Survival motor neuron protein (SMN1) has been identified as the gene that is defective in spinal muscular atrophy (SMA), a neurodegenerative autosomal recessive disease characterized by paralysis and muscular atrophy which results from the loss of motor neurons in the spinal cord. There are two closely related SMN genes that do not appear to be functionally redundant. SMN1 represents the telomeric copy while SMN2 represents the centromeric copy. In the cell, SMN1 is part of a large complex of proteins involved in snRNP biogenesis. The functional role of SMN1 is proposed to play a role in messenger and ribosomal RNA transcription and processing.