increase in the expression of SMN2 (an overall 5.6-fold increase; *P ≤ 0.05), as confirmed by the Western blot analysis. The PNA treatment increased the levels of ChAT, Isl1, Hb9, and Nkx2 expression in MN-like cells. Our findings highlight the role of PNA in the upregulation of SMN2 genes from MSC-derived MN-like cells, which may serve as a potential candidate in cellular therapy for SMA patients.

Electrocardiographic Evaluation in Patients With Spinal Muscular Atrophy: A Case-Control Study

BACKGROUND

This study aimed to show the impairment of autonomic cardiac conduction causing bradycardia and/or electrocardiographic alterations in children affected by spinal muscular atrophy type 1 and 2 (SMA 1 and 2).

METHODS

We included 25 spinal muscular atrophy patients, admitted from November 2016 to May 2017. All patients underwent an electrocardiographic examination and we studied PR and QRS intervals, P-waves and QRS amplitudes, and heart rate in spinal muscular atrophy patients compared to a control group.

RESULTS

In all patients, we found longer PRi and QRSi ( P < .05), lower P-wave and QRS complex amplitudes ( P < .01), and a decreased heart rate ( P < .01) with respect to controls. When we divided our patients into SMA1 and SMA2 subgroups, we found that statistical differences were maintained for P-wave and QRS complex amplitudes and heart rate, but not for PRi and QRSi with respect to controls.

CONCLUSION

We suggest the hypothesis of SMN expression on cardiac tissue condition and/or autonomic cardiac conduction.

Cyclic tetrapeptide HDAC inhibitors as potential therapeutics for spinal muscular atrophy: Screening with iPSC-derived neuronal cells

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder that is caused by inactivating mutations in the Survival of motor neuron 1 (SMN1) gene, resulting in decreased SMN protein expression. Humans possess a paralog gene, SMN2, which contains a splicing defect in exon 7 leading to diminished expression of full-length, fully functional SMN protein. Increasing SMN2 expression has been a focus of therapeutic development for SMA. Multiple studies have reported the efficacy of histone deacetylase inhibitors (HDACi) in this regard. However, clinical trials involving HDACi have been unsatisfactory, possibly because previous efforts to identify HDACi to treat SMA have employed non-neuronal cells as the screening platform. To address this issue, we generated an SMA-patient specific, induced pluripotent stem cell (iPSC) derived neuronal cell line that contains homogenous Tuj1+neurons. We screened a small library of cyclic tetrapeptide HDACi using this SMA neuronal platform and discovered compounds that elevate SMN2 expression by an impressive twofold or higher. These candidates are also capable of forming gems intranuclearly in SMA neurons, demonstrating biological activity. Our study identifies new potential HDACi therapeutics for SMA screened using a disease-relevant SMA neuronal cellular model.

Characterizing Semaphorin-Mediated Effects on Sensory and Motor Axon Pathfinding and Connectivity During Embryonic Development

How are precise connectivity to peripheral targets and corresponding sensory-motor networks established during developmental innervation of the vertebrate extremities? The formation of functional sensory-motor circuits requires highly appropriate temporal and spatial regulation of axon growth which is achieved through the combination of different molecular mechanisms such as communication between heterotypic fiber systems, axon-environment, or axon-glia interactions that ensure proper fasciculation and accurate pathfinding to distal targets. Family members of the class 3 semaphorins and their cognate receptors, the neuropilins, were shown to govern various events during wiring of central and peripheral circuits, with mice lacking Sema3-Npn signaling showing deficits in timing of growth, selective fasciculation, guidance fidelity, and coupling of sensory axon growth to motor axons at developmental time points. Given the accuracy with which these processes have to interact in a stepwise manner, deficiency of the smallest cog in the wheel may impact severely on the faithful establishment and functionality of peripheral circuitries, ultimately leading to behavioral impairments or even cause the death of the animal. Reliable quantitative analyses of sensory-motor fasciculation, extension, and guidance of axons to their cognate target muscles and the skin during development, but also assessment of physiological and behavioral consequences at adult age, are therefore a necessity to extend our understanding of the molecular mechanisms of peripheral circuit formation. In this chapter we provide a detailed methodology to characterize class 3 semaphorin-mediated effects on peripheral sensory and motor axon pathfinding and connectivity during embryonic development.

