Spinal muscular atrophy: a time for screening

Nusinersen therapy changed the natural course of spinal muscular atrophy type 1: What about spine and hip?

Purpose

Spinal muscular atrophy type 1 has a devastating natural course and presents a severe course marked by scoliosis and hip subluxation in nonambulatory patients. Nusinersen, Food and Drug Administration-approved spinal muscular atrophy therapy, extends survival and enhances motor function. However, its influence on spinal and hip deformities remains unclear.

Methods

In a retrospective study, 29 spinal muscular atrophy type 1 patients born between 2017 and 2021, confirmed by genetic testing, treated with intrathecal nusinersen, and had registered to the national electronic health database were included. Demographics, age at the first nusinersen dose, total administrations, and Children's of Philadelphia Infant Test of Neuromuscular Disorders scores were collected. Radiological assessments included parasol rib deformity, scoliosis, pelvic obliquity, and hip subluxation.

Results

Mean age was 3.7 ± 1.1 (range, 2-6), and average number of intrathecal nusinersen administration was 8.9 ± 2.9 (range, 4-19). There was a significant correlation between Children's of Philadelphia Infant Test of Neuromuscular Disorders score and the number of nusinersen administration (r = 0.539, p = 0.05). The correlation between Children's of Philadelphia Infant Test of Neuromuscular Disorders score and patient age (r = 0.361) or the time of first nusinersen dose (r = 0.39) was not significant (p = 0.076 and p = 0.054, respectively). While 93.1% had scoliosis, 69% had pelvic obliquity, and 60.7% had hip subluxation, these conditions showed no significant association with patient age, total nusinersen administrations, age at the first dose, or Children's of Philadelphia Infant Test of Neuromuscular Disorders scores.

Conclusion

Disease-modifying therapy provides significant improvements in overall survival and motor function in spinal muscular atrophy type 1. However, progressive spine deformity and hip subluxation still remain significant problems in the majority of cases which would potentially need to be addressed.

Breaking genetic shackles: The advance of base editing in genetic disorder treatment

The rapid evolution of gene editing technology has markedly improved the outlook for treating genetic diseases. Base editing, recognized as an exceptionally precise genetic modification tool, is emerging as a focus in the realm of genetic disease therapy. We provide a comprehensive overview of the fundamental principles and delivery methods of cytosine base editors (CBE), adenine base editors (ABE), and RNA base editors, with a particular focus on their applications and recent research advances in the treatment of genetic diseases. We have also explored the potential challenges faced by base editing technology in treatment, including aspects such as targeting specificity, safety, and efficacy, and have enumerated a series of possible solutions to propel the clinical translation of base editing technology. In conclusion, this article not only underscores the present state of base editing technology but also envisions its tremendous potential in the future, providing a novel perspective on the treatment of genetic diseases. It underscores the vast potential of base editing technology in the realm of genetic medicine, providing support for the progression of gene medicine and the development of innovative approaches to genetic disease therapy.

Diaphragm Fatigue in SMNΔ7 Mice and Its Molecular Determinants: An Underestimated Issue

Spinal muscular atrophy (SMA) is a genetic disorder characterized by the loss of spinal motor neurons leading to muscle weakness and respiratory failure. Mitochondrial dysfunctions are found in the skeletal muscle of patients with SMA. For obvious ethical reasons, the diaphragm muscle is poorly studied, notwithstanding the very important role that respiratory involvement plays in SMA mortality. The main goal of this study was to investigate diaphragm functionality and the underlying molecular adaptations in SMNΔ7 mice, a mouse model that exhibits symptoms similar to that of patients with intermediate type II SMA. Functional, biochemical, and molecular analyses on isolated diaphragm were performed. The obtained results suggest the presence of an intrinsic energetic imbalance associated with mitochondrial dysfunction and a significant accumulation of reactive oxygen species (ROS). In turn, ROS accumulation can affect muscle fatigue, cause diaphragm wasting, and, in the long run, respiratory failure in SMNΔ7 mice. Exposure to the antioxidant molecule ergothioneine leads to the functional recovery of the diaphragm, confirming the presence of mitochondrial impairment and redox imbalance. These findings suggest the possibility of carrying out a dietary supplementation in SMNΔ7 mice to preserve their diaphragm function and increase their lifespan.

Daily Quantity and Kinematic Characteristics of Leg Movement in a Child With SMA (2 Copies SMN2)

PURPOSE

This case report describes daily leg movement quantity and kinematic characteristics of a child with spinal muscular atrophy (SMA) with 2 copies of SMN2, who was symptomatic at the time of treatment with disease-modifying therapies.

KEY POINTS

Compared with infants with typical development, this child had differing values for leg movement quantity, duration, average acceleration, and peak acceleration measured across full days in the natural environment by wearable sensors. In addition, movement quantity and clinician-rated outcomes increased with age.

CONCLUSIONS

Wearable sensors recorded movement quantity and kinematic characteristics in a treated infant with SMA (2 copies SMN2). These movement parameters were consistently different compared anecdotally with published data from infants with typical development, demonstrating their potential to add unique and complementary information to the assessment of motor function in SMA.

RECOMMENDATIONS

Larger longitudinal studies are needed to determine the utility of wearable sensors as an assessment tool and an early predictor of motor outcomes in children with SMA.

