Epidemiological data on Werdnig-Hoffmann disease in Germany (West-Thüringen)

Common complications in spinal muscular atrophy (SMA) type 1 after nusinersen treatment

BACKGROUND

Spinal muscular atrophy (SMA) is an inherited disease with progressive muscle weakness and atrophy. Despite the new treatments developed recently, primary and secondary effects of muscle weakness in patients with SMA cause mortality and morbidity. The aim of this study is to identify common problems in the follow-up of patients after new treatment modalities and to examine the difficulties in management of these problems.

METHODS

The study included 16 patients diagnosed with SMA type 1 according to clinical findings and genetic results between 2017 and 2022. The patients were divided into two groups as living and deceased, and complications were examined and compared between the groups.

RESULTS

The patients comprised 8 (50%) females and 8 (50%) males with a median age at diagnosis of 3 months. The patients had a history of gastrointestinal problems, orthopedic problems, infection and sepsis, and especially respiratory distress. Death occurred in 8 (50%) patients during follow-up (median age 38 months). Mortality was higher in patients who needed tracheostomy and had gastroesophageal reflux. The survival rate was better in patients who received more nusinersen treatment and had a higher CHOP-INTEND score.

CONCLUSIONS

Despite new-generation treatments for SMA type 1, morbidity and mortality rates remain very high. As the survival rate in SMA type 1 increases, the incidence of complications similar to those frequently seen in SMA type 2 and type 3 patients also increases. The follow-up and treatment of patients with SMA should be undertaken by a multidisciplinary team.

Childhood spinal muscular atrophy

Spinal muscular atrophy (SMA) is caused by biallelic mutations in the SMN1 (survival motor neuron 1) gene on chromosome 5q13.2, which leads to a progressive degeneration of alpha motor neurons in the spinal cord and in motor nerve nuclei in the caudal brainstem. It is characterized by progressive proximally accentuated muscle weakness with loss of already acquired motor skills, areflexia and, depending on the phenotype, varying degrees of weakness of the respiratory and bulbar muscles. Over the past decade, disease-modifying therapies have become available based on splicing modulation of the SMN2 with SMN1 gene replacement, which if initiated significantly modifies the natural course of the disease. Newborn screening for SMA has been implemented in an increasing number of centers; however, available evidence for these new treatments is often limited to a small spectrum of patients concerning age and disease stage.

Epidemiological investigation of spinal muscular atrophy in Japan

BACKGROUND

International reporting of epidemiological surveys of spinal muscular atrophy (SMA) in Japan has been limited to Shikoku, despite the epidemiology of the disease in countries worldwide becoming clearer. Treatments of 5q-SMA have been developed, and epidemiological studies are needed.

PURPOSE

This study aimed to conduct a nationwide epidemiological survey of SMA in Japan to clarify the actual situation of SMA in Japan.

METHOD

Patients with all clinical types of SMA, including neonates and adults, were selected from 1,005 medical facilities in Japan.

RESULTS

As of December 2017, the actual number of reported patients with SMA was 658 and the genetic testing rate was 79.5%. The estimated number of patients was 1,478 (95% confidence interval (CI), 1,122-1,834), with a prevalence of 1.17 (95%CI, 0.89-1.45) per 100,000 people and an incidence of 0.51 (95%CI, 0.32-0.71) per 10,000 live births. Incidence rates of 5q-SMA by clinical type were 0.27 (95%CI, 0.17-0.38) and 0.08 (95%CI, 0.04-0.11) per 10,000 live births for type 1 and 2, respectively, in cases with a definitive diagnosis by genetic testing. We found that 363 cases (82.7%) occurred less than 2 years and 88 (20.0%) occurred age of 2 months old or under.

CONCLUSION

This study clarifies the prevalence and incidence of SMA in Japan. As infantile onset accounts for most cases of SMA, newborn screening and subsequent treatment are important to save lives.