A novel role for CARM1 in promoting nonsense-mediated mRNA decay: potential implications for spinal muscular atrophy

Loss of ‘Survival of Motor Neurons’ (SMN) leads to spinal muscular atrophy (SMA), a disease characterized by degeneration of spinal cord alpha motor neurons, resulting in muscle weakness, paralysis and death during early childhood. SMN is required for assembly of the core splicing machinery, and splicing defects were documented in SMA. We previously uncovered that Coactivator-Associated Methyltransferase-1 (CARM1) is abnormally up-regulated in SMA, leading to mis-regulation of a number of transcriptional and alternative splicing events. We report here that CARM1 can promote decay of a premature terminating codon (PTC)-containing mRNA reporter, suggesting it can act as a mediator of nonsense-mediated mRNA decay (NMD). Interestingly, this pathway, while originally perceived as solely a surveillance mechanism preventing expression of potentially detrimental proteins, is now emerging as a highly regulated RNA decay pathway also acting on a subset of normal mRNAs. We further show that CARM1 associates with major NMD factor UPF1 and promotes its occupancy on PTC-containing transcripts. Finally, we identify a specific subset of NMD targets that are dependent on CARM1 for degradation and that are also misregulated in SMA, potentially adding exacerbated targeting of PTC-containing mRNAs to the already complex array of molecular defects associated with this disease.

Aspectos da comunicação na síndrome de Werdning-Hoffman: estudo de caso clínico

Resumo: A Síndrome de Werdnig-Hoffman é uma doença neuromuscular hereditária, caracterizada pela atrofia e fraqueza muscular progressiva, que inviabiliza o desenvolvimento de habilidades motoras. O desenvolvimento mental encontra-se preservado, vivacidade e inteligência destacam-se, em contraste à precária atividade motora. O sujeito acometido por essa síndrome tem limitações físicas para a efetiva interação com o outro, o que pode acarretar problemas de comunicação. Este estudo tem como objetivo analisar as possibilidades comunicativas de uma criança com Síndrome de Werdnig-Hoffman no decorrer do processo terapêutico fonoaudiológico. É um estudo de caso de uma criança com quatro anos de idade, gênero feminino, filha única (de casal jovem), atendida em terapia fonoaudiológica em centro de reabilitação de deficiências múltiplas no período de agosto de 2013 a abril de 2014. Na avaliação fonoaudiológica observou-se que a paciente comunica-se por expressões faciais e raras vocalizações. No decorrer do processo terapêutico, a interação foi sustentada dialogicamente por meio de perguntas da fonoaudióloga respondidas afirmativa ou negativamente pela paciente. Para "sim", elevava a sobrancelha concomitante à maior abertura dos olhos e um discreto sorriso. Para "não", contraia a sobrancelha e realizava leve movimento de negação com a cabeça. Embora predominantemente silente e corporalmente inerte, a paciente expressa sua subjetividade por meio de condutas comunicativas que, mesmo precárias, indicam atividade simbólica na inserção e interpretação da realidade.

"3 . . 2 . . 1 . . Impact [factor]: target [academic career] destroyed!": just another statistical casualty

