Carrier screening for spinal muscular atrophy in Italian population

Pilot Program of Newborn Screening for 5q Spinal Muscular Atrophy in the Russian Federation

5q spinal muscular atrophy (5q SMA) is one of the most common autosomal recessive disorders in the Russian Federation. The first medication to treat 5q SMA was registered in the Russian Federation for treatment of all 5q SMA types in 2019, and the last of the three currently available in December 2021. We launched the pilot newborn screening (NBS) program for 5q SMA in Moscow, the Russian Federation, starting in 2019. During the pilot program, 23,405 neonates were tested for the deletion of exon 7 of the SMN1 gene, the most common cause of 5q SMA. We used the SALSA® MC002 SMA Newborn Screen Kit (MRC Holland) to specifically detect homozygous deletions of SMN1 exon 7. We used the restriction fragment length polymorphism (RFLP) approach to validate detected homozygous deletions and the SALSA MLPA Probemix P060 SMA Carrier Kit (MRC Holland) to determine the SMN2 exon 7 copy number to prescribe gene therapy for 5q SMA. Three newborns with a homozygous deletion of the SMN1 gene were detected. The calculated birth prevalence of 1:7801 appears to be similar to the results in other European countries. The children did not show any signs of respiratory involvement or bulbar weakness immediately after birth. Until now, no 5q SMA case missed by NBS has been detected.

Next generation sequencing is a highly reliable method to analyze exon 7 deletion of survival motor neuron 1 (SMN1) gene

Spinal muscular atrophy (SMA) is one of the most common and severe genetic diseases. SMA carrier screening is an effective way to identify couples at risk of having affected children. Next-generation sequencing (NGS)-based expanded carrier screening could detect SMN1 gene copy number without extra experiment and with high cost performance. However, its performance has not been fully evaluated. Here we conducted a systematic comparative study to evaluate the performance of three common methods. 478 samples were analyzed with multiplex ligation probe amplification (MLPA), real-time quantitative polymerase chain reaction (qPCR) and NGS, simultaneously. Taking MLPA-based results as the reference, for 0 copy, 1 copy and ≥ 2 copy SMN1 analysis with NGS, the sensitivity, specificity and precision were all 100%. Using qPCR method, the sensitivity was 100%, 97.52% and 94.30%, respectively; 98.63%, 95.48% and 100% for specificity; and 72.72%, 88.72% and 100% for precision. NGS repeatability was higher than that of qPCR. Moreover, among three methods, NGS had the lowest retest rate. Thus, NGS is a relatively more reliable method for SMN1 gene copy number detection. In expanded carrier screening, compared with the combination of multiple methods, NGS method could reduce the test cost and simplify the screening process.

Carrier frequency of SMN1-related spinal muscular atrophy in north Indian population: The need for population based screening program

Chromosome 5q related Spinal muscular atrophy (SMA) is an autosomal recessive, progressive, neuromuscular disorder most commonly caused by homozygous deletion of exon 7 or exon 7 and 8 of SMN1 gene. Being the leading genetic cause of infant mortality, studies of its prevalence and incidence are necessary. Carrier testing for the common pathogenic variant for SMA is offered to the couples visiting our tertiary care hospital in North India. Subjects were tested for SMA carrier status by Multiplex Ligation-dependent Probe amplification (MLPA) technique for deletion of exons 7 and 8 of SMN1 gene. The retrospective data of individuals tested for SMA carrier status in last 4 years (2016-2019) was evaluated. Six hundred and six individuals without family history of SMA or carrier of SMA who were subjected to MLPA based screening for SMA carrier status were included in the study. The carrier frequency of SMN1 deletion (deletion of exon 7 and/or exon 8) was found to be 1 in 38 (16 out of 606). The catchment area of our medical genetics clinic covering the state of Uttar Pradesh (16.5% of Indian population according to censusindia.gov.in, 2011) and neighboring states, showing SMA carrier frequency of 1:38 in a cohort with no prior positive family history has important significance for policy making.

Systemic and ICV Injections of Antisense Oligos into SMA Mice and Evaluation

Spinal muscular atrophy (SMA) is the most common genetic cause of infantile death caused by mutations in the SMN1 gene. Nusinersen (Spinraza), an antisense therapy-based drug with the 2'-methoxyethoxy (2'MOE) chemistry approved by the FDA in 2016, brought antisense drugs into the spotlight. Antisense-mediated exon inclusion targeting SMN2 leads to SMN protein expression. Although effective, 2'MOE has weaknesses such as the inability to cross the blood-brain barrier and the high cost of treatment. To investigate new chemistries of antisense oligonucleotides (ASOs), SMA mouse models can serve as an important source. Here we describe methods to test the efficacy of ASOs, such as phosphorodiamidate morpholino oligomers (PMOs), in a severe SMA mouse model.

In Vitro Evaluation of Antisense-Mediated Exon Inclusion for Spinal Muscular Atrophy

Spinal muscular atrophy (SMA), the most common gentic cause of infantile death caused by mutations in the SMN1 gene, presents a unique case in the field of splice modulation therapy, where a gene (or lack of) is responsible for causing the disease phenotype but treatment is not focused around it. Antisense therapy targeting SMN2 which leads to SMN protein expression has been at the forefront of research when it comes to developing a feasible therapy for treating SMA. Recent FDA approval of an antisense-based drug with the 2'-methoxyethoxy (2'MOE) chemistry, called nusinersen (Spinraza), brought antisense drugs into the spotlight. The 2'MOE, although effective, has weaknesses such as the inability to cross the blood-brain barrier and the high cost of treatment. This propelled the research community to investigate new chemistries of antisense oligonucleotides (ASOs) that may be better in both treatment and cost efficiency. Here we describe two types of ASOs, phosphorodiamidate morpholino oligomers (PMOs) and locked nucleic acids (LNA)-DNA mixmers, being investigated as potential treatments for SMA, and methods used to test their efficacy, including quantitative RT-PCR, Western blotting, and immunofluorescence staining to detect SMN in nuclear gems/Cajal bodies, in type I SMA patient fibroblast cell lines.

Prevalence, incidence and carrier frequency of 5q-linked spinal muscular atrophy - a literature review

Spinal muscular atrophy linked to chromosome 5q (SMA) is a recessive, progressive, neuromuscular disorder caused by bi-allelic mutations in the SMN1 gene, resulting in motor neuron degeneration and variable presentation in relation to onset and severity. A prevalence of approximately 1-2 per 100,000 persons and incidence around 1 in 10,000 live births have been estimated with SMA type I accounting for around 60% of all cases. Since SMA is a relatively rare condition, studies of its prevalence and incidence are challenging. Most published studies are outdated and therefore rely on clinical rather than genetic diagnosis. Furthermore they are performed in small cohorts in small geographical regions and only study European populations. In addition, the heterogeneity of the condition can lead to delays and difficulties in diagnosing the condition, especially outside of specialist clinics, and contributes to the challenges in understanding the epidemiology of the disease. The frequency of unaffected, heterozygous carriers of the SMN1 mutations appears to be higher among Caucasian and Asian populations compared to the Black (Sub-Saharan African ancestry) population. However, carrier frequencies cannot directly be translated into incidence and prevalence, as very severe (death in utero) and very mild (symptom free in adults) phenotypes carrying bi-allelic SMN1 mutations exist, and their frequency is unknown. More robust epidemiological data on SMA covering larger populations based on accurate genetic diagnosis or newborn screening would be helpful to support planning of clinical studies, provision of care and therapies and evaluation of outcomes.