Fasciculations in Children

Fasciculations are the most common form of spontaneous muscle contraction. They frequently occur in healthy individuals. However, there are a minority of situations that fasciculations are observed in association with specific neurologic disorders. Publications concerning the evaluation of pediatric patients experiencing fasciculations are limited. These children may undergo invasive or expensive diagnostic investigations that are unnecessary. Moreover, without careful consideration of differential diagnoses, rare neuromuscular disorders that present with fasciculations in the pediatric age group can be under-recognized by pediatric neurologists. This review examines the most important pediatric disorders presenting with fasciculations and other spontaneous muscle contractions to guide pediatric neurologists in evaluating these children.

Multisite Evaluation and Validation of a Sensitive Diagnostic and Screening System for Spinal Muscular Atrophy that Reports SMN1 and SMN2 Copy Number, along with Disease Modifier and Gene Duplication Variants

Spinal muscular atrophy is a severe autosomal recessive disease caused by disruptions in the SMN1 gene. The nearly identical SMN2 gene copy number is associated with disease severity. SMN1 duplication markers, such as c.∗3+80T>G and c.∗211_∗212del, can assess residual carrier risk. An SMN2 disease modifier (c.859G>C) can help inform prognostic outcomes. The emergence of multiple precision gene therapies for spinal muscular atrophy requires accurate and rapid detection of SMN1 and SMN2 copy numbers to enable early treatment and optimal patient outcomes. We developed and evaluated a single-tube PCR/capillary electrophoresis assay system that quantifies SMN1/2 copy numbers and genotypes three additional clinically relevant variants. Analytical validation was performed with human cell lines and whole blood representing varying SMN1/2 copies on four capillary electrophoresis instrument models. In addition, four independent laboratories used the assay to test 468 residual clinical genomic DNA samples. The results were ≥98.3% concordant with consensus SMN1/2 exon 7 copy numbers, determined using multiplex ligation-dependent probe amplification and droplet digital PCR, and were 100% concordant with Sanger sequencing for the three variants. Furthermore, copy number values were 98.6% (SMN1) and 97.1% (SMN2) concordant to each laboratory's own reference results.

Dual Mechanism of a New SMN1 Variant (c.835G>C, p.Gly279Arg) by Interrupting Exon 7 Skipping and YG Oligomerization in Causation of Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disorder caused by deletion or subtle variant of survival motor neuron 1 (SMN1) gene. By multiplex ligation-dependent probe amplification, genomic sequencing, and T-A cloning on cDNA level, we identified one novel SMN1 subtle variant c.835G>C (p.Gly279Arg) in a non-homozygous patient with type 1 SMA. Full-length SMN1 (fl-SMN1) transcripts in the peripheral bloods of the patient were significantly decreased compared with those in healthy individuals and the carries (p < 0.05). And two fragments of SMN1 transcripts including fl-SMN1 and △7-SMN1 were observed by RT-PCR, which indicated Exon 7 skipping of SMN1 gene. To further evaluate its splicing effects on Exon 7, we performed ex vivo splicing analysis, which showed that the mutant mini gene with c.835G>C reduced Exon 7 inclusion to 54%. In addition, self-oligomerization between mutant SMN protein with the c.835G>C (p.Gly279Arg) and wild SMN was decreased in self-interaction assays. Our study clearly demonstrates that the c.835G>C (p.Gly279Arg) variant can lead to a decrease in fl-SMN1 transcripts by interrupting correct splicing of SMN1. What is more, the variant also affects SMN self-oligomerization via amino acid substitution from Gly to Arg at amino acid position of 279. This work presents the first evidence that it does exit double-hit events for the novel variant, which is crucial to understanding a severe SMA phenotype (type 1).

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.

The Epidemiology of Neuromuscular Diseases

Neuromuscular disorders as a group are linked by anatomy with significant differences in pathogenetic mechanisms, clinical expression, and time course of disease. Each neuromuscular disease is relatively uncommon, yet causes a significant burden of disease socioeconomically. Epidemiologic studies in different global regions have demonstrated certain neuromuscular diseases have increased incidence and prevalence rates over time. Understanding differences in global epidemiologic trends will aid clinical research and policies focused on prevention of disease. There is a critical need to understand the global impact of neuromuscular diseases using metrics currently established for communicable and noncommunicable diseases.

