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SMN, the product of the spinal muscular atrophy gene, binds preferentially to dimethylarginine-containing protein targets.

The survival of motor neurons protein (SMN), the product of the neurodegenerative disease spinal muscular atrophy (SMA) gene, functions as an assembly factor for snRNPs and likely other RNPs. SMN binds the arginine- and glycine-rich (RG) domains of the snRNP proteins SmD1 and SmD3. Specific arginines in these domains are modified to dimethylarginines, a common modification of unknown function. We show that SMN binds preferentially to the dimethylarginine-modified RG domains of SmD1 and SmD3. The binding of other SMN-interacting proteins is also strongly enhanced by methylation. Thus, methylation of arginines is a novel mechanism to promote specific protein-protein interactions and appears to be key to generating high-affinity SMN substrates. It is reasonable to expect that protein hypomethylation may contribute to the severity of SMA.

Amino Acid Sequence↗

Quantitative analysis of survival motor neuron copies: identification of subtle SMN1 mutations in patients with spinal muscular atrophy, genotype-phenotype correlation, and implications for genetic counseling.

Problems with diagnosis and genetic counseling occur for patients with autosomal recessive proximal spinal muscular atrophy (SMA) who do not show the most common mutation: homozygous absence of at least exon 7 of the telomeric survival motor neuron gene (SMN1). Here we present molecular genetic data for 42 independent nondeleted SMA patients. A nonradioactive quantitative PCR test showed one SMN1 copy in 19 patients (45%). By sequencing cloned reverse-transcription (RT) PCR products or genomic fragments of SMN1, we identified nine different mutations in 18 of the 19 patients, six described for the first time: three missense mutations (Y272C, T274I, S262I), three frameshift mutations in exons 2a, 2b, and 4 (124insT, 241-242ins4, 591delA), one nonsense mutation in exon 1 (Q15X), one Alu-mediated deletion from intron 4 to intron 6, and one donor splice site mutation in intron 7 (c.922+6T-->G). The most frequent mutation, Y272C, was found in 6 (33%) of 18 patients. Each intragenic mutation found in at least two patients occurred on the same haplotype background, indicating founder mutations. Genotype-phenotype correlation allowed inference of the effect of each mutation on the function of the SMN1 protein and the role of the SMN2 copy number in modulating the SMA phenotype. In 14 of 23 SMA patients with two SMN1 copies, at least one intact SMN1 copy was sequenced, which excludes a 5q-SMA and suggests the existence of further gene(s) responsible for approximately 4%-5% of phenotypes indistinguishable from SMA. We determined the validity of the test, and we discuss its practical implications and limitations.

Cyclic AMP Response Element-Binding Protein↗

Rapid detection of single nucleotide polymorphisms associated with spinal muscular atrophy by use of a reusable fibre-optic biosensor.

Rapid (<2 min) and quantitative genotyping for single nucleotide polymorphisms (SNPs) associated with spinal muscular atrophy was done using a reusable (approximately 80 cycles of application) fibre-optic biosensor over a clinically relevant range (0-4 gene copies). Sensors were functionalized with oligonucleotide probes immobilized at high density (approximately 7 pmol/cm2) to impart enhanced selectivity for SNP discrimination and used in a total internal reflection fluorescence detection motif to detect 202 bp PCR amplicons from patient samples. Real-time detection may be done over a range of ionic strength conditions (0.1-1.0 M) without stringency rinsing to remove non-selectively bound materials and without loss of selectivity, permitting a means for facile sample preparation. By using the time-derivative of fluorescence intensity as the analytical parameter, linearity of response may be maintained while allowing for significant reductions in analysis time (10-100-fold), permitting for the completion of measurements in under 1 min.

Biosensing Techniques↗

Biphasic intra-abdominal desmoplastic small cell tumor in a patient with proximal spinal muscular atrophy.

