Respiratory failure in infants due to spinal muscular atrophy with respiratory distress type 1

Exploring the relationship between IGHMBP2 gene mutations and spinal muscular atrophy with respiratory distress type 1 and Charcot-Marie-Tooth disease type 2S: a systematic review

Background

IGHMBP2 is a crucial gene for the development and maintenance of the nervous system, especially in the survival of motor neurons. Mutations in this gene have been associated with spinal muscular atrophy with respiratory distress type 1 (SMARD1) and Charcot-Marie-Tooth disease type 2S (CMT2S).

Methods

We conducted a systematic literature search using the PubMed database to identify studies published up to April 1st, 2023, that investigated the association between IGHMBP2 mutations and SMARD1 or CMT2S. We compared the non-truncating mutations and truncating mutations of the IGHMBP2 gene and selected high-frequency mutations of the IGHMBP2 gene.

Results

We identified 52 articles that investigated the association between IGHMBP2 mutations and SMARD1/CMT2S. We found 6 hotspot mutations of the IGHMBP2 gene. The truncating mutations in trans were all associated with SMARD1.

Conclusion

This study provides evidence that the complete LOF mechanism of the IGHMBP2 gene defect may be an important cause of SMARD1.

Evaluation of exonic copy numbers of SMN1 and SMN2 genes in SMA

SMA is a neuromuscular disease and occurs primarily through autosomal recessive inheritance. Identification of deletions in the SMN1 gene especially in the exon 7 and exon 8 regions (hot spot), are used in carrier testing. The exact copy numbers of those exons in the SMN1 and SMN2 genes in 113 patients who presented with a pre-diagnosis of SMA were determined using MLPA method. We aimed to reveal both the most common copy number profiles of different SMA types. It was found that the frequency of homozygous deletions in SMN1 was 15.9%, while heterozygous deletions was 16.9%. The most common SMN-MLPA profile was 0-0-3-3. In the cases with homozygous deletion, SMA type III diagnosis was observed most frequently (44%), and the rate of consanguineous marriage was found 33%. Two cases with the same exonic copy number profile but with different clinical subtypes were identified in a family. We also detected distinct exonic deletion and duplication MLPA profiles for the first time. We created "the SMA signature" that can be added to patient reports. Furthermore, our data are important for revealing potential local profiles of SMA and describing the disease in genetic reports in a way that is clear and comprehensive.

Severe Infantile Axonal Neuropathy with Respiratory Failure Caused by Novel Mutation in X-Linked LAS1L Gene

LAS1L encodes a nucleolar ribosomal biogenesis protein and is also a component of the Five Friends of Methylated CHTOP (5FMC) complex. Mutations in the LAS1L gene can be associated with Wilson−Turner syndrome (WTS) and, much more rarely, severe infantile hypotonia with respiratory failure. Here, we present an eighteen-month old boy with a phenotype of spinal muscular atrophy with respiratory distress (SMARD). By applying WES, we identified a novel hemizygous synonymous variant in the LAS1L gene inherited from an unaffected mother (c.846G > C, p.Thr282=). We suggest that the identified variant impairs the RNA splicing process. Furthermore, we proved the absence of any coding regions by qPCR and sequencing cDNA using amplicon deep sequencing and Sanger sequencing methods. According to the SMARD phenotype, severe breathing problems causing respiratory insufficiency, hypotonia, and feeding difficulties were observed in our patient from the first days of life. Remarkably, our case is the second described patient with a SMARD-like phenotype due to a mutation in the LAS1L gene and the first with a variant impacting splicing.

