Proximal spinal muscular atrophy (SMA) or type 1 SMA is a fatal autosomal recessive disorder usually caused by homozygous deletion of exons 7 and 8 in the survivor motor neuron (SMN) gene.
Proximal spinal muscular atrophy, the most frequent genetic cause of childhood lethality, is caused by homozygous loss or mutation of the SMN1 gene on human chromosome 5, which codes for the survival motor neuron (SMN) protein.
The survival motor neuron (SMN) gene is present in two copies on chromosome 5q13 and the evidence is now compelling that mutations in the telomeric copy (SMNt) of the gene underlie childhood onset proximal spinal muscular atrophy (SMA).
The autosomal recessive neuromuscular disorder proximal spinal muscular atrophy (SMA) is caused by the loss or mutation of the survival motor neuron (SMN) gene, which exists in two nearly identical copies, telomeric SMN (telSMN) and centromeric SMN (cenSMN).
Recently, deletions of the neuronal apoptosis inhibitory protein gene NAIP, of the survival motor neuron gene SMN, and of a further cDNA fragment, XS2G3, have been reported in childhood-onset proximal spinal muscular atrophy (SMA), another disorder with pathology restricted to the motor system.
Molecular diagnosis of childhood proximal spinal muscular atrophy has been enhanced by the discovery of the survival motor neuron (SMN) gene, which is absent or truncated in 98.6% of patients.