"Publish or perish" is the time-honored "principle" for academicians who race to accumulate lines under the "publications" section of a curriculum vitae. The original intent of publication-to inform others of findings and further scientific knowledge-has been corrupted by factors including (1) exponential growth of journals and the journal industry, fueled in part by intrusion of the Internet into all aspects of academic life; and (2) adoption of journal metrics (rather than written content) as the measure of scientific quality. The proprietary Thomson Reuters Impact Factor is the most pernicious metric, having caused editors and publishers to change editorial practices to boost the number. At the same time, gullible administrators and government agencies have been persuaded that metrics for the journal in which materials are published can be used as a measure of the worth of individual investigators (and institutions) and their research efforts: simple numbers can be substituted for the burdensome effort required to read and assess research quality. Thus, granting of research funds, awarding of academic rank and tenure, and determination of salaries (including bonus payments) have become tied to manipulable journal metrics rather than the significance or quality of reported research. Therefore, it is no wonder that the integrity of science is more often being questioned. How should a young investigator approach the "publish or perish" dilemma? Performing sound research and preparing optimal materials for publication must remain the overriding goals: properly articulate the question addressed by the study; thoroughly document all methods and case information; carefully describe results including any conflicting or negative findings; discuss the importance of the findings along with how the results address the initial question and whether findings refute or confirm previous studies; prepare properly cited bibliographic references; list all author contributions, potential conflicts of interest, financial support, and required ethical approvals; and provide a catchy title and an abstract containing sufficient information that other investigators perusing scientific indices will be enticed to read the published article. Submit the completed manuscript to the most appropriate journal based on that journal's previously published content and relevance to the field of study regardless of journal metrics. On publication, notify investigators in the same field to ask for their comments on the work. Thus, an individual will become known for the quality of his or her work product and the worshiping of publication metrics will be unnecessary.

Recommendations for the diagnosis and management of typical childhood spinal muscular atrophy

Typical childhood spinal muscular atrophy is a disease that affects the anterior horn of the spinal cord related to SMN1 gene defects. Since no etiological treatment is currently available, its management is necessarily symptomatic and involves multidisciplinary care. The national plan on rare diseases for 2005-2008 developed by the French Ministry of Health resulted in the creation of 12 reference centres for neuromuscular diseases, mainly to improve their diagnosis and management. During the first one-day clinical research meeting on neuromuscular disorders, organized by the French Association to fight myopathies (AFM) in May 2007, clinicians from the 12 national reference centers led workshops for each of the main neuromuscular diseases. Concerning spinal muscular atrophy, discussions involving specialists from medical and allied professions were led by clinicians in charge of the workshop sessions. This paper reports the final version of their recommendation regarding the diagnosis, monitoring and management of typical infantile spinal muscular atrophy, which is necessarily multidisciplinary, including orthopedic, pulmonary, gastroenterology and nutrition care.

Physical exercise reduces cardiac defects in type 2 spinal muscular atrophy-like mice

Spinal muscular atrophy (SMA), the leading genetic cause of death in infants worldwide, is due to the misexpression of the survival of motor neuron protein, causing death of motor neurons. Several clinical symptoms suggested that, in addition to motor neurons, the autonomic nervous systems could be implicated in the cardiac function alterations observed in patienst with SMA. These alterations were also found in a severe SMA mouse model, including bradycardia and a reduction of sympathetic innervation, both associated with autonomic imbalance. In the present study, we investigate the extent of autonomic dysfunction and the effects of a running-based exercise on the altered cardiorespiratory function in type 2 SMA-like mice. We observed that the SMA induced: (1) a dramatic alteration of intrinsic cardiac conduction associated with bradycardia; (2) a severe cardiomyopathy associated with extensive ventricular fibrosis; and (3) a delay in cardiac muscle maturation associated with contractile protein expression defects. Furthermore, our data indicate that the sympathetic system is not only functioning, but also likely contributes to alleviate the bradycardia and the arrhythmia in SMA-like mice. Moreover, physical exercise provides many benefits, including the reduction of cardiac protein expression defect, the reduction of fibrosis, the increase in cardiac electrical conduction velocity, and the drastic reduction in bradycardia and arrhythmias resulting in the partial restoration of the cardiac function in these mice. Thus, modulating the cardiorespiratory function in SMA could represent a new target for improving supportive care and for developing new pharmacological and non-pharmacological interventions that would most certainly include physical exercise.

