Treatment Algorithm for Infants Diagnosed with Spinal Muscular Atrophy through Newborn Screening

Advances in Treatment of Spinal Muscular Atrophy - New Phenotypes, New Challenges, New Implications for Care

Spinal Muscular Atrophy (SMA) is caused by autosomal recessive mutations in SMN1 and results in the loss of motor neurons and progressive muscle weakness. The spectrum of disease severity ranges from early onset with respiratory failure during the first months of life to a mild, adult-onset type with slow rate of progression. Over the past decade, new treatment options such as splicing modulation of SMN2 and SMN1 gene replacement by gene therapy have been developed. First drugs have been approved for treatment of patients with SMA and if initiated early they can significantly modify the natural course of the disease. As a consequence, newborn screening for SMA is explored and implemented in an increasing number of countries. However, available evidence for these new treatments is often limited to a small spectrum of patients concerning age and disease stage. In this review we provide an overview of available and emerging therapies for spinal muscular atrophy and we discuss new phenotypes and associated challenges in clinical care. Collection of real-world data with standardized outcome measures will be essential to improve both the understanding of treatment effects in patients of all SMA subtypes and the basis for clinical decision-making in SMA.

Spinal Muscular Atrophy Diagnosed by Newborn Screening

A panel of experts representing academic centers, family foundations and pharmaceutical industry came together to formulate a treatment algorithm for infants diagnosed via newborn screening (NBS) with Spinal muscular atrophy (SMA).

A Novel System for Spinal Muscular Atrophy Screening in Newborns: Japanese Pilot Study

Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by SMN1 gene deletion/mutation. The drug nusinersen modifies SMN2 mRNA splicing, increasing the production of the full-length SMN protein. Recent studies have demonstrated the beneficial effects of nusinersen in patients with SMA, particularly when treated in early infancy. Because nusinersen treatment can alter disease trajectory, there is a strong rationale for newborn screening. In the current study, we validated the accuracy of a new system for detecting SMN1 deletion (Japanese patent application No. 2017-196967, PCT/JP2018/37732) using dried blood spots (DBS) from 50 patients with genetically confirmed SMA and 50 controls. Our system consists of two steps: (1) targeted pre-amplification of SMN genes by direct polymerase chain reaction (PCR) and (2) detection of SMN1 deletion by real-time modified competitive oligonucleotide priming-PCR (mCOP-PCR) using the pre-amplified products. Compared with PCR analysis results of freshly collected blood samples, our system exhibited a sensitivity of 1.00 (95% confidence interval [CI] 0.96-1.00) and a specificity of 1.00 (95% CI 0.96-1.00). We also conducted a prospective SMA screening study using DBS from 4157 Japanese newborns. All DBS tested negative, and there were no screening failures. Our results indicate that the new system can be reliably used in SMA newborn screening.

The Effectiveness and Value of Treatments for Spinal Muscular Atrophy

DISCLOSURES

Funding for this summary was contributed by the Laura and John Arnold Foundation and California Health Care Foundation to the Institute for Clinical and Economic Review (ICER), an independent organization that evaluates the evidence on the value of health care interventions. ICER's annual policy summit is supported by dues from Aetna, AHIP, Anthem, Blue Shield of California, CVS Caremark, Express Scripts, Harvard Pilgrim Health Care, Cambia Health Solutions and MedSavvy, United Healthcare, Kaiser Permanente, Premera Blue Cross, AstraZeneca, Genentech, GlaxoSmithKline, Johnson & Johnson, Merck, National Pharmaceutical Council, Sanofi, Alnylam, Novartis, HealthPartners, Blue Cross Blue Shield of Massachusetts, Health Care Services Corporation, Mallinkrodt Pharmaceuticals, Prime Therapeutics, Regeneron, National Institute for Health Care Management, Commonwealth Fund, Partners Healthcare, New England States Consortium Systems, Allergan, Biogen, Editas, LEO Pharma, and HealthFirst. ICER has also received grants from Kaiser Foundation Health Plan, California Health Care Foundation, and the Laura and John Arnold Foundation. Pearson and Rind are employees of ICER. Thokala and Stevenson have no potential conflicts of interest to disclose.

Molecular based newborn screening in Germany: Follow-up for cystinosis

BACKGROUND

Newborn screening (NBS) programs for treatable metabolic disorders have been enormously successful, but molecular-based screening has not been broadly implemented so far.

