Spinal Muscular Atrophy Testing Research Articles

PND62 - Willingness-to-Pay for Newborn Genetic Testing for Spinal Muscular Atrophy

PND62 - Willingness-to-Pay for Newborn Genetic Testing for Spinal Muscular Atrophy

SMA carrier testing: a meta-analysis of differences in test performance by ethnic group.

Spinal muscular atrophy (SMA) is a severe autosomal recessive genetic disease that occurs in about one in every 10 000 births. Prenatal carrier testing is available for SMA, and the utility of universal screening is actively debated. The aim of this study was to perform a systematic review and meta-analysis of SMA genotype frequency, carrier frequency, and carrier test performance in different ethnic groups. We performed a systematic review of the literature for studies on SMA carrier screening test performance. Ethnicity-specific allele frequencies, carrier rates, and screening test performance were determined from data of 169 000 individuals in 14 published studies. Pooled estimates were calculated for each ethnic group using a random effects meta-analysis. The detection rate of SMA screening in the non-Black population was 87-95%; however, detection rates fell to 71% among the Black population. These results highlight that although SMA carrier testing generally performs well and could be considered as a routine prenatal screen, SMA testing should be used cautiously in the Black population.

Ten years of experience in molecular prenatal diagnosis and carrier testing for spinal muscular atrophy among families from Serbia

ObjectiveTo describe 10years of experience of prenatal analysis of spinal muscular atrophy (SMA). MethodsData were retrospectively evaluated from prenatal analysis and carrier screening among parents and close relatives between January 2003 and December 2012. Screening was done before the parents were offered prenatal diagnosis. Polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) were used to detect the most frequent homozygous deletions in the SMN1 gene in fetal samples. A commercial MLPA kit (SALSA P060) was used to analyze SMN1 copy number for carrier status determination among healthy individuals. Bayesian calculation was used to accurately assess the risk of having a child affected with SMA. ResultsDuring the study period, 66 fetal samples from 44 Serbian families were analyzed, and 13 (19.7%) showed a homozygous deletion in the SMN1 gene. Among 28 healthy individuals, carrier status was confirmed for 16 (57.1%). For 7 couples, quantitative analyses and Bayesian calculation reduced the final risk of having a child with SMA from 1 in 200 to 1 in 2448. ConclusionOwing to disease severity and lack of a curative treatment, prenatal diagnosis of SMA is the best way to prevent recurrence. Carrier detection allows accurate risk assessment and appropriate genetic counseling for all family members.

Nothing About Us Without Us: Guidelines for Genetic Testing

Guidelines for genetic testing developed by professional societies may be more centered on the concerns of society members than the needs of the individuals and families that may undergo testing. This could be considered appropriate because it will be the healthcare provider who will assess whether to test; when to test; whom to test; and how to provide the right support, interpretation, and follow-up to the individual or family tested. Genetic testing requires guidelines because of the complexity of testing for the individual and his or her family. It also requires flexibility because context matters a great deal in genetics. For this very reason, multiple stakeholders should be involved in guideline development. Professional societies have a deliberative process for their members, and those closely associated with their practice, to engage in discourse that leads to guidelines. We believe that the testing guidelines should reflect more than the professionals’ perspective. Ultimately, the ramifications of testing guidelines do not exist in isolation from the whole healthcare experience of the individual. This means that the perspectives of other providers, the individuals, and families should be a part of the deliberative process. One might ask why the advocacy organizations don’t establish guidelines themselves. We believe that multiple stakeholder groups should be involved. A striking example of where two groups of professionals create difficulties for each other and the people they serve is the guidelines for spinal muscular atrophy (SMA) carrier screening. Obstetricians disagree with geneticists about carrier testing for this condition. Geneticists believe that carrier testing for SMA should be offered to the general population, and obstetricians do not believe it should be offered broadly. In statements made by the two societies, the contrast is clear, but from the point of view of the patient, it is confusing. The American College of Obstetricians and Gynecologists’ Committee on Genetics concludes: ‘‘[The committee] agrees that preconception and prenatal screening for SMA is not recommended in the general population at this time’’ (American College of Obstetricians and Gynecologists, 2009). The American College of Medical Genetics, on the other hand, concludes: ‘‘Because SMA is present in all populations, carrier testing should be offered to all couples regardless of race or ethnicity. Ideally, the testing should be offered before conception or early in pregnancy. The primary goal is to allow carriers to make informed reproductive choices’’ (Prior 2008). As a result of these two guidelines, obstetricians, midwives, geneticists, nurses, nurse practitioners, pediatricians, genetic counselors, and potential parents do not have a clear guideline on which to base a decision. It does not appear that either professional society engaged the other stakeholders from the ‘‘medical home’’ to any great degree, particularly in the guideline articulation. It is not apparent that either society invited the very individuals whose lives are affected by the decision into the process of creating guidelines. This case of SMA carrier screening is also a good example because of the complexity of the issue for parents as well. There are parents of children with SMA who desperately wish carrier screening had been available to them before they had to witness their baby die of the condition. There are also parents of children with the condition, albeit a milder form, who are very concerned that carrier screening might limit the number of children born with the condition. This might decrease appreciation for these children and perhaps reduce research activity and funding for the condition. The American College of Medical Genetics recently released guidelines for genetic testing in children (American College of Medical Genetics, 2013). This is a revision of a statement they made more than 10 years ago, so it was a welcome addition to current considerations for all of the stakeholders. It is not apparent that the deliberative process included parents of children affected by genetic conditions. It did not include advocates of the various disease advocacy organizations. Although it would be much more difficult to come to consensus with multiple stakeholders, doing so is a worthy endeavor. The silos that exist in medicine, from basic discovery through translational science to delivery of services, severely limit progress. The learning healthcare system (Institute of Medicine, 2011) requires that all stakeholders be involved in the entire process. Starting with clinical questions emerging from clinical care and the lived experience of individuals and families with disease will help accelerate diagnostic and treatment development. Engaging clinicians (of all specialties) and citizens in formulating basic research plans will help to make discovery more relevant to translational science. Empowering communities, whether geographic, ethnic, or disease affinities, to be responsible for characterizing cohorts will stitch together a national clinical research network of engaged communities (Seifer S, 2013). Learning from the people who

