Salbutamol increases survival motor neuron (SMN) transcript levels in leucocytes of spinal muscular atrophy (SMA) patients: relevance for clinical trial design.

BACKGROUND

Spinal muscular atrophy (SMA) is a neuromuscular disorder caused by mutations of the SMN1 gene. Based on severity, three forms of SMA are recognised (types I-III). All patients usually have 2-4 copies of a highly homologous gene (SMN2) which produces insufficient levels of functional survival motor neuron (SMN) protein. Recently, evidence has been provided that SMN2 expression can be enhanced in vitro by salbutamol, a β2-adrenergic agonist. This compound has also been shown to improve motor function of SMA patients in two different pilot trials.

AIM: To evaluate the in vivo molecular efficacy of salbutamol in SMA patients.

METHODS

Twelve type II-III patients took salbutamol orally for 6 months. SMN2 full length transcript levels were determined in peripheral blood leucocytes by absolute real-time PCR, at baseline and after 3 and 6 months of treatment.

RESULTS

A significant and constant increase in SMN2 full length transcript levels was detected; the response was directly proportional to SMN2 gene copy number.

CONCLUSIONS

The data strongly support salbutamol as a candidate for treating SMA, and suggest that SMN2 copy number may predict the molecular response to treatment and may be a useful randomisation parameter in a double blind placebo controlled clinical trial design.