METHODS

This prospective pilot study was performed within the German NBS framework. DNA, extracted from dried blood cards was collected as part of the regular NBS program. As cystinosis has a prevalence of only 1:100,000-1:200,000, a molecular genetic assay for detection of the SMN1 gene mutation with a higher prevalence was also included in the screening process, a genetic defect that leads to spinal muscular atrophy (SMA). First tier multiplex PCR was employed for both diseases. The cystinosis screening employed assays for the three most common CTNS mutations covering 75% of German patients; in case of heterozygosity for one of these mutations, samples were screened by next generation sequencing (NGS) of the CTNS exons for 101 CTNS mutations. A detection rate of 98.5% is predicted using this approach.

RESULTS

Between January 15, 2018 and May 31, 2019, 257,734 newborns were screened in Germany for cystinosis. One neonate was diagnosed with cystinosis, consistent with the known incidence of the disease. No false positive or false negatives were detected so far. Screening, communication of findings to parents, and confirmation of diagnosis were accomplished in a multi-disciplinary setting. This program was accomplished with the cooperation of hospitals, physicians, and parents. In the neonate diagnosed with cystinosis, oral cysteamine treatment began on day 18. After 16 months of treatment the child has no clinical signs of renal tubular Fanconi syndrome.

CONCLUSIONS

This pilot study demonstrates the efficacy of a molecular-based neonatal screening program for cystinosis using an existing national screening framework.

244th ENMC international workshop: Newborn screening in spinal muscular atrophy May 10-12, 2019, Hoofdorp, The Netherlands

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Age-dependent SMN expression in disease-relevant tissue and implications for SMA treatment

BACKGROUNDSpinal muscular atrophy (SMA) is caused by deficient expression of survival motor neuron (SMN) protein. New SMN-enhancing therapeutics are associated with variable clinical benefits. Limited knowledge of baseline and drug-induced SMN levels in disease-relevant tissues hinders efforts to optimize these treatments.METHODSSMN mRNA and protein levels were quantified in human tissues isolated during expedited autopsies.RESULTSSMN protein expression varied broadly among prenatal control spinal cord samples, but was restricted at relatively low levels in controls and SMA patients after 3 months of life. A 2.3-fold perinatal decrease in median SMN protein levels was not paralleled by comparable changes in SMN mRNA. In tissues isolated from nusinersen-treated SMA patients, antisense oligonucleotide (ASO) concentration and full-length (exon 7 including) SMN2 (SMN2-FL) mRNA level increases were highest in lumbar and thoracic spinal cord. An increased number of cells showed SMN immunolabeling in spinal cord of treated patients, but was not associated with an increase in whole-tissue SMN protein levels.CONCLUSIONSA normally occurring perinatal decrease in whole-tissue SMN protein levels supports efforts to initiate SMN-inducing therapies as soon after birth as possible. Limited ASO distribution to rostral spinal and brain regions in some patients likely limits clinical response of motor units in these regions for those patients. These results have important implications for optimizing treatment of SMA patients and warrant further investigations to enhance bioavailability of intrathecally administered ASOs.FUNDINGSMA Foundation, SMART, NIH (R01-NS096770, R01-NS062869), Ionis Pharmaceuticals, and PTC Therapeutics. Biogen provided support for absolute real-time RT-PCR.

Nusinersen initiated in infants during the presymptomatic stage of spinal muscular atrophy: Interim efficacy and safety results from the Phase 2 NURTURE study

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NURTURE is an ongoing study of nusinersen started in a presymptomatic stage of SMA.

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All infants were ≥25 months old, and alive without permanent ventilation.

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All infants achieved independent sitting and 88% (22/25) were walking alone.

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Nusinersen demonstrated durability of effect with a median 2.9 years of follow up.

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Nusinersen was well tolerated with no new safety concerns over extended follow up.