Respiratory outcome of spinal muscular atrophy type 1 patients treated with nusinersen

BACKGROUND

Respiratory failure is the leading cause of mortality in spinal muscular atrophy type 1 (SMA1) children. The current study aims to evaluate the effect of nusinersen treatment on respiratory outcome of the patients with SMA1.

METHODS

In this retrospective, single-center study, 52 SMA1 patients treated with nusinersen were included in the analysis. Patients were divided into two groups based on their age at the time of their first nusinersen treatment (Group 1: ≤6 months, Group 2: >6 months). Respiratory outcome on the 180th day of treatment is defined as the type of ventilation support (spontaneous breathing, noninvasive ventilation (NIV), and tracheostomized or intubated on invasive mechanical ventilation). Demographic data, respiratory outcome, and Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders scores were obtained from medical records.

RESULTS

On the 180th day of treatment, 46 of the 52 (88.4%) children were alive. Prevalence of the mortality was similar in both groups (P = 0.65). The comparison of respiratory outcome in patients between group 1 and group 2 was as follows: spontaneous breathing, 7 (43.7%) versus 4 (13.3%) (P = 0.03); NIV <16 h/day, 3 (18.7%) versus 4 (13.3%) (P = 0.68); invasive mechanical ventilation, 6 (37.5%) versus 22 (73.3%) (P = 0.01). There were no patients using NIV ≥16 h/day. There were significant improvements in Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders scores of the patients at day 180 in comparison with the baseline (P < 0.001).

CONCLUSIONS

Early initiation of nusinersen treatment in SMA1 patients may alter the disease's natural course.

Newborn Screening for 5q Spinal Muscular Atrophy: Comparisons between Real-Time PCR Methodologies and Cost Estimations for Future Implementation Programs

Since the approval of modifying therapies for Spinal Muscular Atrophy (SMA), several protocols aiming to screen SMN1 homozygous deletion in a neonatal context have been published. However, no work has compared different methodologies along with detailed implementation costs for centers where the neonatal screening of SMA has not yet been implemented. Therefore, our work compared different qualitative real-time PCR approaches for SMA screening and the estimated costs of test implementation. Using Brazilian blood samples, the presence and absence (P/A) and melt curve protocols were analyzed. MLPA was used as a confirmatory test. The costs were calculated for the simplex and multiplex tests plus equipment. The test workflow was based on the present experience and literature report. The accuracy of the P/A protocol was 1 (95% CI 0.8677-1) using dried blood spots (DBS). The melt curve protocol also achieved 100% concordance. The consumable costs ranged from USD 1.68 to 4.42 and from USD 2.04 to 12.76 per reaction, for the simplex and multiplex tests, respectively. The equipment acquisition costs ranged from USD 44,817.07 to 467,253.10, with several factors influencing this value presented. Our work presents a framework for decision-making, with a project demonstration of the different assays that will be useful in dealing with the issues of cost and availability of reagents. Moreover, we present a literature review and discussion of important concerns regarding treatment policies. We take the first step towards a future SMA NBS pilot program where it is not yet a reality.

Natural history in spinal muscular atrophy Type I in Taiwanese population: A longitudinal study

INTRODUCTION

Spinal muscular atrophy (SMA) is caused by a defect in the survival motor neuron 1 (SMN1) gene. The Cooperative Study of the natural history of SMA Type I in Taiwan is a retrospective, longitudinal, observational study that helps in further understanding SMA disease progression in patients who have not received disease-modifying therapeutic interventions.

METHODS

Case report forms were used to collect demographics; genetic confirmation; SMN2 copy number; treatment patterns; and clinical outcomes including ventilator use, endotracheal tube intubation, tracheostomy, gastrostomy, complications, and survival.

RESULTS

A total of 111 patients with SMA Type I were identified over the study period (1979-2015). Mean (median) age of onset and age at confirmed diagnosis were 1.3 (0.8) and 4.9 (4.4) months, respectively. SMN1 deletion/mutation was documented in 70 patients and SMN2 copy number in 32 (2 copies, n = 20; 3 copies, n = 12). At 240 months, survival probability for patients born during 1995-2015 versus 1979-1994 was significantly longer (p = 0.0057). Patients with 3 SMN2 copies showed substantially longer 240-month survival versus patients with 2 SMN2 copies. Over the 36-year period, mean (median) age at death was 31.9 (8.8) months. As of December 2015, 95 patients had died, 13 were alive, and 3 were lost to follow-up. The use of supportive measures (tracheostomy and gastrostomy) was associated with improved survival.

CONCLUSIONS

These data describe the short survival of patients with SMA Type I in Taiwan in the pretreatment era, emphasizing the positive impact of supportive measures on survival.

Nusinersen safety and effects on motor function in adult spinal muscular atrophy type 2 and 3

OBJECTIVE

To retrospectively investigate safety and efficacy of nusinersen in a large cohort of adult Italian patients with spinal muscular atrophy (SMA).

METHODS

Inclusion criteria were: (1) clinical and molecular diagnosis of SMA2 or SMA3; (2) nusinersen treatment started in adult age (>18 years); (3) clinical data available at least at baseline (T0-beginning of treatment) and 6 months (T6).

