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Lack of cervical paraspinal muscle involvement in juvenile distal spinal muscular atrophy: an electromyographic study on 15 cases.

Electromyography (EMG) of the lower cervical paraspinal muscles was performed in 15 young Chinese males with distal spinal muscular atrophy of the upper extremities. The lack of fibrillation and positive sharp waves in all patients, both in early or active and chronic or steady stages, did not correlate with the EMG status in the affected upper extremity on the same side. This finding is in striking contrast with that in amyotrophic lateral sclerosis.

Adolescent↗

Sleep related breathing patterns in patients with spinal muscular atrophy.

A clinical and polygraphic study of nocturnal sleep was performed in 8 (4 males, 4 females; age range 10-37 years) patients with spinal muscular atrophy, whose baseline respiratory function assessment during wakefulness showed restrictive ventilatory syndrome but blood-gas tension within normal limits. No patient reported any significant sleep complaint suggestive of sleep-disordered breathing. However, in 4 patients HbSaO2 desaturations below 90% (HbSaO2 nadir 68%) were detected during nocturnal polysomnography. The HbSaO2 desaturations occurred during brief central apneas or hypopneas, mainly during REM sleep, the apnoea hypopnea index being within normal limits in all cases. The data suggest that nocturnal polysomnography can detect otherwise clinically silent hypoxemia in SMA patients without any predisposing factor to sleep-disordered breathing other than their illness and still showing normal blood-gas tensions during wakefulness. Further studies are needed to determine the long-term evolution and the prognostic significance of nocturnal hypoxemia in these patients.

Adolescent↗

An extended inhibitory context causes skipping of exon 7 of SMN2 in spinal muscular atrophy.

SMN1 and SMN2 represent the two nearly identical copies of the survival of motor neuron gene in humans. The most frequent cause of spinal muscular atrophy (SMA) is loss of SMN1 accompanied by the inability of SMN2 to compensate due to an inhibitory mutation at position 6 in exon 7 (C6U) that causes exon 7 exclusion. How this single exonic nucleotide regulates exon 7 recognition has been of major interest. Based on score matrices and in vitro assays, abrogation of an exonic splicing enhancer (ESE) associated with SF2/ASF has been considered as the cause of exon 7 exclusion. However, a recent report supports the creation of an exonic splicing silencer (ESS) associated with hnRNP A1 as the determining factor for exon 7 exclusion. Here we show that C6U strengthens an inhibitory context that covers a larger sequence than the hnRNP A1 binding site. The inhibitory context can also be strengthened by the addition of a G residue at the first position of exon 7 in SMN1, promoting exon 7 skipping despite the presence of SF2/ASF binding site. Through in vivo selection and a series of mutations we demonstrate that the strengthening of the extended inhibitory context at the 5' end of exon 7 is exercised through overlapping sequence motifs that collaborate to regulate exon usage.

Amino Acid Motifs↗

Analysis of the SMN and NAIP genes in slovak spinal muscular atrophy patients.

We identified homozygous absence of exon 7 of the telomeric copy of the survival motor neuron gene (telSMN) in 88.4% (38/43) of spinal muscular atrophy (SMA) patients from Slovakia. Additional deletions within the neuronal apoptosis inhibitory protein (NAIP) gene were found in 38.5% of type I, 12.5% of type II and never in type III SMA patients. Neither the SMN nor the NAIP gene was deleted in 81 healthy relatives and 25 controls tested. In one family, pseudodominant inheritance was identified. Both the type III SMA father and type II SMA son carried the homozygous deletion of the telSMN gene. One SMA I patient showed an SMN hybrid gene, probably created by intrachromosomal deletion. In two haploidentical type II SMA sibs, the telSMN exon 7 was absent on one chromosome, while the other carried an A-->G transition 96 bp upstream of exon 7 of the telSMN gene, a potential disease-causing mutation in these patients.

Cyclic AMP Response Element-Binding Protein↗

In situ hybridization of two markers closely flanking the spinal muscular atrophy gene to 5q12----q13.3.

In order to refine the physical location of the p105-153Ra and M4 probes which closely flank the spinal muscular atrophy gene (SMA) on human chromosome 5q, in situ hybridization has been carried out on prometaphase chromosomes. Our results demonstrate that the disease gene is located between the 5q12----q13.1 and 5q13.3 bands. The present study will hopefully contribute to microdissection of the chromosomal region of the SMA gene.

Child↗

Application of DNA-based tests for diagnosis of spinal muscular atrophy in Saudi Arabia.

We examined the deletion of the survival motor neuron (SMN) and neuronal apoptosis inhibitory protein (NAIP) genes in patients with spinal muscular atrophy (SMA) using polymerase chain reaction followed by restriction site assay methods. The study included 16 Saudi patients (9 SMA type I and 7 SMA type II) and 6 healthy Saudi volunteers. The homozygous deletions of exons 7 and 8 of the telomeric SMN gene, and exon 5 of the NAIP gene were found in all SMA type I patients. Exons 7 and 8 of telomeric SMN were deleted in all SMA type II patients. However, exon 5 of NAIP was deleted in three of the seven cases. All control volunteers and all family members of the patients had normal SMN and NAIP. The incidence of NAIP deletion was higher in the more severe SMA cases and the dual deletion of the SMN and NAIP genes was more common in Saudi SMA type I patients compared with patients of other ethnic groups.

Case-Control Studies↗

Hereditary distal spinal muscular atrophy with vocal cord paralysis.