Spinal muscular atrophy (SMA) is a neurodegenerative disease associated with severe muscle atrophy and weakness in the limbs and trunk. We report interim efficacy and safety outcomes as of March 29, 2019 in 25 children with genetically diagnosed SMA who first received nusinersen in infancy while presymptomatic in the ongoing Phase 2, multisite, open-label, single-arm NURTURE trial. Fifteen children have two SMN2 copies and 10 have three SMN2 copies. At last visit, children were median (range) 34.8 [25.7–45.4] months of age and past the expected age of symptom onset for SMA Types I or II; all were alive and none required tracheostomy or permanent ventilation. Four (16%) participants with two SMN2 copies utilized respiratory support for ≥6 h/day for ≥7 consecutive days that was initiated during acute, reversible illnesses. All 25 participants achieved the ability to sit without support, 23/25 (92%) achieved walking with assistance, and 22/25 (88%) achieved walking independently. Eight infants had adverse events considered possibly related to nusinersen by the study investigators. These results, representing a median 2.9 years of follow up, emphasize the importance of proactive treatment with nusinersen immediately after establishing the genetic diagnosis of SMA in presymptomatic infants and emerging newborn screening efforts.

[Treatment evaluation in patients with 5q-associated spinal muscular atrophy : Real-world experience]

Spinal muscular atrophy (SMA) is a progressive autosomal recessive neurodegenerative disease with an incidence of 1:10,000 live births. With a deeper understanding of the molecular basis of SMA in the past two decades, a major focus of therapeutic development has been on increasing the proportion of functionally capable SMN protein by increasing the inclusion of exon 7 in SMN2 transcripts, enhancing SMN2 gene expression, stabilizing the SMN protein or replacing the SMN1 gene. Since June 2017, the antisense oligonucleotide nusinersen/Spinraza® (Biogen GmbH, Ismaning, Germany) has been approved for 5qSMA treatment. Nusinersen modifies premessenger RNA splicing of exon 7, leading to stable SMN protein expression and for the first time an effective disease-modifying treatment is available. In several controlled trials nusinersen showed a favorable benefit-risk profile along with clinically relevant improvements in motor function. The efficacy was most pronounced in presymptomatic patients, which underlines the necessity for a newborn screening program and is the key to start efficient treatment prior to motor neuron death. The repeated intrathecal administration of nusinersen is associated with practical challenges, in particular for patients with severe scoliosis or after spinal straightening surgery. As the vast majority of SMA patients were outside previous study populations regarding age and disease duration, experts complained about a lack of data on efficacy and safety beyond childhood. To fill these gaps a systematic data collection has been initiated by the SMArtCARE initiative, aiming at collecting comprehensive data in the clinical routine, regardless of the patients' individual treatment regimen.

Biomarkers and the Development of a Personalized Medicine Approach in Spinal Muscular Atrophy

Recent unprecedented advances in treatment for spinal muscular atrophy (SMA) enabled patients to access the first approved disease modifying therapy for the condition. There are however many uncertainties, regarding timing of treatment initiation, response to intervention, treatment effects and long-term outcomes, which are complicated by the evolving phenotypes seen in the post-treatment era for patients with SMA. Biomarkers of disease, with diagnostic, prognostic, predictive, and pharmacodynamic value are thus urgently required, to facilitate a wider understanding in this dynamic landscape. A spectrum of these candidate biomarkers, will be evaluated in this review, including genetic, epigenetic, proteomic, electrophysiological, and imaging measures. Of these, SMN2 appears to be the most significant modifier of phenotype to date, and its use in prognostication shows considerable clinical utility. Longitudinal studies in patients with SMA highlight an emerging role of circulatory markers such as neurofilament, in tracking disease progression and response to treatment. Furthermore, neurophysiological biomarkers such as CMAP and MUNE values show considerable promise in the real word setting, in following the dynamic response and output of the motor unit to therapeutic intervention. The specific value for these possible biomarkers across diagnosis, prognosis, prediction of treatment response, efficacy, and safety will be central to guide future patient-targeted treatments, the design of clinical trials, and understanding of the pathophysiological mechanisms of disease and intervention.

High-throughput genetic newborn screening for spinal muscular atrophy by rapid nucleic acid extraction from dried blood spots and 384-well qPCR

Establishing nucleic acid-based assays for genetic newborn screening (NBS) provides the possibility to screen for genetically encoded diseases like spinal muscular atrophy (SMA), best before the onset of symptoms. Such assays should be easily scalable to 384-well reactions that make the screening of up to 2000 samples per day possible. We developed a test procedure based on a cleanup protocol for dried blood spots and a quantitative (q)PCR to screen for a homozygous deletion of exon 7 of the survival of motor neuron 1 gene (SMN1) that is responsible for >95% of SMA patients. Performance of this setup is evaluated in detail and tested on routine samples. Our cleanup method for nucleic acids from dried blood spots yields enough DNA for diverse subsequent qPCR applications. To date, we have applied this approach to test 213,279 samples within 18 months. Thirty patients were identified and confirmed, implying an incidence of 1:7109 for the homozygous deletion. Using our cleanup method, a rapid workflow could be established to prepare nucleic acids from dried blood spot cards. Targeting the exon 7 deletion, no invalid, false-positive, or false-negative results were reported to date. This allows timely identification of the disease and grants access to the recently introduced treatment options, in most cases before the onset of symptoms. Carriers are not identified, thus, there are no concerns of whether to report them.