RESULTS

We included 116 patients (13 SMA2 and 103 SMA3) with median age at first administration of 34 years (range 18-72). The Hammersmith Functional Rating Scale Expanded (HFMSE) in patients with SMA3 increased significantly from baseline to T6 (median change +1 point, p<0.0001), T10 (+2, p<0.0001) and T14 (+3, p<0.0001). HFMSE changes were independently significant in SMA3 sitter and walker subgroups. The Revised Upper Limb Module (RULM) in SMA3 significantly improved between T0 and T14 (median +0.5, p=0.012), with most of the benefit observed in sitters (+2, p=0.018). Conversely, patients with SMA2 had no significant changes of median HFMSE and RULM between T0 and the following time points, although a trend for improvement of RULM was observed in those with some residual baseline function. The rate of patients showing clinically meaningful improvements (as defined during clinical trials) increased from 53% to 69% from T6 to T14.

CONCLUSIONS

Our data provide further evidence of nusinersen safety and efficacy in adult SMA2 and SMA3, with the latter appearing to be cumulative over time. In patients with extremely advanced disease, effects on residual motor function are less clear.

Effect of new modalities of treatment on physicians management plan for patients with spinal muscular atrophy

Objectives:

To determine physicians’ attitudes and stated practice in the management of patients with spinal muscular atrophy (SMA). We also aimed to explore their knowledge about consensus statement for standard of care in SMA and the role of new treatment modalities in changing the method of practice in the management of these cases.

Methods:

This is a quantitative observational cross-sectional study, conducted from February to May 2017 among physicians who manage SMA patients in Kingdom of Saudi Arabia. The study cohort included pediatric neurologists, adult neurologists, and physicians of other sub-specialties who manage SMA patients. We used online and paper-based questionnaires.

Results:

Half of the 169 participants were aware of the consensus guidelines for the care of SMA patients. With regard to the newly released Nursinersen treatment protocol for SMA-diagnosed patients, half of the participants were uncertain, and the other half were hesitant about its outcomes. Junior physicians tended to be significantly more inclined to reverse the do-not-resuscitate (DNR) status of an SMA-diagnosed child than more senior physicians.

Conclusion:

Our results indicate the existence of wide differences in physician practice with children of SMA disease. Our data demonstrate a need for increased awareness of consensus guidelines and further awareness about the physician’s role in the variability of care for children with SMA.

AAV9 Vector: a Novel modality in gene therapy for spinal muscular atrophy

Spinal muscular atrophy (SMA), the leading genetic cause of infant mortality, is characterized by the deterioration of alpha motor neurons in the brainstem and spinal cord. Currently, there is no cure for SMA, which calls for an urgent need to explore affordable and effective therapies and to maximize patients' independence and quality of life. Adeno-associated virus (AAV) vector, one of the most promising and well-investigated vehicles for delivering transgenes, is a compelling candidate for gene therapy. Some of the hallmarks of AAVs are their nonpathogenicity, inability to incur an immune response, potential to achieve robust transgene expression, and varied tropism for several tissues of the body. Recently, these features were harnessed in a clinical trial conducted by AveXis in SMA patients, where AAV9 was employed as a vehicle for one-time administration of the SMN gene, the causative gene in SMA. The trial demonstrated remarkable improvements in motor milestones and rates of survival in the patients. This review focuses on the advent of SMA gene therapy and summarizes different preclinical studies that were conducted leading up to the AAV9-SMA trial in SMA patients.

Drug screening with human SMN2 reporter identifies SMN protein stabilizers to correct SMA pathology

Spinal muscular atrophy (SMA), the leading genetic cause of infant mortality, is caused by reduced levels of functional survival motor neuron (SMN) protein. To identify therapeutic agents for SMA, we established a versatile SMN2-GFP reporter line by targeting the human SMN2 gene. We then screened a compound library and identified Z-FA-FMK as a potent candidate. Z-FA-FMK, a cysteine protease inhibitor, increased functional SMN through inhibiting the protease-mediated degradation of both full-length and exon 7-deleted forms of SMN. Further studies reveal that CAPN1, CAPN7, CTSB, and CTSL mediate the degradation of SMN proteins, providing novel targets for SMA. Notably, Z-FA-FMK mitigated mitochondriopathy and neuropathy in SMA patient-derived motor neurons and showed protective effects in SMA animal model after intracerebroventricular injection. E64d, another cysteine protease inhibitor which can pass through the blood-brain barrier, showed even more potent therapeutic effects after subcutaneous delivery to SMA mice. Taken together, we have successfully established a human SMN2 reporter for future drug discovery and identified the potential therapeutic value of cysteine protease inhibitors in treating SMA via stabilizing SMN proteins.

An Integrated Safety Analysis of Infants and Children with Symptomatic Spinal Muscular Atrophy (SMA) Treated with Nusinersen in Seven Clinical Trials

BACKGROUND

Treatment with nusinersen has demonstrated significant and clinically meaningful benefits in clinical trials in infants and children with spinal muscular atrophy (SMA).

OBJECTIVE

The objective of this analysis was to characterize the safety of nusinersen across the clinical trial program in infants and children with symptomatic SMA.

METHODS

An integrated safety analysis evaluated end of study data from seven completed clinical trials that enrolled infants and children with symptomatic SMA who were treated with intrathecal nusinersen or underwent sham procedures. Two of the studies were conducted in symptomatic infants with infantile-onset SMA (most likely to develop SMA type I or II) and the remaining five in symptomatic children and adolescents with later-onset SMA (have or are most likely to develop SMA type II or III). Safety assessments included incidence of adverse events (AEs), physical and neurological examinations, vital signs, clinical laboratory tests (serum chemistry, hematology, and urinalysis), and electrocardiograms.