Molecular Analysis of Spinal Muscular Atrophy: a genotyping protocol based on TaqMan® real-time PCR

Spinal muscular atrophy (SMA) is an autosomal recessive inherited disorder caused by alterations in the survival motor neuron I (SMN1) gene. SMA patients are classified as type I-IV based on severity of symptoms and age of onset. About 95% of SMA cases are caused by the homozygous absence of SMN1 due to gene deletion or conversion into SMN2. PCR-based methods have been widely used in genetic testing for SMA. In this work, we introduce a new approach based on TaqMan(®)real-time PCR for research and diagnostic settings. DNA samples from 100 individuals with clinical signs and symptoms suggestive of SMA were analyzed. Mutant DNA samples as well as controls were confirmed by DNA sequencing. We detected 58 SMA cases (58.0%) by showing deletion of SMN1 exon 7. Considering clinical information available from 56 of them, the patient distribution was 26 (46.4%) SMA type I, 16 (28.6%) SMA type II and 14 (25.0%) SMA type III. Results generated by the new method was confirmed by PCR-RFLP and by DNA sequencing when required. In conclusion, a protocol based on real-time PCR was shown to be effective and specific for molecular analysis of SMA patients.

Technical standards and guidelines for spinal muscular atrophy testing

Spinal muscular atrophy is a common autosomal recessive neuromuscular disorder caused by mutations in the survival motor neuron (SMN1) gene, affecting approximately 1 in 10,000 live births. The disease is characterized by progressive symmetrical muscle weakness resulting from the degeneration and loss of anterior horn cells in the spinal cord and brainstem nuclei. The disease is classified on the basis of age of onset and clinical course. Two almost identical SMN genes are present on 5q13: the SMN1 gene, which is the spinal muscular atrophy-determining gene, and the SMN2 gene. The homozygous absence of the SMN1 exon 7 has been observed in the majority of patients and is being used as a reliable and sensitive spinal muscular atrophy diagnostic test. Although SMN2 produces less full-length transcript than SMN1, the number of SMN2 copies has been shown to modulate the clinical phenotype. Carrier detection relies on the accurate determination of the SMN1 gene copies. This document follows the outline format of the general Standards and Guidelines for Clinical Laboratories. It is designed to be a checklist for genetic testing professionals who are already familiar with the disease and methods of analysis.

Developing standard procedures for pre-clinical efficacy studies in mouse models of spinal muscular atrophy: Report of the expert workshop “Pre-clinical testing for SMA”, Zürich, March 29–30th 2010

A workshop was held in Zurich (Switzerland) to develop standard procedures and protocols for pre-clinical efficacy studies in mouse models of spinal muscular atrophy (SMA). The workshop was organized by the Network of Excellence TREAT-NMD (Translational Research in Europe – Assessment and Treatment of Neuromuscular Disorders), launched 2007, that addresses the fragmentation currently existing in the evaluation, diagnosis and care of neuromuscular diseases on one side, and in the procedures of drug development from research to the design of clinical trials on the other side. Within this frame, one aspect that needs particular care is the design and performance of pre-clinical animal studies that should predict the efficacy of a new treatment in patients. In the absence of commonly accepted guidelines and standardized protocols, data from different laboratories are often not comparable and the result is a duplication of efforts. The workshop was attended by 30 key researchers from Europe and North America, as well as industry representatives (Santhera Pharmaceuticals, Psychogenics, Genyzme, Trophos) and patient organisations (SMA Foundation, AFM-Association Franc aise contre les Myopathies). The goals of the workshop were (1) to select endpoints that best assess drug efficacy in mouse

