What is SMA?

SMA is a neurodegenerative disorder that—left untreated—can result in progressive muscular atrophy, and in its most severe forms, premature death1,2

Spinal muscular atrophy (SMA) is a rare genetic disease caused by the deletion or mutation of the survival motor neuron 1 (SMN1) gene. The SMN1 gene produces survival motor neuron (SMN) protein that is critical for normal function of motor neurons.
Patients with SMA have an insufficient amount of SMN protein, which leads to permanent loss of motor neurons. Untreated, SMA Type 1 is the number one genetic cause of infant death.3-5

Key signs of SMA 

At birth, infants may appear normal, but can develop some of these signs as they age3,4,6:

  • Muscle weakness and hypotonia
  • Areflexia
  • Impaired head control
  • Reduced bulbar function, including impaired swallowing, feeding, and weak cry and cough
  • Tongue fasciculations
  • Paradoxical breathing, also known as “belly breathing,” and bell-shaped chest due to intercostal muscle weakness
  • Progressive respiratory failure requiring noninvasive ventilation (NIV)
  • Missed motor milestones
Floppy baby syndrome
Frog-leg position

Image used with permission from CureSMA7,8

Impaired head control

Genetic testing is the gold standard in diagnosing SMA4

SMA is classically categorized by type. Clinical features and expected outcomes are based on the natural history of untreated patients.3

If SMA is suspected, a genetic test can confirm a homozygous mutation of the SMN1 gene. Further genetic testing can determine SMN2 copy number, which is an indicator for severity. Patients with SMA rely on the SMN2 backup gene for SMN protein production; however, approximately only 10% of SMN protein produced by SMN2 is functional.3,4

SMA TypeType 1Type 2Type 3
SMN15Nearly all patients with SMA, regardless of type, will have bi-allelic deletions or mutations of SMN1
SMN2 copy number5,91-32-33-4
Incidence rate10~60%~27%~12%
Age of onset110-6 months6-18 months>18 months
Maximal motor milestones achieved11Never achieve sittingSit but never walkStand and walk
Key clinical features3,4Severe hypotonia, respiratory insufficiency, poor feeding and head controlScoliosis, unable to walk independently, proximal weaknessProximal weakness, may lose ability to walk over time

The Novartis Gene Therapies Laboratory Testing Program can support in assisting genetic testing. For more information, please contact your Novartis Gene Therapies Regional Account Associate Director or call the OneGene Program™ at 1-855-441-GENE (4363)