IGHMBP2 Research Articles

Gene therapy rescues disease phenotype in a spinal muscular atrophy with respiratory distress type 1 (SMARD1) mouse model.

Spinal muscular atrophy with respiratory distress type 1 (SMARD1) is an autosomal recessive motor neuron disease affecting children. It is caused by mutations in the IGHMBP2 gene (11q13) and presently has no cure. Recently, adeno-associated virus serotype 9 (AAV9)-mediated gene therapy has been shown to rescue the phenotype of animal models of another lower motor neuron disorder, spinal muscular atrophy 5q, and a clinical trial with this strategy is ongoing. We report rescue of the disease phenotype in a SMARD1 mouse model after therapeutic delivery via systemic injection of an AAV9 construct encoding the wild-type IGHMBP2 to replace the defective gene. AAV9-IGHMBP2 administration restored protein levels and rescued motor function, neuromuscular physiology, and life span (450% increase), ameliorating pathological features in the central nervous system, muscles, and heart. To test this strategy in a human model, we transferred wild-type IGHMBP2 into human SMARD1-induced pluripotent stem cell-derived motor neurons; these cells exhibited increased survival and axonal length in long-term culture. Our data support the translational potential of AAV-mediated gene therapies for SMARD1, opening the door for AAV9-mediated therapy in human clinical trials.

Truncating and Missense Mutations in IGHMBP2 Cause Charcot-Marie Tooth Disease Type 2

Using a combination of exome sequencing and linkage analysis, we investigated an English family with two affected siblings in their 40s with recessive Charcot-Marie Tooth disease type 2 (CMT2). Compound heterozygous mutations in the immunoglobulin-helicase-μ-binding protein 2 (IGHMBP2) gene were identified. Further sequencing revealed a total of 11 CMT2 families with recessively inherited IGHMBP2 gene mutations. IGHMBP2 mutations usually lead to spinal muscular atrophy with respiratory distress type 1 (SMARD1), where most infants die before 1 year of age. The individuals with CMT2 described here, have slowly progressive weakness, wasting and sensory loss, with an axonal neuropathy typical of CMT2, but no significant respiratory compromise. Segregating IGHMBP2 mutations in CMT2 were mainly loss-of-function nonsense in the 5' region of the gene in combination with a truncating frameshift, missense, or homozygous frameshift mutations in the last exon. Mutations in CMT2 were predicted to be less aggressive as compared to those in SMARD1, and fibroblast and lymphoblast studies indicate that the IGHMBP2 protein levels are significantly higher in CMT2 than SMARD1, but lower than controls, suggesting that the clinical phenotype differences are related to the IGHMBP2 protein levels.

G.P.240: Next Generation Sequencing reveals IGHMBP2 variants as a cause for distal hereditary motor neuronopathy in two children

IGHMBP2 variants are associated with autosomal recessive distal spinal muscular atrophy 1 and distal hereditary motor neuronopathy type VI (dHMN6). Here we present two patients with potentially pathogenic variants in IGHMBP2 gene. Case 1-A 16 year old male patient with a progressive distal weakness and deformity of both hands and feet which presented in childhood. He also had marked pain (possibly radicular in origin) mainly in toes and chest, which was severe enough to require opiates. His hands showed marked thenar and hypothenar loss of muscle bulk. Neurophysiological investigations revealed an active and partial chronic denervation. Initial genetic investigations did not reveal any abnormalities. His DNA was subsequently analysed by gene panel testing. Gene panel testing (simultaneous testing of 56 genes associated with the common and the rare causes of different types of inherited peripheral neuropathy) revealed a single heterozygous frameshift variant in exon 5 of the IGHMBP2 gene; c.661del, p. (Thr221Profs*12). No second variant was identified in this patient. It is likely to be pathogenic as it is expected to cause premature truncation of the mRNA, leading either to the production of a non-functional protein, or no protein product from that allele due to nonsense mediated decay. Case 2 -A 12 year old female presented with gait problems, clumsiness, and recurrent falls at the age of 5 years. Neurophysiological investigations revealed a demyelinating neuropathy. Her initial gene testing was negative. Her DNA was subsequently analysed by gene panel testing. Two heterozygous frameshift variants were detected in the IGHMBP2 gene; c.2356delG, p. (Ala786Profs*45) in exon 13, and c.2911_2912delAG, p. (Arg971Glufs*4) in exon 15. Parents of the proband were tested and each was found to be heterozygous for one IGHMBP2 variant, confirming that the two variants are in trans in their daughter. Further studies will be needed to establish pathogenicity. IGHMBP2 variants are associated with autosomal recessive distal spinal muscular atrophy 1 and distal hereditary motor neuronopathy type VI (dHMN6). Here we present two patients with potentially pathogenic variants in IGHMBP2 gene. Case 1-A 16 year old male patient with a progressive distal weakness and deformity of both hands and feet which presented in childhood. He also had marked pain (possibly radicular in origin) mainly in toes and chest, which was severe enough to require opiates. His hands showed marked thenar and hypothenar loss of muscle bulk. Neurophysiological investigations revealed an active and partial chronic denervation. Initial genetic investigations did not reveal any abnormalities. His DNA was subsequently analysed by gene panel testing. Gene panel testing (simultaneous testing of 56 genes associated with the common and the rare causes of different types of inherited peripheral neuropathy) revealed a single heterozygous frameshift variant in exon 5 of the IGHMBP2 gene; c.661del, p. (Thr221Profs*12). No second variant was identified in this patient. It is likely to be pathogenic as it is expected to cause premature truncation of the mRNA, leading either to the production of a non-functional protein, or no protein product from that allele due to nonsense mediated decay. Case 2 -A 12 year old female presented with gait problems, clumsiness, and recurrent falls at the age of 5 years. Neurophysiological investigations revealed a demyelinating neuropathy. Her initial gene testing was negative. Her DNA was subsequently analysed by gene panel testing. Two heterozygous frameshift variants were detected in the IGHMBP2 gene; c.2356delG, p. (Ala786Profs*45) in exon 13, and c.2911_2912delAG, p. (Arg971Glufs*4) in exon 15. Parents of the proband were tested and each was found to be heterozygous for one IGHMBP2 variant, confirming that the two variants are in trans in their daughter. Further studies will be needed to establish pathogenicity.