RESULTS

Data were analyzed from 323 infants and children, including 240 treated with nusinersen (100 with infantile-onset SMA and 140 with later-onset SMA) and 83 who underwent sham procedures (41 infantile-onset, 42 later-onset). Median (range) exposure to nusinersen was 449.0 (6-1538) days (375.9 participant-years). The most common AEs with nusinersen were pyrexia, upper respiratory tract infection, nasopharyngitis, vomiting, headache, and constipation. The incidence of serious AEs was lower with nusinersen than with the sham procedure (41% vs. 61%). The overall incidence of respiratory, thoracic, and mediastinal AEs was higher in participants with symptomatic infantile-onset SMA than those with symptomatic later-onset SMA and similar in nusinersen- versus sham procedure-treated participants. Rates of post-lumbar puncture syndrome and related events were higher with nusinersen versus sham procedure in later-onset SMA participants. No abnormal patterns or trends in laboratory test results were observed.

CONCLUSIONS

Nusinersen demonstrated a favorable safety profile in children with symptomatic infantile- and later-onset SMA. Most reported AEs and serious AEs were consistent with the nature and frequency of events typically seen with SMA or in the context of lumbar puncture procedures.

REGISTRATION

NCT01494701, NCT01703988, NCT01839656, NCT02193074, NCT02292537, NCT01780246, NCT02052791.

Seamless Genetic Conversion of SMN2 to SMN1 via CRISPR/Cpf1 and Single-Stranded Oligodeoxynucleotides in Spinal Muscular Atrophy Patient-Specific Induced Pluripotent Stem Cells

Spinal muscular atrophy (SMA) is a kind of neuromuscular disease characterized by progressive motor neuron loss in the spinal cord. It is caused by mutations in the survival motor neuron 1 (SMN1) gene. SMN1 has a paralogous gene, survival motor neuron 2 (SMN2), in humans that is present in almost all SMA patients. The generation and genetic correction of SMA patient-specific induced pluripotent stem cells (iPSCs) is a viable, autologous therapeutic strategy for the disease. Here, c-Myc-free and non-integrating iPSCs were generated from the urine cells of an SMA patient using an episomal iPSC reprogramming vector, and a unique crRNA was designed that does not have similar sequences (≤3 mismatches) anywhere in the human reference genome. In situ gene conversion of the SMN2 gene to an SMN1-like gene in SMA-iPSCs was achieved using CRISPR/Cpf1 and single-stranded oligodeoxynucleotide with a high efficiency of 4/36. Seamlessly gene-converted iPSC lines contained no exogenous sequences and retained a normal karyotype. Significantly, the SMN expression and gems localization were rescued in the gene-converted iPSCs and their derived motor neurons. This is the first report of an efficient gene conversion mediated by Cpf1 homology-directed repair in human cells and may provide a universal gene therapeutic approach for most SMA patients.

Benefits of Maxillary Expansion for a Patient With Spinal Muscular Atrophy Type 2

This case report involves a 10-yr-old boy diagnosed with spinal muscular atrophy type 2 who underwent nighttime mechanical ventilation with bilevel positive airway pressure. The oral examination revealed restricted mouth opening, lip interposition, dental crowding, and maxillary compression. After maxillary expansion, the upper airway volume increased 18.6%; 13 episodes of airway infections (20 days of hospitalization) were recorded in the 2 yrs before the maxillary expansion and only 4 episodes (no hospital admissions) in the 2 subsequent years. In conclusion, maxillary expansion in children with systemic disease that involves respiratory impairment may, in some cases, provide functional and clinical improvements, increase upper airway airflows, and possibly decrease the number of respiratory infections.

Spinal muscular atrophy

Autosomal-recessive proximal spinal muscular atrophy (Werdnig-Hoffmann, Kugelberg-Welander) is caused by mutation of the SMN1 gene, and the clinical severity correlates with the number of copies of a nearly identical gene, SMN2. The SMN protein plays a critical role in spliceosome assembly and may have other cellular functions, such as mRNA transport. Cell culture and animal models have helped to define the disease mechanism and to identify targets for therapeutic intervention. The main focus for developing treatment has been to increase SMN levels, and accomplishing this with small molecules, oligonucleotides, and gene replacement has been quite. An oligonucleotide, nusinersen, was recently approved for treatment in patients, and confirmatory studies of other agents are now under way.

Self-oligomerization regulates stability of survival motor neuron protein isoforms by sequestering an SCFSlmb degron

Spinal muscular atrophy (SMA) is caused by homozygous mutations in human SMN1 Expression of a duplicate gene (SMN2) primarily results in skipping of exon 7 and production of an unstable protein isoform, SMNΔ7. Although SMN2 exon skipping is the principal contributor to SMA severity, mechanisms governing stability of survival motor neuron (SMN) isoforms are poorly understood. We used a Drosophila model system and label-free proteomics to identify the SCFSlmb ubiquitin E3 ligase complex as a novel SMN binding partner. SCFSlmb interacts with a phosphor degron embedded within the human and fruitfly SMN YG-box oligomerization domains. Substitution of a conserved serine (S270A) interferes with SCFSlmb binding and stabilizes SMNΔ7. SMA-causing missense mutations that block multimerization of full-length SMN are also stabilized in the degron mutant background. Overexpression of SMNΔ7S270A, but not wild-type (WT) SMNΔ7, provides a protective effect in SMA model mice and human motor neuron cell culture systems. Our findings support a model wherein the degron is exposed when SMN is monomeric and sequestered when SMN forms higher-order multimers.

