Molecular bases of spinal muscular atrophy: the survival motor neuron gene

Abstract

Spinal muscular atrophy (SMA) is an autosomal recessive neuromuscular disease characterized by degeneration and loss of motor neurons of the anterior horn of the spinal cord. The clinical manifestations include proximal symmetric weakness and progressive muscle atrophy. The identification of the SMN1 gene as determinant of SMA has opened alternative ways of studying the disease. Absence of SMN1 (either by deletion or conversion) was detected in the majority of patients and subtle mutations were described in a minority. SMN1 absence was associated with a wide spectrum of manifestations, from congenital disease to asymptomatic cases. Modifier factors, such as the number of copies of SMN2, its homologous copy present in all patients, could influence the phenotype and help to find a treatment for the disease. The SMN gene is expressed in various neuronal populations, although only motor neurons are responsible for the manifestations of the disease. The SMN protein is part of a complex with various proteins involved in the splicing reaction. This apparently essential function of all cells is critical for motor neurons, and warrants further research to elucidate the mechanisms of disease.