[From gene to disease; 'survival' motor neuron protein and hereditary proximal spinal muscle atrophy]

The majority of patients with hereditary proximal spinal muscular atrophy (SMA) have a homozygous deletion of the survival motor neuron gene (SMN1). The number of SMN2 gene copies modifies the phenotype, which ranges from a lethal infantile disorder to an adult-onset disease causing mild impairment and disability. The SMN protein plays a role in an apparently essential cell metabolism process, the splicing of pre-mRNA in the spliceosomes. Why SMN1 deletions are only clinically expressed in motor neuron cells and not in other cell types is still unknown. DNA analysis, prenatal diagnosis and carrier testing as means of diagnosing SMA are all routinely available in the Netherlands and are currently performed at the DNA laboratory of the University of Groningen.