Spinal muscular atrophies

Spinal muscular atrophies (SMAs) are hereditary degenerative disorders of lower motor neurons associated with progressive muscle weakness and atrophy. Proximal 5q SMA is caused by decreased levels of the survival of motor neuron (SMN) protein and is the most common genetic cause of infant mortality. Its inheritance pattern is autosomal recessive, resulting from mutations involving the SMN1 gene on chromosome 5q13. Unlike other autosomal recessive diseases, the SMN gene has a unique structure (an inverted duplication) that presents potential therapeutic targets. Although there is currently no effective treatment of SMA, the field of translational research in this disorder is active and clinical trials are ongoing. Advances in the multidisciplinary supportive care of children with SMA also offer hope for improved life expectancy and quality of life.

Genetisches Modell der autosomal-rezessiv erblichen proximalen spinalen Muskelatrophie

Die proximale infantile und juvenile spinale Muskelatrophie (SMA) ist eine der häufigsten autosomal-rezessive Erbkrankheiten. Man unterteilt die Patienten in 3 Gruppen, SMA Typ I-III, abhängig von der Schwere der Erkrankung (den erreichten Meilensteinen). Das hauptsächlich verantwortliche Gen, das Survival-motor-neuron(SMN1)-Gen, ist auf Chromosom 5 lokalisiert. Während das Normalallel meist mit einer oder 2 SMN1-Kopien vorliegt, sind die Defektallele bei den meisten Patienten von einer Deletion betroffen; bei einigen liegen Punktmutationen vor. Bei den Deletionen wiederum unterscheidet man zwischen einfacher und großer Deletion, die über das SMN1-Gen hinausgeht. Ein homozygotes Auftreten letzterer führt zu pränataler Letalität.

Für die vorliegende Arbeit wurden zahlreiche in der Literatur verfügbare Daten zur SMA Typ I-III zusammengetragen und in ihrer Abhängigkeit in einem genetischen Modell zusammengefasst. So war es möglich, fehlende Parameter zu schätzen, um genauere Aussagen über Genotypen machen zu können. Die einzelnen Allelfrequenzen konnten wie folgt geschätzt werden:

Normalallel b (1 SMN1-Kopie): ≈ 0,9527; Normalallel c (2 SMN1-Kopien): ≈ 0,0362; einfache Deletion a (0 SMN1-Kopien): ≈ 0,0104; Punktmutation d (1 SMN1-Kopie): ≈ 0,0003; große Deletion g (0 SMN1-Kopien): ≈ 0,0004. Die Genhäufigkeit beträgt etwa 1:90 mit einer Heterozygtenfrequenz von 1:46.

Spinal muscular atrophy: a clinical and research update

Spinal muscular atrophy, a hereditary degenerative disorder of lower motor neurons associated with progressive muscle weakness and atrophy, is the most common genetic cause of infant mortality. It is caused by decreased levels of the "survival of motor neuron" (SMN) protein. Its inheritance pattern is autosomal recessive, resulting from mutations involving the SMN1 gene on chromosome 5q13. However, unlike many other autosomal recessive diseases, the SMN gene involves a unique structure (an inverted duplication) that presents potential therapeutic targets. Although no effective treatment for spinal muscular atrophy exists, the field of translational research in spinal muscular atrophy is active, and clinical trials are ongoing. Advances in the multidisciplinary supportive care of children with spinal muscular atrophy also offer hope for improved life expectancy and quality of life.

Evaluation of muscle strength and motor abilities in children with type II and III spinal muscle atrophy treated with valproic acid

Background

Spinal muscular atrophy (SMA) is an autosomal recessive disorder that affects the motoneurons of the spinal anterior horn, resulting in hypotonia and muscle weakness. The disease is caused by deletion or mutation in the telomeric copy of SMN gene (SMN1) and clinical severity is in part determined by the copy number of the centromeric copy of the SMN gene (SMN2). The SMN2 mRNA lacks exon 7, resulting in a production of lower amounts of the full-length SMN protein. Knowledge of the molecular mechanism of diseases has led to the discovery of drugs capable of increasing SMN protein level through activation of SMN2 gene. One of these drugs is the valproic acid (VPA), a histone deacetylase inhibitor.

