ICD-11

Spinal muscular atrophy (SMA) is a progressive disorder with loss of anterior horn cells leading to muscle weakness and wasting. The weakness is typically symmetrical. Typically, upper motor neuron signs are absent and there is no sensory deficit. Feeding and swallowing can be affected, and involvement of respiratory muscles may occur. SMA is an autosomal recessive disorder linked to chromosome 5q13 and the disorder is caused by deletion or mutation of SMN 1 (spinal motor neuron 1) gene. The four types of SMA I, II, III and IV are categorised based on the age of onset of the disease and the ability to achieve motor milestones.

In SMA type 3, weakness of muscles is seen after 18 months of age. The child is able to sit and stand independently. There is a limb girdle-type of distribution of weakness causing waddling gait, falls, and difficulty with running. The ability to walk may be lost, requiring a wheelchair as the disease progresses. The life expectancy may be normal.