Current understanding of and emerging treatment options for spinal muscular atrophy with respiratory distress type 1 (SMARD1)

Spinal muscular atrophy (SMA) with respiratory distress type 1 (SMARD1) is an autosomal recessive motor neuron disease that is characterized by distal and proximal muscle weakness and diaphragmatic palsy that leads to respiratory distress. Without intervention, infants with the severe form of the disease die before 2 years of age. SMARD1 is caused by mutations in the IGHMBP2 gene that determine a deficiency in the encoded IGHMBP2 protein, which plays a critical role in motor neuron survival because of its functions in mRNA processing and maturation. Although it is rare, SMARD1 is the second most common motor neuron disease of infancy, and currently, treatment is primarily supportive. No effective therapy is available for this devastating disease, although multidisciplinary care has been an essential element of the improved quality of life and life span extension in these patients in recent years. The objectives of this review are to discuss the current understanding of SMARD1 through a summary of the presently known information regarding its clinical presentation and pathogenesis and to discuss emerging therapeutic approaches. Advances in clinical care management have significantly extended the lives of individuals affected by SMARD1 and research into the molecular mechanisms that lead to the disease has identified potential strategies for intervention that target the underlying causes of SMARD1. Gene therapy via gene replacement or gene correction provides the potential for transformative therapies to halt or possibly prevent neurodegenerative disease in SMARD1 patients. The recent approval of the first gene therapy approach for SMA associated with mutations in the SMN1 gene may be a turning point for the application of this strategy for SMARD1 and other genetic neurological diseases.

Diagnostic value of whole-exome sequencing in Chinese pediatric-onset neuromuscular patients

BACKGROUND

Neuromuscular disorders (NMDs) comprise a group of heterogeneous genetic diseases with a broad spectrum of overlapping the clinical presentations that makes diagnosis challenging. Notably, the recent introduction of whole-exome sequencing (WES) is introducing rapid changes on the genetic diagnosis of NMDs. We aimed to investigate the diagnostic value of WES for pediatric-onset NMDs.

METHODS

We applied integrated diagnostic approach and performed WES in 50 Chinese subjects (30 males, 20 females) with undiagnosed pediatric-onset NMDs despite previous specific tests. The patients were categorized in four subgroups according to phenotyping and investigation findings. Variants on NMDs gene list and open exome analysis for those with initial negative findings were identified.

RESULTS

WES identified causative variants in ACTA1 (n = 2), POMT1, COL6A1 (n = 2), MTMR2, LMNA, SELENON, DNM2, TGFB1, MPZ, IGHMBP2, and LAMA2 in 13 patients. Two subjects have variants of uncertain significance (VUSs) in TTN and SCN11A, unlikely to be pathogenic due to incompatible phenotypes. The mean interval time from symptom onset to genetic diagnosis was 10.4 years (range from 1 month to 33 years). The overall diagnostic yield of WES in our cohort was 26%. Open exome analysis was necessary to identify the pathogenic variant in TGFB1 that caused skeletal dysplasia with neuromuscular presentation.

CONCLUSION

Our study shows a clear role of WES in the pathway of integrated diagnostic approach to shorten the diagnostic odyssey in patients with rare NMDs.

Spinal muscular atrophy with respiratory distress type 1: Clinical phenotypes, molecular pathogenesis and therapeutic insights

Spinal muscular atrophy with respiratory distress type 1 (SMARD1) is a rare autosomal recessive neuromuscular disorder caused by mutations in the IGHMBP2 gene, which encodes immunoglobulin μ‐binding protein 2, leading to progressive spinal motor neuron degeneration. We review the data available in the literature about SMARD1. The vast majority of patients show an onset of typical symptoms in the first year of life. The main clinical features are distal muscular atrophy and diaphragmatic palsy, for which permanent supportive ventilation is required. No effective treatment is available yet, but novel therapeutic approaches, such as gene therapy, have shown encouraging results in preclinical settings and thus represent possible methods for treating SMARD1. Significant advancements in the understanding of both the SMARD1 clinical spectrum and its molecular mechanisms have allowed the rapid translation of preclinical therapeutic strategies to human patients to improve the poor prognosis of this devastating disease.

Distal Spinal Muscular Atrophy: An Overlooked Etiology of Weaning Failure in Children with Respiratory Insufficiency

Spinal muscular atrophy with respiratory distress type 1 (SMARD1) is a rare autosomal recessive neuromuscular disorder that involves the anterior horn motor neurons. It is a disease with a poor prognosis presenting with progressive distal motor weakness and respiratory insufficiency from diaphragmatic paralysis followed by distal muscle weakness before 6 months of age. With the intent to spread the awareness of this rare and life-threatening disease, we report a 2.5-month-old female infant with a subsequent diagnosis of SMARD1, who was admitted in our pediatric intensive care unit with chief complaint of progressive respiratory distress and poor feeding.