IPSC-Derived Neural Stem Cells Act via Kinase Inhibition to Exert Neuroprotective Effects in Spinal Muscular Atrophy with Respiratory Distress Type 1

SummarySpinal muscular atrophy with respiratory distress type 1 (SMARD1) is a motor neuron disease caused by mutations in the IGHMBP2 gene, without a cure. Here, we demonstrate that neural stem cells (NSCs) from human-induced pluripotent stem cells (iPSCs) have therapeutic potential in the context of SMARD1. We show that upon transplantation NSCs can appropriately engraft and differentiate in the spinal cord of SMARD1 animals, ameliorating their phenotype, by protecting their endogenous motor neurons. To evaluate the effect of NSCs in the context of human disease, we generated human SMARD1-iPSCs motor neurons that had a significantly reduced survival and axon length. Notably, the coculture with NSCs ameliorate these disease features, an effect attributable to the production of neurotrophic factors and their dual inhibition of GSK-3 and HGK kinases. Our data support the role of iPSC as SMARD1 disease model and their translational potential for therapies in motor neuron disorders.

Differentiation defects in primary motoneurons from a SMARD1 mouse model that are insensitive to treatment with low dose PEGylated IGF1.

Muscle atrophy and diaphragmatic palsy are the clinical characteristics of spinal muscular atrophy with respiratory distress type 1 (SMARD1), and are well represented in the neuromuscular degeneration (Nmd2J) mouse, modeling the juvenile form of SMARD1. Both in humans and mice mutations in the IGHMBP2 gene lead to motoneuron degeneration. We could previously demonstrate that treatment with a polyethylene glycol-coupled variant of IGF1 (PEG-IGF1) improves motor functions accompanied by reduced fiber degeneration in the gastrocnemius muscle and the diaphragm, but has no beneficial effect on motoneuron survival. These data raised the question which cell autonomous disease mechanisms contribute to dysfunction and loss of Ighmbp2-deficient motoneurons. An analysis of primary Ighmbp2-deficient motoneurons exhibited differentiation deficits such as reduced spontaneous Ca2+ transients and altered axon elongation, which was not compensated by PEG-IGF1. This points to an IGF1 independent mechanism of motoneuron degeneration that deserves treatment approaches in addition to IGF1.

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.

Variations ofIGHMBP2Gene Was Not the Major Cause of Han Chinese Patients With Non-5q-Spinal Muscular Atrophies

Spinal muscular atrophy with respiratory distress type 1 (SMARD1), a notably common form of non-5q-spinal muscular atrophy, can be confused with infantile spinal muscular atrophy and is characterized by the early onset of diaphragmatic palsy and predominantly distal muscle weakness. The defective gene, immunoglobulin mu-binding protein 2 (IGHMBP2), is located on chromosome 11q13-q21. In this study, we screened the IGHMBP2 gene in 53 unrelated Han Chinese non-5q-spinal muscular atrophy patients and 100 healthy controls. Two novel mutations (c.711+1G>C and c.1817G>A) and 5 nucleotide polymorphisms (c.57T>C, c.1554C>T, c.1914G>A, c.2080C>T, and c.2270G>C) were identified. However, only 1 patient harbored the compound heterozygous mutations (c.711+1G>C, c.1817G>A). Furthermore, the homozygous c.2636C>A (p.T879K) variation, which has been included as a mutation in the Human Gene Mutation Database, was found both in patients and healthy individuals. In conclusion, the IGHMBP2 gene was not found to be a major causative gene linked to Han Chinese non-5q-spinal muscular atrophy patients.