Newborn genetic screening for spinal muscular atrophy in the UK: The views of the general population

Background

Spinal muscular atrophy (SMA) is an inherited neuromuscular disorder and a leading genetic cause of infant death worldwide. However, there is no routine screening program for SMA in the UK. Lack of treatments and the inability of screening tests to accurately predict disease severity are among the key reasons implementation of screening has faltered in the UK. With the recent release of the first therapy for SMA (Nusinersen), calls are being made for a reconsideration of this stance; however, very little is known about the views of the general public.

Methods

An online survey was administered to 232 individuals with no prior relationship with SMA to assess their attitudes toward a newborn screening program for it. Results are compared with previously gathered data on the views of SMA‐affected families toward screening.

Results

Eighty‐four percent of participants were in favor of newborn screening. Key reasons for support were a belief that it would lead to better healthcare and life expectancy for affected infants and facilitate informed decision‐making for future pregnancies. Key reasons for nonsupport were a belief in the potential for significant negative impact on the family unit in terms of bonding and stress.

Conclusions

Public acceptability is a key component in the evaluation of any potential screening program in the UK. This study demonstrates that newborn screening for SMA is viewed largely positively by people unfamiliar with the condition. The importance of early identification overrode all other social and ethical concerns about screening for the majority of participants.

Nusinersen versus Sham Control in Infantile-Onset Spinal Muscular Atrophy

BACKGROUND

Spinal muscular atrophy is an autosomal recessive neuromuscular disorder that is caused by an insufficient level of survival motor neuron (SMN) protein. Nusinersen is an antisense oligonucleotide drug that modifies pre-messenger RNA splicing of the SMN2 gene and thus promotes increased production of full-length SMN protein.

METHODS

We conducted a randomized, double-blind, sham-controlled, phase 3 efficacy and safety trial of nusinersen in infants with spinal muscular atrophy. The primary end points were a motor-milestone response (defined according to results on the Hammersmith Infant Neurological Examination) and event-free survival (time to death or the use of permanent assisted ventilation). Secondary end points included overall survival and subgroup analyses of event-free survival according to disease duration at screening. Only the first primary end point was tested in a prespecified interim analysis. To control the overall type I error rate at 0.05, a hierarchical testing strategy was used for the second primary end point and the secondary end points in the final analysis.

RESULTS

In the interim analysis, a significantly higher percentage of infants in the nusinersen group than in the control group had a motor-milestone response (21 of 51 infants [41%] vs. 0 of 27 [0%], P<0.001), and this result prompted early termination of the trial. In the final analysis, a significantly higher percentage of infants in the nusinersen group than in the control group had a motor-milestone response (37 of 73 infants [51%] vs. 0 of 37 [0%]), and the likelihood of event-free survival was higher in the nusinersen group than in the control group (hazard ratio for death or the use of permanent assisted ventilation, 0.53; P=0.005). The likelihood of overall survival was higher in the nusinersen group than in the control group (hazard ratio for death, 0.37; P=0.004), and infants with a shorter disease duration at screening were more likely than those with a longer disease duration to benefit from nusinersen. The incidence and severity of adverse events were similar in the two groups.

CONCLUSIONS

Among infants with spinal muscular atrophy, those who received nusinersen were more likely to be alive and have improvements in motor function than those in the control group. Early treatment may be necessary to maximize the benefit of the drug. (Funded by Biogen and Ionis Pharmaceuticals; ENDEAR ClinicalTrials.gov number, NCT02193074 .).

Clinical applications of MARSALA for preimplantation genetic diagnosis of spinal muscular atrophy

Conventional PCR methods combined with linkage analysis based on short tandem repeats (STRs) or Karyomapping with single nucleotide polymorphism (SNP) arrays, have been applied to preimplantation genetic diagnosis (PGD) for spinal muscular atrophy (SMA), an autosome recessive disorder. However, it has limitations in SMA diagnosis by Karyomapping, and these methods are unable to distinguish wild-type embryos with carriers effectively. Mutated allele revealed by sequencing with aneuploidy and linkage analyses (MARSALA) is a new method allowing embryo selection by a one-step next-generation sequencing (NGS) procedure, which has been applied in PGD for both autosome dominant and X-linked diseases in our group previously. In this study, we carried out PGD based on MARSALA for two carrier families with SMA affected children. As a result, one of the couples has given birth to a healthy baby free of mutations in SMA-causing gene. It is the first time that MARSALA was applied to PGD for SMA, and we can distinguish the embryos with heterozygous deletion (carriers) from the wild-type (normal) ones accurately through this NGS-based method. In addition, direct mutation detection allows us to identify the affected embryos (homozygous deletion), which can be regarded as probands for linkage analysis, in case that the affected family member is absent. In the future, the NGS-based MARSALA method is expected to be used in PGD for all monogenetic disorders with known pathogenic gene mutation.

Understanding the experiences and needs of individuals with Spinal Muscular Atrophy and their parents: a qualitative study

BACKGROUND

The clinical features of SMA, which range along a spectrum of severity, are relatively well described. In contrast, the literature on how individuals with SMA and their families experience this condition is limited. To address this gap, we undertook a qualitative study with individuals affected by SMA Types I, II and III, parents of those affected, and clinicians.

