Prenatal diagnosis of spinal muscular atrophy type I (Werdnig- hoffmann) by DNA deletion analysis of cultivated amniocytes.
AIM: Presentation of a prenatally diagnosed case of Werdnig-Hoffmann disease, the most severe type of spinal muscular atrophy. METHODS: DNA obtained from cultivated amniocytes was analyzed for deletions in the survival motor neuron gene and neuronal apoptosis inhibitory protein gene. RESULTS: The fetus was diagnosed as an affected homozygote for deletions in exon 7 and exon 8 of the survival motor neuron gene. No deletions of exon 5 in the neuronal apoptosis inhibitory protein gene were found. CONCLUSION: Direct DNA deletion analysis of the survival motor neuron gene and neuronal apoptosis inhibitory protein gene in affected families represents a highly reliable and fast method for prenatal diagnosis of Werdnig-Hoffmann disease. (+info
Reduced survival motor neuron (Smn) gene dose in mice leads to motor neuron degeneration: an animal model for spinal muscular atrophy type III.
Spinal muscular atrophy (SMA) is caused by deletion or specific mutations of the telomeric survival motor neuron ( SMN ) gene on human chromosome 5. The human SMN gene, in contrast to the Smn gene in mouse, is duplicated and the centromeric copy on chromosome 5 codes for transcripts which preferentially lead to C-terminally truncated SMN protein. Here we show that a 46% reduction of Smn protein levels in the spinal cord of Smn heterozygous mice leads to a marked loss of the cytoplasmic Smn pool and motor neuron degeneration resembling spinal muscular atrophy type 3. Smn heterozygous mice described here thus represent a model for the human disease. These mice could allow screening for SMA therapies and help in gaining further understanding of the pathophysiological events leading to motor neuron degeneration in SMA. (+info
Juvenile muscular atrophy of distal upper extremity (Hirayama disease).
This disease is characterized by initially progressive muscular weakness and wasting of the distal upper limb(s) in young people predominantly in men, followed by a spontaneous arrest within several years. This disease has been thought to be separate from motor neuron diseases, yet some authors still consider the illness a variant of motor neuron disease. However, the pathological evidence of ischemic changes in the lower cervical anterior horn should facilitate differentiation of the disorder from degenerative motor neuron disease. Recent radiological investigations proved compressive flattening of the lower cervical cord due to forward displacement of the cervical dural sac and spinal cord induced by neck flexion. These findings suggest that sustained or repeated neck flexion may cause ischemic changes in the cervical anterior horn. Application of a cervical collar to minimize neck flexion prevents progressive muscular weakness in an early stage of the disease. (+info
An essential SMN interacting protein (SIP1) is not involved in the phenotypic variability of spinal muscular atrophy (SMA).
The survival motor neuron (SMN) protein and the SMN interacting protein 1 (SIP1) are part of a 300 kD protein complex with a crucial role in snRNP biogenesis and pre-mRNA splicing. Both proteins are colocalised in nuclear structures called gems and in the cytoplasm. Approximately 96% of patients with autosomal recessive spinal muscular atrophy (SMA) show mutations in the SMN1 gene, while about 4% fail to show any mutation, despite a typical SMA phenotype. Additionally, sibs with identical 5q13 homologs and homozygous absence of SMN1 can show variable phenotypes which suggest that SMA is modified by other, yet unknown factors. Since both genes, SMN1 and SIP1, belong to the same pathway and are part of the same protein complex, it is obvious to ask whether mutations within SIP1 are responsible for both the phenotypic variability and the appearance of non-SMN mutated SMA patients. First, we identified the chromosomal location of SIP1 and assigned it to chromosomal region 14q13-q21 by fluorescence in situ hybridisation. No SMA related disorder has yet been assigned to this chromosomal region. Next, we determined the exon-intron structure of the SIP1 gene which encompasses 10 exons and identified five transcription isoforms. We sequenced either RT-PCR products or genomic DNA covering the complete coding region from 23 typical SMA patients who had failed to show any SMN1 mutation. No mutation and no polymorphism was found within SIP1. Additionally, we sequenced RT-PCR products or genomic fragments of the entire SIP1 coding region from 26 sibs of 11 SMA families with identical genotypes (delta7SMN/delta7SMN or delta7SMN/other mutation) but different phenotypes and again no mutation was found. Finally, we performed quantitative analysis of RT-PCR products from the same 26 sibs. No difference in expression level of the five isoforms among phenotypically variable sibs was observed. Based on these data, we suggest that neither the phenotypic variability nor the 5q-unlinked SMA are caused by mutations within SIP1. (+info
Non-progressive juvenile spinal muscular atrophy of the distal upper limb (Hirayama's disease): a clinical variant of the benign monomelic amyotrophy.
