Primary Outcome Measures:
Secondary Outcome Measures:
- SMN isoform mRNA levels [ Time Frame: up to 2 years ]
The levels of full-length SMN and SMNdelta7 (lacking exon 7) mRNA transcripts will be measured using quantitative PCR.
- Protein levels of putative SMA phenotypic modifiers [ Time Frame: up to 2 years ]
The levels of previously identified modifiers of SMA clinical phenotype (i.e. plastin-3 and ZPR-1) will be examined by immunoblot.
- cell viability in response to DNA damaging agents [ Time Frame: up to 2 years ]
The responsiveness of SMA fibroblasts to DNA damaging agents such as camptothecin, etoposide, bleomycin and actinomycin D will be measured using cell viability assays
- SMN protein levels [ Time Frame: up to 2 years ]
SMN protein levels will be measured by immunoblot.
- cell viability in response to cell death-inducing agents [ Time Frame: up to 2 years ]
The responsiveness of SMA fibroblasts to cell death-inducing agents such as staurosporine, tunicamycin and hydrogen peroxide will be examined using cell viability assays.
- SMN2 copy number [ Time Frame: up to 2 years ]
SMN2 copy number will be determined by quantitative PCR of genomic DNA isolated from established fibroblast lines.
Spinal muscular atrophy (SMA) is a neuromuscular disease characterized by degeneration of motor neurons and progressive muscle atrophy. The disease is one of the most common genetic causes of infant death. The gene responsible for SMA, survival motor neuron (SMN), exists in humans as two nearly identical copies (SMN1 and SMN2). Only deletion or mutation(s) of the telomeric copy of the gene (SMN1) causes the disease. The SMN protein has been known to function in assembly of the RNA splicing complex, however, the mechanism(s) by which SMN-deficiency causes cell death in SMA are not clear. The long-term goal is to understand the mechanism(s) of motor neuron death in SMA and develop a means of prevention. SMN protein has been reported to have some survival promoting functions in cultured cells. Preliminary studies show that skin fibroblasts from SMA patients are more sensitive to certain death promoting stimuli than control fibroblasts. The investigators hypothesize that the SMN protein is directly involved in cell survival and that loss of this survival function of SMA results in motor neuron death in SMA. The investigators will use fibroblasts from SMA patients, fibroblasts from controls without SMA, motor neuron-like cell lines (such as NSC-34) and rodent primary motor neuron cultures as model systems to test our hypothesis. The investigators will determine the effect of expression of SMN protein in regulating cell death of SMA fibroblasts. The investigators will further investigate the role of SMN in neuronal cell survival. Finally, the investigators will determine biological pathway(s) of SMN-mediated cell protection. Results from the proposed studies will provide insight into the mechanism(s) by which SMN protects cells from death and how a decrease in SMN function leads to the SMA phenotype. Ultimately, the obtained information could lead to develop therapeutic strategies for SMA.