Methods

Twenty-two patients with type II and III SMA, aged between 2 and 18 years, were treated with VPA and were evaluated five times during a one-year period using the Manual Muscle Test (Medical Research Council scale-MRC), the Hammersmith Functional Motor Scale (HFMS), and the Barthel Index.

Results

After 12 months of therapy, the patients did not gain muscle strength. The group of children with SMA type II presented a significant gain in HFMS scores during the treatment. This improvement was not observed in the group of type III patients. The analysis of the HFMS scores during the treatment period in the groups of patients younger and older than 6 years of age did not show any significant result. There was an improvement of the daily activities at the end of the VPA treatment period.

Conclusion

Treatment of SMA patients with VPA may be a potential alternative to alleviate the progression of the disease.

Trial Registration

ClinicalTrials.gov: NCT01033331

Coexistence of an unbalanced chromosomal rearrangement and spinal muscular atrophy in an infant with multiple congenital anomalies

Unbalanced chromosomal abnormalities are frequent and account for about 10% of all chromosomal abnormalities identified in live births. Diagnosis of a coinherited neuromuscular genetic disorder in these individuals is often challenging based on the severity and variability of the phenotype resulting from the genomic imbalance. Herein, we report on a 4-month-old male with multiple congenital anomalies, craniosynostosis, dysmorphic features, and hypotonia. Karyotype analysis revealed an abnormal male karyotype: 46,XY,der(3)(3;7)(p25;q36), with partial monosomy of 3pter and partial trisomy of 7qter. The targeted array-based comparative genomic hybridization (array-CGH) validated the cytogenetic abnormality, with further elucidation of trisomy of the Sonic Hedgehog (SHH) locus on chromosome 7. Based on the severity of hypotonia in this infant, molecular analysis for spinal muscular atrophy (SMA) was performed and the common homozygous deletion of exon 7 in the survival of motor neuron 1 gene (SMN1) was identified. This case demonstrates the challenges in diagnoses of coexisting genetic disorders in infants with neuromuscular disease. A high index of suspicion in such cases is essential for appropriate case management and family risk assessment.

Genetic carrier screening for spinal muscular atrophy and spinal muscular atrophy with respiratory distress 1 in an isolated population in Israel

Spinal muscular atrophy (SMA) is an autosomal recessive disease characterized by progressive muscle weakness. It is caused by a mutation in the survival motor neuron gene 1 (SMN1) gene. SMA with respiratory distress 1 (SMARD1), an uncommon variant of infantile SMA also inherited in an autosomal recessive manner, is caused by mutations in the immunoglobulin mu-binding protein 2 (IGHMBP2) gene. We carried out genetic carrier screening among the residents of an isolated Israeli Arab village with a high frequency of SMA in order to identify carriers of SMA type I and SMARD1. During 2006, 168 women were tested for SMA, of whom 13.1% were found to be carriers. Of 111 women tested for SMARD1, 9.9% were found to be carriers. Prenatal diagnosis was performed in one couple where both spouses were carriers of SMARD1; the fetus was found to be affected, and the pregnancy was terminated. To the best of our knowledge, this is the first example of the establishment of a large-scale carrier-screening program for SMA and SMARD1 in an isolated population. SMA has a carrier frequency of 1:33-1:60 in most populations and should be considered for inclusion in a population-based genetic-screening program.

Nonsense-mediated messenger RNA decay of survival motor neuron 1 causes spinal muscular atrophy

