Spinal Muscular Atrophy (SMA)

Also known as: SMA, Werdnig-Hoffman Syndrome, Kugelberg-Welander Syndrome, infantile onset SMA, chronic SMA, mild SMA

What is spinal muscular atrophy?

Spinal muscular atrophy is a rare degenerative disorder in which the nerve cells in the upper and lower parts of the spinal cord don’t function normally, resulting in muscle wasting and weakness. There are 4 types of SMA (Types I, II, III, and IV) based on symptoms and age of onset.

What causes spinal muscular atrophy?

Spinal muscular atrophy is an autosomal recessive genetic disorder caused by an abnormal gene in each parent which is passed on to their baby.

What are the symptoms of spinal muscular atrophy?

Symptoms depend on the type of SMA.

  • Type I (Werdnig-Hoffman or infantile-onset SMA), the most severe type, may present at birth with generalized weakness, difficulty holding the head up, poor sucking or swallowing ability and poor breathing movements. Death may occur between 2-6 years of age.

  • Type II (juvenile or chronic SMA), presents around 6-18 months of age with generalized muscle weakness which may require braces/a walker or a wheelchair for ambulation. Children affected with Type II frequently live into their 20-30’s.

  • Type III (mild SMA or Kugelberg-Welander syndrome), usually affects children between the ages of 18 months to adolescence. Symptoms include difficulty walking, clumsiness, some muscle weakness and possible developmental delay. Children live well into adulthood.

  • Type IV presents in adulthood with walking difficulties.

What are spinal muscular atrophy care options?

There are several treatment options for SMA including:

  • Nusinersen (Spinraza): An antisense oligonucleotide that modifies the splicing of the SMN2 gene, increasing the production of the survival motor neuron (SMN) protein.  Medication is injected intrathecally (via lumbar puncture) every 4 months and is FDA approved for use in all ages
  • Onasemnogene abeparvovec-xioi (Zolgensma): A gene therapy that replaces the mutated SMN1 gene with a healthy copy. Medication is given via IV once and is FDA approved for use in patients 2 years and younger
  • Risdiplam (Evrysdi): A small molecule that modifies the splicing of the SMN2 gene, similar to nusinersen. It is given by mouth or via feeding tube  (liquid or tablet) once a day and is FDA approved for use in all ages

Reviewed by: Jack Wolfsdorf, MD, FAAP

This page was last updated on: September 24, 2025 01:05 PM

Neuromuscular Program

Specializing in the treatment of infants, children and adolescents with muscular dystrophies, neuropathies, spinal muscular atrophy and congenital myopathies.

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