One Novel and One Recurrent Mutation in IGHMBP2 Gene, Causing Severe Spinal Muscular Atrophy Respiratory Distress 1 With Onset Soon After Birth

A family with 2 siblings with severe spinal muscular atrophy with respiratory distress 1 (SMARD1) was genetically proved to be caused by mutations in IGHMBP2 gene. Both patients developed progressive muscular weakness and respiratory distress and died before 6 months of age. One novel deletion, c.780delG;p.(Gln260Hisfs*24), inherited from the father and a nonsense mutation, c.1488C>A;p.(Cys496*), inherited from the mother were detected. An attempt was made to correlate the genetic-clinical data available in the literature. The clinical case presented in this study might be considered as the most severe form of spinal muscular atrophy respiratory distress 1 reported so far, presumably because of the total absence of IGHMBP2 enzyme activity.

The Natural Course of Infantile Spinal Muscular Atrophy With Respiratory Distress Type 1 (SMARD1)

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. 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. 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. 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. 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.

A New Nonsense Mutation of the IGHMBP2 Gene Responsible for the First Case of SMARD1 in a Sardinian Patient with Giant Cell Hepatitis

We describe the case of a Sardinian female child affected by SMARD1, a genetic composite heterozygote, in whom a new nonsense mutation (R788X) was found. A sister was affected by generalized muscular hypotonia and died from respiratory insufficiency at the age of 9 months, before a diagnostic definition had been formulated. Our patient died at 6 months due to respiratory insufficiency. At autopsy some differences with previous published cases were observed. In fact, our case is to the best of our knowledge the first report of giant cell hepatitis and myocarditis in SMARD1-affected patients, although this could be a chance association.

Characterization of the promoter region of the human IGHMBP2 ( Sμbp-2) gene and its response to TPA in HL-60 cells

Immunoglobulin mu-binding protein 2 (IGHMBP2/Sμbp-2) is a helicase motif-containing DNA-binding protein that has been suggested to regulate various nuclear functions. Recent studies indicated that mutations in the IGHMBP2 gene are responsible for spinal muscular atrophy with respiratory distress type I (SMARD1). However, the mechanism of regulation of IGHMBP2 gene expression remains unclear. In the present study, a 2.0-kb fragment of the 5′-flanking (promoter) region of the human IGHMBP2 gene was isolated from the HL-60 genome by PCR and ligated into a luciferase (Luc) expression vector, pGL3, to generate the pSmu-Luc plasmid. Deletion analyses revealed that a 108-bp region is essential for basal promoter activity with a response to TPA in HL-60 cells. TF-SEARCH analysis showed that overlapping ets (GGAA) motifs are located upstream of the transcription start sites. Chromatin immunoprecipitation (ChIP) assay, electropheretic mobility shift assay (EMSA) and competition analyses indicated that PU.1 (Spi-1) recognizes and binds to the duplicated ets motifs in this 108-bp region. Moreover, co-transfection of the PU.1 expression plasmid and pSmu-Luc into HL-60 cells revealed that PU.1 modulates TPA-induced IGHMBP2 promoter activity. Taken together, these observations suggest that the duplicated GGAA motifs are essential for the IGHMBP2 promoter activity and its positive response to TPA in HL-60 cells.

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.

Sporadic ALS with early-onset respiratory failure is not associated with IGHMBP2 gene mutations

Few distinct motor neurone disease (MND) variants—for example, familial amyotrophic lateral sclerosis (fALS) and spinal muscular atrophy (SMA)—are caused by definitive gene mutations. Within the phenotypic spectrum of the superoxide...

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.

NMP05 Infantile spinal muscular atrophy with respiratory distress type 1 (SMARD1) associated with delayed CNS myelination and novel mutation in IGHMBP2 gene

NMP05 Infantile spinal muscular atrophy with respiratory distress type 1 (SMARD1) associated with delayed CNS myelination and novel mutation in IGHMBP2 gene

A new form of spinal muscular atrophy

Spinal muscular atrophies with mutations in the telomeric SMN1 gene (chromosome 5q13) are one of the most frequent autosomal recessively inherited disorders. Due to a progressive loss of α-motorneurons a muscular atrophy with flaccid, proximally accentuated palsy appears. The spinal muscular atrophy with respiratory distress (SMARD1) results from a mutation in the IGHMBP2 gene (chromosome 11q13) and the first symptom is often weakness of the diaphragm and respiratory insuffiency.