Autosomal recessive proximal spinal muscular atrophy (SMA) is a neurodegenerative disorder resulting from functional loss of survival motor neuron 1 (SMN1). Homozygous absence of SMN1 due to deletion or gene conversion accounts for about 96% of SMA cases. In the remaining 4%, subtle SMN1 mutations are commonly identified. Here, we describe two novel intragenic SMN1 mutations in three type I SMA individuals: a point mutation in exon 3 (c.469C > T) and a substitution in intron 4 (c.628-140A > G). In-vivo splicing assays demonstrated that the intronic substitution creates a novel splice donor site, culminating in aberrant splicing and insertion of 65 bp from intron 4 between exons 4 and 5 in SMN1 transcripts (c.627_628ins65). Both mutations render SMN1 transcripts susceptible to nonsense-mediated mRNA decay (NMD), resulting in mRNA degradation, insufficient SMN protein levels and development of an SMA phenotype. Treatment of patient cell lines with the translation inhibitors puromycin and emetine markedly increased the levels of mutant SMN1 transcripts. A similar effect was observed after siRNA-mediated knockdown of UPF1, a factor essential for NMD. This study provides first evidence that NMD of SMN1 transcripts is responsible for the molecular basis of disease in a subset of SMA patients.

Evidence of reduced frequency of spinal muscular atrophy type I in the Cuban population

The authors reviewed all cases of type I spinal muscular atrophy (SMA) in Cuba over a 6-year period. The incidence of SMA type I was 3.53 per 100,000 livebirths. When the population was classified according to self-reported ethnicity, the incidence was eight per 100,000 for whites; 0.89 per 100,000 for blacks, and 0.96 per 100,000 for those of mixed ethnicity. Type 1 SMA may occur less frequently in individuals of African ancestry.

Best practice guidelines for molecular analysis in spinal muscular atrophy

With a prevalence of approximately 1/10 000, and a carrier frequency of 1/40-1/60 the proximal spinal muscular atrophies (SMAs) are among the most frequent autosomal recessive hereditary disorders. Patients can be classified clinically into four groups: acute, intermediate, mild, and adult (SMA types I, II, III, and IV, respectively). The complexity and instability of the genomic region at chromosome 5q13 harbouring the disease-causing survival motor neuron 1 (SMN1) gene hamper molecular diagnosis in SMA. In addition, affected individuals with SMA-like phenotypes not caused by SMN1, and asymptomatic individuals with two mutant alleles exist. The SMN gene is present in at least one telomeric (SMN1) and one centromeric copy (SMN2) per chromosome in normal (non-carrier) individuals, although chromosomes containing more copies of SMN1 and/or SMN2 exist. Moreover, the two SMN genes (SMN1 and SMN2) are highly homologous and contain only five base-pair differences within their 3' ends. Also, a relatively high de novo frequency is present in SMA. Guidelines for molecular analysis in diagnostic applications, carrier detection, and prenatal analysis using direct and indirect approaches are described. Overviews of materials used in the molecular diagnosis as well as Internet resources are included.

Genotype determination at the survival motor neuron locus in a normal population and SMA carriers using competitive PCR and primer extension

Precise quantitation of SMN1 copy number is of great interest in many clinical applications such as direct detection of SMA carriers or detection of an SMA-affected patient with a hemizygous deletion of the SMN1 gene. We describe a method that combines two independent nonradioactive PCR assays: determination of the relative ratio of the SMN1 and SMN2 genes using a primer extension assay and of the total SMN copy number using competitive PCR. Consistency of the results of two independent approaches ensures the reliability of the deduced genotype and thus avoids false interpretation of borderline results that can occur in quantitative assays. In all, 135 subjects were tested, including 91 normal controls and 44 SMA-affected children or SMA carriers. Two main genotypes were observed in controls: 2T/2C (45%) and 2T/1C (32%). A wide variability at the SMN locus is observed with nine different genotypes and up to six SMN genes. SMA carriers showed three frequent genotypes, 1T/2C (50%), 1T/3C (29%), and 1T/1C (18%). Normal chromosomes with two SMN1 genes per chromosome are not infrequent and thus, about 3% of SMA carriers are not detected using SMN1 copy number quantitation. Finally, as this method does not detect point mutations (4% of SMN1 gene mutations), reliability ranges from 93% to 100% depending on data available from the propositus.

Chronic childhood spinal muscular atrophy in Germany (West-Thüringen)--an epidemiological study

This study presents the most extensive epidemiological data on chronic forms of spinal muscular atrophy in childhood (CSMA) in West-Thüringen in Germany. The incidence of CSMA was calculated to be 1 in 9,420 live births. The prevalence was 1.624 in 100,000 of the general population (as of 31 December 1980).