SMN1
SMN1 (Survival of Motor Neuron 1) is a gene located on chromosome 5 at the 5q13.2 region. It encodes the SMN protein, which is crucial for the survival of motor neurons. Mutations in the SMN1 gene are responsible for spinal muscular atrophy (SMA), a genetic disorder characterized by the loss of motor neurons and progressive muscle wasting.
Function[edit | edit source]
The SMN1 gene provides instructions for making the SMN protein, which is part of a complex that is essential for the assembly of small nuclear ribonucleoproteins (snRNPs). These snRNPs are critical components of the spliceosome, a cellular machinery responsible for RNA splicing, a process that removes introns from pre-mRNA.
Clinical Significance[edit | edit source]
Mutations in the SMN1 gene lead to a deficiency of the SMN protein, which results in the degeneration of motor neurons in the spinal cord and lower brainstem. This degeneration causes the symptoms of spinal muscular atrophy, which include muscle weakness and atrophy.
Spinal Muscular Atrophy[edit | edit source]
Spinal muscular atrophy is classified into several types based on the age of onset and severity of symptoms:
- SMA Type 1 (Werdnig-Hoffmann disease) is the most severe form, with symptoms appearing before 6 months of age.
- SMA Type 2 presents in children between 6 and 18 months.
- SMA Type 3 (Kugelberg-Welander disease) appears after 18 months and is less severe.
- SMA Type 4 is the adult-onset form.
Genetic Testing and Diagnosis[edit | edit source]
Genetic testing for SMN1 mutations is the primary method for diagnosing spinal muscular atrophy. The most common mutation is a deletion of exon 7 in the SMN1 gene. Carrier testing and prenatal testing are also available for families with a history of SMA.
Treatment[edit | edit source]
While there is no cure for SMA, treatments such as nusinersen (Spinraza), gene therapy with onasemnogene abeparvovec (Zolgensma), and risdiplam (Evrysdi) have been developed to increase SMN protein levels and improve motor function.
See Also[edit | edit source]
References[edit | edit source]
External Links[edit | edit source]
- [GeneReviews/NCBI/NIH/UW entry on Spinal Muscular Atrophy]
- [OMIM entry on Spinal Muscular Atrophy]
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Contributors: Prab R. Tumpati, MD