"Be an ambassador for change that you would like to see": a call to action to all stakeholders for co-creation in healthcare and medical research to improve quality of life of people with a neuromuscular disease

Background

Patient and public involvement for co-creation is increasingly recognized as a valuable strategy to develop healthcare research targeting patients’ real needs. However, its practical implementation is not as advanced and unanimously accepted as it could be, due to cultural differences and complexities of managing healthcare programs and clinical studies, especially in the rare disease field.

Main body

The European Neuromuscular Centre, a European foundation of patient organizations, involved its key stakeholders in a special workshop to investigate the position of the neuromuscular patient community with respect to healthcare and medical research to identify and address gaps and bottlenecks. The workshop took place in Milan (Italy) on January 19–20, 2018, involving 45 participants who were mainly representatives of the patient community, but also included experts from clinical centers, industry and regulatory bodies. In order to provide practical examples and constructive suggestions, specific topics were identified upfront. The first set of issues concerned the quality of life at specific phases of a patient’s life, such as at the time of diagnosis or during pediatric to adult transition, and patient involvement in medical research on activities in daily living including patient reported outcome measures. The second set of issues concerned the involvement of patients in the management of clinical research tools, such as registries and biobanks, and their participation in study design or marketing authorization processes. Introductory presentations were followed by parallel working group sessions, to gain constructive contributions from all participants. The concept of shared decision making was used to ensure, in discussions, a partnership-based identification of the wishes and needs of all stakeholders involved, and the “ladder of participation” tool served as a model to evaluate the actual and the desired level of patients’ involvement in all topics addressed. A general consensus on the outcome of the meeting was collected during the final plenary session.

This paper reports the outcome of the workshop and the specific suggestions derived from the analysis of the first set of topics, related to quality of life. The outcomes of the second set of topics are reported elsewhere and are only briefly summarized herein for the sake of completeness.

Conclusions

The neuromuscular community proved to be very active and engaged at different levels in the healthcare initiatives of interest. The workshop participants critically discussed several topics, providing practical examples where different stakeholders could play a role in making a change and bridging gaps. Overall, they indicated the need for education of all stakeholders for better communication, where everyone should become an ambassador to promote real change. Support should also come from institutions and healthcare bodies both at structural and economic level.

Validation of a Fast, Robust, Inexpensive, Two-Tiered Neonatal Screening Test algorithm on Dried Blood Spots for Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is one of the leading genetic causes of infant mortality with an incidence of 1:10,000. The recently-introduced antisense oligonucleotide treatment improves the outcome of this disease, in particular when applied at an early stage of progression. The genetic cause of SMA is, in >95% of cases, a homozygous deletion of the survival motor neuron 1 (SMN1) gene, which makes the low-cost detection of SMA cases as part of newborn screening programs feasible. We developed and validated a new SALSA MC002 melting curve assay that detects the absence of the SMN1 exon 7 DNA sequence without detecting asymptomatic carriers and reliably discriminates SMN1 from its genetic homolog SMN2 using crude extracts from newborn screening cards. Melting curve analysis shows peaks specific for both the SMN1 gene and the disease modifying SMN2 homolog. The detection of the SMN2 homolog, of which the only clinically relevant difference from the SMN1 gene is a single nucleotide in exon 7, was only used to confirm a correct reaction in samples that lacked the SMN1 gene, and not for SMN2 quantification. We retrieved 47 DBS samples from children with genetically-confirmed SMA, after informed consent from parents, and 375 controls from the national archive of the Dutch National Institute for Public Health and the Environment (RIVM). The assay correctly identified all anonymized and randomized SMA and control samples (i.e., sensitivity and specificity of 100%), without the detection of carriers, on the three most commonly-used PCR platforms with melting curve analysis. This test's concordance with the second-tier 'golden standard' P021 SMA MLPA test was 100%. Using the new P021-B1 version, crude extracts from DBS cards could also be used to determine the SMN2 copy number of SMA patients with a high level of accuracy. The MC002 test showed the feasibility and accuracy of SMA screening in a neonatal screening program.

