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Strength gains without muscle injury after strength training in patients with postpolio muscular atrophy.

We evaluated changes in the dynamic and isometric strength in the newly weakened quadriceps muscles and asymptomatic triceps muscles of 6 patients with postpolio muscular atrophy (PPMA) after 10 weeks of progressive resistance strength training. Alterations in muscle size were determined with magnetic resonance imaging. Serum creatine kinase levels were measured throughout training, and histological signs of muscle injury and changes in muscle fiber size and types were assessed with muscle biopsies before and after training. Exercise training led to an increase in dynamic strength of 41% and 61% for the two knee extensor tests, and 54% and 71% for the two elbow extensor tests. Up to 20% of the improvement was maintained 5 months after cessation of training. Isometric strength, whole muscle cross-sectional areas of quadriceps and triceps muscles, and serum muscle enzymes did not change. No destructive histopathological changes were noted in the repeat muscle biopsies, and no consistent changes in muscle fiber size or fiber type percentages were observed. These results demonstrate that a supervised resistance training program can lead to significant gains in dynamic strength of both symptomatic and asymptomatic muscles of PPMA patients without serological or histological evidence of muscular damage.

Biopsy↗

Localization of the gene for X-linked spinal muscular atrophy.

We used probes for DNA polymorphisms on the X chromosome to study genetic linkage in seven families with X-linked adult-onset spinal muscular atrophy. We found significant linkage to the marker DXYS1 on the proximal X chromosome long arm and loose linkage or nonlinkage to markers elsewhere. Our analysis localizes the gene defect for this form of anterior horn cell disease.

Adult↗

SMN, the spinal muscular atrophy protein, forms a pre-import snRNP complex with snurportin1 and importin beta.

The survival of motor neuron (SMN) protein is mutated in patients with spinal muscular atrophy (SMA). SMN is part of a multiprotein complex required for biogenesis of the Sm class of small nuclear ribonucleoproteins (snRNPs). Following assembly of the Sm core domain, snRNPs are transported to the nucleus via importin beta. Sm snRNPs contain a nuclear localization signal (NLS) consisting of a 2,2,7-trimethylguanosine (TMG) cap and the Sm core. Snurportin1 (SPN) is the adaptor protein that recognizes both the TMG cap and importin beta. Here, we report that a mutant SPN construct lacking the importin beta binding domain (IBB), but containing an intact TMG cap-binding domain, localizes primarily to the nucleus, whereas full-length SPN localizes to the cytoplasm. The nuclear localization of the mutant SPN was not a result of passive diffusion through the nuclear pores. Importantly, we found that SPN interacts with SMN, Gemin3, Sm snRNPs and importin beta. In the presence of ribonucleases, the interactions with SMN and Sm proteins were abolished, indicating that snRNAs mediate this interplay. Cell fractionation studies showed that SPN binds preferentially to cytoplasmic SMN complexes. Notably, we found that SMN directly interacts with importin beta in a GST-pulldown assay, suggesting that the SMN complex might represent the Sm core NLS receptor predicted by previous studies. Therefore, we conclude that, following Sm protein assembly, the SMN complex persists until the final stages of cytoplasmic snRNP maturation and may provide somatic cell RNPs with an alternative NLS.

Carrier Proteins↗

A study of environmental factors in relation to fatal infantile spinal muscular atrophy (SMA type I). An analysis of birth order and parental age effects, social class, seasonal influence, and clustering in time and place.

Major studies of the childhood spinal muscular atrophies have suggested that environmentally-produced phenocopies might occur, and that environmental factors might be important in some clinical features of these diseases. A formal analysis of some possible intra-uterine and post-natal influences has been undertaken in 78 index cases (72 families) of acute infantile SMA (acute Werdnig-Hoffmann disease; SMA Type I). There is no evidence to suggest that social class, parental age, birth order, or season of birth influences this disease or that clustering in time and place occurs.

Acute Disease↗

Normal vitamin E status in spinal muscular atrophy.

In an attempt to confirm prior reports of vitamin E deficiency in Werdnig-Hoffmann disease, we assessed vitamin E nutritional status in 11 children and 6 adults with spinal muscular atrophy (SMA). Serum vitamin E levels (10.6 +/- 3.3 micrograms/ml for those less than 12 years old, 13.2 +/- 4.5 for those older than 12) and the ratio of serum vitamin E to total serum lipids were normal in all patients. Vitamin E nutritional status appears to be normal in SMA, and vitamin E therapy is not indicated.

Adolescent↗

Castration restores function and neurofilament alterations of aged symptomatic males in a transgenic mouse model of spinal and bulbar muscular atrophy.

Transgenic models of neurodegenerative disease have proved uniquely powerful for delineating pathways of neuronal dysfunction and cell death. We have developed a transgenic model of the polyglutamine disease spinal and bulbar muscular atrophy (SBMA), an adult-onset, slowly progressive motor neuron disease caused by polyglutamine expansion in the androgen receptor (AR). Mice bearing a human AR with 112 glutamines reproduce many aspects of SBMA, including slowly progressive, gender-specific motor deficits, and neuronal intranuclear inclusions. Despite substantial motor deficits in male AR112Q mice, no motor neuron loss was observed, indicating that neuronal dysfunction, rather than neuronal death, is central to disease. Moreover, reduced levels of unphosphorylated neurofilament heavy chain (NF-H) were observed in motor neurons, suggesting a role for NF-H in SBMA neuronal dysfunction. The elimination of androgens by surgical castration of severely affected, aged 112Q male mice partially restored motor function as well as NF-H levels. These data suggest that hormone-based therapies designed to treat SBMA patients, even with advanced disease, are likely to be effective.

Animals↗