A case is reported of intra-abdominal desmoplastic small cell tumor (IDSCT) with biphasic histologic features in a patient with proximal spinal muscular atrophy. The tumor was composed of small epithelial cell nests with spindle cell sarcomatous areas. Both areas were surrounded by a desmoplastic stroma. Immunohistochemical studies revealed reactivity for low molecular weight cytokeratin, epithelial membrane antigen, vimentin, desmin and Leu-7 in both areas. Electron microscopic examination demonstrated paranuclear aggregates of intermediate filaments, zonula adherens and basement membrane-like material in the epithelial cells, while spindle cells in the tumor had fewer intracytoplasmic organelles. However, intermediate or transitional forms of both types of tumor cells were frequently observed. Although IDSCT are known to express multi-phenotypes immunohistochemically, attention should be paid to the broad spectrum of cell morphology in these tumors.

Adult↗

Epidemiology of spinal muscular atrophies in a sample of the Italian population.

In the course of an epidemiological survey in four provinces of Veneto (northeastern Italy) 67 spinal muscular atrophy (SMA) cases (types I, II and III) were recorded. The survey spanned the period 1960-1983 and involved 859,891 consecutive live-born infants in a population of 2,635,800 inhabitants. The overall prevalence at birth for SMA types I, II and III was 7.8/100,000 live births. Type I alone accounted for 4.1/100,000 live births. If the hypothesis that SMA types I, II and III are clinical manifestations of allelic mutations is assumed, the mutation rate would be about 70 x 10(-6) and the frequency of the heterozygotes 1 in 57.

Female↗

[Genetic diagnosis and prenatal diagnosis of spinal muscular atrophy by restriction endonucleases digestion of PCR product].

OBJECTIVE: To establish an efficient and rapid method for genetic diagnosis and prenatal diagnosis of spinal muscular atrophy (SMA). METHODS: 11 SMA patients were detected for the deletion and mutation in the survival motor neuron (SMN) gene by restriction endonucleases digestion of PCR products based on the difference between the two homologous copies of SMN. Linkage analysis was performed using four (CA) n repeats. RESULTS: Both eon 7 and exon 8 were deleted in 10 patients. Only exon 7 deletion was found in one patient. Prenatal diagnosis of four SMA pedigrees was performed by restriction endonucleases digestion. SMN gene fragments of three fetuses were different from those of probands, and the SMN gene fragments of one fetus was the same as those of proband. CONCLUSION: Restriction endonucleases digestion of PCR products is an efficient and rapid method for diagnosis of SMA.

Cyclic AMP Response Element-Binding Protein↗

Proximal spinal muscular atrophy (SMA) types II and III in the same sibship are not caused by different alleles at the SMA locus on 5q.

Proximal spinal muscular atrophy (SMA) is a group of progressive muscular diseases recently mapped to chromosome 5q. SMA is usually classified into types I-III, and there are cases of two types of SMA in the same sibship. Becker and others later proposed that these sibships might be due to the existence of several alleles at the same locus predisposing to the different forms of the disease. In a sample of four sibships in which both SMA type II and SMA type III occur, this hypothesis was clearly rejected for the SMA locus on 5q, by using information on the segregation of linked markers (P less than .001). Thus the difference between SMA type II and SMA type III is not due to different alleles at the SMA locus on 5q. This finding is suggestive of an involvement of other factors, genetic or environmental, in the determination of disease severity in SMA.

Alleles↗

[Distribution of androgen receptors in bulbo-spinal muscular atrophy].

Immunohistochemical staining with anti-androgen receptor (AR) antibody was performed in skeletal muscle specimens obtained from 3 cases with bulbo-spinal muscular atrophy (BSMA) and 12 cases with other neuromuscular disease. Anti-AR antibody staining was found exclusively in the muscle nuclei of Type 2A fibers in all of the 3 cases. But there was no positive staining in the muscle nuclei of other disease. As above mentioned, very specific immuno-staining of AR in skeletal muscle would be of benefit to diagnosis of BSMA in addition to identification of a mutation of AR gene.

Adult↗

Early infantile form of spinal muscular atrophy (Werdnig-Hoffmann disease) with prolonged survival.