Clinical and molecular features and therapeutic perspectives of spinal muscular atrophy with respiratory distress type 1

Spinal muscular atrophy with respiratory distress (SMARD1) is an autosomal recessive neuromuscular disease caused by mutations in the IGHMBP2 gene, encoding the immunoglobulin μ-binding protein 2, leading to motor neuron degeneration. It is a rare and fatal disease with an early onset in infancy in the majority of the cases. The main clinical features are muscular atrophy and diaphragmatic palsy, which requires prompt and permanent supportive ventilation. The human disease is recapitulated in the neuromuscular degeneration (nmd) mouse. No effective treatment is available yet, but novel therapeutical approaches tested on the nmd mouse, such as the use of neurotrophic factors and stem cell therapy, have shown positive effects. Gene therapy demonstrated effectiveness in SMA, being now at the stage of clinical trial in patients and therefore representing a possible treatment for SMARD1 as well. The significant advancement in understanding of both SMARD1 clinical spectrum and molecular mechanisms makes ground for a rapid translation of pre-clinical therapeutic strategies in humans.

Severe phenotypes of SMARD1 associated with novel mutations of the IGHMBP2 gene and nuclear degeneration of muscle and Schwann cells

Spinal muscular atrophy with respiratory distress type 1 (SMARD1) is a very rare autosomal recessive form of spinal muscular atrophy manifested in low birth weight, diaphragmatic palsy and distal muscular atrophy. Caused by a mutation in the IGHMBP2 gene, the disease is addressed here by reference to five Polish patients in which SMARD1 has been confirmed genetically. All presented a severe form of the disease and had evident symptoms during the second month of life; with four displaying weak cries, feeding difficulties and hypotonia from birth. Two were afflicted by severe dysfunction of the autonomic nervous system. Ultrastructural analysis of a muscle biopsy revealed progressive degeneration within the nuclei of the muscle cells and Schwann cells. Neuromuscular junctions were also defective. It proved possible to identify in our patients 6 novel IGHMBP2 mutations: three missense (c.595G>C, c.1682T>C and c.1794C>A), two nonsense (c.94C>T and c.1336C>T) and one in-frame deletion (c.1615_1623del). One nonsense mutation (c.429C>T) that had been described previously was also identified. Observation of our patients makes it clear that clinical picture is still the most important factor suggesting diagnosis of SMARD1, though further investigations concerning some of the symptoms are required. As the IGHMBP2 gene is characterized by significant heterogeneity, genetic counseling of affected families is rendered more complex. IGHMBP2 protein deficiency can lead to the degeneration of nuclei, in both muscle and Schwann cells.

Diaphragmatic weakness with progressive sensory and motor polyneuropathy: case report of a neonatal IGHMBP2-related neuropathy

The authors present a child affected with diaphragmatic paralysis in the early neonatal period. Although no electroneuromyographic abnormalities were reported, the patient developed dramatic motor and respiratory impairment with impossibility to wean from mechanical ventilation. Repeated electroneuromyographic study at age 4 months revealed severe neurogenic changes and sensory nerve abnormalities with more preserved nerve conduction velocities. Genetic studies identified 2 mutations in the gene IGHMBP2. These results support the consideration of this entity as a form of sensory-motor rapidly progressive polyneuropathy rather than a primary anterior horn disease (IGHMBP2-related neuropathy). A review of the series of mutated patients in the French National Database gives new insights of the incidence of this disease in France.

Heterogeneity in spinal muscular atrophy with respiratory distress type 1

Spinal muscular atrophy with respiratory distress type 1 (SMARD1) is a clinically heterogeneous disorder linked to mutations in the immunoglobulin mu-binding protein 2 (IGHMBP2) gene on chromosome 11q13-q21. Most infants with SMARD1 present between six weeks and six months of age with respiratory distress secondary to diaphragmatic weakness and progressive distal weakness. Sensory and autonomic dysfunctions sometimes accompany the motor weakness. This report describes a male infant with genetically confirmed SMARD1 presenting with onset of disease in the first two weeks of life with respiratory compromise and urinary retention, which has not been reported before and adds to the phenotypic variability of SMARD 1.