A large kindred is described in which an unusual form of spinal muscular atrophy is segregating in an autosomal dominant manner. The disease presents most commonly in the teens with small muscle wasting in the hands, particularly involving median nerve musculature. Subsequently distal muscle wasting and weakness occur in the lower limbs. Vocal cord paralysis is a characteristic and potentially hazardous feature. No previous report of this condition has been found.

Adult↗

Motor function-muscle strength relationship in spinal muscular atrophy.

The relationship between motor function and muscle strength in patients with spinal muscular atrophy (SMA) is still controversial. In 120 genetically proven SMA patients, aged 5 years or older, we measured muscle strength in the arms and legs by a hand-held dynamometer, forced vital capacity by a spirometer, and the time needed to walk 10 m, arise from the floor, and climb steps. SMA patients had markedly reduced muscle strength, approximating 20% of that predicted from age- and gender-matched normative data. Knee extensors were the weakest muscles in SMA patients. The young ambulant SMA patients performed better than adults in all the timed tests and had greater muscle strength on knee extension. This study shows a good relationship between motor ability and muscle strength in SMA and confirms that age-related loss of function in SMA is due to loss of muscle strength.

Adolescent↗

SMN2-deletion in childhood-onset spinal muscular atrophy.

The human genome has two homologous survival motor neuron genes, SMN1 and SMN2. Although deletions of SMN1 are frequently reported in childhood-onset spinal muscular atrophy (SMA), SMN2 have been found to be intact in patients with the disorder. We report on a 5-year-old boy with childhood-onset SMA who has a homozygous deletion of SMN2. He had wasting, weakness, and hyporeflexia, predominantly in the distal muscles. The muscles involved showed chronic neurogenic changes on electromyogram. There was no sensory involvement. A nerve conduction study showed near normal conduction velocity with reduction in the amplitude of the compound muscle action potential. Analysis of polymerase chain reaction-restriction fragment length polymorphism as well as single-strand conformation polymorphism on exons 7 and 8 of the SMN genes revealed the SMN2-deletion. Base sequencing and densitometric analysis of the critical region (exon 7) did not show any microdeletion or duplication of SMN1, but confirmed the deletion of SMN2. We conclude that a deletion of SMN2 may also result in the SMA phenotype.

Child↗

Lack of serum neutralizing antibody against poliovirus in patients with juvenile distal spinal muscular atrophy of upper extremities.

Serum neutralizing antibodies for type 1, 2 and 3 poliovirus were studied in 15 Chinese patients in Taiwan with juvenile distal spinal muscular atrophy of the upper extremities and 15 age-matched normal subjects. Significantly lower serum antibody titers were found in the study group, suggesting that patients with this chronic focal form of acquired motor neuron disease are, to some degree, immunologically unresponsive to the neutralizing epitope of poliovirus.

Adolescent↗

Fine-mapping of the spinal muscular atrophy locus to a region flanked by MAP1B and D5S6.

The microtubule-associated protein 1B (MAP1B) locus has been mapped in close proximity to spinal muscular atrophy (SMA) on chromosome 5q13. We have identified a second microsatellite within a MAP1B intron, which increases the heterozygosity of this locus to 94%. Two unambiguous recombination events establish MAP1B as a closely linked, distal flanking marker for the disease locus, while a third recombinant establishes D5S6 as the proximal flanking marker. The combination of key recombinants and linkage analysis place the SMA gene in an approximately 2-cM interval between loci D5S6 and MAP1B. Physical mapping and cloning locate MAP1B within 250 kb of locus D5S112. The identification and characterization of a highly polymorphic gene locus tightly linked to SMA will facilitate isolation of the disease gene, evaluation of heterogeneity, and development of a prenatal test for SMA.

Base Sequence↗

Linkage and apparent heterogeneity in proximal spinal muscular atrophies.

Linkage studies with 9 highly informative DNA markers on the long arm of chromosome 5 were performed in 12 multiplex families (29 patients) with spinal muscular atrophy (SMA) from The Netherlands. The results of the linkage analysis were compatible with localization of a major SMA gene in the chromosomal region 5q12-13. By minimum recombinant analysis the most likely position of the SMA locus was between loci D5S6/D5S125 and D5S112/MAP1B, which is in agreement with several linkage studies from other countries. In four families, however, more than one crossover between SMA and a flanking DNA marker appeared, and in one family the observed hybridization phenotype for the markers closely flanking the SMA locus was identical for an unaffected individual and for his two affected sibs with SMA type III. For this latter family, among several explanations the most likely are either the presence of a double crossover or linkage heterogeneity.

Chromosome Mapping↗

A contig of non-chimaeric YACs containing the spinal muscular atrophy gene in 5q13.

We have constructed a contig of non-chimaeric yeast artificial chromosomes (YACs) across the candidate region for childhood autosomal recessive spinal muscular atrophy (SMA) in 5q13. A novel microsatellite reduces the candidate region to approximately 400kb of DNA distal to D5S435. The candidate region contains blocks of chromosome 5 specific repeats which have copies on 5p as well as elsewhere on 5q. Restriction mapping of the YACs reveals at least one CpG island in the SMA gene region. The YAC maps indicate that the contig contains minimal rearrangements or deletions. The data show the value of screening several YAC libraries simultaneously in order to construct a set of overlapping sequences suitable for candidate gene searches and direct genomic sequencing.

Base Sequence↗