Genetic counseling for the orthodox jewish couple undergoing preimplantation genetic diagnosis

Orthodox Jewish patients who seek genetic counseling are often placed in a difficult position of having to choose between their desire to follow Jewish religious instruction (halacha) and following the advice of the genetic counselor. In this article we will present the work of the Puah Institute based in Jerusalem that is dedicated to assisting and guiding such couples to navigate through the medical system and medical recommendations and create a harmony between modern genetic counseling and the Orthodox Jewish tradition. In light of the expanding use of preimplantation genetic diagnosis (PGD) for a variety of medical and non-medical conditions, this dilemma is even more poignant. There is an ethical debate regarding PGD and the correct parameters for its use. Here we present the Orthodox Jewish view of the use and abuse of PGD. We present three case studies that sought the assistance and guidance of the Puah Institute. Each of these cases raises ethical dilemmas for the genetic counselor and for the rabbinic counselor. We discuss; the status of the embryo, the status of a carrier of a genetic abnormality and whether PGD is an obligation or good practice. In addition we deal with whether PGD and the search for the desired traits can be defined as eugenics or not.

A rigorous approach to facilitate and guarantee the correctness of the genetic testing management in human genome information systems

Background

Recent medical and biological technology advances have stimulated the development of new testing systems that have been providing huge, varied amounts of molecular and clinical data. Growing data volumes pose significant challenges for information processing systems in research centers. Additionally, the routines of genomics laboratory are typically characterized by high parallelism in testing and constant procedure changes.

Results

This paper describes a formal approach to address this challenge through the implementation of a genetic testing management system applied to human genome laboratory. We introduced the Human Genome Research Center Information System (CEGH) in Brazil, a system that is able to support constant changes in human genome testing and can provide patients updated results based on the most recent and validated genetic knowledge. Our approach uses a common repository for process planning to ensure reusability, specification, instantiation, monitoring, and execution of processes, which are defined using a relational database and rigorous control flow specifications based on process algebra (ACP). The main difference between our approach and related works is that we were able to join two important aspects: 1) process scalability achieved through relational database implementation, and 2) correctness of processes using process algebra. Furthermore, the software allows end users to define genetic testing without requiring any knowledge about business process notation or process algebra.

Conclusions

This paper presents the CEGH information system that is a Laboratory Information Management System (LIMS) based on a formal framework to support genetic testing management for Mendelian disorder studies. We have proved the feasibility and showed usability benefits of a rigorous approach that is able to specify, validate, and perform genetic testing using easy end user interfaces.

Thigh muscle volume measured by magnetic resonance imaging is stable over a 6-month interval in spinal muscular atrophy

Changes in thigh muscle volume over 6 months were assessed using magnetic resonance imaging in 11 subjects aged 6 to 47 years with spinal muscular atrophy (4 type 2 and 7 type 3; 4 ambulatory and 3 nonambulatory). Muscle volume with normal and abnormal signal was measured using blinded, semiautomated analysis of reconstructed data. Volumes at baseline and 6 months were correlated with clinical function at each epoch. There was minimal increase in normal (0.3 ± 1.4 mL/cm) and total (0.1 ± 1.3 mL/cm) muscle. Muscle volume correlated closely with clinical function. Minimal interval change in muscle volume is consistent with the established clinical history of minimal disease progression over intervals shorter than 1 year. Relative constancy of muscle volume estimation and correlation with established functional measures suggest a role for segmental magnetic resonance imaging as a biomarker of treatment effect in future therapeutic trials.

Conservative care of temporomandibular joint disorder in a 35-year-old patient with spinal muscular atrophy type III: a case study

OBJECTIVE

This article describes the chiropractic clinical management and therapeutic benefits accruing to a patient with temporomandibular joint (TMJ) disorder and spinal muscular atrophy type III.

CLINICAL FEATURES

A 35-year-old white man presented at the university chiropractic outpatient clinic with a complaint of masseter muscle pain and mouth-opening restriction. Temporomandibular joint range of motion evaluation revealed restricted opening (11 mm interincisival), and pain was rated by the patient at an intensity of 5 on a pain scale of 0 to 10.

INTERVENTION AND OUTCOME

Chiropractic care was provided and included TMJ mobilization, myofascial therapy, trigger point therapy, and light spinal mobilizations of the upper cervical vertebrae. Final evaluation of TMJ range of motion showed active opening of 12 mm with absence of pain and muscle tenderness of the jaw.

CONCLUSION

This case suggests that a patient with musculoskeletal disorders related to underlying neurodegenerative pathologies may benefit from chiropractic management adapted to their condition. In the present case, chiropractic treatment of the TMJ represented a viable, low-cost approach with limited adverse effects compared with surgery.