[A rare cause of respiratory failure in infants: distal spinal-muscular atrophy 1 (DSMA1 or SMARD1)]

Distal spinal-muscular atrophy 1 (DSMA1) or spinal-muscular atrophy with respiratory distress type 1 (SMARD1) is a rare neuromuscular disorder resulting from IGHMBP2 mutations. It is an autosomal recessive disease. We present the case of a 1-year-old girl admitted for respiratory failure associated with pneumonia. Right hemidiaphragmic elevation on the chest radiograph and distal retractions suggested the diagnosis of DSMA1. It was confirmed by muscle biopsy and molecular analysis. This unrecognized diagnosis should be considered when respiratory failure develops in the first year of life and is associated with diaphragmatic paralysis and distal muscle atrophy. Electromyography with measurement of nerve conduction velocity and muscle biopsy suggest the diagnosis, which must be confirmed by genetic analysis. After identifying the mutations, it is possible to perform prenatal diagnosis.

The Ighmbp2 helicase structure reveals the molecular basis for disease-causing mutations in DMSA1

Mutations in immunoglobulin µ-binding protein 2 (Ighmbp2) cause distal spinal muscular atrophy type 1 (DSMA1), an autosomal recessive disease that is clinically characterized by distal limb weakness and respiratory distress. However, despite extensive studies, the mechanism of disease-causing mutations remains elusive. Here we report the crystal structures of the Ighmbp2 helicase core with and without bound RNA. The structures show that the overall fold of Ighmbp2 is very similar to that of Upf1, a key helicase involved in nonsense-mediated mRNA decay. Similar to Upf1, domains 1B and 1C of Ighmbp2 undergo large conformational changes in response to RNA binding, rotating 30° and 10°, respectively. The RNA binding and ATPase activities of Ighmbp2 are further enhanced by the R3H domain, located just downstream of the helicase core. Mapping of the pathogenic mutations of DSMA1 onto the helicase core structure provides a molecular basis for understanding the disease-causing consequences of Ighmbp2 mutations.

Prediction of death in the SMNΔ7 mouse model of spinal muscular atrophy: insight into disease stage and progression

Proximal Spinal Muscular Atrophy (SMA) is a debilitating neuromuscular disease and a leading inherited genetic cause of infant death. To date, there is no effective treatment for SMA. The SMNΔ7 neonatal mouse model of SMA recapitulates key features of the severe form of SMA and remains a valuable tool in preclinical drug discovery. At any particular postnatal age (P), the disease progression in the SMNΔ7 mouse model is not universal, as some animals die as early as the day of birth and others live for up to three weeks. Identification of the disease stage in SMNΔ7 mice, independent of age, would aid in the design and interpretation of preclinical studies. We developed a score (CD score), derived from body weight analysis, that allowed us to gain insight into the disease progression and predict death. Respiratory complication is a leading cause of mortality in the SMA patient and this phenotype has been reported in severe mouse models of SMA. We subsequently measured muscle and brain tissue lactate levels, an indirect measure of hypoxia, in SMNΔ7 mice at P10 and correlated these measures to respiratory rate. SMNΔ7 mice showed a significant increase in tissue lactate and a decrease in respiratory rate in comparison to control. The CD score correlates linearly with tissue lactate level and respiratory rate. The finding of lactate buildup in the SMNΔ7 mouse and the correlation with a score that is predictive of disease stage provide an interesting insight into the disease pathophysiology and a possible biomarker for SMA.

The natural course of infantile spinal muscular atrophy with respiratory distress type 1 (SMARD1)

BACKGROUND

Only scarce information is available on the long-term outcome and the natural course of children with infantile spinal muscular atrophy with respiratory distress type 1 (SMARD1) due to mutations in the IGHMBP2 gene.

OBJECTIVE

To describe the natural disease course, to systematically quantify the residual capacities of children with SMARD1 who survive on permanent mechanical respiration, and to identify markers predicting the disease outcome at the time of manifestation.