Hirayama's disease (HD) is frequently found in Asia, and is rarely referred among westerners. It affects young people with higher incidence in males. It is a focal distal amyotrophy with unilateral or asymmetric bilateral involvement of C7, C8 and T1 innervated muscles. HD appears sporadically and has a benign evolution with clinical stabilization in around one year. We report four young male patients with clinical and electrophysiological alterations described in HD, which were followed-up during 5 years. Electromyographic findings were indicative of lower motor neuron involvement. We analyzed cervical MRI aiming at understanding if a questionable spinal cord compression could be implicated in the pathogenesis, but no abnormality was verified. In view of its clinical, and EMG characteristics, HD is no more than a benign monomelic amyotrophy (BMA) clinical variant, and not a specific disease. This eponym could be considered only for the distal upper limb variant (Hirayama's variant) of the BMA. (+info
Correlation between genotype and phenotype in Korean patients with spinal muscular atrophy.
The goal of this study was to define the correlation between genotype and phenotype in Korean patients with spinal muscular atrophy (SMA). The SMA can be classified into three groups based on the age of onset and the clinical course. The candidate genes, survival motor neuron (SMN) gene, neuronal apoptosis inhibitory protein (NAIP) gene, and p44 gene were mapped and duplicated with telomeric and centromeric. The loss of the telomeric SMN occurs by a different mechanism. That is the deletion or conversion of telomeric SMN to centromeric SMN, in which case the conversion could produce a mild phenotype and deletion could produce a severe one. It has been known that there may be a balance between the numbers of copies expressed by the centromeric and telomeric SMN genes. In our study, ten patients with type I SMA and two type II patients were identified by their clinical findings and DNA studies. The major deletion of SMA candidate genes, deletion of the SMN gene, NAIP gene, and p44 gene were identified in six patients with type I SMA, while the rest of type I and all the type II patients showed the deletion of the SMN gene only. Allele numbers of the C212 marker were compared in patients and normal controls in order to find the correlation between the copy numbers and the clinical severity. The result was that type I patients had 2-5 alleles and the normal controls had 4-6. This suggests that the deletion is a major determining factor in the clinical phenotype. However, two type I patients with telomeric NAIP gene deletion notably had 4-5 alleles, as in the normal controls. This result implies that the correlation between the copy numbers and the severity is uncertain as opposed to the previous hypothesis. One type I patient showed the conversion of the centromeric SMN gene to the telomeric, which supports the conclusion that gene conversion is an important molecular mechanism for SMA. In the study of one hundred normal newborns, two physically normal newborns showed deletion of the centromeric SMN gene, suggesting frequent rearrangement in the locus. (+info
Aclarubicin treatment restores SMN levels to cells derived from type I spinal muscular atrophy patients.
Proximal spinal muscular atrophy (SMA) is a common motor neuron disorder caused by mutation of the telomeric survival of motor neuron gene SMN1. The centromeric survival of motor neuron SMN2 gene is retained in all SMA patients but does not produce sufficient SMN protein to prevent the development of clinical symptoms. The SMN1 and SMN2 genes differ functionally by a single nucleotide change. This change affects the efficiency with which exon 7 is incorporated into the mRNA transcript. Thus, SMN2 produces less full-length mRNA and protein than SMN1. We have screened a library of compounds in order to identify ones that can alter the splicing pattern of the SMN2 gene. Here, we report that the compound aclarubicin increases the retention of exon 7 into the SMN2 transcript. We show that aclarubicin effectively induces incorporation of exon 7 into SMN2 transcripts from the endogenous gene in type I SMA fibroblasts as well as into transcripts from a SMN2 minigene in the motor neuron cell line NSC34. In type I fibroblasts, treatment resulted in an increase in SMN protein and gems to normal levels. Our results suggest that alteration of splicing pattern represents a new approach to modification of gene expression in disease treatment and demonstrate the feasibility of high throughput screens to detect compounds that affect the splicing pattern of a gene. (+info
Neuronal death is enhanced and begins during foetal development in type I spinal muscular atrophy spinal cord.
Spinal muscular atrophy (SMA) is an autosomal recessive disorder caused by mutations in the survival motor neurone gene (SMN). The degeneration and loss of the anterior horn cells is the major neuropathological finding in SMA, but the mechanism and timing of this abnormal motor neurone death remain unknown. A quantitative study was carried out comparing neuronal death in controls and SMA foetuses and neonates. Between 12 and 15 weeks of gestational age, a significant increase in nuclear DNA vulnerability, as revealed with the method of in situ end-labelling of nuclear DNA fragmentation, was detected in SMA foetuses and was reflected by a decrease in the number of neurones of the anterior horn. Neurones with nuclear DNA vulnerability are no longer detected at the end of the foetal period and the post-natal period. On the other hand, abnormal morphology of motor neurones, mainly early chromatolytic changes, was observed only after birth. Our findings indicate that in type I SMA, the absence or dysfunction of SMN is reflected by an enhanced neuronal death that is already detectable at 12 weeks, the earliest SMA foetal stage analysed. This is associated with a progressive loss of motor neurones towards the neonatal period. Given that a proportion of the remaining SMA motor neurones in the neonatal period appear with pathological findings not detected at earlier stages, it can be hypothesized that type I SMA results in differential age-dependent responses leading to cell death and motor neurone degeneration during development. (+info