Spinal muscular atrophy other forms

Editors-in-Chief: C. Michael Gibson, M.S., M.D.; Priyamvada Singh, MBBS

Other Forms
Spinal muscular atrophy (SMA) is a collection of different muscle diseases. Grouped together, it is the second leading cause of neuromuscular disease. The autosomal recessive SMA is the commonest type (>95%) and is caused by the mutation in the chromosome 5q13. The non-5q13 associated spinal muscular atrophies, are a heterogeneous group of motor neuron diseases associated with mutations in a variety of different known genes and others not yet defined (e.g. X linked, autosomal dominant, mutations in IGHMBP2 gene on chromosome 11q). Patients with these disorders generally have some clinical characteristics that can help differentiate them from those with 5q13-associated or “proximal” SMA. All forms of SMA have in common weakness caused by denervation, that is, the muscle atrophies because it has lost the signal to contract due to loss of the innervating nerve. Spinal muscular atrophy only affects motor nerves. Heritable disorders that cause both weakness due to motor denervation along with sensory impairment due to sensory denervation are known by the inclusive label Charcot-Marie-Tooth or Hereditary Motor Sensory Neuropathy. The term spinal muscular atrophy thus refers to atrophy of muscles due to loss of motor neurons within the spinal cord.


 * Hereditary Bulbo-Spinal SMA Kennedy's disease (X linked, Androgen receptor)
 * Spinal Muscular Atrophy with Respiratory Distress (SMARD 1) (chromsome 11, IGHMBP2 gene)
 * Distal SMA with upper limb predominance (chromosome 7, glycyl tRNA synthase)
 * X-Linked infantile SMA (gene UBE1)