METHODS

We conducted a longitudinal study of 11 infantile SMARD1 patients over a mean observational period of 7.8 (SD 3.2) years. Disease-specific features were continuously assessed by using a semiquantitative scoring system. Additionally, we analyzed the residual enzymatic activity of 6 IGHMBP2 mutants in our patients.

RESULTS

After an initial rapid decline of the clinical score until the age of 2 years, residual capabilities reached a plateau or even improved. The overall clinical outcome was markedly heterogeneous, but clinical scores at the age of 3 months showed a positive linear correlation with the clinical outcome at 1 year and at 4 years of age. If expressed in an in vitro recombinant system, mutations of patients with more favorable outcomes retained residual enzymatic activity.

CONCLUSIONS

Despite their severe disabilities and symptoms, most SMARD1 patients are well integrated into their home environment and two thirds of them are able to attend kindergarten or school. This information will help to counsel parents at the time of disease manifestation.

Infantile spinal muscular atrophy with respiratory distress type I (SMARD 1): an atypical phenotype and review of the literature

Spinal muscular atrophy with respiratory distress (SMARD 1) is a very rare autosomal recessive motor neuron disorder that affects infants and is characterized by diaphragmatic palsy, symmetrical distal muscular weakness, muscle atrophy, peripheral sensory neuropathy and autonomic nerve dysfunction. SMARD 1 is inherited as an autosomal recessive trait and the mutations have been identified in the gene encoding immunoglobulin μ-binding protein 2 (IGHMBP2), located on chromosome 11q13. It is considered a fatal form of infantile motoneuron disease and most of the patients dies within the first 13 months of life. We present a female child with genetically confirmed SMARD 1 displaying a mild phenotype and no severe signs of respiratory involvement, typically found in this form, up to 38 months despite a diaphragmatic palsy diagnosed at 6 months of age. Therefore, our clinical observation suggests that respiratory failure is not secondary, in any case, to the diaphragmatic palsy but other pathogenetic mechanisms might be involved.

Infantile-onset spinal muscular atrophy with respiratory distress-1 diagnosed in a 20-year-old man

Spinal muscular atrophy with respiratory distress (SMARD1) presents within the first 13months of age with low birth weight, progressive length dependent motor neuropathy, and respiratory failure from diaphragmatic paralysis. SMARD1 is caused by mutations in IGHMBP2, encoding the immunoglobulin μ-binding protein 2. Because of the severity of the disorder, many infantile-onset SMARD1 patients do not live past the first decade of life. This report documents the clinical course of a 20-year-old man diagnosed with SMARD1.

Infantile spinal muscular atrophy with respiratory distress type 1: a case report

The condition, currently known as spinal muscular atrophy with respiratory distress type 1, is an unusual variant of spinal muscular atrophy type 1 that is characterized by early respiratory failure due to diaphragmatic paralysis. The defective gene, the immunoglobulin mu-binding protein 2 (IGHMBP2 gene), of this autosomal recessive disorder is located on chromosome 11q13 and encodes immunoglobulin mu-binding protein 2. The natural history and phenotypic spectrum of the disease are still not clear. The authors present the first genetically proven case of spinal muscular atrophy with respiratory distress type 1 to be reported from Saudi Arabia. The parents are first cousins and the causative gene sequencing revealed mutation in exon 7 reported for the first time in a homozygous form. The clinical scenario of the case is discussed. The findings in the muscle magnetic resonance imaging (MRI) are presented.

Interfamilial phenotypic heterogeneity in SMARD1

Spinal muscular atrophy with respiratory distress (SMARD1: mu-binding protein 2 gene mutation) is characterised by low birth weight, progressive distal limb weakness, diaphragmatic paralysis and subsequent respiratory failure manifesting before 13 months of age. Our case report illustrates marked phenotype variability in two siblings with an identical genetic mutation of SMARD1, one of whom died of fulminant respiratory failure aged 6 months, whereas the other shows limb weakness but, only mild sleep hypoventilation aged 12 years. This suggests other compensatory mechanisms may play a role in modifying SMARD1; broadening our perception of phenotype. Therefore, SMARD1 phenotype should be considered in cases of atypical spinal muscular atrophy even in the absence of overt diaphragmatic weakness.