Carrier testing for spinal muscular atrophy

Spinal muscular atrophy is the most common fatal hereditary disease among newborns and infants. There is as yet no effective treatment. Although a carrier test is available, currently there is disagreement among professional medical societies who proffer standards of care as to whether or not carrier screening for spinal muscular atrophy should be offered as part of routine reproductive care. This leaves health care providers without clear guidance. In fall 2009, a meeting was held by National Institutes of Health to examine the scientific basis for spinal muscular atrophy carrier screening and to consider the issues that accompany such screening. In this article, the meeting participants summarize the discussions and conclude that pan-ethnic carrier screening for spinal muscular atrophy is technically feasible and that the specific study of implementing a spinal muscular atrophy carrier screening program raises broader issues about determining the scope and specifics of carrier screening in general.

Newborn and carrier screening for spinal muscular atrophy

Spinal muscular atrophy (SMA) is a common autosomal recessive neuromuscular disorder caused by mutations in the survival motor neuron (SMN1) gene, affecting approximately 1 in 10,000 live births. The homozygous absence of SMN1 exon 7 has been observed in the majority of patients and is being utilized as a reliable and sensitive SMA diagnostic test. Treatment and prevention of SMA are complementary responses to the challenges presented by SMA. Even though a specific therapy for SMA is not currently available, a newborn screening test may allow the child to be enrolled in a clinical trial before irreversible neuronal loss occurs and enable patients to obtain more proactive treatments. Until an effective treatment is found to cure or arrest the progression of the disease, prevention of new cases through accurate diagnosis and carrier and prenatal diagnosis is of the utmost importance. The goal of population-based SMA carrier screening is to identify couples at risk for having a child with SMA, thus allowing carriers to make informed reproductive choices. During this study we performed two pilot projects addressing the clinical applicability of testing in the newborn period and carrier screening in the general population. We have demonstrated that an effective technology does exist for newborn screening of SMA. We also provide an estimate of the carrier frequency among individuals who accepted carrier screening, and report on patient's knowledge and attitudes toward SMA testing.

The cost-effectiveness of prenatal screening for spinal muscular atrophy

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

Neuromuscular defects and breathing disorders in a new mouse model of spinal muscular atrophy

Spinal muscular atrophy (SMA) is caused by insufficient levels of the survival motor neuron (SMN) protein leading to muscle paralysis and respiratory failure. In mouse, introducing the human SMN2 gene partially rescues Smn - / - embryonic lethality. However current models were either too severe or nearly unaffected precluding convenient drug testing for SMA. We report here new SMN2; Smn -/- lines carrying one to four copies of the human SMN2 gene. Mice carrying three SMN2 copies exhibited an intermediate phenotype with delayed appearance of motor defects and developmental breathing disorders reminiscent of those found in severe SMA patients. Although normal at birth, at 7 days of age respiratory rate was decreased and apnea frequency was increased in SMA mice in parallel with the appearance of neuromuscular junction defects in the diaphragm. With median survival of 15 days and postnatal onset of neurodegeneration, these mice could be an important tool for evaluating new therapeutics.

Genetic testing for spinal muscular atrophy

Genetic testing for spinal muscular atrophy

Detection of Spinal Muscular Atrophy Carriers by Nested Polymerase Chain Reaction of Single Sperm Cells

Spinal muscular atrophy (SMA) is an autosomal recessive disorder with a carrier frequency of approximately 1 in 40. Approximately 95% of patients have homozygous deletions of exon 7 and/or 8 of the SMN1 gene. Carrier testing for SMA is relatively complex and requires quantitative polymerase chain reaction (PCR) of genomic DNA to determine SMN1 copy number. The purpose of this study was to assess the feasibility of carrier testing for SMA in males, by nested PCR analysis of SMN1 deletions in single sperm cells. A nested PCR method was developed to amplify SMN1 exon 7 in single cells. Restriction enzyme digestion with DraI was used to differentiate between the highly homologous SMN1 and SMN2 genes. Single sperm cells from five known SMA carriers and six noncarriers were analyzed. Among the five carriers, a total of 132 single sperm cells were analyzed and SMN1 exon 7 deletion was detected in 68 cells (51.5%). In contrast, among the six noncarriers, a total of 136 single sperm cells were analyzed. Of these, an apparent SMN1 exon 7 deletion was detected in four sperm cells. This was interpreted as an allele dropout (ADO) rate of 2.9%. We conclude that nested PCR of SMN1 exon 7 is an accurate and reproducible method for detection of SMA male carriers with a SMN1 deletion.