Evaluating Benefit-risk Decision-making in Spinal Muscular Atrophy: A First-ever Study to Assess Risk Tolerance in the SMA Patient Community

PURPOSE

Patients' perceptions of benefit-risk are essential to informing the regulatory process and the context in which potential therapies are evaluated. To bring this critical information to regulators, Cure SMA launched a first-ever Benefit-Risk Survey for spinal muscular atrophy (SMA) to characterize decision-making and benefit-risk trade-offs in SMA associated with a potential therapy. We hypothesized that risk tolerance would be correlated with SMA type/severity and disease progression. This article presents the results of a benefit-risk survey to enhance understanding of how patients with SMA and caregivers evaluate specific benefits and risks associated with potential therapies.

METHODS

Affected adults, representing all SMA types (I-IV) within the Cure SMA database, and caregivers of affected individuals of all ages/types were invited via e-mail to participate. Best-worst scaling (BWS) was used to assess participants' priorities on benefit-risk trade-offs, as it provides higher discrimination and importance scaling among tested attributes. Twelve potentially clinically meaningful treatment benefits and 11 potential risks (ranging in severity and immediacy) were tested. Multiple factors were correlated with individual responses, including: SMA type/disease severity, stage of disease, respondent type, sex, and quality of life/level of independence (current and expected). Survey respondents were also evaluated for "risk-taking attitudes."

FINDINGS

A total of 298 responses were evaluated (28% affected adults and 72% caregivers, mostly parents). Most respondents were diagnosed >5 years ago (67.3%), with 22.1% SMA type I, 45.6% SMA type II, and 27.9% SMA type III. No strong correlation was found between risk tolerance and SMA type, stage of disease progression, respondent type, sex, quality of life assessment, or rated levels of independence. Irrespective of SMA type, respondents consistently rated the following risks, associated with a potential treatment, as "least tolerable": life-threatening allergic reactions; 1 in 1000 risk of life-threatening side effects leading to possible organ failure; or worsening quality of life. Furthermore, all SMA type respondents rated these risks as "most tolerable": invasive mode of treatment administration (including need for general anesthesia); side effect of dizziness; and other common side effects such as nausea, vomiting, loss of appetite, headaches, back pain, or fatigue.

IMPLICATIONS

With the approval of the first SMA treatment, these findings offer a unique opportunity to assess and characterize baseline risk-tolerance in SMA against which to evaluate future SMA treatment options. Although differences had been expected in risk tolerance among respondents based on disease baseline and certain patient attributes, this was not observed. Survey results should inform future SMA drug development and benefit-risk assessments.

Perspectives in genetic counseling for spinal muscular atrophy in the new therapeutic era: early pre-symptomatic intervention and test in minors

Spinal muscular atrophy (SMA) is an autosomal-recessive neuromuscular disorder representing a continuous spectrum of muscular weakness ranging from compromised neonates to adults with minimal manifestations. Patients show homozygous absence or disease-causing variants of the SMN1 gene (−/− or 0/0) and in carriers only one copy is absent or mutated (1/0). Genetic diagnosis and counseling in SMA present several challenges, including the existence of carriers (2/0) that are undistinguishable of non-carriers (1/1) with current genetic testing methods and the report of patients (0/0) with very mild manifestations and even asymptomatic that are discovered when a full symptomatic case appears in the family. Younger asymptomatic siblings of symptomatic SMA patients are usually never tested until adolescence or adult life. However, following regulatory approval of the first tailored treatment for SMA, the prospects for care of these patients have changed. Early testing, including pre-symptomatic newborn screening and confirmation of diagnosis would change proactive measures and opportunities for therapy based in the actual landscape of new treatments. This review discusses the challenges and new perspectives of genetic counseling in SMA.

Current Treatment Options in Neurology-SMA Therapeutics

PURPOSE OF REVIEW

In this review, we discuss the clinical and genetic features of 5q spinal muscular atrophy and highlight approved and upcoming therapies.