N.P.2 08 Infantile spinal muscular atrophy with respiratory distress type 1 (SMARD1) associated with delayed CNS myelination and novel mutation in the IGHMBP2 gene

N.P.2 08 Infantile spinal muscular atrophy with respiratory distress type 1 (SMARD1) associated with delayed CNS myelination and novel mutation in the IGHMBP2 gene

Dilated cardiomyopathy in the nmd mouse: transgenic rescue and QTLs that improve cardiac function and survival

Mutations in the immunoglobulin mu binding protein-2 (Ighmbp2) gene cause motor neuron disease and dilated cardiomyopathy (DCM) in the neuromuscular degeneration (nmd) mouse and spinal muscular atrophy with respiratory distress (SMARD1) in humans. To investigate the role of IGHMBP2 in the pathogenesis of DCM, we generated transgenic mice expressing the full-length Ighmbp2 cDNA specifically in myocytes under the control of the mouse titin promoter. This tissue-specific transgene increased the lifespan of nmd mice up to 8-fold by preventing primary DCM and showed complete functional correction as measured by ECG, echocardiography and plasma creatine kinase-MB. Double-transgenic nmd mice expressing Ighmbp2 both in myocytes and in neurons display correction of both DCM and motor neuron disease, resulting in an essentially wild-type appearance. Additionally, quantitative trait locus (QTL) analysis was undertaken to identify genetic modifier loci responsible for the preservation of cardiac function and a marked delay in the onset of cardiomyopathy in a CAST/EiJ backcross population. Three major CAST-derived cardiac modifiers of nmd were identified on chromosomes 9, 10 and 16, which account for over 26% of the genetic variance and that continue to suppress the exacerbation of cardiomyopathy, otherwise resulting in early death, as incipient B6.CAST congenics. Overall, our results verify the tissue-specific requirement for IGHMBP2 in cardiomyocyte maintenance and survival and describe genetic modifiers that can alter the course of DCM through cardiac functional adaptation and physical remodeling in response to changes in load and respiratory demand.

A new mutation of IGHMBP2 gene in spinal muscular atrophy with respiratory distress type 1

This report presents a new mutation in the first Japanese female infant with spinal muscular atrophy with respiratory distress type 1. She manifested the characteristic clinical features, including early-onset respiratory failure due to diaphragmatic paralysis and severe distal muscle weakness. Muscle biopsy in the femoral muscle indicated massive neurogenic changes. Sural nerve biopsy disclosed a moderate reduction of myelinated fibers, predominantly reduced large fibers. She had a novel homozygous missense mutation 2685 C -->A, leading to a T879K substitution in the immunoglobulin mu-binding protein 2 gene. Both parents were heterozygous for this mutation.

Characterization of Ighmbp2 in motor neurons and implications for the pathomechanism in a mouse model of human spinal muscular atrophy with respiratory distress type 1 (SMARD1).

Spinal muscular atrophy with respiratory distress type 1 (SMARD1) is caused by recessive mutations of the IGHMBP2 gene. The role of IGHMBP2 (immunoglobulin mu-binding protein 2) in the pathomechanism of motor neuron disease is unknown. We have generated antibodies against Ighmbp2 and showed that low levels of Ighmbp2 immunoreactivity are present in the nucleus of spinal motor neurons and high levels in cell bodies, axons and growth cones. Ighmbp2 protein levels are strongly reduced in neuromuscular degeneration (nmd) mice, the mouse model of SMARD1. Mutant mice show severe motor neuron degeneration before first clinical symptoms become apparent. The loss of motor neuron cell bodies in lumbar spinal cord is followed by axonal degeneration in corresponding nerves such as the femoral quadriceps and sciatic nerve and loss of axon terminals at motor endplates. Motor neuron degeneration and clinical symptoms then slowly progress until the mice die at the age of 3-4 months. In addition, myopathic changes seem to contribute to muscle weakness and especially to respiratory failure, which is characteristic of the disorder in humans. Cultured motor neurons from embryonic nmd mice did not show any abnormality with respect to survival, axonal growth or growth cone size, thus differing from motor neurons derived from, e.g. Smn (survival motor neuron) deficient mice, the model of spinal muscular atrophy (SMA). Our data suggest that the pathomechanism in SMARD1 is clearly distinct from other motor neuron diseases such as classic SMA.