METHODS

We completed 16 focus group sessions and 37 interviews in the US with 96 participants including: 21 with individuals with SMA; 64 parents of individuals affected by SMA; and 11 clinicians who specialize in the care of SMA patients.

RESULTS

The Diagnostic Journey: Families reported substantial diagnostic delays owing to: 1) lack of awareness and knowledge about SMA; 2) the difficulty of distinguishing normal from abnormal development; and 3) the challenge of differential diagnosis. Lack of sensitivity in how clinicians communicated this potentially devastating diagnosis compounded parents' negative impressions. Newborn Screening: Parents generally held positive views about adding SMA to newborn screening panels. For example, it would: 1) enable earlier access to care; 2) shorten the diagnostic journey; and 3) give families more time to prepare to care for a disabled child. Some noted negative outcomes such as prematurely affecting a parent's relationship with a child before symptoms are evident. The Psychosocial Impact of Living with SMA: Ten thematic areas characterized the impact: 1) confronting premature death; 2) making difficult treatment choices; 3) fearing the loss of functional ability; 4) coming to terms with lost expectations; 5) loss of sleep and stress; 6) stigma; 7) limitations on social activities; 8) independence; 9) uncertainty and helplessness; and 10) family finances.

CONCLUSIONS

The results of this study suggest high levels of burden experienced by individuals with SMA and their families. The difficulties of living with SMA begin with the long and often arduous process of finding a diagnosis for their child. Newborn screening for SMA is seen as an important step toward shortening this journey. The psychosocial effects of coping with SMA are substantial and wide ranging both for the individual living with this condition and family members of affected individuals.

Delay in Diagnosis of Spinal Muscular Atrophy: A Systematic Literature Review

BACKGROUND

Spinal muscular atrophy is a rare genetic disease with devastating neurodegenerative consequences. Timing of diagnosis is crucial for spinal muscular atrophy because early diagnosis may lead to early supportive care and reduction in patient and caregiver stress. The purpose of this study was to examine the published literature for diagnostic delay in spinal muscular atrophy.

METHODS

A systematic literature search was conducted in the PubMed and Web of Science databases for studies published between 2000 and 2014 that listed any type of spinal muscular atrophy and without molecular, mouse, or pathology in the keywords. Mean and/or median age of onset and diagnosis and delay in diagnosis was extracted or calculated. All estimates were weighted by the number of patients and descriptive statistics are reported.

RESULTS

A total of 21 studies were included in the final analysis. The weighted mean (standard deviation) ages of onset were 2.5 (0.6), 8.3 (1.6), and 39.0 (32.6) months for spinal muscular atrophy types I, II, and III, respectively, and the weighted mean (standard deviation) ages of confirmed spinal muscular atrophy genetic diagnosis were 6.3 (2.2), 20.7 (2.6), and 50.3 (12.9) months, respectively, for types I, II, and III. For studies reporting both age of onset and diagnosis, the weighted diagnostic delay was 3.6, 14.3, and 43.6 months for types I, II, and III, respectively.

CONCLUSIONS

Diagnostic delay is common in spinal muscular atrophy. The length of delay varied by severity (type) of spinal muscular atrophy. Further studies evaluating this delay and tools such as newborn screening are warranted to end the diagnostic delay in spinal muscular atrophy.

Newborn blood spot screening test using multiplexed real-time PCR to simultaneously screen for spinal muscular atrophy and severe combined immunodeficiency

BACKGROUND

Spinal muscular atrophy (SMA) is a motor neuron disorder caused by the absence of a functional survival of motor neuron 1, telomeric (SMN1) gene. Type I SMA, a lethal disease of infancy, accounts for the majority of cases. Newborn blood spot screening (NBS) to detect severe combined immunodeficiency (SCID) has been implemented in public health laboratories in the last 5 years. SCID detection is based on real-time PCR assays to measure T-cell receptor excision circles (TREC), a byproduct of T-cell development. We modified a multiplexed real-time PCR TREC assay to simultaneously determine the presence or absence of the SMN1 gene from a dried blood spot (DBS) punch in a single reaction well.

METHOD

An SMN1 assay using a locked nucleic acid probe was initially developed with cell culture and umbilical cord blood (UCB) DNA extracts, and then integrated into the TREC assay. DBS punches were placed in 96-well arrays, washed, and amplified directly using reagents specific for TREC, a reference gene [ribonuclease P/MRP 30kDa subunit (RPP30)], and the SMN1 gene. The assay was tested on DBS made from UCB units and from peripheral blood samples of SMA-affected individuals and their family members.

RESULTS

DBS made from SMA-affected individuals showed no SMN1-specific amplification, whereas DBS made from all unaffected carriers and UCB showed SMN1 amplification above a well-defined threshold. TREC and RPP30 content in all DBS were within the age-adjusted expected range.

CONCLUSIONS

SMA caused by the absence of SMN1 can be detected from the same DBS punch used to screen newborns for SCID.

Respiratory muscle function in infants with spinal muscular atrophy type I

OBJECTIVE

To determine the feasibility and safety of respiratory muscle function testing in weak infants with a progressive neuromuscular disorder.

RATIONALE

Respiratory insufficiency is the major cause of morbidity and mortality in infants with spinal muscular atrophy type I (SMA-I).