RECENT FINDINGS

We emphasize that multidisciplinary care has been a key component of the improved quality and length of life seen in these individuals in the past decade. We discuss the evidence leading to the approval of nusinersen and the evidence leading to the anticipated approval of onasemnogene abeparvovec-xioi. Additional clinical therapies that are on the horizon are discussed and the importance of continued multidisciplinary care even after treatment is emphasized. The pursuit of therapies for spinal muscular atrophy is becoming a success story and continued development of biomarkers will allow for more informed therapeutic decision making and eventual cost-effective utilization of available therapies.

Neurofilament as a potential biomarker for spinal muscular atrophy

Objective

To evaluate plasma phosphorylated neurofilament heavy chain (pNF‐H) as a biomarker in spinal muscular atrophy (SMA).

Methods

Levels of pNF‐H were measured using the ProteinSimple^® platform in plasma samples from infants with SMA enrolled in ENDEAR (NCT02193074) and infants/children without neurological disease.

Results

Median pNF‐H plasma level was 167.0 pg/mL (7.46–7,030; n = 34) in children without SMA (aged 7 weeks–18 years) and was higher in those aged < 1 versus 1–18 years (P = 0.0002). In ENDEAR participants with infantile‐onset SMA, median baseline pNF‐H level (15,400 pg/mL; 2390–50,100; n = 117) was ~10‐fold higher than that of age‐matched infants without SMA (P < 0.0001) and ~90‐fold higher than children without SMA (P < 0.0001). Higher pretreatment pNF‐H levels in infants with SMA were associated with younger age at symptom onset, diagnosis, and first dose; lower baseline Children's Hospital of Philadelphia Infant Test of Neuromuscular Disorders score; and lower peroneal compound muscle potential amplitude. Nusinersen treatment was associated with a rapid and greater decline in pNF‐H levels: nusinersen‐treated infants experienced a steep 71.9% decline at 2 months to 90.1% decline at 10 months; sham control–treated infants declined steadily by 16.2% at 2 months and 60.3% at 10 months.

Interpretation

Plasma pNF‐H levels are elevated in infants with SMA. Levels inversely correlate with age at first dose and several markers of disease severity. Nusinersen treatment is associated with a significant decline in pNF‐H levels followed by relative stabilization. Together these data suggest plasma pNF‐H is a promising marker of disease activity/treatment response in infants with SMA.

[Association of copy number of SMN1 and SMN2 with clinical phenotypes in children with spinal muscular atrophy]

OBJECTIVE

To study the association of copy number of SMN1 and SMN2 with clinical phenotypes in children with spinal muscular atrophy (SMA).

METHODS

A total of 45 children with SMA were enrolled. Multiplex ligation-dependent probe amplification was used to measure the gene copy numbers of SMN1 and SMN2. The association of copy number of SMN1 and SMN2 with clinical phenotypes was analyzed.

RESULTS

Of the 45 children with SMA, 42 (93%) had a homozygous deletion of SMN1 exons 7 and 8, and 3 (7%) had a deletion of SMN1 exon 7 alone. No association was found between SMA clinical types and the deletion types of SMN1 exons 7 and 8 (P>0.05). There was a significant difference in the distribution of SMN2 gene copy numbers between the children with SMA and the healthy children (P<0.05). The children with SMA usually had two or three copies of SMN2 gene, while the healthy children usually had one or two copies of SMN2 gene. There was a significant difference in the distribution of SMN2 copy numbers among the children with different SMA clinical types (P<0.05). The children with two copies of SMN2 gene had a significantly lower age of onset than those with three or four copies. Most of the children with type I SMA had two or three copies of SMN2 gene. Most of the children with type II SMA had three copies of SMN2 gene. Most of the children with type III SMA had three or four copies of SMN2 gene. Children with a higher copy number of SMN2 gene tended to have an older age of onset and better motor function and clinical outcome, and there was a significant association between SMN2 gene copy number and clinical outcome (P<0.05).

CONCLUSIONS

The SMN2 gene can reduce the severity of SMA via the dosage compensation effect. SMN2 copy number is associated with the phenotype of SMA, and therefore, it can be used to predict disease severity.

[Association of copy number of SMN1 and SMN2 with clinical phenotypes in children with spinal muscular atrophy]

OBJECTIVE

To study the association of copy number of SMN1 and SMN2 with clinical phenotypes in children with spinal muscular atrophy (SMA).

