SMN

SMN is an acronym that can refer to different concepts across science and technology. The most widely recognized use in human biology is the survival motor neuron, a protein essential for motor neuron function.

In genetics and molecular biology, SMN refers to the SMN1 and SMN2 genes located on chromosome 5q13. These genes encode the SMN protein, which is involved in the assembly of small nuclear ribonucleoproteins (snRNPs) required for pre-mRNA splicing. SMN1 generally provides full-length, functional protein, while SMN2 mostly produces a truncated variant due to alternative splicing that reduces its activity. Deletions or mutations of SMN1 cause spinal muscular atrophy (SMA), an autosomal recessive disorder characterized by progressive muscle weakness and atrophy. SMN2 copy number modulates disease severity, with more copies often correlating with milder phenotypes.

Clinically, SMA is treated with approaches aimed at increasing functional SMN protein levels. Nusinersen (Spinraza) is an antisense oligonucleotide that enhances SMN2 exon 7 inclusion, raising functional SMN protein. Risdiplam is an oral small molecule that modifies SMN2 splicing. Gene-replacement therapy with onasemnogene abeparvovec (Zolgensma) delivers a functional SMN1 gene via viral delivery. Early diagnosis and treatment are associated with improved motor outcomes and survival. Diagnosis typically relies on genetic testing to determine SMN1 deletions and SMN2 copy number.

Other uses of SMN exist in different domains and contexts. As an acronym, its precise meaning depends on the field and subject matter, so context is needed to identify the intended term.