HYPOTHESIS

Tests of respiratory muscle strength, endurance, and breathing patterns can be performed safely in SMA-I infants. Useful data can be collected which parallels the clinical course of pulmonary function in SMA-I.

STUDY DESIGN AND SUBJECT SELECTION

An exploratory study of respiratory muscle function testing and breathing patterns in seven infants with SMA-I seen in our neuromuscular clinic. Measurements were made at initial study visit and, where possible, longitudinally over time.

METHODOLOGY

We measured maximal inspiratory (MIP) and transdiaphragmatic pressures, mean transdiaphragmatic pressure, airway occlusion pressure at 100 msec of inspiration, inspiratory and total respiratory cycle time, and aspects of relative thoracoabdominal motion using respiratory inductive plethysmography (RIP). The tension time index of the diaphragm and of the respiratory muscles, phase angle (Φ), phase relation during the total breath, and labored breathing index were calculated.

RESULTS

Age at baseline study was 54-237 (median 131) days. Reliable data were obtained safely for MIP, phase angle, labored breathing index, and the invasive and non-invasive tension time indices, even in very weak infants. Data obtained corresponded to the clinical estimate of severity and predicted the need for respiratory support.

CONCLUSIONS

The testing employed was both safe and feasible. Measurements of MIP and RIP are easily performed tests that are well tolerated and provide clinically useful information for infants with SMA-I.

Molecular, genetic and stem cell-mediated therapeutic strategies for spinal muscular atrophy (SMA)

Spinal muscular atrophy (SMA) is an autosomal recessive motor neuron disease. It is the first genetic cause of infant mortality. It is caused by mutations in the survival motor neuron 1 (SMN1) gene, leading to the reduction of SMN protein. The most striking component is the loss of alpha motor neurons in the ventral horn of the spinal cord, resulting in progressive paralysis and eventually premature death. There is no current treatment other than supportive care, although the past decade has seen a striking advancement in understanding of both SMA genetics and molecular mechanisms. A variety of disease modifying interventions are rapidly bridging the translational gap from the laboratory to clinical trials. In this review, we would like to outline the most interesting therapeutic strategies that are currently developing, which are represented by molecular, gene and stem cell-mediated approaches for the treatment of SMA.

Molecular therapeutic strategies for spinal muscular atrophies: current and future clinical trials

BACKGROUND

Spinal muscular atrophy (SMA) is an autosomal recessive motor neuron disease caused by mutations in the survival motor neuron gene (SMN1) and the leading genetic cause of infant mortality. Currently, there is no effective treatment other than supportive care.

OBJECTIVE

This article provides a general overview of the main aspects that need to be taken into account to design a more efficient clinical trial and to summarize the most promising molecular trials that are currently in development or are being planned for the treatment of SMA.

METHODS

A systematic review of the literature was performed, identifying key clinical trials involving novel molecular therapies in SMA. In addition, abstracts presented at the meetings of the Families of Spinal Muscular Atrophy were searched and the Families of Spinal Muscular Atrophy Web site was carefully analyzed. Finally, a selection of SMA clinical trials registered at clinical-trials.gov has been included in the article.

RESULTS

The past decade has seen a marked advancement in the understanding of both SMA genetics and molecular mechanisms. New molecules targeting SMN have shown promise in preclinical studies, and various clinical trials have started to test the drugs that were discovered through basic research.

CONCLUSIONS

Both preclinical and early clinical trial results involving novel molecular therapies suggest that the clinical care paradigm in SMA will soon change.

Solving the puzzle of spinal muscular atrophy: what are the missing pieces?

Spinal muscular atrophy (SMA) is an autosomal recessive, lower motor neuron disease. Clinical heterogeneity is pervasive: three infantile (type I-III) and one adult-onset (type IV) forms are recognized. Type I SMA is the most common genetic cause of death in infancy and accounts for about 50% of all patients with SMA. Most forms of SMA are caused by mutations of the survival motor neuron (SMN1) gene. A second gene that is 99% identical to SMN1 (SMN2) is located in the same region. The only functionally relevant difference between the two genes identified to date is a C → T transition in exon 7 of SMN2, which determines an alternative spliced isoform that predominantly excludes exon 7. Thus, SMN2 genes do not produce sufficient full length SMN protein to prevent the onset of the disease. Since the identification of the causative mutation, biomedical research of SMA has progressed by leaps and bounds: from clues on the function of SMN protein, to the development of different models of the disease, to the identification of potential treatments, some of which are currently in human trials. The aim of this review is to elucidate the current state of knowledge, emphasizing how close we are to the solution of the puzzle that is SMA, and, more importantly, to highlight the missing pieces of this puzzle. Filling in these gaps in our knowledge will likely accelerate the development and delivery of efficient treatments for SMA patients and be a prerequisite towards achieving our final goal, the cure of SMA.

Genetic testing of sperm donors for cystic fibrosis and spinal muscular atrophy: evaluation of clinical utility

OBJECTIVE

To evaluate the clinical utility of genetic testing for cystic fibrosis (CF) and spinal muscular atrophy (SMA) in sperm donors.

STUDY DESIGN

We studied the results of the genetic tests for CF and SMA applied to 372 sperm donor candidates. The CF carrier screening test analysed 32 mutations on the CFTR gene. Regarding SMA, the carrier test studied possible deletions of SMN1/2 by Multiplex Ligation-dependent Probe Amplification (MLPA) methodology.