METHODS

A total of 45 children with SMA were enrolled. Multiplex ligation-dependent probe amplification was used to measure the gene copy numbers of SMN1 and SMN2. The association of copy number of SMN1 and SMN2 with clinical phenotypes was analyzed.

RESULTS

Of the 45 children with SMA, 42 (93%) had a homozygous deletion of SMN1 exons 7 and 8, and 3 (7%) had a deletion of SMN1 exon 7 alone. No association was found between SMA clinical types and the deletion types of SMN1 exons 7 and 8 (P>0.05). There was a significant difference in the distribution of SMN2 gene copy numbers between the children with SMA and the healthy children (P<0.05). The children with SMA usually had two or three copies of SMN2 gene, while the healthy children usually had one or two copies of SMN2 gene. There was a significant difference in the distribution of SMN2 copy numbers among the children with different SMA clinical types (P<0.05). The children with two copies of SMN2 gene had a significantly lower age of onset than those with three or four copies. Most of the children with type I SMA had two or three copies of SMN2 gene. Most of the children with type II SMA had three copies of SMN2 gene. Most of the children with type III SMA had three or four copies of SMN2 gene. Children with a higher copy number of SMN2 gene tended to have an older age of onset and better motor function and clinical outcome, and there was a significant association between SMN2 gene copy number and clinical outcome (P<0.05).

CONCLUSIONS

The SMN2 gene can reduce the severity of SMA via the dosage compensation effect. SMN2 copy number is associated with the phenotype of SMA, and therefore, it can be used to predict disease severity.

Novel challenges in spinal muscular atrophy - How to screen and whom to treat?

In recent years, disease‐modifying and life‐prolonging therapies for spinal muscular atrophy (SMA) have been developed. However, patients are currently diagnosed with significant delay and therapies are often administered in advanced stages of motor neuron degeneration, showing limited effects. Methods to identify children in presymptomatic stages are currently evaluated in newborn screening programs. Yet, not all children develop symptoms shortly after birth raising the question whom to treat and when to initiate therapy. Finally, monitoring disease progression becomes essential to individualize management. Here, we review the literature on screening approaches, strategies to predict disease severity, and biomarkers to monitor therapy.

Prenatal aspects in spinal muscular atrophy: From early detection to early presymptomatic intervention

With the recent advances in spinal muscular atrophy therapies, the complete scenario of standard of care and following up is changing not only in the clinical field with new phenotypes emerging but also with new expectations for patients, caregivers and health providers. The actual evidence indicates that early intervention and treatment is crucial for better response and prognosis. Knowledge of the prenatal and pre-symptomatic postnatal stages of the disease are becoming essential to consider the opportunities of timely diagnosis and to decide the earliest therapeutic intervention.

Multiplex Droplet Digital PCR Method Applicable to Newborn Screening, Carrier Status, and Assessment of Spinal Muscular Atrophy

BACKGROUND

Spinal muscular atrophy (SMA) is a progressive neuromuscular disorder with neuronal degeneration leading to muscular atrophy and respiratory failure. SMA is frequently caused by homozygous deletions that include exon 7 of the survival motor neuron gene SMN1, and its clinical course is influenced by the copy number of a nearby 5q SMN1 paralog, SMN2. Multiple ligation probe amplification (MLPA) and real-time quantitative PCR (qPCR) can detect SMN1 deletions. Yet, qPCR needs normalization or standard curves, and MLPA demands DNA concentrations above those obtainable from dried blood spots (DBSs). We developed a multiplex, droplet digital PCR (ddPCR) method for the simultaneous detection of SMN1 deletions and SMN2 copy number variation in DBS and other tissues. An SMN1 Sanger sequencing process for DBS was also developed.

METHODS

SMN1, SMN2, and RPP30 concentrations were simultaneously measured with a Bio-Rad AutoDG and QX200 ddPCR system. A total of 1530 DBSs and 12 SMA patients were tested.

RESULTS

Population studies confirmed 1 to 5 SMN1 exon 7 copies detected in unaffected specimens, whereas patients with SMA revealed 0 SMN1 copies. Intraassay and interassay imprecisions were <7.1% CV for individuals with ≥1 SMN1 copies. Testing 12 SMA-positive samples resulted in 100% sensitivity and specificity.

CONCLUSIONS

This ddPCR method is sensitive, specific, and applicable to newborn screening and carrier status determination for SMA. It can also be incorporated with a parallel ddPCR T-cell excision circles assay for severe combined immunodeficiencies.