Genetic risk assessment in carrier testing for spinal muscular atrophy.

As evidenced by the complete absence of a functionally critical sequence in exon 7, approximately 94% of individuals with clinically typical spinal muscular atrophy (SMA) lack both copies of the SMN1 gene at 5q13. Hence most carriers have only one copy of SMN1. Combining linkage and dosage analyses for SMN1, we observed unaffected individuals who have two copies of SMN1 on one chromosome 5 and zero copies of SMN1 on the other chromosome 5. By dosage analysis alone, such individuals, as well as carriers of non-deletion disease alleles, are indistinguishable from non-carrier individuals. We report that approximately 7% of unaffected individuals without a family history of SMA have three or four copies of SMN1, implying a higher frequency of chromosomes with two copies of SMN1 than previously reported. We present updated calculations for disease and non-disease allele frequencies and we describe how these frequencies can be used for genetic risk assessment in carrier testing for SMA.

Spinal Muscular Atrophy Genetic Testing Experience at an Academic Medical Center

Approximately 94% of spinal muscular atrophy (SMA) patients lack both copies of SMN1 exon 7. We report our SMA genetic testing experience (total 1281 cases), using SMA linkage analysis (32 families), SMA diagnostic testing by PCR-RFLP (restriction fragment length polymorphism) to detect the homozygous absence of SMN1 exon 7 (and exon 8) (533 cases), and an assay to determine copy number of SMN1 exon 7 (SMN1 gene dosage analysis) (716 cases). SMN1 gene dosage analysis is used for SMA carrier testing as well as for the confirmation of a heterozygous SMN1 deletion in symptomatic individuals who do not lack both copies of SMN1. We conclude that comprehensive SMA testing, including SMN1 deletion analysis, SMN1 gene dosage analysis, and linkage analysis, offers the most complete evaluation of SMA patients and their families.

Duplications and de novo deletions of theSMNt gene demonstrated by fluorescence-based carrier testing for spinal muscular atrophy

Approximately 95% of individuals with spinal muscular atrophy (SMA) lack both copies of the SMNt gene at 5q13. The presence of a nearly identical centromeric homolog of the SMNt gene, SMNc, necessitates a quantitative polymerase chain reaction approach to direct carrier testing. Adapting a radioactivity-based method described previously, multiplex polymerase chain reaction was performed using fluorescently labeled primers followed by analysis on an ABI 373a DNA sequencer. The SMNt copy number was calculated from ratios of peak areas using both internal and genomic standards. Samples from 60 presumed carriers (50 parents of affected individuals and 10 relatives implicated by linkage analysis) and 40 normal control individuals were tested. Normalized results (to the mean of five or more control samples harboring two copies of the SMNt gene) were consistently within the ranges of 0.4 to 0.6 for carriers (one copy) and 0.8 to 1.2 for normal controls (two copies), without overlap. Combining linkage analyses with direct carrier test results demonstrated de novo deletions associated with crossovers, unaffected individuals carrying two SMNt gene copies on one chromosome and zero SMNt gene copies on the other chromosome, and unaffected individuals with three copies of the SMNt gene. This report demonstrates that fluorescence-based carrier testing for SMA is accurate, reproducible, and useful for genetic risk assessment, and that carrier testing may need to be combined with linkage analysis in certain circumstances.

Duplications and de novo deletions of the SMNt gene demonstrated by fluorescence‐based carrier testing for spinal muscular atrophy

Approximately 95% of individuals with spinal muscular atrophy (SMA) lack both copies of the SMNt gene at 5q13. The presence of a nearly identical centromeric homolog of the SMNt gene, SMNc, necessitates a quantitative polymerase chain reaction approach to direct carrier testing. Adapting a radioactivity-based method described previously, multiplex polymerase chain reaction was performed using fluorescently labeled primers followed by analysis on an ABI 373a DNA sequencer. The SMNt copy number was calculated from ratios of peak areas using both internal and genomic standards. Samples from 60 presumed carriers (50 parents of affected individuals and 10 relatives implicated by linkage analysis) and 40 normal control individuals were tested. Normalized results (to the mean of five or more control samples harboring two copies of the SMNt gene) were consistently within the ranges of 0.4 to 0.6 for carriers (one copy) and 0.8 to 1.2 for normal controls (two copies), without overlap. Combining linkage analyses with direct carrier test results demonstrated de novo deletions associated with crossovers, unaffected individuals carrying two SMNt gene copies on one chromosome and zero SMNt gene copies on the other chromosome, and unaffected individuals with three copies of the SMNt gene. This report demonstrates that fluorescence-based carrier testing for SMA is accurate, reproducible, and useful for genetic risk assessment, and that carrier testing may need to be combined with linkage analysis in certain circumstances. Am. J. Med. Genet. 85:463–469, 1999. © 1999 Wiley-Liss, Inc.