According to several previously used classification systems, spinal muscular atrophy (SMA) type I has been characterised by an early onset (< 6 months), severe course (patients are never able to sit without support) and fatal prognosis (death before 2-4 years). We report 36 out of 349 SMA type I patients (10%) who had an onset before 6 months and never learnt to sit but survived at least beyond their fifth birthday, in spite of total immobility and frequent respiratory infections. These data support a classification avoiding age at death as a criterion. In the subgroup of type I with prolonged survival, there was no difference in life span between those individuals who had an onset of disease at birth or before and those with symptoms starting after 3 months. Life span may be related to the ability to withstand repeated respiratory insult, as several of the sibships with children affected by similar neuromuscular compromise showed discordant ages at death. "Chronic" SMA I and SMA II may represent overlapping phenotypes as our index patients with SMA I had a sib with SMA.

Adolescent↗

[Spinal pathology in spinal muscular atrophy in comparison with amyotrophic lateral sclerosis].

We analyze neuronal cytopathology and secondary reactions in spinal-muscular atrophy (SMA) in comparison with amyotrophic lateral sclerosis (ALS). In a series of SMA and ALS cases, immunohistochemistry was performed on spinal cord sections for neuronal, astroglial and microglial antigens, ubiquitin and tau proteins. Swollen motoneurons staining for phosphorylated neurofilament proteins are seen in most SMA but few ALS cases. Ubiquitinated inclusions are found only in ALS. In SMA, glial bundles are prominent in anterior roots, to lesser extent in posterior roots. In ALS, glial bundles are seen only in some cases. While basic histopathologies are similar in both types of motor neurone diseases, neuronal cytoskeletal pathology is more prominent in SMA, possibly reflecting a more acute degenerative process. The presence of axon spheroids and glial bundles also in posterior horns/roots of both types of motor neurone disease suggests spread of degenerative pathology beyond the motor system.

Amyotrophic Lateral Sclerosis↗

A placebo-controlled trial of gabapentin in spinal muscular atrophy.

OBJECTIVE: To evaluate the efficacy of gabapentin in increasing muscle strength of patients with spinal muscular atrophy (SMA). BACKGROUND: Preclinical data in experimental models of motor neuron disease suggest a neuroprotective effect of gabapentin. METHODS: Gabapentin (1200 mg), or placebo, was administered three times daily in a randomized, double-blind trial for 12 months. The primary outcome measure was the average percent change from baseline, based on the measurement of strength in four muscles (elbow flexion and hand grip bilaterally) for each patient. Drug efficacy was examined by comparing the percent change in strength for patients on drug vs. placebo. Secondary efficacy variables included: forced vital capacity (FVC), SMA functional rating scale (SMAFRS), and mini-Sickness Impact Profile (SIP). RESULTS: Eighty-four patients, with type II or III SMA, were enrolled at eight sites across the United States. There were no differences in baseline features. There was no difference between the placebo and drug groups in any outcome measure. CONCLUSIONS: This study demonstrates the feasibility of this trial design and provides data for the design of future clinical trials in SMA.

Acetates↗

The orthopaedic aspects of spinal muscular atrophy.

To clarify the role of the orthopaedic surgeon in the management of spinal muscular atrophy, the records of 130 patients were reviewed. Seventy-three had died. Of the remaining fifty-seven, fifty were re-examined. The clinical manifestations of the disease, particularly those giving rise to orthopaedic problems, were studied. At the time of review the average age of the patients was 11.5 years. Thirty-five could not walk and all had some degree of muscle weakness, more marked proximally and in the lower limbs. The most common medical problem was repeated respiratory infection and the major orthopaedic problem was scoliosis, often severe. Nine of the thirty-five patients with scoliosis had had spine fusion. Most of them suffered some functional loss in attaining spinal stability.

Adolescent↗

Spinal motor neurones in murine muscular dystrophy and spinal muscular atrophy. A quantitative histological study.

Recent electrophysiological studies of human and mouse muscular dystrophy have prompted the hypothesis that both are of neurogenic rather than myogenic origin. A decreased number of spinal motor neurones might be expected if this hypothesis were correct. The total number of neurones in the anterior grey horns of seven normal mice, six Bar Harbor 129 strain dystrophic mice, and six mice suffering from genetically-determined spinal muscular atrophy have been counted. The number of neurones in the cell types believed to include the motor neurones was significantly reduced to 13 to 71% of normal in mice with spinal muscular atrophy. In mice with muscular dystrophy, the number of anterior horn neurones was higher rather than lower than normal. The significance of these findings is discussed.

Animals↗