Spinal muscular atrophy type I mimicking critical illness neuropathy in a paediatric intensive care neonate: electrophysiological features

We report the case of a neonate with spinal muscular atrophy type I (SMA type I or Werdnig-Hoffman disease) who was initially misdiagnosis as having critical illness neuropathy. Electromyography (EMG) showed a moderate loss of voluntary and motor unit potentials of both neurogenic and myopathic appearance. Nerve conduction studies revealed the presence of a severe sensory-motor axonal neuropathy. Finally, a biopsy of quadriceps was compatible with the diagnosis of SMA type I. A genetic study confirmed the existence of a homozygous absence of exons 7 and 8 of the telomeric supervival motoneuron gene (SMN1 gene).

[Distal spinal-muscular atrophy 1 (DSMA1 or SMARD1)]

In this article, we review the clinical, neuropathological and genetic aspects of distal spinal-muscular atrophy 1 (DSMA1; MIM#604320), formerly designated as autosomal recessive spinal muscular atrophy with respiratory distress type 1 (SMARD1) and also known as distal hereditary-motor neuropathy type 6 (dHMN6 or HMN6).

Spinal muscular atrophy with respiratory distress type 1 (SMARD1)

Autosomal recessive spinal muscular atrophy with respiratory distress type 1 (SMARD1), recently referred to as distal spinal muscular atrophy 1 (DSMA1; MIM#604320) and also known as distal hereditary motor neuropathy type 6 (dHMN6 or HMN6), results from mutations in the IGHMBP2 gene on chromosome 11q13.3 encoding the immunoglobulin micro-binding protein 2. In contrast to the infantile spinal muscular atrophy type 1 (SMA1; Werdnig-Hoffmann disease) with weakness predominantly of proximal muscles and bell-shaped thorax deformities due to intercostal muscle atrophy, infants with distal spinal muscular atrophy 1 usually present with distal muscle weakness, foot deformities, and sudden respiratory failure due to diaphragmatic paralysis that often requires urgent intubation. In this article, the authors review the clinical, neuropathological, and genetic aspects of distal spinal muscular atrophy 1 and discuss differential diagnoses.

Clinical and mutational profile in spinal muscular atrophy with respiratory distress (SMARD): defining novel phenotypes through hierarchical cluster analysis

Autosomal recessive spinal muscular atrophy with respiratory distress (SMARD) is a heterogeneous disorder. Mutations in the immunoglobulin micro-binding protein gene (IGHMBP2) lead to SMARD1, but clinical criteria that delineate SMARD1 from other SMARD syndromes are not well established. Here we present a retrospective clinical and genetic study to determine the criteria that would predict the presence or absence of IGHMBP2 mutations. From 141 patients with respiratory distress and a spinal muscular atrophy phenotype we recorded the clinical features through a questionnaire and sequenced the entire coding region of IGHMBP2. In 47 (33%) patients we identified IGHMBP2 mutations, 14 of which were not described before. Clinical features and combinations thereof associated with the presence of IGHMBP2 mutations were discovered through hierarchical cluster analysis. This method detects common traits not evident at first sight by grouping items according to their similarity. The combination of "manifestation of respiratory failure between 6 weeks and 6 months" AND ("presence of diaphragmatic eventration" OR "preterm birth") predicted the presence of IGHMBP2 mutations with 98% sensitivity and 92% specificity. Non-SMARD1 patients fell into two different symptom clusters, mainly separated by the age at respiratory failure and the presence of multiple congenital contractures. The 14 novel IGHMBP2 mutations comprised missense, frameshift, splice-site, and nonsense mutations. All missense mutations altered conserved residues within or adjacent to the putative DNA helicase domain. The c.1235+3A>G splice-site mutation did not entirely suppress correct splicing and we found a residual wild-type IGHMBP2 mRNA steady-state level of 24.4+/-6.9%, which was, however, not sufficient to avert SMARD1 in this patient.