GTR Home > Conditions/Phenotypes > Spinal muscular atrophy, type II

Disease characteristics

Excerpted from the GeneReview: Spinal Muscular Atrophy
Spinal muscular atrophy (SMA) is characterized by progressive muscle weakness resulting from degeneration and loss of the anterior horn cells (i.e., lower motor neurons) in the spinal cord and the brain stem nuclei. Onset ranges from before birth to adolescence or young adulthood. Poor weight gain, sleep difficulties, pneumonia, scoliosis, and joint contractures are common complications. Before the genetic basis of SMA was understood, it was classified into clinical subtypes; however, it is now apparent that the phenotype of SMA associated with disease-causing mutations of SMN1 spans a continuum without clear delineation of subtypes. Nonetheless, classification by age of onset and maximum function achieved is useful for prognosis and management; subtypes include: SMA 0 (proposed), with prenatal onset and severe joint contractures, facial diplegia, and respiratory failure; SMA I, with onset before age six months; SMA II, with onset between age six and 12 months; SMA III, with onset in childhood after age 12 months and ability to walk at least 25 meters achieved; and SMA IV, with adult onset.

Available tests

8 tests are in the database for this condition. Compare labs offering these tests.

Check Associated genes and Related conditions for additional relevant tests.

Associated genes

  • Also known as: BCD541, GEMIN1, SMA, SMA1, SMA2, SMA3, SMA4, SMA@, SMN, SMNT, T-BCD541, TDRD16A, SMN1
    Summary: survival of motor neuron 1, telomeric

Clinical features

  • Muscle weakness
  • Hand tremor
  • EMG abnormality
  • Degeneration of anterior horn cells
  • Tongue fasciculations
  • Amyotrophy
  • Recurrent respiratory infections
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