Muscle volume estimation by magnetic resonance imaging in spinal muscular atrophy

Thigh muscle volume was assessed using magnetic resonance imaging in 16 subjects with spinal muscular atrophy. Scans were successful for 14 of 16 subjects (1 type 1, 6 type 2, and 7 type 3) as young as 5.7 years. Muscle volume with normal and abnormal signal was measured using blinded, semiautomated analysis of reconstructed data. Results were compared with segmental lean mass estimated by dual-energy X-ray absorptiometry and correlated with clinical and electrophysiological measures of disease severity. Muscle volume was reduced with abnormal signal quality. Test-retest reliability (r = .99) and correlation with dual-energy X-ray absorptiometry (r = .91) were excellent. Type 2 subjects had lower volume (3.5 ± 1.6 vs 6.3 ± 2.8 mL/cm height; P = .06) and higher percentage of muscle with abnormal signal (68% ± 20% vs 47% ± 27%; P = .14) than type 3. Reproducibility, tolerability, and strong correlation with clinical measures make magnetic resonance imaging a candidate biomarker for clinical research.

Multi-exon genotyping of SMN gene in spinal muscular atrophy by universal fluorescent PCR and capillary electrophoresis

In this study, we established the first method for simultaneous evaluation of nine exons in the survival motor neuron (SMN) genes for full-scale genotyping. This method was used not only to quantify the copy numbers of highly homogenous telomeric SMN (SMN1)/centromeric SMN genes in exons 7 and 8 but also to determine intragenic mutations in all nine exons for complete diagnosis of spinal muscular atrophy (SMA). Additionally, we utilized the "universal fluorescent PCR" for simultaneously fluorescent labeling of eleven gene fragments (nine exons in SMN and two internal standards). Such technique is very beneficial for multi-exon analysis due to only requirement of one universal fluorescent primer which could fluorescently amplify all gene fragments. Of all 262 detected individuals, three subjects possessing different ratios of SMN1/centromeric SMN in the two exons were determined as gene conversion, and we also detected three interesting intragenic mutations (c.1 -39A>G, c.22_23insA in exon 1, c.84C>T in exon 2a) which were associated with the SMA patients owning one copy of SMN1 including two mutations never reported previously. This high-resolved method provided better potential technique for genotyping and identifying SMA, carrier and normal controls in large population.

The cost-effectiveness of prenatal screening for spinal muscular atrophy

OBJECTIVE

We sought to investigate the cost-effectiveness of prenatal screening for spinal muscular atrophy (SMA).

STUDY DESIGN

A decision analytic model was created to compare a policy of universal SMA screening to that of no screening. The primary outcome was incremental cost per maternal quality-adjusted life year. Probabilities, costs, and outcomes were estimated through literature review. Univariate and multivariate sensitivity analyses were performed to test the robustness of our model to changes in baseline assumptions.

RESULTS

Universal screening for SMA is not cost-effective at $4.9 million per quality-adjusted life year. In all, 12,500 women need to be screened to prevent 1 case of SMA, at a cost of $5.0 million per case averted. Our results were most sensitive to the baseline prevalence of disease.

CONCLUSION

Universal prenatal screening for SMA is not cost-effective. For populations at high risk, such as those with a family history, SMA testing may be a cost-effective strategy.

The role of RNP biogenesis in spinal muscular atrophy

Mutations that affect pre-mRNA processing are the cause for many genetic diseases. Most such mutations target cis-acting regulatory sequences in a given transcript, thus preventing its proper maturation. Only recently however, mutations in trans-acting factors involved in pre-mRNA processing have likewise been linked to disease. One prominent example is spinal muscular atrophy (SMA), a monogenic, neuromuscular disorder caused by reduced levels of functional survival motor neuron (SMN) protein. This ubiquitous factor is part of a complex that mediates the formation of spliceosomal snRNPs. The detailed biochemical investigation of SMN under normal conditions and in SMA has provided clues how mutations in factors with general functions elicit tissue-specific phenotypes.