What it is
Spinal muscular atrophy (SMA) is a genetic neuromuscular disease in which loss of a working SMN1 gene leads to the breakdown of the nerve cells that drive muscles (motor neurons). The result is progressive muscle weakness. Severity ranges widely and tracks loosely with how many copies of a backup gene, SMN2, a person carries.
Signs and symptoms
Death in childhood
Historically, the most severe (untreated) form of SMA was a leading genetic cause of death in infancy. This describes the natural history before disease-modifying treatment; outcomes have since changed (see Treatment).
Autosomal recessive inheritance
SMA is inherited in an autosomal recessive pattern: a child develops it when they inherit a non-working SMN1 gene from both parents, who are usually unaffected carriers.
Proximal amyotrophy
Because motor neurons are lost, the muscles they supply shrink and waste (atrophy), typically affecting muscles closer to the trunk earliest.
Respiratory failure
As the muscles that drive breathing weaken, SMA can lead to respiratory failure. Breathing support is a central part of care, especially in the more severe forms.
Treatment and management
What the research describes, not a recommendation. Treatment decisions belong with your clinician.
This covers treatments that appear in the published research mapped here. Investigational and experimental therapies are not included, so their absence is a boundary of this map, not a sign they do not exist.
Nusinersen
Nusinersen (Spinraza) is an antisense oligonucleotide given by intrathecal injection. It boosts production of working SMN protein from the SMN2 backup gene. It was the first disease-modifying therapy approved for SMA.
Used to help with: Spinal muscular atrophy, type I.
“The therapeutic ASO nusinersen (marketed as SpinrazaTM) targets intronic splicing silencer N1 (ISS-N1) located downstream of the predominantly skipped exon 7 of Survival Motor Neuron 2 (SMN2) gene.”
Risdiplam
Risdiplam (Evrysdi) is an oral medicine that also increases working SMN protein from SMN2. Being taken by mouth, it is an option across pediatric and adult patients.
Used to help with: Spinal muscular atrophy, type I.
“Risdiplam is an oral disease-modifying therapy approved for the treatment of SMA in both pediatric and adult patient…”
Onasemnogene abeparvovec
Onasemnogene abeparvovec (Zolgensma) is a one-time gene-replacement therapy given by vein, delivering a working copy of the SMN1 gene. Eligibility includes a test for pre-existing immunity to the viral vector.
Used to help with: Spinal muscular atrophy, type I.
“…eligible for intravenous onasemnogene abeparvovec…”
Turn this into questions for your doctor
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How to read the evidence labels
Where this comes from
This guide is built from 4 published source(s). Every claim above links back to one of them. Click any source ID to read the original on PubMed.