RESULTS

The carrier frequency obtained was greater for SMA than for CF. After adjusting the results obtained for the sensitivity of the tests, and taking into account the prevalence of female carriers in our population, the probability of transmission of the disease to the child from a donor with a negative genetic test was about five times lower in the case of SMA than in CF, although this difference was not statistically significant. The number of donors needed to screen (NNS) to avoid the occurrence of a child being affected by CF and SMA in our population was similar in both cases (1591 vs. 1536).

CONCLUSIONS

This study demonstrates the need to include SMA among the diseases for which genetic screening is performed in the process of sperm donor selection. We believe that testing donors for SMA is as important and as useful as doing so for CF.

Clinical decision making in hypotonia and gross motor delay: a case report of type 1 spinal muscular atrophy in an infant

BACKGROUND AND PURPOSE

Children often are referred for physical therapy with the diagnosis of hypotonia when the definitive cause of hypotonia is unknown. The purpose of this case report is to describe the clinical decision-making process using the Hypothesis-Oriented Algorithm for Clinicians II (HOAC II) for an infant with hypotonia and gross motor delay.

CASE DESCRIPTION

The patient was a 5-month-old infant who had been evaluated by a neurologist and then referred for physical therapy by his pediatrician. Physical therapist evaluation results and clinical observations of marked hypotonia, significant gross motor delay, tongue fasciculations, feeding difficulties, and respiratory abnormalities prompted necessary referral to specialists. Recognition of developmental, neurologic, and respiratory abnormalities facilitated clinical decision making for determining the appropriate physical therapy plan of care.

OUTCOMES

During the brief episode of physical therapy care, the patient was referred to a feeding specialist and diagnosed with pharyngeal-phase dysphasia and mild aspiration. Continued global weakness, signs and symptoms of type 1 spinal muscular atrophy (SMA), and concerns about increased work of breathing and respiratory compromise were discussed with the referring physician. After inconclusive laboratory testing for metabolic etiologies of hypotonia, a genetics consult was recommended and confirmed the diagnosis of type 1 SMA at 9 months of age.

DISCUSSION

Physical therapists use clinical decision making to determine whether to treat patients or to refer them to other medical professionals. Accurate and timely referral to appropriate specialists may assist families in obtaining a diagnosis for their child and guide necessary interventions. In the case of type 1 SMA, early diagnosis may affect outcomes and survival rate in this pediatric population.

Genetically modified pig models for human diseases

Genetically modified animal models are important for understanding the pathogenesis of human disease and developing therapeutic strategies. Although genetically modified mice have been widely used to model human diseases, some of these mouse models do not replicate important disease symptoms or pathology. Pigs are more similar to humans than mice in anatomy, physiology, and genome. Thus, pigs are considered to be better animal models to mimic some human diseases. This review describes genetically modified pigs that have been used to model various diseases including neurological, cardiovascular, and diabetic disorders. We also discuss the development in gene modification technology that can facilitate the generation of transgenic pig models for human diseases.

SMN-inducing compounds for the treatment of spinal muscular atrophy

Spinal muscular atrophy (SMA) is a leading genetic cause of infant mortality. A neurodegenerative disease, it is caused by loss of SMN1, although low, but essential, levels of SMN protein are produced by the nearly identical gene SMN2. While no effective treatment or therapy currently exists, a new wave of therapeutics has rapidly progressed from cell-based and preclinical animal models to the point where clinical trials have initiated for SMA-specific compounds. There are several reasons why SMA has moved relatively rapidly towards novel therapeutics, including: SMA is monogenic; the molecular understanding of SMN gene regulation has been building for nearly 20 years; and all SMA patients retain one or more copies of SMN2 that produces low levels of full-length, fully functional SMN protein. This review primarily focuses upon the biology behind the disease and examines SMN1- and SMN2-targeted therapeutics.

Spinal muscular atrophy: manifestations and management

Spinal muscular atrophy (SMA) is an autosomal recessive disorder caused by a homozygous deletion in the SMN1 gene and is manifested by loss of the anterior horn cells of the spinal cord. Classifications of the disorder are based on age of onset and the patient's level of function. Scoliosis and hip subluxation or dislocation are two musculoskeletal manifestations associated with SMA. Severity of scoliosis correlates with age at presentation. Bracing has been unsuccessful in halting curve progression and may interfere with respiratory effort. Early onset scoliosis associated with SMA has been successfully treated with growing rod constructs, and posterior spinal fusion can be used in older children. Hip subluxations and dislocations are best treated nonsurgically if the patient reports no pain because a high rate of recurrent dislocation has been reported with surgical intervention.

Carrier screening in preconception consultation in primary care

Discussing carrier screening during preconception consultation in primary care has a number of advantages in terms of promoting autonomy and enabling the greatest range of reproductive choices. For those with a family history of an inherited condition, this ought to be a routine discussion; however, this can be expanded to include the wider population, especially for those conditions for which carrier frequencies are considered relatively common. There is published literature from around the world regarding experiences with carrier screening in primary care for cystic fibrosis, haemoglobinopathies, fragile X syndrome, Tay-Sachs disease and spinal muscular atrophy, although many of these have tended to focus on consultations during rather than before pregnancy. Overall, these studies reveal that population carrier screening is well received by the participants with apparent minimal psychosocial harms; however, challenges exist in terms of approaches to ensure couples receive adequate information to make personally relevant decisions and for ongoing health professional engagement.